The solubility of kno3 is 155g per 100g of water at 75 degree c and 38g at 25degreec the mass of kno3 will crystallize out of solution if 100g of it saturated solution is cooled from 75c to 25 c is?

Answer 1

I have read two methods to solve this up:

the first says that

at 75 degrees the solution mass is 100g of water + 155 g of KNO3 so its mass is 255g

at 25 degrees the solution mass is 100 g of water + 38 g of KNO3 so its mass is 38

when we cool it down from 75 to 25 we will get 255-138=117g but this is the solution mass and u only want the mass of KNO3 because that is what will really crystallize...so for some reason i really dont get u do 117/255 and then multiply it by the mass of the demanded solution which is 100 g so the answer will be 45.88g nearly 45.9 g

the second method is to assume that at 75 degrees there is in 100g of saturated solution, x g of water

so KNO3 will be 1.55x

total mass 100

x+1.55x=100

x= 39.126

1.55x=60.784

so at 25 degrees there is 0.39 x of KNO3 and x is 39.126 that means there is 0.38*39.126= 14.867 g of KNO3

therefore the mass of KNO3 that will crystallize is 60.784-14.867=45.917= 45.917

why 1.55x? because for each 100 g of water we have 155 g of solute...so 155/100 = the mass of solute for the new water mass/ the new water mass (x)

so the mass of solute for the new water mass will be: 155x/100 or 1.55x!

the same applies to 0.38x

hope this helped =)

Answer 2

65grams

Answer 3

10g