Question

Consider a sample of 10.0 g of the gaseous hydrocarbon C2H6 to answer the following question: How many moles are present in this sample?
When answering the question, include the following:

State how to find the molar mass for the hydrocarbon.
State how you know if you need to multiply or divide by the molar mass.
Give the correct number of significant figures and explain why the answer has that many significant figures.

Answer 1

Answer: The moles of given hydrocarbon is 0.3 moles

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

We are given:

Given mass of ethane = 10.0 g

Molar mass of ethane = $[(2\times 12)+(6\times 1)]=30g/mol$

We need to divide the given value by the molar mass.

Putting values in above equation, we get:

$\text{Moles of ethane}=\frac{10.0g}{30g/mol}=0.3mol$

In case of multiplication and division, the number of significant digits is taken from the value which has least precise significant digits. Here, the least precise number of significant digits are 1.

Hence, the moles of given hydrocarbon is 0.3 moles