Q27 of 40 Page 2

Pragya tested the solubility of four 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).


(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 in temperature on the solubility of a salt?

(a) Mass of KNO3 to produce a saturated solution of KNO3 in 100 gm of water at 313 K = 62 g

Therefore, mass of KNO3 in 50 g of water at 313 K = 62.050/100 = 31.0 g


31 g of potassium nitrate is needed to produce a saturated solution of potassium nitrate at 313 K.


(b) When the saturated solution of potassium nitrate is left to cool at room temperature, then solid potassium chloride will separate gradually from the solution. Solubility of a substance depends on the temperature. Solubility increases with increase in temperature of the solution. Room temperature is lower than 313 K hence, the crystals of solute will separate out from the solution.


(c) The solubility of different salts at 293 K is: Potassium nitrate 32g ; Sodium chloride 36g; Potassium chloride 35g; and Ammonium chloride 37g. Ammonium chloride has the highest solubility of 37 g at 293 K.


(d) Solubility of a substance depends on the temperature. The given data shows that the solubility of a salt increases on increasing the temperature.

More from this chapter

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25

Draw a labelled diagram to show separation of dyes in black ink using a chromatography method.

 26

Draw a labelled diagram showing the process of fractional distillation.

 28

Which separation technique will you apply for the separation of the following?

(a) Sodium chloride from its solution in water


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


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


(d) Different pigments from an extract of flower petals.


(e) Butter from curd.


(f) Oil from water.


(g) Tea leaves from tea.


(h) Iron pins from sand.


(i) Wheat grains from husk.


(j) Fine mud particles suspended in water.

 29

There are three substances X, Y and Z. The substance X does not have a fixed melting point or boiling point and it still shows the individual properties of its constituents. The substance Y is a pure substance which occurs in nature as such. The substance Y has a fixed melting point and boiling point but it cannot be broken down into simpler substances by any chemical means. The substance Z is also a pure substance whose properties are entirely different from those of its constituents. The substance Z can, however, be divided by electrolysis into two substances which belong to the same class of substances as Y.

(a) What type of substance could X be? Name one substance like X.


(b) What type of substance could Y be? Name one substance like Y.


(c) What type of substance could Z be? Name one substance like Z.


(d) Which process involves absorption or release of an appreciable amount of energy: formation of substance X or formation of substance Z?


(e) Name the three groups into which all the substances like Y are divided on the basis of their properties.