The solubility of a substance at 298 K and 348 K is 91.0 and 147.0 respectively. Calculate the mass of crystals formed when 100 gm of a saturated solution of the solid is cooled from 348 K to 298 K.
Answers
Explanation:
(a) At 313 K 62 g of potassium nitrate dissolved in 100 g of water. So to produce a saturated solution of potassium nitrate in 50 g of water we need
100
62
×50=31 g of potassium nitrate.
(b)Some soluble potassium chloride will separate out in the form of crystal at room temperature because the solubility of potassium chloride will decrease.
(c)
(i) Solubility of Potassium nitrate at 293 K is 32 g.
(ii) Solubility of sodium chloride at 293 K is 36 g.
(iii) Solubility of Potassium chloride at 293 K is 35 g.
(iv) Solubility of Ammonium chloride at 293 K is 37 g.
The solubility of Ammonium chloride is highest at this temperature.
(d)The solubility of salt increases with the increase in temperature
Answer:
Solubility and temperature
The solubility of solids increases as temperature increases, while the solubility of gases decreases as temperature increases.
You can determine the solubility of a solid in water:
Weigh a known mass of a solid.
Measure 10cm3 of water. (The density of water is 1 g/cm3, so 10cm3 = 10 g)
Add the solid to the water and heat until the solid dissolves.
Cool the mixture and record the temperature, in °C, at which crystals begin to form.
The mass of solid added is the mass of this substance required to saturate 10 g of water at the temperature recorded.
A solid’s solubility decreases with decreasing temperature. When a hot, concentrated solution is cooled, some of the solute will be deposited.
Example
Calculate the mass of solid that is deposited if a solution containing 15 g per 100 g of water at 30°C is cooled to 10°C.
Solubility of the solid at 30°C is 15 g / 100 g water, and 10 g / 100 g water at 10°C.
Mass of solid deposited = 15 – 10 = 5 g per 100 g of water
Simple scaling may be required.
Multiplying the mass of the substance by 10 gives the solubility in g/100 g water.
- Repeat with different masses of solid.
Plot a graph of the mass of solid in grams per 100 g of water, against the temperature in °C.