-The solubility of KNO3 is 155 g per 100 g of water at 75 degrees Celcius and 38.0 at 25 degrees celcius. What mass (in grams) of KNO3 will crystallize out of the solution if exactly 100 g of its saturated solution at 75 degrees celcius is cooled to 25 degrees celcius?
let us assume that at 75 degree celcius 100 g of saturated solution contains x g of water
so, quantity of KNO3 = 1.55x
total mass = 100 g
therefore, x + 1.55x = 100
x = 39.126
1.55x = 60.784
so,100 g saturated sol means that 60.784 g of KNO3 is dissolved in 39.126 g of water.
now, when cooled to 25 degree celcius
mass of KNO3 still dissolved in 39.126 g of water = 39.126 * 0.38 = 14.867 g
therefore, mass of KNO3 crystallizing out = 60.784 – 14.867 = 45.917g
So you start with 100g of KNO3 in solution.
When you cool that solution only 38g will be able to stay in solution, so the rest will crystallize out. so:
100-38=62g crystallized out.
CaCl2 –> Ca2+ + 2Cl- -s +s +2s K= (s^2)(2s)^2 K= 4s^3 where s= 26.7 g/ 100mL 1. convert 26.7 g to moles (26.7 g)(1 mole/ 110.986 g)= 0.2406 mole 2. convert 100 mL to L (100 mL) (1 L/ 1000 mL)= 0.100 L 3. divide mole by liter volume to get molarity .2406 mole / 0.100 L = 2.406 mole/ L or 2.406 M 4. fix sigfigs 2.41 M Therefore, CaCl2’s molarity is 2.41 M
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