Question

How many moles of lithium atoms are contained in 5.2 g of lithium

Answer 1

`\boxed {\boxed {\sf 0.75 \ mol \ Li}}`

Step-by-step explanation:

We are asked to convert 5.2 grams of lithium to moles of lithium.

1. Molar Mass

To convert from grams to moles, we need the molar mass. This is the measurement of the mass in 1 mole of a substance. It can be found on the Periodic Table because it is the same value as the atomic mass, but the units are grams per mole instead of atomic mass units.

Look up the molar mass of lithium.

• Li: 6.94 g/mol

2. Convert Grams to Moles

Create a ratio using the molar mass of lithium.

`\frac { 6.94 \ g \ Li}{ 1 \ mol \ Li}`

Multiply by the value we are converting: 5.2 grams of lithium.

`5.2 \ g \ Li *\frac { 6.94 \ g \ Li}{ 1 \ mol \ Li}`

Flip the ratio so the units of grams of lithium cancel.

`5.2 \ g \ Li *\frac{ 1 \ mol \ Li} { 6.94 \ g \ Li}`

`5.2 *\frac{ 1 \ mol \ Li} { 6.94 }`

`\frac{5.2} { 6.94 } \ mol \ LI`

`0.749279538905 \ mol \ Li`

3. Round

The original measurement of grams (5.2) has 2 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place. The 9 in the thousandths place to the right tells us to round the 4 up to a 5.

`0.75 \ mol \ Li`

5.2 grams of lithium is equal to 0.75 moles of lithium atoms.