Question

A solution with the concentration of 0.15 M is made using 8.00 grams of K2CrO4. How many milliliters of H2O should be used?

Answer 1

Answer:

274.7mL

Explanation:

Molarity is defined as the number of mols of solute per liter of the solvent. Here, the solute is potassium chromate ($K_{2}CrO_{4}$) and the solvent is water. Hence, molarity is defined as the number of mols of potassium chromate per litre of water. And this molarity is equal to 0.15M.

Now, the molar mass of potassium chromate can be found by simply adding the atomic masses of the component atoms. This is equal to : 2×atomic mass of potassium + 1×atomic mass of chromium + 4×atomic mass of oxygen = 2×39 + 52 + 4×16 = 194g /mol.

The number of mols of potassium chromate is the ratio of the given mass of potassium chromate to the molar mass of potassium chromate.

Here, this is equal to $\frac{8}{194}$ = 0.0412 mols.

This much potassium chromate is present in 'V' litres of water. Hence, molarity is given by : 0.15 = $\frac{0.0412}{V}$.

Thus, V = $\frac{0.0412}{0.15}$ = 0.2747L = 274.7mL