CBSE Class 9 Science Practical Skills – Mixture and Compound
(a) a mixture
(b) a compound using iron filings and sulphur powder and distinguish between these on the basis of:
- appearance, i.e. homogeneity and heterogeneity
- behaviour towards a management
- behaviour towards carbon disulphide (a solvent)
- effect of heat
China dish, tripod stand, wire gauze, iron filings, sulphur burner, test tube stand and test tube holder.
Formation of mixture is a physical change while formation of compound is a chemical change. Mixture may be homogeneous or heterogeneous while compounds are always homogeneous. In a mixture, components retain their individual properties while the components of a compound lose their individual properties. The components of a mixture can be separated by physical methods while the components of compounds cannot be separated by physical methods.
Preparation of mixture of iron and sulphur:
Take 7 g iron filing and 4 g sulphur powder in a petri dish and mix them properly. Label this mixture as A.
Preparation of compound iron sulphide:
Take 7 g iron filing and 4 g sulphur in a china dish. Heat this mixture gently and then strongly. Stir constantly till black mass or compound of iron and sulphur is formed.
Cool the content of china dish and powder the black mass. Label compound powder as B.
PROCEDURE, OBSERVATION AND INFERENCE
- ‘A’ is a mixture which is prepared by mixing iron filings and sulphur.
- ‘B’ is a compound which is formed by strongly heating a mixture of iron filings and sulphur. The chemical equation for this change is as follows:
- Mixture of iron filings and sulphur is heterogeneous while the compound iron sulphide is homogeneous.
- Properties of FeS are different from the properties of its constituents.
- Handle the chemicals carefully.
- Do not bring CS2 near the flame as it is highly inflammable.
- Heating of mixture of iron filing and sulphur should be done in china dish.
- Wash your hands properly with soap after the experiment.
What is a mixture?
Two or more components when present together in any ratio, without undergoing a chemical change, is called a mixture.
Give two examples of a mixture.
Sand and salt, aerated drinks.
What are the different types of mixture based upon their compositions?
Based upon the composition mixtures are of two types; homogeneous and heterogeneous.
What is a compound? ’
When two or more substances are chemically combined in a fixed ratio, a compound is formed.
Give two examples of a compound.
What is a homogeneous mixture?
A homogeneous mixture has uniform distribution of components.
What is a heterogeneous mixture?
A mixture in which components are not distributed evenly is a heterogeneous mixture.
Give two examples of each type of a mixture.
Homogeneous mixture: sugar solution, sulphur in CS2
Heterogeneous mixture: sand in water, milk in water.
How can mixtures be separated?
Mixtures can be separated by different physical methods based upon the properties of the constituents, e.g. filtration, decantation, evaporation and magnetic separation.
Why can a mixture of iron and sulphur be separated using a magnet?
Iron being magnetic and retaining its properties in a mixture, gets attracted towards the magnet and can therefore, be separated from sulphur which is not attracted towards the magnet.
Why is mixing of iron and sulphur a physical change?
Iron and sulphur do not lose their properties, therefore, mixing of iron and sulphur is a physical change.
What happens when a mixture of iron and sulphur are heated?
A black compound called iron sulphide (FeS) is formed.
Give the equation involved.
Is this combination of iron and sulphur a physical or a chemical change? Why?
It is a chemical change as both iron and sulphur lose their properties.
How can you separate the components of a compound? ‘
The components of a compound are separated by chemical methods.
Is the reaction between FeS and H2S04 [FeS + H2S04 —> FeS04 + H2S] , a chemical or a physical change?
It is a chemical change.
Which out of iron and sulphur would be soluble in CS2?
Sulphur is soluble in CS2
Which out of Fe and S is a metal and which is a non-metal?
Fe is a metal, whereas sulphur is a non-metal.
Is rusting of iron a physical or a chemical change?
Rusting of iron is a chemical process.
Give two examples of a chemical change in daily life.
Digestion and curdling of milk.
Is melting of butter a physical or a chemical change?
Melting of butter is a physical change.
Why is FeS unaffected by a magnet?
FeS is a compound in which iron has lost its properties so it is unaffected by a magnet.
NCERT LAB MANUAL QUESTION
Why does brass react with dilute hydrochloric acid and is corroded in rainy season to form CUC03.CU(0H)2?
Brass is an alloy and is a homogeneous mixture and thus retains the properties of its constituents. It, therefore, reacts with dil. HCl and is corroded in rainy season due to the formation of basic copper carbonate CUC03.CU(0H)2.
PRACTICAL BASED Questions/VSA
Multiple Choice Questions/VSA
When iron filings and powdered sulphur are mixed together in a china dish
(а) a heterogeneous mixture results.
(b) the constituents present can easily be seen.
(c) the constituents can be separated by a magnet.
(d) all the above are correct.
To prepare iron sulphide, by heating a mixture of iron filings and sulphur powder, we should use a
(a) copper dish
(b) watch glass
(c) china dish
(d) petri dish.
The reaction between iron and sulphur is accompanied by
(a) evolution of light
(b) absorption of heat
(c) release of heat
(d) both (a) and (c).
When magnet is rolled in the compound of iron sulphide then
(a) Iron particles are attracted towards the magnet
(b) Iron sulphide clings to the magnet
(c) Iron sulphide does not cling to the magnet
(d) None of the above.
When a mixture of iron filings and sulphur is put in carbon disulphide in a test tube, we observe that
(a) yellow particles of sulphur get dissolved in it.
(b) grey particles of iron get dissolved in it.
(c) both iron and sulphur particles get dissolved in it.
(d) neither iron nor sulphur particles get dissolved in it.
Sulphur is insoluble in
(d) both (b) and (c)
The production of HCl gas on the addition of H2S04 to NaCl is
(a) physical change
(b) chemical change
(c) initially physical then chemical
(d) initially chemical then physical.
In laboratory, what precaution has to be taken with carbon disulphide?
(a) Kept away from flame.
(b) Kept away from carbon.
(c) Kept away from distilled water.
(d) Kept away from iron sulphide.
A magnet is repeatedly moved closely over a mixture of iron powder and sulphur powder. Which of the following statements is false?
(а) Iron powder is attracted towards magnet.
(б) Sulphur powder is left behind.
(c) Black FeS will be formed.
(d) Iron powder and sulphur powder are separated.
Which one of the following will result in the formation of a mixture?
(а) Crushing of a marble tile into small particles.
(b) Breaking of ice cubes into small pieces.
(c) Adding sodium metal to water.
(d) Agitating a detergent with water in a washing machine.
Four students A, B, C and D added carbon disulphide to (i) A mixture of iron filings and sulphur and (ii) Iron sulphide. They made the following observations:
Student A – Iron dissolved in CS2, in case (i) but iron sulphide did not dissolve in CS2 in (ii).
Student B – Iron sulphide dissolved inCS2 whereas neither iron nor sulphur dissolved in the mixture.
Student C – Sulphur dissolved in CS2 from the mixture of iron and sulphur but iron sulphide did not dissolve.
Student D – Sulphur, in the mixture of iron and sulphur, as well as iron sulphide were solution in CS2
The correct observation is that of student
Observe the following diagram and give the correct option.
(a) III is an element
(b) II is a mixture
(c) IV is a compound
(d) I is a element
Sample (X) is a mixture of iron and sulphur. On separately heating sulphur in excess of air, (Y) is formed. Which of the following is true for (X) and (Y) respectively?
(a) Heterogeneous, homogeneous
(b) Heterogeneous, heterogeneous
(c) Homogeneous, homogeneous
(d) Homogeneous, heterogeneous.
The correct representation for the formation of iron sulphide from a reaction between iron and sulphur on heating is
Take mixture of iron filings and sulphur powder in one watch glass. In the other watch glass, put iron sulphide. Now, move a bar magnet over both the watch glasses. The correct observation would be ‘
(a) Bar magnet attracts iron filings from one watch glass and iron sulphide from the other watch glass.
(b) Only iron sulphide is attracted by the bar magnet.
(c) Bar magnet attracts all the substances present in the two watch glasses.
(d) Bar magnet attracts only iron filings.
Multiple Choice Questions/VSA