A 10.00 g mixture of NaHCO3 and Na2CO3 is heated strongly until constant mass, when the mass decreases by 1.40 g. Molar masses: NaHCO3 84, CO2 44, H2O 18 g/mol. Calculate the percentage by mass of NaHCO3 in the original mixture, to the nearest integer.

JEE Advanced levelNumerical answerDifficulty 3 of 3sb161

A $10.00 g$ mixture of $NaHCO X_{3}$ and $Na X_{2} CO X_{3}$ is heated strongly until constant mass, when the mass decreases by $1.40 g$ . Molar masses: $NaHCO X_{3}$ 84, $CO X_{2}$ 44, $H X_{2} O$ 18 g/mol. Calculate the percentage by mass of $NaHCO X_{3}$ in the original mixture, to the nearest integer.

Numerical answer type, answer in %, tolerance 0.5.

Na X_{2} CO X_{3}

is unchanged and only

2 NaHCO X_{3} Na X_{2} CO X_{3} + CO X_{2} + H X_{2} O

occurs. 168 g of

NaHCO X_{3}

lose 62 g, so the mass of

NaHCO X_{3}

is 1.40

\times

168/62 = 3.794 g. Percentage = 3.794/10.00

\times

100 = 37.9%, which is 38 to the nearest integer.