# Question 4a230

Sep 17, 2015

You have $9.5 \cdot {10}^{21}$ atoms of copper in one gram of copper.

#### Explanation:

To figure out how many atoms of copper you get in 1 gram of copper, you need to use copper's molar mass.

An element's molar mass tells you what the mass of one mole of that element is.

Now, one mole of an element is defined as $6.022 \cdot {10}^{23}$ atoms of that element - this is known as Avogadro's number. This means that if you know what the mass of one mole is, you can calculate how many atoms would fit into a single gram by using Avogadro's number.

In copper's case, you know that its molar mass is 63.546 g/mol.

This tells you that $6.022 \cdot {10}^{23}$ atoms of copper can be found in $\text{63.546 g}$ of copper, which means that $\text{1 g}$ of copper will contain

1color(red)(cancel(color(black)("g"))) * (6.022 * 10^(23)"atoms of Cu")/(63.546color(red)(cancel(color(black)("g")))) = color(green)(9.5 * 10^(21)"atoms of Cu")#

I'll leave the answer rounded to two sig figs, despite the fact that you only gave one sig fig for the mass of the copper sample.