Question

A chemist prepares a solution by adding 293 mgmg of K2Cr2O7K2Cr2O7 (MWMW = 294.19 g/molg/mol ) to a volumetric flask, and then adding water until the total volume of the contents of the flask reaches the calibration line that indicates 250 mLmL . Determine the molarity of the prepared solution.

Answer 1

Answer: The molarity of solution will be 0.00325 M

Explanation:

Molarity : It is defined as the number of moles of solute present per liter of the solution.

Formula used :

$Molarity=\frac{n\times 1000}{V_s}$

where,

n= moles of solute =$\frac{\text{Given mass}}{\text{Molar mass}}$

given mass = 239 mg = 0.239 g  (1g=1000mg)

moles of $K_2Cr_2O_7=\frac{0.239g}{294.19g/mol}=8.12\times 10^{-4}mol$

${V_s}$ = volume of solution in ml = 250 ml

Now put all the given values in the formula of molarity, we get

$Molarity=\frac{8.12\times 10^{-4}\times 1000}{250ml}=3.25\times 10^{-3}mole/L$

Therefore, the molarity of solution will be 0.00325 M