Is Matter Around Us Pure

(a) Sodium chloride from its solution in water — Evaporation

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride — Sublimation

(c) Small pieces of metal in the engine oil of a car — Filtration

(d) Different pigments from an extract of flower petals — Chromatography

(e) Butter from curd — Centrifugation

(f) Oil from water — By a separating funnel

(g) Tea leaves from tea — By using stainer for filtration

(h) Iron pins from sand — By using a magnet

(i) Wheat grains from husk — Sedimentation/winnowing

(j) Fine mud particles suspended in water — Sedimentation/decantation

Steps for making tea are:

1. Take one cup of water as solvent and boil it for few minutes.
2. When solvent boils, add solutes, i.e., milk, tea leaves, sugar. Boil the solution for a few minutes.
3. Milk is soluble in water. Sugar also dissolves in the solution but tea leaves remain as filtrate.
4. The insoluble residue of tea leaves is filtered using a strainer and the tea is ready.

(a) Given,

Mass of potassium nitrate required to produce a saturated solution in 100 g of water at 313 K = 62g

Mass of potassium nitrate required to produce a saturated solution in 50 g of water = ?

Required amount = $\dfrac{62}{100}$ x 50 = 31

Hence, 31 g of potassium nitrate is required.

(b) The solubility of potassium chloride in water is decreased when the saturated solution of potassium chloride loses heat at 353 K. So, Pragya would observe crystals of potassium chloride, which would have surpassed its solubility at low temperatures.

(c) As per the given data :

Solubility of potassium nitrate at 293 K = 32 g

Solubility of sodium chloride at 293 K = 36 g

Solubility of potassium chloride at 293 K = 35 g

Solubility of ammonium chloride at 293 K = 37 g

We can observe from this data that ammonium chloride has the highest solubility at 293 K.

(d) The solubility of the salt increases with an increase in temperature.

(a) Saturated solution — A saturated solution is one which cannot dissolve more of the solute at a given temperature.

Example: Excess carbon leaves off as bubbles from a carbonated water solution saturated with carbon.

(b) Pure substance — A substance is said to be pure when it comprises of only one kind of molecules or atoms.

Example: Sulphur, diamonds etc.

(c) Colloid — A colloid is a heterogeneous mixture in which the size of solute particles is intermediate between true solution and suspension and it shows tyndall effect.

Examples: Soap solution, starch solution, milk.

(d) Suspension — It is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it. Particles of a suspension are visible to the naked eye.

Examples: Chalk water mixture, muddy water etc.

The given elements are classified below:

1. Soda water — Homogenous mixture
2. Wood — Heterogeneous mixture
3. Air — Heterogeneous mixture
4. Soil — Heterogeneous mixture
5. Vinegar — Homogenous mixture
6. Filtered tea — Homogenous mixture

We can confirm if a colourless liquid is pure water by boiling it. If it boils at 100°C, then its pure. However, if there is an increase or decrease in the boiling point, then we can say that impurities are added to water.

Following substances from the above-mentioned list are pure substances:

• Ice

• Iron

• Hydrochloric acid

• Calcium oxide

• Mercury

The following are the solutions from the above-mentioned list of mixtures:

• Sea water

• Air

• Soda water

Tyndall effect is shown by:

(a) milk

(b) starch solution

The following are chemical changes :

(a) Growth of a plant

(b) Rusting of iron

(c) Cooking of food

(d) Digestion of food

(e) Burning of a candle

A substance is a pure single form of matter. It is made up of one kind of atoms or molecules and has definite properties.

Example: Copper, oxygen, hydrogen etc.

Differences between homogeneous and heterogeneous mixtures are:

Given,

Mass of solute (NaCl) = 36 g

Mass of solvent (H₂O) = 100 g

Mass of solution (NaCl + H₂O) = 100 + 36 = 136 g

Concentration = $\dfrac{\text{Mass of solute}}{\text{Mass of solution}}$ x 100

Concentration = $\dfrac{36}{136}$ x 100 = 26.47%

Hence, the concentration of the solution is 26.47%

The following is the classification into physical and chemical change:

1. Cutting of trees — Physical change
2. Melting of butter in a pan — Physical change
3. Rusting of almirah — Chemical change
4. Boiling of water to form steam — Physical change
5. Passing of electric current through water and the water breaking down into hydrogen and oxygen gases. — Chemical change
6. Dissolving common salt in water — Physical change
7. Making a fruit salad with raw fruits — Physical change
8. Burning of paper and wood — Chemical change

Listed below are the classifications based on pure substances and mixtures: