Question of Exercise 6 (Subjective)

Is matter around us pure of Class 9

Question
Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

Substance Dissolved

Temperature in K

283

293

313

333

353

Potassium nitrate
Sodium chloride
Potassium chloride
Ammonium chloride

21
36
35
24

32
36
35
37

62
36
40
41

106
37
46
55

167
37
54
66

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?

Solution

(a) As per table : 100 g of water dissolves potassium nitrate = 62 g

∴ 50 g of water dissolves potassium nitrate = = 31 g.

Hence, 31 g of potassium nitrate would be needed to produce a saturated solution of potassium nitrate.

(b) On changing the temperature of the saturated solution from 353 K to room temperature, cooling takes place. Since the solution is saturated, solubility of potassium chloride will decrease due to cooling. Consequently, the crystals of potassium chloride will be observed in the solution. As the solubility of potassium chloride at 353 K is 54 g while at 293 K (Room temperature) it is 35 g, therefore 54 − 35 = 19 g salt will precipitate out.

(c) The solubility of a solute is the maximum amount of solute that can be dissolved in 100 g of the given solvent to obtain a saturated solution at a particular temperature. Hence, the solubilities of different salts at 293 K are :

Salt Solubility at 293 K

(i) Potassium nitrate : 32 g per 100 g of water.

(ii) Sodium chloride : 36 g per 100 g of water.

(iii) Potassium chloride : 35 g per 100 g of water.

(iv) Ammonium chloride : 37 g per 100 g of water.

Thus, ammonium chloride has the highest solubility at this temperature of 293K.

(d) The solubility of a salt increases with an increase in temperature. The solubility of a salt decreases with a decrease in temperature.

Frequently Asked Questions

What is the chemical formula of ferrous sulphate

Solution:

Solution:

Explanation:

The chemical formula of ferrous sulphate is FeSO_4.

The cationic part is ferrous i.e Fe⁺² while the anionic part is sulphate i.e SO₄^2-.

Since the charge on both species is equal and opposite i.e 2 , so they balance each other in the compound.

Final Answer:

Hence, the correct chemical formula of ferrous sulphate is FeSO₄..

Isotonic solutions are solutions having the same

A: Surface tension

B: Vapour pressure

C: Osmotic pressure

D: Viscosity

Solution:

Correct option is: (C) osmotic pressure.

Explanation:-

Isotonic solutions have the same osmotic pressure because they have the same solute concentration.

Osmotic pressure depends only on solute concentration and temperature.

Name the method you will use to separate two immiscible liquids

Solution:

Explanation:

Separation of immiscible liquids can be done by a separating funnel.
The two liquids are put into the funnel and left for some time.
After some time that settles out and forms two different layers.
The cork of the funnel is opened to allow the bottom liquid to flow.
The bottom liquid is collected in another vessel.

Final Answer: Hence Separation of immiscible liquids can be done by a separating funnel.

What is the chemical formula of Aluminium hydroxide

A. Al (OH)₂

B. Al (OH)₃

C. Al₂ (OH)₃

D. Al₂ (OH)

Solution:

Explanation:-

The atomic number of Aluminium is 13 and its electronic configuration is [Ne]3s²3p¹.

It contain three electron in its valence shell so in a neutral state it can expand it covalency upto 3 So the formula becomes Al (OH)₃

Two immiscible liquids are separated by

A: Separating funnel

B: Fractional distillation

C: Chromatography

D: Sublimation

Solution:

Correct Option is: (A)

Separating funnel

Explanation:

Immiscible liquids are those which don't dissolve into each other
They can be separated by using a separating funnel.
Fractional distillation is used to separate two miscible liquids which have significant differences in their boiling point.
Chromatography is a laboratory method used for the separation of a mixture into its components.
Sublimation Is conversion of a substance from the solid to the gaseous state without becoming liquid.

Is matter around us pure of Class 9

Frequently Asked Questions

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