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Is Matter Around Us Pure ? — Science STD 9 — Question

Rajasthan BoardEnglish MediumSTD 9ScienceIs Matter Around Us Pure ?4 Marks
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
Solubility
Potassium nitrate 21 32 62 106 167
Sodium chloride 36 36 36 37 37
Potassium chloride 35 35 40 46 54
Ammonium chloride 24 37 41 55
66
  1. What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313K?
  2. Pragya makes a saturated solution of potassium chloride in water at 353K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
  3. Find the solubility of each salt at 293K. Which salt has the highest solubility at this temperature?
  4. What is the effect of change of temperature on the solubility of a salt?
✓

Answer

  1. Mass of potassium nitrate required to produce a saturated solution in 100g of water at 313K = 62g
Mass of potassium nitrate required to produce a saturated solution in 50g of water = ?
Required amount = 62 × 50100 = 31
Hence 31g of potassium nitrate is required.
  1. When the solution cools down, Pragya observes salt crystals of potassium chloride precipitating.
  1. Solubility of each salt at 293K is as follows:
  • Potassium nitrate → 21g
  • Sodium chloride → 36g
  • Potassium chloride → 35g
  • Ammonium chloride → 24g
It is observed that the potassium chloride salt has the highest amount of solubility when compared to any other salt at 293K.
  1. Effect of change of temperature in the solubility of salts:
It is observed from the given table that the solubility of the salt increases with the increase in temperature. This means that when a salt reaches its saturation point at a particular temperature, more salt can be dissolved yet by increasing the temperature of the solution.

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