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Is Matter Around Us Pure — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceIs Matter Around Us Pure5 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 $313\ K$?
  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 $293\ K$. 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 $= 62 \times 50100 = 31$
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 $\rightarrow 21g$
  • Sodium chloride $\rightarrow 36g$
  • Potassium chloride $\rightarrow 35g$
  • Ammonium chloride $\rightarrow 24g$
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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