Question

A chemist prepares a solution by adding 258 mg of K2Cr2O7 (MW = 294.19 g/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 500 mLmL. Determine the molarity of the prepared solution.

Answer 1

Answer: Molarity of the prepared solution is $1.75\times 10^{-3}mole/L$

Explanation:

Molarity is defined as the number of moles of solute dissolved per liter of the solution.

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

where,

n= moles of solute

$V_s$ = volume of solution in ml = 500 ml

moles of solute =$\frac{\text {given mass}}{\text {molar mass}}=\frac{0.258g}{294.19g/mol}=8.77\times 10^{-4}mol$

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

$Molarity=\frac{8.77\times 10^{-4}moles\times 1000}{500ml}=1.75\times 10^{-3}mole/L$

Thus molarity of the prepared solution is $1.75\times 10^{-3}mole/L$