Question

How many moles of O are there in 41.8 grams of O?

Answer 1

`\boxed {\boxed {\sf 2.61 \ mol \ O}}`

Step-by-step explanation:

To convert from grams to moles, the molar mass is used. This number tells us the grams per mole of a substance. It can be found on the Periodic Table. Look for oxygen.

• Oxygen (O): 15.999 g/mol

Use this number as a ratio.

`\frac {15.999 \ g \ O }{ 1 \ mol \ O }`

Multiply by the given number of moles.

`41.8 \ g \ O *\frac {15.999 \ g \ O }{ 1 \ mol \ O }`

Flip the fraction so the grams of oxygen cancel.

`41.8 \ g \ O *\frac { 1 \ mol \ O }{ 15.999 \ g \ O}`

`41.8 *\frac { 1 \ mol \ O }{ 15.999 }`

`\frac { 41.8 \ mol \ O }{ 15.999 }= 2.61266329146 \ mol \ O`

The original measurement of grams has 3 significant figures (4, 1, and 8). Our answer must have the same. For the number we calculated, that is the hundredth place. The 2 in the thousandth place tells us to leave the 1.

`2.61 \ mol \ O`

41.8 grams of O has 2.61 moles of oxygen.