Question

How many moles of cobalt (Co, 58.93 g/mol)are in 27.4 grams of cobalt?[?] moles Co

Answer 1

Step 1 - Understanding molar mass

The molar mass of a substance is the mass, in grams, of one mole of that substance. The molar mass is expressed in unities of g/mol, i.e., how many grams do we need in order to get exactly one mole.

Let's take a look at an example. The molar mass of water is 18 g/mol. If we weight 18g of water, we woud have one mole of water. If we weight 36g of water, we would have two moles and so on.

We can simplify this relation by using a formula:

`n=(m)/(M)`

In the formula above, n represents the number of moles, m represents the mass and M the molar mass.

Step 2 - Calculating the number of moles of Cobalt

Let's plug the values in the equation. We already know that:

`\begin{gathered} m=27.4g \\ M=58.93\text{g}/\text{mol} \end{gathered}`

We need to find n, the number of moles, so:

`n=(m)/(M)=(27.40)/(58.93)=0.46\text{ moles of Co}`

There are thus 0.46 moles of cobalt in the given mass.