Question

A sample compound with a molar mass of 34.00g/mol is found to consist of 0.44g H and 6.92g O. Calculate both empirical and molecular formulas.

Answer 1

Answer:

Empirical: OH

Molecular: $H_{2} O_{2}$

Explanation:

First of all, we are going to use the formula: mass = no. moles x Molar Mass And rearrange it to find No. moles: No. moles = mass/Molar Mass

Let's start with Hydrogen:

The given mass is 0.44g, and hydrogen's molar mass is 1.01, therefore the number of moles is: 0.44/1.01 = 0.4356

Now we do the same for Oxygen:

Given mass = 6.92, Molar mass of Oxygen = 16.00, No. Moles = 6.92/16.00 = 0.4325

Now we identify the smaller one (Oxygen as 0.4325 < 0.4356) and we divide both values by that number:

0.4325/0.4325 = 1

0.4356/0.4325 = 1.01

We round both to the nearest 0.2 or 0.25 (depending on what you're taught), and we get: 1 and 1.

This means that the empirical formula has one of each: OH

Now to find the molecular formula we find the relative mass of OH and divide the given mass by that:

M(OH) = 16.00+1.01 = 17.01

34.00/17.01 = 2

We now multiply both by this number to get:

$H_{2} O_{2}$

Hope this helped!