# Question 24c67

Jun 27, 2015

That much sodium nitrate contains $1.4 \cdot {10}^{22}$ formula units.

#### Explanation:

Since sodium nitrate is an ionic compound, you can't really say that you're dealing with molecules, but with formula units.

In order to calculate how many formula units a certain mass of a substance contains, you need to do two things

• determine how many moles are present in that many grams by using the substance's molar mass;
• determine how many formula units you have in that many moles by using Avogadro's number.

So, use sodium nitrate's molar mass to determine how many moles are present in 2 g

2cancel("g") * "1 mole "/(85.0cancel("g")) = "0.0253 moles"

Avogadro's number tells you that 1 mole of any substance contains exactly $6.022 \cdot {10}^{23}$ molecules of that substance.

This means that you have

0.02353cancel("moles") * (6.022 * 10^(23)"f. units")/(1cancel("mole")) = color(green)(1.4 * 10^(22)"f. units"#