General Chemistry 10th Edition

Published by Cengage Learning
ISBN 10: 1-28505-137-8
ISBN 13: 978-1-28505-137-6

Chapter 3 - Calculations with Chemical Formulas and Equations - Questions and Problems - Page 121: 3.73

Answer

Molecular formula is $C_{4}H_{12}N_{2}$.

Work Step by Step

Strategy: 1- Find the empirical formula mass. 2- by dividing molecular mass with empirical formula mass, we can find the number that empirical formula mass must be multiplied to find the molecular formula. The empirical formula mass for $C_{2}H_{6}N$ : 12x2 + 1x6 + 1x14 = 44 amu We are given the molecular mass of compound range from 87 to 90 amu. So the molecular mass is around 88.5 amu ( $\frac{87+88+89+90}{4}$ ). We can now find the number empirical formula mass must be multiplied to find the molecular mass: n = $\frac{Molecular mass}{empirical (formula-mass)}$ n = $\frac{88.5}{44}$ = 2.02 or n = 2 ( within experimental error) So molecular formula should be $(C_{2}H_{6}N)_2$. Therefore molecular formula is $C_{4}H_{12}N_{2}$.
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