combinepdf (2)

12. 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 Solubility
Potassium chloride 21 32 62 106 167
Ammonium Chloride 36 36 36 37 37
35 35 40 46 54
24 37 41 55 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
salt?

a) Mass of potassium nitrate in 50 gm of water in the saturated
solution a 313 K = 62 g x 50 g = 31 g

100 g

b) As the solution cools solubility decreases. Hence potassium
chloride crystals separate out.

c) Solubility of potassium nitrate at 293 K = 32g / 100g water
Solubility of Sodium chloride at 293 K = 36 g / 100g water
Solubility of Potassium chloride at 293 K = 35g / 100g water
Solubility of Ammonium Chloride at 293 K = 37g / 100g water

Ammonium chloride has the highest solubility at 293 K.

d) The solubility of salt increases with increase in temperature. The
solubility of potassium nitrate increases appreciably, that of
Ammonium chloride increases slightly, that of potassium chloride
increases marginally while that of sodium chloride almost remains
constant.

13. Alloys cannot be separated into their components by
physical methods, yet it is considered to be a mixture. Why?

• Alloys can have variable composition.
• It shows the properties of its components.

So it is considered as a mixture.

14. To make a saturated solution, 36 gram of sodium chloride is
dissolved in 100 gram of water at 293K. Find its concentration at
this temperature.

Concentration means amount of a solute dissolved in 100 gram of
solvent. Here, 36 gram of sodium chloride are dissolved in 100
gram of water, therefore, concentration of the solution is 36 gram
per 100 gram of water.

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