Question

The weight of a china dish with a saturated solution of sodium nitrate at 40°C is 80 g. After evaporating

the whole solution the dish's weight along with the crystals is 40 g and solubility of NaNO3 at 40°C is

20 g. What is the weight of empty china dish ?

(1) 30 g (2) 32 g (3) 34 g (4) 28 g

Answer 1

let the weight of the China dish be x and the weight of the solute be y and the weight of the solvent be z

so the weight of the solution =y+z
given
x+y+z=80
and when it is evaporated (means the solvent is removed)
x+y=40
so z=40
and we are also given that the solubility of the compound is 20g.
this means that to saturate 100g of solvent we require 20g of solute.
or
for 1g of solvent we require 20/100gm of solute
therefore
for 40gm of solvent requires 1/5×40
8gm
so now we the weight of solute also
we know that x+y+z=80
x+40+8=80
x=80-48
=32