A 2.000 g salt sample contains 52.0% NaCl by mass, the rest being inert. It is heated with excess solid K2Cr2O7 and concentrated H2SO4 (K2Cr2O7 + 4NaCl + 6H2SO4 -> 2CrO2Cl2 + 4NaHSO4 + 2KHSO4 + 3H2O), and the chromyl chloride is collected with an 80.0% yield. Find the mass of CrO2Cl2 collected in grams, to two decimal places. (Na 23, Cl 35.5, Cr 52, O 16.)

JEE Advanced levelNumerical answerDifficulty 3 of 3qa165

A 2.000 g salt sample contains 52.0% $NaCl$ by mass, the rest being inert. It is heated with excess solid $K X_{2} Cr X_{2} O X_{7}$ and concentrated $H X_{2} SO X_{4}$ ( $K X_{2} Cr X_{2} O X_{7} + 4 NaCl + 6 H X_{2} SO X_{4} 2 CrO X_{2} Cl X_{2} + 4 NaHSO X_{4} + 2 KHSO X_{4} + 3 H X_{2} O$ ), and the chromyl chloride is collected with an 80.0% yield. Find the mass of $CrO X_{2} Cl X_{2}$ collected in grams, to two decimal places. (Na 23, Cl 35.5, Cr 52, O 16.)

Numerical answer type, answer in g, tolerance 0.01.

Mass of NaCl =

2.000 \times 0.520 = 1.040 g

, i.e.

1.040/58.5 = 0.017778 mol

. Four NaCl give two

CrO X_{2} Cl X_{2}

, so theoretical

n = 0.008889 mol

. Molar mass of

CrO X_{2} Cl X_{2}

= 155, so the theoretical mass is

1.3778 g

and at 80.0% yield the mass is

1.1022 \approx 1.10 g