Is Matter Around Us Pure

NCERT Activity: 2.7 Solution (Chapter: Is matter around us pure)

• Take a thin strip of filter paper.

• Draw a line on it using a pencil, approximately 3 cm above the lower edge [Fig. 2.8 (a)].

• Put a small drop of ink (water-soluble, that is, from a sketch pen or fountain pen) at the centre of the line. Let it dry.

• Lower the filter paper into a jar/glass/beaker/test tube containing water so that the drop of ink on the paper is just above the water level, as shown in Fig. 2.8(b) and leave it undisturbed.

• Watch carefully, as the water rises up on the filter paper. Record your observations.

Now answer

• What do you observe on the filter paper as the water rises on it?

• Do you obtain different colours on the filter paper strip?

• What according to you, can be the reason for the rise of the coloured spot on the paper strip?

Question: What do you observe on the filter paper as the water rises on it?

Answer Different colours also rise along with the rising of water on filter paper.

Question: Do you obtain different colours on the filter paper strip?

Answer Different colours are obtained on the filter paper strip.

Question: What according to you, can be the reason for the rise of the coloured spot on the paper strip?

Dye present in ink dissolves in water and rises up along with water on the filter paper. Colour that has more solubility rises higher on the filter paper.

This method to separate components of ink is called Chromatography

NCERT Activity: 2.8 Solution (Chapter: Is matter around us pure)

• Let us try to separate acetone and water from their mixture.

• Take the mixture in a distillation flask. Fit it with a thermometer.

• Arrange the apparatus as shown in Fig. 2.9.

• Heat the mixture slowly keeping a close watch on the thermometer.

• The acetone vaporizes, condenses in the condenser, and can be collected from the condenser outlet.

• Water is left behind in the distillation flask.

Now answer

• What do you observe as you start heating the mixture?

• At what temperature does the thermometer reading become constant for some time?

• What is the boiling point of acetone?

• Why do the two components separate?

Question: What do you observe as you start heating the mixture?

Answer

After starting heating following things are observed.

• After some time, some bubbles get condensed on the upper wall of the flask.

• After some more time, more bubbles start getting condensed on the upper wall, that cooler area of the flask.

• At about 40⁰ C, more bubbles start coming out of the mixture, and some liquid gets condensed near the mouth of the condenser.

• At about 50⁰ C, liquid, acetone is started collecting in the collecting flask drop by drop.

• Temperature became almost constant near 57⁰C.

Question: At what temperature does the thermometer reading become constant for some time?

Answer At about 57⁰C the temperature on the thermometer became constant for some time.

Question: What is the boiling point of acetone?

Answer As, temperature became constant near 57⁰C for some time, so the boiling point of the acetone is around 56⁰C to 57⁰C.

Question: Why do the two components separate?

Answer

We can separate two components because of the difference in their physical properties.

In the case of the mixture of acetone and water, the boiling point of acetone is lower than that of the water.

The boiling point of acetone is 56.2⁰C while the boiling point of water is 100⁰C.

Because of enough difference in the boiling point of acetone and water, these components can be separated easily using the method of distillation. As we did in this activity.

Activity: 2.9 Solution (Chapter: Is matter around us pure)

• Take some (approximately 5 g) impure sample of copper sulphate in a china dish.

• Dissolve it in minimum amount of water.

• Filter the impurities out.

• Evaporate water from the copper sulphate solution so as to get a saturated solution.

• Cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day.

• You will obtain the crystals of copper sulphate in the china dish.

• This process is called crystallisation.

Now answer

• What do you observe in the china dish?

• Do the crystals look alike?

• How will you separate the crystals from the liquid in the china dish?

Question: What do you observe in the china dish?

Answer Observation in china dish:

• On heating, water vapour starts coming out of china dish

• After some time, gradually blue colored crystals are started forming

Question: Do the crystals look alike?

Answer Yes, all crystals are look alike, but different in sizes.

Question: How will you separate the crystals from the liquid in the china dish?

Answer Crystals of copper sulphate have been put on a filter paper using a spatula. In this way, the liquid left in the china dish is soaked with filter paper, and dry crystals of copper sulphate have been obtained.

Activity: 2.10 Solution (Chapter: Is matter around us pure)

• Divide the class into two groups. Give 5 g of iron filings and 3 g of sulphur powder in a china dish to both the groups.

Group I

• Mix and crush iron filings and sulphur powder.

Group II

• Mix and crush iron filings and sulphur powder. Heat this mixture strongly till red hot. Remove from flame and let the mixture cool.

Groups I and II

• Check for magnetism in the material obtained. Bring a magnet near the material and check if the material is attracted towards the magnet.

• Compare the texture and colour of the material obtained by the groups.

• Add carbon disulphide to one part of the material obtained. Stir well and filter.

• Add dilute sulphuric acid or dilute hydrochloric acid to the other part of the material obtained. (Note: teacher supervision is necessary for this activity).

• Perform all the above steps with both the elements (iron and sulphur) separately.

Now Answer

• Did the material obtained by the two groups look the same?

• Which group has obtained a material with magnetic properties?

• Can we separate the components of the material obtained?

• On adding dilute sulphuric acid or dilute hydrochloric acid, did both the groups obtain a gas? Did the gas in both the cases smell the same or different?

Question: Did the material obtained by the two groups look the same?

Answer

No. Materials obtained by the two groups do not look same.

Group I obtained a heterogeneous mixture of iron fillings and sulphur, in which iron fillings are visible.

While group II obtained a different material in which no iron fillings are visible, i.e. appears homogeneous.

Question: Which group has obtained a material with magnetic properties?

Answer Group – I obtained a material with magnetic properties.

Question Can we separate the components of the material obtained?

Answer

Material obtained by group – I can be separated into its component.

Material obtained by group – II cannot be separated into its component.

Question: On adding dilute sulphuric acid or dilute hydrochloric acid, did both the groups obtain a gas? Did the gas in both the cases smell the same or different?

Answer

Yes. Gas is obtained on adding dilute sulphuric acid or dilute hydrochloric acid in materials obtained by both of the groups.

Group – I: On adding dilute sulphuric acid or dilute hydrochloric acid a gas is evolved which burns with a pop sound when a lighted match stick is brought near the test tube.

Group – II: On adding dilute sulphuric acid or dilute hydrochloric acid a gas is evolved does not burn with a pop sound when a lighted match stick is brought near the test tube. Rather it gives a black precipitate when it is passed to copper sulphate solution.

This shows this gas is hydrogen sulphide.