# Question #6c48c

##### 1 Answer

You have **Ne-22** in that much neon.

The first thing you need to do is determine the *abundance* of each of the two isotopes. Since you're only dealing with two isotopes, you can express the abundance of one as **x** and the abundance of the other as **1 - x**.

This means that you'll get

where

*decimal abundance* of **Ne-20**;

*decimal abundance* of **Ne-22**.

Solve for

**Ne-20** will have a percent abundance of **90.5%** and **Ne-22** will have a percent abundance of **9.5%**.

**SIDE NOTE** *You get percent abundance by multiplying the decimal abundance by 100.*

So, for **1 mole** of neon, you get **0.905 moles** of **Ne-20** and **0.095 moles** of **Ne-22**.

Determine how many moles of neon you have in **12.55 g** by using its molar mass

This means that you get

You know that *1 mole* of any substance contains exactly **Avogadro's number** - so the number of atoms present in that many moles of **Ne-22** will be

Rounded to four sig figs, the answer will be