CBSE Class 10 Science Practical Skills – Introduction
Theoretical knowledge supplemented by practical knowledge, helps the student anchor the science concepts firmly into their mind. It is this that makes lab experiments an integral part of school curriculum and laboratories, the primary workshops where theoretical aspects are verified.
General Lab Instructions
- Always carry practical record book, laboratory manual, notebook (to record observations), pen, pencil, scale, eraser, sharpener, scissors, forceps, scalpel, dissecting needle, brush, blades, etc. to the laboratory.
- Maintain discipline and silence in the lab.
- Keep your seat neat and tidy.
- Follow the instructions given by the teacher attentively.
- Perform the experiment carefully and note down the observations.
- Handle the lab apparatus and glassware with care.
- Do not manipulate your results in any circumstances.
- Use newspaper or blotting paper while using stains so as not to spoil the table.
- Draw the diagrams neatly and label them correctly. Use fine HB pencil while drawing.
- Do not play, whistle or stoop into your partner’s set-up.
Since specified marks are reserved for the presentation of the record file in the Annual Practical Examination, it is important to maintain neatness and clarity while recording instructions and observations.
How to record:
Plotting A Graph
All experiments should include measurements. In all measurements, data can be presented in tabular and/or graphical form.
Tabular form is presented in the following forms:
- headed columns,
- numbered rows, and
- mixed format.
To make the dependence between two quantities more visible or to visualise easily, results are presented in graphical form.
Graph is the most convenient way to show the dependence between the quantities clearly. It is also a quick way to make an average set of observations. Therefore, a graph is a straight line or a curve showing the variation of two variable quantities (or their powers or functions) of which one varies due to change in the other. It enables us to
- determine the value of a quantity which is not observed during the experiment.
- deduce the mathematical relationships between the two quantities which were earlier not known.
- verify laws like Ohm’s law, Boyle’s law, etc.
- perceive the error in the result at a glance.
- calibrate certain instruments, such as ammeter, voltmeter and to determine their true readings.
To plot a graph between two variables (independent and dependent variables) following seven steps are followed :
- Select the title
- Draw two axes with proper origin
- Label of both the axes
- Mention proper units of the quantities on each axis,
- Select and mention the scale used on each axis
- Plot of points with crosses or dots and circles,
- Draw of best fit straight line or smooth curve.
In plotting the graph between dependent and independent variables, the dependent variable should be plotted as ordinate on the y-axis e.g., in the verification of Boyle’s law where volume is measured for various values of pressure. Here, pressure is independent variable and volume is the dependent variable.
The scale used should be convenient for calculation work and occupy a wide sweep of the space available. If scale chosen will be too large, it will tend to highlight the errors of observation and hide the relationship between the variables taken along abscissa (x-axis) and ordinate (y-axis). Each point on the graph shows an actual observation but departure of the point from the final curve is a measure of experimental error in that observation.
Whenever we have to get some information, it should be obtained from a straight line graph because it is more accurately drawn and deductions from such graph are more reliable than the curved graphs. If the relationship between two variables is not a linear relationship, try to obtain a linear relationship by plotting powers of one or other or both of the quantities e.g., in a simple pendulum experiment a plot of time period T against length of the pendulum L is a parabolic graph while T2 versus L is a straight line.
Determination of the slope of a line:
To calculate the slope, take two points on the line well apart. Read the values on x-axis and y-axis respectively at these two points drawing the abscissa and ordinate clearly.
Determination of the slope of a curve:
To determine the slope of a curve at a point P on the curve, a tangent is drawn at that point. Take a strip of plane mirror and place it edgewise such that its reflecting surface MN is over the point P. See the image of the portion PQ of the curve in the mirror and adjust its position by slightly turning about the point P such that the image of PQ coincides with the portion PR of the curve. This will happen when the mirror is exactly normal to the curve at point P. Mark a straight line MPN along the edge of the mirror. Now draw a line MPN’ perpendicular to MPN at point P with the help of a protractor. This line MPN’ is tangent to the curve at point P. Now, draw a perpendicular N’L from N’ on the x-axis. From the AM’N’L
Similarly, if you take different points on the curve, you will observe that the inclination or slope of different parts of the curve is different.
Handling A Microscope
- Clean the lenses and metal parts including stage with tissue paper or muslin cloth.
- Do not remove objective lenses from nosepiece.
- Be careful so that objective lens should not touch the slide in any case. While adjusting, do not move the lens downward, it should always be moved from bottom towards upward direction.
- Keep the microscope covered when not in use.
- Always hold the microscope with both the hands in an upright position while carrying it.
- First focus the slide in low power and then only change to high power.
- Do not use coarse adjustment screw while using high power objective lens.
- Keep the microscope in upright position, do not move the stage in a slanting position.
- Act responsibly at all times in the laboratory.
- Follow all written and verbal instructions carefully. In case you do not understand a direction or any part of the experiment, ask your teacher before proceeding.
- Never work in the laboratory without the presence of the teacher.
- While entering a science room, do not touch any equipment, chemical or other material in the laboratory area until you are instructed to do so.
- Perform only those experiments which are authorized by your teacher.
- Do not use laboratory glassware as containers for food or beverages.
- Always work in a well-ventilated area.
- Keep the work area clean and tidy at all times.
- Be alert. Notify the teacher immediately of any unsafe conditions you observe.
- Dispose all chemical waste properly. Never mix chemicals in sink drains. Sinks are to be used only for water. Check with your teacher for disposal of chemicals and solutions.
- Set up and use the equipments as directed by your teacher.
- Keep hands away from face, eyes, mouth, and body while using chemicals or any lab equipment. Wash your hands with soap and water after performing all experiments.
- Experiments must be performed at all times.
- Know the locations and operating procedures of all safety equipments including: first aid kit(s) and fire extinguisher. Know where the fire alarm and the exits are located.
- Whenever you use chemical, heat substances or glassware, wear safety goggles.
- Contact lenses should never be worn in the laboratory.
- Dress properly during a laboratory activity. Long hair, dangling jewellery and loose or baggy clothing are a hazard in the laboratory.
- A lab coat or smock should be worn during laboratory experiments.
- If a chemical splashes in your eye(s) or on your skin, immediately flush with running water for at least 20 minutes.
- All chemicals in the laboratory are to be considered dangerous. Avoid handling chemicals with fingers. Always use a tweezer. When making an observation, keep at least 1 foot away from the specimen.
- Do not taste or smell any chemicals.
- Check the label on all chemical bottles twice before taking any of the contents. Take only as much chemical as you need.
- Never put back the unused chemicals to their original container.
- Never remove chemicals or other materials from the laboratory area.
- Examine glassware before each time you use. Never use chipped, cracked or dirty glassware.
- Do not immerse hot glassware in cold water. The glassware may shatter.
- Do not place hot apparatus directly on the laboratory desk. Always use an insulated pad.
- Heated glassware remains very hot for a long time. They should be set aside in a designated place to cool, and picked up with caution. Use tongs or heat protective gloves if necessary.
- Never look into a container that is being heated.
Lab Safety Symbols
Be it a middle school science lab or an advanced genetic research laboratory, the lab safety symbols are mandatory. Students should understand them and do the needful, so as to maintain a safe place to work in.
Poison Safety: The universal cross-bone symbol indicates danger and to follow safety tips. The poison symbol is same as the danger sign, which is used for labelling a poisonous substance in a bottle, test tube or package.
Eye Safety: The eye safety symbol is very easy to identify. If you notice a goggle sign outside a lab, it indicates the necessity to wear safety glasses before entering the lab. Putting safety goggles is a part of chemistry lab safety rules.
Fire Safety: As the name suggests, fire safety symbol is put in the lab so that students take care of themselves when they are around flames. This personal safety symbol is a flame without any signs attached to it.
Sharp Object Safety: Using needles, scalpels or other sharp instruments is quite common in biology experiments. The sharp object safety symbol is a hand with a cut in the forefinger. This is to alert the students while using sharp objects.
Biohazard Alert: Biological hazard refers to dangers from living organisms. Appeared in biology and microbiology labs, the biological hazard symbol is to make people aware about the harmful effects of bacteria and alike pathogens used in practical.
Radioactive Safety: Radioactive and radiation symbols are nearly similar to each other. These symbols appear as if some rays are radiated from the centre to the peripheral parts. Often, they are put with bright colours, so that people can see from a distance.
Thermal Safety: Heating and boiling are common steps for science practical. The thermal safety symbol is very simple and resembles a hand glove. It is used to remind students to take precaution while handling a hot object.
Open Flame Alert: Students using open flame should take precaution while conducting flame involved experiments. The symbol is a flame with a diagonal line over it. The objective is to avoid explosion and fire, which may be caused due to negligence in handling open flames.
Chemical Safety: You will find this in the list of chemistry and biold’gy lab safety symbols. The symbol is a bottle with something pouring from it. Chemical safety sign is put up, if the chemicals used in experiments are detrimental to the skin.
First Aid: The first aid symbol attached in laboratories can be as simple as a white coloured plus sign in a green background, a first aid box, a heart sign with a defibrillator or other complex figures which are specific to a particular theme.
Some Common Lab Apparatus