Category: CBSE

CBSE Class 9 Maths Lab Manual – Relations of Inequalities in Triangles

Objective
To verify that a triangle is possible only if the sum of any two sides of triangle is always greater than the third side and difference of any two sides is always less than the third side.

Prerequisite Knowledge

1. Measurement of line segments.
2. Comparison of line segments.

Materials Required
Broom sticks or straws, scale, geometry box.

Procedure

1. Take some sticks according to the given measurements.
2. Collect three triplets of sticks as given.
   • Set I
   • 3cm, 5cm, 10cm
     
   • 4cm, 4cm, 8cm
     
   • 5cm, 4cm, 8cm
     
   • Set II
   • 3cm, 4cm, 8cm
     
   • 4cm, 6cm, 10cm
     
   • 4cm, 5cm, 7cm
     
   • Set III
   • 5cm, 3cm, 6cm
     
   • 5cm, 5cm, 11cm
     
   • 3cm, 2cm, 5cm
     
3. Now from the above three sets, try to form a triangle and name them.
   
   

Observation and Calculation
Table

Set	Side 1	Side 2	Side 3	Possibility of ∆	Reason
I
(i)	3	5	10	not possible	3 +5 < 10
(ii)	4	4	8	not possible	4 + 4 = 8
(iii)	5	4	8	possible	5 + 4 > 8; 5 + 8 > 4; 4 + 8 > 5
II
(i)	3	4	8	not possible	3 + 4 < 8
(ii)	4	6	10	not possible	4 + 6 = 10
(iii)	4	5	7	possible	4+5 > 7; 5 + 7 > 4; 4 + 7 > 5
III
(i)	5	3	6	possible	5 + 3> 6; 5 + 6 > 3; 3 + 6 > 5
(ii)	5	5	11	not possible	5 + 5 < 11
(iii)	3	2	5	not possible	3 + 2 = 5

 In each set, we observe that triangle is possible only when the sum of the two sides is greater than the third side.

Result
We verified that the triangle is possible only when sum of any two sides is greater than the third side.

Learning Outcome
We learnt that, for any three line segments, we cannot construct triangle always because for a triangle the sum of any two sides of a triplet is always greater than the third side.

Activity Time

1. For a triplet, verify that the difference of any two sides is always less than third side in a triangle.
2. Are the following triangles possible?
   • Right-angled equilateral triangle.
   • Obtuse equilateral triangle.
   • All angles are acute angle.
   • Two obtuse angles in a triangle.

Viva Voce

Question 1.
State, if the following triangles are possible:

• 7cm, 9cm, 11cm
• 10cm, 9cm, 19cm,

Answer:

• Yes
• No.

Question 2.
What are an equilateral, scalene, isosceles triangles ?
Answer:
Equilateral triangle → having all sides equal.
Scalene triangle → having all three sides different.
Isosceles triangle → having any two equal sides.

Question 3.
Is right angled equilateral triangle possible ?
Answer:
No.

Question 4.
Is right angled isosceles triangle possible ?
Answer:
Yes.

Question 5.
Is obtuse equilateral triangle possible ?
Answer:
No.

Question 6.
Will a triangle be possible with all acute angles ?
Answer:
Yes.

Question 7.
Is a triangle possible, if the area of triangle is zero ?
Answer:
No.

Question 8.
What is the angle sum property of a triangle ?
Answer:
In a triangle, the sum of its all three angles is 180°.

Question 9.
What is the relationship between the sum of two sides of a triangle ?
Answer:
In a triangle, sum of two sides is always greater than third side.

Question 10.
What is the relationship between the difference of two sides of a triangle to the third side ?
Answer:
In a triangle, difference of two side is always less than the third side.

Multiple Choice Questions

Question 1.
In a AABC, ∠A = 95°, ∠B = 60°, what will be the least side of ∆ABC ?
(i) AB
(ii) BC
(iii) AC
(iv) none of these

Question 2.
Arrange the sides of ∆PQR in ascending order of magnitude, if in ∆PQR, ∠P = 90°, ∠Q = 60°:
(i) PQ < PR < QR (ii) QR > PR > PQ
(iii) QR > PQ > PR
(iv) none of these

Question 3.
In the given figure, if x > y, what is the relationship between ∠PQR and ∠PRQ:

(i) ∠PQR = ∠PRQ
(ii) ∠PQR > ∠PRQ
(iii) ∠PRQ > ∠PQR
(iv) none of these

Question 4.
In a quadrilateral, what is the relationship between sum of four sides and sum of two diagonals :
(i) sum of four sides > sum of diagonals
(ii) sum of diagonals > four sides
(iii) sum of four sides = sum of diagonals
(iv) none of these

Question 5.
Which is the longest side in right angled triangle ?
(i) altitude
(ii) base
(iii) hypotenuse
(iv) none of these

Question 6.
If three triplets are 7, 9, 6, is the triangle possible by using these triplets ?
(i) not possible
(ii) yes
(iii) right triangle is possible
(iv) none of these

Question 7.
Is the obtuse right triangle possible ?
(i) no
(ii) yes
(iii) can’t say
(iv) none of these

Question 8.
The three values of angles are 60°, 90°, 30°. Is the triangle possible by using these angles ?
(i) right triangle
(ii) yes
(iii) no
(iv) none of these

Question 9.
What is the shortest distance between a point and a line ?
(i) any distance
(ii) perpendicular distance
(iii) not particular distance
(iv) none of these

Answers

1. (i)
2. (i)
3. (iii)
4. (i)
5. (iii)
6. (ii)
7. (i)
8. (i), (ii)
9. (ii)

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CBSE Class 9 Maths Lab Manual – Property of Cyclic Quadrilateral

Objective
To verify that the opposite angles of a cyclic quadrilateral are supplementary by paper folding activity.

Prerequisite Knowledge

1. A quadrilateral whose all four vertices lies on the circle is known as cyclic quadrilateral.
2. Concept of opposite angles of a quadrilateral.
3. Concept of Supplementary angles.

Materials Required
White paper sheet, compass, glazed papers, pencil, a pair of scissors, gluestick.

Procedure

1. Draw a circle of radius 2 cm on a white glazed paper with centre O.
2. Cut this circle with centre O and draw one more circle of same radius.
3. Take any four points A, B, C, D on the circumference of both the circles.
4. Join AB, BC, CD, DA by paper folding on the both the circles.
5. We get a cyclic quadrilateral ABCD on both the circles [fig.(i) and fig.(ii)]. Take ∠A and ∠C of blue colour and ∠B and ∠D of pink colour in both circles.
   
   
6. From the second circle, using transparent sheets make cut outs of ∠A, ∠B, ∠C, ∠D. [fig. (iii)]. Take ∠A and ∠C of blue colour and ∠B and ∠D of pink colour.
   
7. Make a straight line on white paper sheet. Place cut outs of ∠A and ∠C adjacent to each other on a straight line and paste them [fig.(iv)].
8. Take cut outs of ∠B and ∠D and place them adjacent to each other on another straight line and paste them [fig.(iv)].
   

Observation
As ∠A and ∠C forms a linear pair.
∴ ∠A + ∠C = 180°
Similarly, ∠B + ∠D = 180°

Result
Hence, it is verified that in a cyclic quadrilateral, sum of opposite angles is 180°.

Learning Outcome
If a cyclic quadrilateral is a parallelogram then it become a rectangle, this can be proyed by paper folding and cutting method.

Activity Time
By same paper cutting activity students can verify that in a cyclic quadrilateral, the exterior angle is equal to the opposite interior angle.

Viva Voce

Question 1.
What are supplementary angles ?
Answer:
If the sum of two angles is 180°, then angles are supplementary angles.

Question 2.
What are complementary angles?
Answer:
If the sum of two angles is 90°, then angles are complementary angles.

Question 3.
What are adjacent angles of a quadrilateral ?
Answer:
Two angles lying on the same side of a quadrilateral.

Question 4.
What is the sum of four angles of a quadrilateral ?
Answer:
360°.

Question 5.
If one of the angles of a cyclic quadrilateral is 30°, then what will the value of its opposite angle ?
Answer:
150°

Question 6.
What do you mean by a cyclic quadrilateral ?
Answer:
A quadrilateral is called a cyclic if all the four vertices are concyclic.

Question 7.
If a cyclic quadrilateral is a parallelogram, then what will be the kind of parallelogram ?
Answer:
Rectangle.

Question 8.
What will the sum of opposite angles of a cyclic quadrilateral ?
Answer:
180°.

Question 9.
What will be the name of a quadrilateral if the pair of opposite angles is supplementary ?
Answer:
Cyclic quadrilateral.

Multiple Choice Questions

Question 1.
ABCD is a cyclic quadrilateral, in which ∠ABC = 90°. The value of ∠ADC is:
(i) 90°
(ii) 45°
(iii) 70°
(iv) none of these

Question 2.
In a circle with centre O, the angle subtended by arc BCD at the centre is 140°. BC is produced to P. Find ∠DCP:

(i) 70°
(ii) 35°
(iii) 280°
(iv) none of these

Question 3.
In the given figure, ∆ABC is an isosceles triangle with AB = AC and ∠ABC = 50°. Find ∠BDC:

(i) 100°
(ii) 25°
(iii) 80°
(iv) none of these

Question 4.
In the given figure, ∆DEF is an isosceles triangle with DE = DF and ∠DEF = 60°. Find ∠EAF:

(i) 120°
(ii) 30°
(iii) 300°
(iv) none of these

Question 5.
ABCD is a cyclic quadrilateral in which BC is parallel to AD, ∠ADC =110°, ∠BAC = 50°. Find ∠DAC
(i) 100°
(ii) 30°
(ii) 60°
(iv) none of these

Question 6.
ABCD is a cyclic quadrilateral. If ∠BCD = 100°, ∠ABD = 70°, the value of ∠ADB will be:
(i) 60°
(ii) 30°
(iii) 150°
(iv) none of these

Question 7.
If PQRS is a cyclic quadrilateral, ∠P = 3x°, ∠Q =y°, ∠R=x°, ∠S = 5y°, find the value of x° and y°.
(i) 45°, 30°
(ii) 90°, 60°
(iii) 90°, 30°
(iv) none of these

Question 8.
ABCD is a cyclic trapezium in which AD || BC, if ∠B = 70°, find the value of ∠A:
(i) 70°
(ii) 110°
(iii) 35°
(iv) none of these

Question 9.
If ABCD is a cyclic quadrilateral, in which ∠DBC = 70°, ∠BAC = 40°, find ∠BCD :
(i) 100°
(ii) 40°
(iii) 70°
(iv) none of these

Question 10.
Find the measure of the opposite angles of a cyclic quadrilateral if one of them is \(\frac { 11 }{ 4 }\) of the other:
(i) 48°, 132°
(ii) 29°, 132°
(iii) 48°,264°
(iv) none of these

Answers

1. (i)
2. (i)
3. (iii)
4. (i)
5. (ii)
6. (ii)
7. (i)
8. (ii)
9. (iii)
10. (i)

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CBSE Class 9 Maths Lab Manual – Angles in the Same Segment

Objective
To show that the angles subtended by the chord of a circle in the same segment are equal, experimentally.

Prerequisite Knowledge

1. Concept of a circle.
2. Concept of angle subtended by an arc/chord.

Materials Required
Glazed papers, sketch pens, a pair of scissors, gluestick, geometry box, white sheet.

Procedure

1. Take red colour glazed paper and draw a circle of any radius say 2.5 cm on the white side of the paper.
2. Cut this circle with centre O and radius 2.5 cm.
3. Mark any point P on the circumference of the circle.
4. Mark two other points A and B on the circumference of the circle.
5. Fold and press the circle along AB to get a crease which is a chord of the circle.
6. Join PA and PB to get ∠APB as shown in fig. (i).
   
7. Take another coloured glazed paper say, yellow, cut circle of same radius.
8. Draw a chord CD on second circle with centre O’, such that AB = CD.
9. Mark a point R on the circumference of the second circle. Join RC and RD fig (ii).
   
10. Cut out ∆RCD and paste it on the first circle such that R lies on P and RD lies on PB and RC lies on PA as shown in fig. (iii).
    
    ∠APB superimposes ∠DRC

Observation
Since the chord AB = chord CD and ∠APB superimposes ∠DRC, their arcs are same. When two angles superimpose each other it means their two arms lie on one another. This verifies that angles in the same segments are equal.

Result
We verified that two angles subtended by the chord of a circle in the same segment are equal.

Learning Outcome
We learnt that two or more angles subtended by same chord in the same segment of a circle are equal.

Activity Time

1. This theorem can be verified by taking any point on the minor segment of circle.
2. Prove this theorem for different chords, such as diameter, chord in minor segment, chord in major segment.

Viva Voce

Question 1.
Define chord of a circle.
Answer:
A line segment AB joining two points A and B of the circle is called a chord of the circle.

Question 2.
How many longest chords are there in a circle ?
Answer:
There are infinity many longest chords in a circle passing through the centre.

Question 3.
Define minor segment of a circle.
Answer:
A chord divides a circle into two parts the smaller part is called as minor segment.

Question 4.
Define major segment of a circle.
Answer:
The larger part of the circle is called as major segment.

Question 5.
What is the measure of an angle formed in a semicircle ?
Answer:
90°

Question 6.
If the angle subtended by an arc at the centre is 30°, what is the value of angle subtended by it on the remaining part of the circle.
Answer:
15°

Question 7.
If the angle subtended by an arc at the centre in major segment is reflex angle, then what is the angle in the minor segment ?
Answer:
Obtuse angle.

Question 8.
The angle subtented by an arc at the circle in minor segment is obtuse angle. What is the values of angle subtended by it in the major segment ?
Answer:
Acute angle.

Multiple Choice Questions

Question 1.
Find ∠BDC, if ∠ABC = 70°, ∠ACB = 30°:

(i) 80°
(ii) 100°
(iii) 70°
(iv) none of these

Question 2.
If ∠BDC = 30°, find ∠BAC:

(i) 30°
(ii) 60°
(iii) 15°
(iv) none of these

Question 3.
In a circle with centre O, AB is a chord and P, Q, R are three points on the same side of the chord AB of circle. If ∠APB = 40°, what is value of ∠AQB, ∠ARB?
(i) 20°, 40°
(ii) 80°, 80°
(iii) 40°, 40°
(iv) none of these

Question 4.
Calculate the measure of ∠PQB, where O is the centre of the circle:

(i) 50°
(ii) 60°
(iii) 90°
(iv) none of these

Question 5.
If ∠PQS = 40°, ∠SPR = 65°, find ∠RSP.

(i) 70°
(ii) 75°
(iii) 105°
(iv) none of these

Question 6.
In the fig, ∠ABC = 69°, ∠ACB = 31°. Find ∠BDC:

(i) 80°
(ii) 100°
(iii) 70°
(iv) none of these

Question 7.
In the fig, ∠BEC = 130°, ∠ECD = 20°. Find ∠BAC:

(i) 50°
(ii) 110°
(iii) 70°
(iv) none of these

Question 8.
In a circle, ABCD is a cyclic quadrilateral in which ∠DBC = 80° and ∠BAC = 40°, find ∠DCB:

(i) 60°
(ii) 70°
(iii) 80°
(iv) none of these

Question 9.
In a circle, AB is a diameter, Q, P are any points on the circle. What is value of ∠AQB and ∠APB ?
(i) 80°, 90°
(ii) 90°, 90°
(iii) 50°, 50°
(iv) none of these

Answers

1. (i)
2. (i)
3. (iii)
4. (i)
5. (ii)
6. (i)
7. (ii)
8. (i)
9. (ii)

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A report is a factual description of an issue or a problem. A report is written for a clear purpose and for a particular audience. Various forms of reports are: newspaper reports, inquiry reports, progress or action taken report, a police report, a report of a meeting, etc., each having a distinct character and format.

Looking for an easy way to learn English Grammar? then you are in right place. Here we providing basic English Grammar topics like Tenses Verbs, Nouns, etc. In this Section, we are explained Report Writing Class 12

Report Writing for Class 12 Format, Examples, Topics, Samples, Types

A report is a written account of an event. It gives relaying information or recounts certain events in a widely presentable form. The events could be an exhibition, a seminar, a rally, a theatre event, a theft, blood donation campaign, etc. It is often used to display the result of an experiment, investigation or an inquiry. It may use graphics, images or specialized vocabulary to persuade the audience to undertake an action.

Report Writing Format

• • Title and reporter’s name.
• • Date and place.
• • Content – The content covers the ‘wh’ questions – what happened, where, when, how, why, etc.

Points To Remember While Writing Report

1. Make an attractive heading for the topic of the report. This is where you can clue reader as to what to expect without detailing.
2. Provide background information in brief, but be insightful on the selection of your report. Perhaps it is related to something mentioned during class or it might be an answer to a burning question posed by yourself or a classmate.
3. Briefly describe the steps of inquiry or the method used. A good report leaves no questions unanswered. Note that readers always want to know exactly which steps were taken to reach the conclusion.
4. Explain the reasons why the report is meaningful for the audience or readers. Convince through your writing that it is something for them to remember.

Report Writing Notes Pdf

1. Read the report aloud to make sure it flows from concept to concept. Make it interesting enough so as to catch the attention of the reader.
2. Finally, check for spelling and grammar. Remember that a good report is properly edited.

Report Writing Sample Class 12

You are Sandhya/Sameer, the head girl/head boy of R.N. Sisodia School, Roop Nagar, Agra. Your school recently hosted Regional sports meet of eight schools. You have been asked by your principal to write a report in 150 – 200 words of the same for your school magazine. Write the report.

Value Points or Main Clues
(a) Robbery I Accident/Calamity /Disease outbreak/Civic problem

• Catchy headline – expansion of headline in the first sentence highlighting what/when/where
• Give reason, if any/motive
• Details in brief
• Eyewitness account
• Casualties, damage, etc. (if any)
• Action taken
• Relief measures (if applicable)
• Conclusion/comments

(b) Cultural/Sports events

• Occasion/organiser/sponsor, etc.
• Date, venue (time optional)
• Chief guest/special invitees
• Objectives and main highlights Qf the programme
• Prize distribution/Annual report (if applicable)
• Message by chief guest/dignitary
• Vote of thanks
• Overall response

(c) Competitions

• Occasion/organiser
• Date, venue, objective
• Name of the competition, level, topic, if any, participation
• Inaugural ceremony/welcome
• Chief guest, judges, etc.
• Highlights related to performance, result, etc.
• Prize distribution (viii) Special remarks/address (if any)
• Vote of thanks

(d) Workshop!Seminar/Talk

• What, by whom, for whom
• Date, venue, duration, etc.
• Guest speakers, panel of experts, etc.
• Chief Guest, invitees, etc.
• Activities undertaken
• Aids used – MMP, audio – visual charts, documentary films, etc.
• Literary or field activities (if any)
• Interactive session, including question – answer round (if any)
• Expert’s comments
• Vote of thanks
• Overall effect

(e) Rally /Drive / Campaign

• What, by whom
• Duration, venue or places covered
• Objective, motto (if any)
• Activities undertaken
• Any display/educational material used, for example: placard, banner, pamphlet, etc.
• Special remarks by a dignitary/chief guest, etc.
• Overall success

(f) Camp/Visit I Exhibition, etc.

• Place, destination, etc.
• Organiser, sponsor (if any)
• Duration, date, etc.
• Number of persons/visitors, etc.
• Description as applicable
• theme of exhibition, type /range, etc./quality of exhibits
• places of sightseeing, food, scenic beauty, etc.
• purpose and nature of camp, activities undertaken
• Overall response

The following are the news clippings from newspapers. Notice carefully the tense and the form of the verbs used. Also pick out words and expressions which help express the content coherently and specifically. TVy to determine the essential elements of each report according to the following guidelines:

Notice the dateline which contains the place and date of reporting.

Headline and its expansion in the first sentence where and when it happened consequences/effects/results of the happening
What happened. Why/How it happened.

People involved in the event, if any action taken/any conclusion… comments/evidence from people..

Remember, your report should be written within the prescribed word limit.

CBSE Class 10 Science Practical Skills – Cleaning Capacity of Soap in Hard and Soft Water

BASIC BUILDING CONCEPTS
Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it dissolves in water, while the other end is hydrophobic, that is, it dissolves in hydrocarbons. When soap is at the surface of water, the hydrophobic tail of soap will not be soluble in water and the soap will align along the surface of water with the ionic end in water and hydrocarbon tail protruding out of water. Inside the water, these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is accomplished by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface. This formation is called micelle. Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of micelle.

You can also download Science NCERT Solutions Class 10 to help you to revise complete syllabus and score more marks in your examinations.

AIM
To study the comparative cleaning capacity of a sample of soap in soft and hard water.

MATERIALS REQUIRED
Tap water, distilled water,
calcium hydrogen carbonate (0.5 g),
calcium chloride (0.5 g),
calcium sulphate (0.5 g),
soap sample (1 g),
spatula,
physical balance,
weight box,
five test tubes,
three beakers (100 ml),
four glass rods,
measuring cylinder,
a measuring scale and three droppers.

THEORY
Water that does not contain a significant amount of dissolved minerals such as compounds of calcium and magnesium is soft water. It produces lather with a little amount of soap. Hard water is water that has high mineral content, it has high concentrations of Ca2+ and Mg2+ ions. Calcium and magnesium hydrogen carbonates, chlorides and sulphates in water render it hard. When soap is added to hard water, it does not form lather. The calcium and magnesium salts in hard water react with soap and form scum, which is insoluble and floats on top of water. Due to the formation of scum, which is calcium or magnesium salt of soap (soap is sodium or potassium salt of fatty acids), soap becomes ineffective in solution and no cleansing occurs. The equations involved in the formation of scum are as follows:

As the calcium and magnesium salts in water react with soap, cleansing power of soap is reduced and its foaming capacity also decreases.

PROCEDURE
1. Take three beakers (100 ml) and label them as ‘A’, ‘B’ and ‘C

2. Prepare 30 ml soap solution by adding 1 g soap to water in beaker ‘C’.
3. Pour 20 ml tap water in beaker ‘A’ and 50 ml distilled water in beaker ‘B’.
4. Place five test tubes, labelled A, B, C, D and E, in a test tube stand.
5. Using a dropper pour 5 ml of tap water in test tube A, and 5 ml distilled water in the other test tubes labelled as B, C, D and E.

6. To test tube C, D and E add a pinch of calcium hydrogencarbonate, calcium chloride and calcium sulphate respectively using a spatula.

7. Mix the solution well using a glass rod.
8. Using a dropper, add 3 ml of soap solution to the test tube A. Measure the length of the solution present in the test tube A and record this in table.
9. Shake test tube A, ten times by placing thumb on its mouth.
10. Observe whether foam is formed by shaking the test tube and record your observations.
11. Measure the length of content (foam and solution) present in the test tube immediately with the help of a measuring scale.
12. Repeat steps 8 to 11 with the remaining water samples (B, C, D and E) and record your observations.

OBSERVATIONS

1. Volume of water samples taken in test tube = 5 ml.
2.  Volume of soap solution added to each test tube = 3 ml.

RESULTS

1.  Maximum length of foam is produced in water sample(s) …………………………………
2.  Scum is formed in water sample(s) ……………………………
3.  The water sample most suitable for washing purpose is …………………………..

DISCUSSION
For cleaning, foam needs to be produced. Production of foam depends on the free availability of hydrophobic portion of the soap. In hard water due to formation of scum hydrophobic portion of the soap gets trapped. Therefore, hard water is not suitable for cleaning purpose.

PRECAUTIONS

1.  Use same amount of soap for all the samples.
2. Take equal volumes of water samples.
3.  Shake each test tube equal number of times and in a similar manner.
4.  Length of foam should be measured immediately after shaking.

INTERACTIVE SESSION

Question 1:
What is hard water?
Answer:
Hard water is the water that has high mineral content and produces scum on addition of soap.

Question 2:
What is soft water?
Answer:
The water which has low mineral content and produces lather on mixing soap to it is called soft water.

Question 3:
Why does hard water produce scum when soap is added to it?
Answer:

Hard water produces scum when soap is added due to the presence of Ca2+ and Mg2+ salts in it, which react with soap forming precipitates which are calcium and magnesium salts of soap.

Question 4:
How does presence of Ca2+ and Mg2+ ions in water lead to the formation of scum?
Answer:
Ca2+ and Mg2+ ions present in hard water react with soap to form calcium and magnesium salts of soap which are insoluble in water.

Question 5:
Give the equation involved in the formation of scum.
Answer:

Question 6:
Does the presence of all salts of calcium and magnesium cause hardness in water?
Answer:
No.

Question 7:
Which salts cause hardness in water?
Answer:
The hydrogencarbonates, chlorides and sulphates of calcium and magnesium cause hardness in water.

Question 8:
Which ions are present in soft water?
Answer:
Only sodium ion is present in soft water.

Question 9:
Which out of hard water or soft water is better for cleansing?
Answer:
Soft water.

Question 10:
Can hard water be softened?
Answer:
Yes.

Question 11:
How?
Answer:
By boiling or by chemical treatment.

Question 12:
Can hard water be used for washing purposes?
Answer:
No, hard water cannot be used for washing purposes.

Question 13:
Why?
Answer:
Because a large amount of soap gets washed away due to the formation of scum. This also sticks to fibres of garments.

Question 14:
Out of soaps and detergents which form lather in hard water?
Answer:
Detergents.

Question 15:
Would sodium chloride present in water render it hard?
Answer:
No, sodium chloride does not render water hard.

Question 16:
Can you explain why sodium salts in water do not make it hard water?
Answer:
Soaps are sodium salts of fatty acids. On adding sodium salts to water containing soap, no scum is formed as can be understood by the following equation.

NCERT LAB MANUAL QUESTIONS

Question 1:
Do both hard water and soft water produce foam with soap?
Answer:
No, only soft water produces foam with soap.

Question 2:
Why is scum formed when hard water is treated with soap?
Answer:
Scum is formed when hard water is treated with soap because Ca2+, Mg2+ ions present in hard water react with soap and form an insoluble precipitate scum.

Question 3:
With their prolong use, white scales get deposited in the interior of boilers and electric kettles. What is the reason for this observation?
Answer:
On prolong use, scales are deposited in the interior of boilers and electric kettles due to the precipitation of CaCO,, and CaS04. The precipitation of CaC03 is also caused due to the thermal decomposition of bicarbonate ions.

Question 4:
What do you understand by temporary and permanent hardness of water?
Answer:
Temporary hardness is caused due to the presence of calcium and magnesium bicarbonates in water and can be removed by boiling or by adding Na2C03 to hard water.
Permanent hardness is caused due to the presence of chlorides and sulphates of calcium and magnesium and can be removed by using an ion exchanger.

Question 5:
What is the reaction between soap molecules and ions present in hard water?
Answer:

PRACTICAL BASED QUESTIONS
Multiple Choice Questions /VSA (1 Mark)

Question 1:
Soaps work well in
(a) hard water
(b) soft water
(c) acidified water
(d) very cold water

Question 2:
Presence of which salt makes the water hard?
(a) salts of sodium
(b) salts of potassium
(c) salts of calcium
(d) all of these

Question 3:
Scum is the precipitate formed when soap in water reacts with
(a) calcium and magnesium salts
(b) calcium and sodium salts
(c) magnesium and sodium salts
(d) calcium and potassium salts

Question 4:
Which of the following statement is correct about the formation of lather by soap?
(a) In hard water soap forms more lather.
(b) In soft water soap forms more lather.
(c) In both hard and soft water soap forms same amount of lather.
(d) In both hard and soft water soap does not form lather.

Question 5:
Temporary hardness in water is caused by
(a) chlorides of sodium and magnesium
(b) sulphates of calcium and potassium
(c) hydrogencarbonates of calcium and magnesium
(d) hydrogencarbonates of sodium and potassium

Question 6:
Temporary hardness of water can be removed ! by
(a) boiling
(b) reacting with NaCl
(c) reacting with KC1
(d) filtration

Question 7:
Permanent hardness in water is caused by
(а) chlorides and sulphates of sodium and potassium
(б) chlorides and sulphates of sodium and calcium
(c) chlorides and sulphates of calcium and magnesium
(d) chlorides and sulphates of magnesium and potassium.

Question 8:
The soap solution required to compare the cleaning capacity of soap is made by dissolving soap in
(a) well water
(b) tap water
(c) filtered water
(d) distilled water

Question 9:
Which of the following is best suited for washing clothes with soap?
(a) Distilled water containing calcium hydrogen- carbonate
(b) Distilled water containing calcium chloride
(c) Distilled water containing calcium sulphate
(d) Only distilled water.

Question 10:
Why can’t hard water be used for washing clothes?
(a) It forms scum with soap.
(b) It hardens the texture of clothes.
(c) It does not react with soap.
(d) This statement is wrong. Hard water is suited well for washing clothes.

Question 11:
When hard water is used in boilers for a long time, which phenomenon is observed?
(а) The amount of steam formed in boilers ; increases.
(b) The boilers work more efficiently.
(c) White scales get deposited on the interiors of boilers.
(d) Boilers do not work with hard water.

Question 12:
Clothes do not get cleaned when hard water is used for washing them. This is because
(a) hard water reacts with fibres of clothes.
(b) the scum formed by reaction of soap with hard water sticks to the fibres of clothes.
(c) hard water itself is dirty.
(d) fibres of clothes do not get wetted by hard water so they do not get cleaned.

Question 13:
Which of the following statements is wrong?
(а) Soaps and detergents both form lather with soft water.
(б) Soaps form lather with hard water, detergents do not form lather with hard water.
(c) Soaps do not form lather with hard water, detergents form lather with hard water.
(d) Detergents are better cleaning agents than soaps.

Question 14:
Soaps act as cleansing agents by
(а) releasing sodium/potassium ions in solution
(b) undergoing a reaction with fat
(c) forming micelles and trapping dust within the micelle
(d) all of the above.

Question 15:
In the presence of calcium and magnesium salts in water, the cleansing capacity of soap
(a) increases
(b) decreases
(c) no change
(d) depends upon the quality of soap.

Question 16:
Identify the statement which is not correct.
(a) Soap forms micelles in soft water.
(b) Soap forms scum in hard water.
(c) Soap forms lather in soft water.
(d) Both ends of a soap molecule are hydrophobic.

Question 17:
On the addition of Na2C03 to hard water
(a) the foaming capacity increases
(b) the foaming capacity decreases
(c) the foaming capacity increases and then decreases
(d) the foaming capacity decreases and then increases.

Question 18:
The correct equation involved in removal of hardness from water is

Short Answer Type Questions

1.Differentiate between soft water and hard water.
2. Are soap molecules hydrophobic or hydrophilic in nature?
3. How is soap able to clean oily dirt?
4. Soap cannot be used in hard water. Why?
5. Give one advantage of

1.  detergent over soap.
2.  soap over detergent

ANSWER KEY
Multiple Choice Questions /VSA

1. (b)
2. (c)
3. (a)
4. (b)
5. (c)
6. (a)
7. (c)
8. (a)
9. (d)
10. (a)
11. (c)
12. (b)
13. (b)
14. (c)
15. (b)
16. (d)
17. (a)
18. (a)

Short Answer Questions

1.

2. A soap molecule is made up of two parts: a long hydrocarbon part and a short ionic part. The long hydrocarbon chain is hydrophobic in nature but the ionic part is hydrophilic in nature.

3. Inside water, soap molecules form a unique orientation around oil or dirt molecule, called micelles. Soap in the form of micelles is able to clean because oily dirt accumulates in the centre
of micelle. Besides this, soap micelles can be easily rinsed away as they are present in the form of colloid.

4. Hard water contains Ca2+ and Mg2+ ions. When soap is added to hard water, Ca2+ and Mg2+ ions react with soap to form calcium and magnesium salts of soap. There salts of soap are insoluble in water and form scum. As a result, a lot of soap is wasted. Because of this reason soap cannot be used in hard water.

5.

1. Detergents can be used in hard water but soap cannot be used in hard water.
2.  Soaps are biodegradable and hence they do not cause pollution. Detergents are non-biodegradable and hence cause water pollution.

 

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CBSE Class 10 Science Practical Skills – pH of Samples

BASIC BUILDING CONCEPTS
The acidic, basic or neutral character of any solution can be expressed by expressing its H⁺ ion concentration. A Danish biochemist Peter Sorensen suggested a method of expressing the concentration of H⁺ ions in terms of pH. In Danish language, pH stands for protenz de hydrogen which means power of H⁺ ions. pH of a solution is given by
pH = -log [H⁺] = log \(\frac { 1 }{ { [H }^{ + }] }\)
where [H⁺] = concentration of hydrogen ions in solution.
To report the pH, a scale from 0 to 14 was devised.

You can also download Class 10 Science NCERT Solutions to help you to revise complete syllabus and score more marks in your examinations.

• For an acidic solution, pH is less than seven.
• For a basic/alkaline solution, pH is greater than seven.
• For a neutral solution, pH is equal to seven.

The pH of a solution is measured accurately using an apparatus known as pH meter. An approximate value of pH can be obtained by using universal indicator/pH paper.
Indicators: are the substances which change the colour at a certain pH. Some common examples of indicators are litmus, phenolphthalein and methyl orange. Out of these, litmus is a natural indicator while phenolphthalein and methyl orange are synthetic indicators. The colour of these indicators in different medium is given in the following table:Universal indicator is a homogeneous mixture which is prepared by mixing a number of common indicators together. It can undergo series of colour change over a pH value ranging from 1-14 to indicate acidity or alkalinity of solutions.
Colour changes observed using universal indicator are given in the following table:
TABLE: Colour of Universal Indicators at Different pH Values
pH paper is a strip of paper which is coated with universal indicator. It is used to measure the acidity or alkalinity of aqueous solutions. To know the pH value of a solution, a drop of solution is placed on the pH strip. The colour produced tells the pH value of the test solution.

NATURE OF CHEMICALS USED IN THIS EXPERIMENT

1. Hydrochloric acid: The chemical formula of hydrochloric acid is HCl. This is a strong acid which is formed by dissolving hydrogen chloride gas in water. In aqueous solution, it gets ionized completely and forms hydrogen ions and chloride ions. The pH of hydrochloric acid is less than 7.
   
2. Sodium hydroxide: The chemical formula of sodium hydroxide is NaOH. In laboratory, it is found in the form of pellets or flakes. Sodium hydroxide is a strong base. On dissolving in water, sodium hydroxide gets ionized completely into sodium ion and hydroxide ion. The pH of sodium hydroxide solution is more than 7.
   
3. Ethanoic acid: Ethanoic acid is also known as acetic acid. Its chemical formula is CH₃ It is a weak acid. In aqueous solution, it gets ionized partially to give hydrogen ion and acetate ion. The pH of ethanoic acid solution is less than 7.
   
4. Lemon juice: Lemon juice is a mixture of acids, carbohydrates and minerals. Due to presence of acids, it is acidic in nature and has pH less than 7.
5. Water: The chemical formula of water is H₂ It is neutral in nature and thus, its pH value is 7.
6. Sodium bicarbonate: It is also known as baking soda or sodium hydrogen carbonate. Its- chemical formula is NaHCO₃. It is a weak base. On dissolving in water, it gets ionized partially to give sodium ion and bicarbonate ion. The pH of solution of sodium bicarbonate is greater than 7.
   

AIM
To find the pH of the following samples by using pH paper/universal indicator:

1. Dilute hydrochloric acid (HCl)
2. Dilute sodium hydroxide  (NaOH) solution
3. Dilute ethanoic acid (CH₃COOH) solution
4. Lemon juice
5. Water
6. Dilute sodium bicarbonate (NaHCO₃) solution.

MATERIALS REQUIRED
Test tubes, test tube stand, droppers or glass rod, pH paper/universal indicator, standard colour chart, glazed white tile and samples of dil. HCl, dil. NaOH, dil. ethanoic acid (acetic acid/vinegar), lemon juice, distilled water and dil. sodium bicarbonate solution.

THEORY

1. pH is the measure of hydrogen ion concentration of a solution.
2. The hydrogen ion concentration (H⁺) for an acidic solution is always greater than 10^-7 mol L^-1 and its pH is, therefore, always less than 7.
3. The hydrogen ion concentration of a basic solution is always less than 10^-7 mol L^-1 and, therefore, its pH is always greater than 7.
4. The hydrogen ion concentration of a neutral solution is 10^-7 mol L^-1 and, therefore, its pH is 7.
5. The pH of a solution can be measured by using a pH paper, universal indicator or pH meter.

PROCEDURE

1. Take the given solutions in separate test tubes marked as A, B, C, D, E and F and keep them in the test tube stand.
   
2. Take six strips of pH paper and place them on a glazed white tile.
3. Using a dropper or a glass rod, place a drop of the test solution on the pH paper.
4. Note the colour developed on the pH paper and compare it with the colour chart of the pH paper.
5. Record the pH value corresponding to the colour.
6. Similarly, using a fresh dropper each time, perform the experiment with the remaining test samples using a fresh strip of pH paper.
7. Record your observations as indicated in the table below.
8. For using universal indicator, add a few drops of universal indicator to each of the test tubes with the test solutions.
9. Note the colour of each solution and compare it with colour on the indicator bottle.
10. Record your observations.

OBSERVATION TABLE

RESULT

1. The pH of dilute solutions of hydrochloric acid, ethanoic acid and lemon juice is less than 7 and therefore, they are acidic in nature.
2. The pH of dilute solutions of sodium hydroxide and sodium bicarbonate is more than 7 and therefore, these solutions are basic in nature.
3. The pH of water is 7 and therefore, it is neutral in nature.

PRECAUTIONS

1. Mark the test tubes carefully.
2. Use distilled water for preparing solutions.
3. Use only standard colour charts supplied with the pH paper for assessing the pH value.
4. Do not touch the pH paper with unclean and wet hands.
5. Keep the pH paper away from chemical fumes. .
6. Do not touch or taste the solutions.
7. Clean the glass rod/dropper properly before reusing.
8. Do not waste pH paper.

INTERACTIVE SESSION

Question 1:
What is the aim of your experiment?
Answer:
The aim of my experiment is to determine the pH of some sample solutions.
Question 2:
What do you understand by pH?
Answer:
pH is the measure of acidity or alkalinity of a sample.
Question 3:
Define pH.
Answer:
pH is defined as the negative logarithm of the hydrogen ion concentration in moles per litre.
Question 4:
What is the pH of an acidic solution?
Answer:
It is less than 7.
Question 5:
What is the pH of a solution with [H⁺] = 10^-9? Is the solution acidic or basic?
Answer:
Since pH = 9, therefore, the solution is basic in nature.
Question 6:
What happens to the pH of pure water if a small amount of acid is added to it?
Answer:
The pH becomes less than seven as the [H⁺] concentration increases.
Question 7:
For a neutral solution, what is the concentration of [H⁺] and [OH^–] in solution?
Answer:
Since for a neutral solution [H⁺] = [OH^–], therefore, their concentrations are 10 ^-7 mol L^-1.
Question 8:
What is an acid-base indicator?
Answer:
Indicator is a substance which tells us whether a substance is acidic or basic by change in colour.
Question 9:
Name any two indicators.
Answer:
Litmus and methyl orange

Question 10:
What is the pH of a soap solution?
Answer:
It lies within the basic region, i.e., > 7.

Question 11:
What is the pH of rainwater and why?
Answer:
pH of rainwater < 7 due to dissolution of acidic gases like NO₂ and SO₂.

Question 12:
What are bases?
Answer:
Substances furnishing OH” ions in solution are called bases.

Question 13:
Which out of NH₄OH and NaOH will have a higher pH and why?
Answer:
NaOH will have a higher pH value as it is a strong base, whereas NH₄OH (ammonium hydroxide) is a weak base.

Question 14:
Why is NH₄OH a weak base?
Answer:
It is a weak base because it ionizes partially in solution.
NH₄OH(aq) \(\)\leftrightharpoons /latex] NH₄⁺(ag) + OH^– (aq).

Question 15:
What is the pH of fluids in our stomach?
Answer:
2

Question 16:
Why?
Answer:
Due to secretion of HCl in gastric juice.

Question 17:
How do we cure hyperacidity?
Answer:
By using an antacid.

Question 18:
What is an antacid?
Answer:
Which increases the pH of stomach fluids as it is basic in nature.

Question 19:
Name any two antacids.
Answer:
Milk of magnesia, Sodium bicarbonate.

NCERT LAB MANUAL QUESTIONS

Question 1:
What is the pH of pure water at 25 C (298K)?
Answer:
The pH of pure water at 298K is 7.

Question 2:
What according to you should be the pH of dil. HCl and dil. NaOH solutions? Observe and explain your findings.
Answer:
Dil. HCl is an acid as it furnishes hydrogen ion in solution and, therefore, its pH will be less than 7.
HCl(aq) ——> H⁺(aq) + Cl^–(aq)
Dil. NaOH on the other hand, is a base as it furnishes hydroxyl ions in solution and therefore, has pH greater than 7.
NaOH(aq) —–> Na⁺(ag) + OH^–(aq)

Question 3:
On opening the soda water bottle the dissolved CO₂ comes out. Would the pH of the solution increase or decrease as the gas comes out? Explain your answer either way.
Answer:
CO₂ in soda water bottle exists as carbonic acid (H₂CO₃). On opening the bottle, CO₂ escapes out. Therefore, the concentration of carbonic acid decreases and pH increases.

PRACTICAL BASED QUESTIONS

Multiple Choice Questions/VSA

Question 1:
On putting a few drops of an unknown liquid on the pH strip as shown here, the colour of pH strip changed to violet. The liquid taken is likely to be  [CBSE 2012, AI 2010]

(a) dilute hydrochloric acid
(b) dilute sodium hydroxide
(c) water
(d) dilute acetic acid.

Question 2:
Bottle ‘A’ contains oxalic acid and bottle ‘B’ contains sodium carbonate solution. When pH paper is dipped in each of the solutions, the colour seen in ‘A’ and ‘B’ respectively be  [CBSE Sample Paper 2009]
(a) orange, blue
(b) blue, orange
(c) green, blue
(d) orange, green

Question 3:
In an experiment to test the pH of a given sample using pH paper, four students recorded the following observations: [CBSE 2012]

Which one of the above observations is incorrect?
(a) I (b) II (c) III (d) IV

Question 4:
To test the presence of a base with a strip of blue litmus you would
(a) moisten the strip with water and dip in the given solution
(b) dip the strip directly into the given solution
(c) dip the strip firstly into an acidic solution and then use it to test the sample
(d) dip the strip into an alkaline solution and then use it to test the sample.

Question 5:
Which of the following solutions with same concentrations will have lowest pH?
(a) CHgCOOH
(b) H₂C0₃
(c) HCl
(d) HCOOH (formic acid)

Question 6:
The pH of NaOH solution is 10.6. On addition of water to this solution its pH
(a) remains same       (b) increases
(c) decreases              (d) becomes 7

Question 7:
Which one is correct for a universal indicator?
(a) It is a solution of phenolphthalein and methyl orange
(b) It is a solution of aq. HCl and aq. NaOH
(c) It is a solution of methyl orange in water
(d) It is a mixture of many indicators

Question 8:
The correct method of finding the pH of a solution is to [CBSE 2012, Delhi 2007]
(а)  heat the solution in a test tube and expose the pH paper to the vapours formed
(b)  pour few drops of the solution from the test tube on the pH paper
(c) drop the pH paper in the solution
(d) put a drop of the solution on the pH paper using a dropper

Question 9:
Two solutions A and B were found to have pH values of 6 and 8 respectively. The inference which can be drawn is [Delhi 2007C]
(а) the strength of solution B is higher than that of A
(b) A is an acid while B is a base
(c) both are acidic solutions
(d) both are basic solutions

Question 10:
Four students (A), (B), (C) and (D) separately measured the pH values of each one of the given samples of distilled water, acetic acid, dilute hydrochloric acid and a solution of sodium hydroxide using pH papers. [CBSE 2011]

Which one of the following represents correct pH value?
(a) A (b) B (c) C id) D

Question 11:
Solid sodium bicarbonate was placed on a strip of pH paper. The colour of the strip [Delhi 2008]
(a) turned blue
(b) did not change
(c) turned green and suddenly yellow
(d) turned light pink.

Question 12:
A student was given four unknown colourless samples labelled A, B, C and D and asked to test their pH using pH paper. He observed that the colour of pH paper turned to light green, dark red, light orange and dark blue with samples A, B, C and D respectively. The correct sequence of increasing order of the pH value for samples is
(a) A  < B < C  < D
(b) A < D <  C < B
(c) C < B  < A  < D        
(d) B < C <  A  < D

Question 13:
A student has four samples A, B, C, D containing dil. HCl, aq. KCl, dil. NaOH and distilled water respectively. The solutions with equal pH are
(a) A and B
(b) B and C
(c) C and D
(d) B and D

Question 14:
What is the correct order for increasing values of pH?
(a) Water < fruit juice < soap solution
(b) Fruit juice < soap solution < water
(c) Fruit juice < water < soap solution
(d) Soap solution < water < fruit juice

Question 15:
On adding methyl orange to solution ‘A’, it imparts a red colour and on adding it to solution ‘B’ a yellow colour is obtained. Solutions ‘A’ and ‘B’ are respectively
(a) neutral, acidic
(b) acidic, basic
(c) basic, acidic
(d) neutral, basic

Short Answer Questions
1. A solution ‘X’ gives orange colour when a drop of  universal indicator is added to it. On the other hand, another solution ‘Y’ gives bluish-green colour when a drop of universal indicator is added to it.
What are the types of solution ‘X’ and ‘Y’ and what type of pH would they have?

2. Hydrochloric acid is a strong acid while acetic acid is a weak acid. Why?

3. How can the pH of a solution be determined?

4. What is an acid-base indicator? Give any two examples of synthetic indicators.

5. Five solutions P, Q, R, S and T when tested with universal indicator showed pH of 13, 8, 1, 7 and 5 respectively.
(a) Which solution is (i) strongly alkaline (ii) weakly acidic?
(b) Arrange the pH in the increasing order of hydrogen ion concentration.

 ANSWER KEY

Multiple Choice Questions /VSA
1. (b)
2. (a)
3. (a)
4. (c)
5. (c)
6. (c)
7. (d)
8. (d)
9. (b)
10. (d)
11. (b)
12. (d)
13. (d)
14. (c)
15. (b)

Short Answer Questions

1. pH is a number which indicates acidic or basic nature of a solution.
Solution X’ is acidic in nature, i.e. pH < 7.
Solution Y is basic in nature, i.e., pH > 7.

2. The strength of acids depends on the number of H⁺ ions produced in them. Acids which on dissolving in water give rise to more H⁺ ions are called strong acids and acids which give less H⁺ ions are called weak acids. In aqueous solution, hydrochloric acid ionises completely to give more H⁺ ions and therefore, hydrochloric acid is a strong acid. In aqueous solution, acetic acid ionises partially to give less H⁺ ions and therefore, it is a weak acid.

3. pH of a solution can be determined by two methods:

1. By using universal indicator: To measure the pH of a solution, a paper strip impregnated with universal indicator called pH paper can be used
2. By using pH meter: With the help of pH meter, pH of a solution can be measured accurately.

4. A substance that indicates the acidity or basicity of a solution through characteristic colour changes is called acid-base indicator. Methyl orange and phenolphthalein are the two examples of synthetic indicators.

5. (a) (i) Solution- P (ii) Solution- T
(b) The solution with highest pH (13) will have minimum hydrogen ion concentration whereas solution having the least pH (1) will have maximum hydrogen ion concentration. So, we can arrange the given solutions in increasing order of their hydrogen ion concentrations as follows:

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