Question

If you have 85.0 grams of CO₂, calculate how many moles of CO₂ would you have?

Answer 1

Answer:

$\boxed {\boxed {\sf 1.93 \ mol \ CO_2}}$

Explanation:

We are asked to find how many moles of carbon dioxide are in 85.0 grams.

Grams are converted to moles using the molar mass (the mass of 1 mole of a substance). These values are found on the Periodic Table. They are equal to the atomic mass, but the units are grams per mole instead of atomic mass units.

Look up the molar masses of carbon and oxygen.

• C: 12.011 g/mol
• O: 15.999 g/mol

The formula CO₂ has a subscript of 2. There are 2 moles of oxygen in 1 mole of carbon dioxide. Multiply oxygen's molar mass by 2.

• O₂: 15.999 g/mol * 2 =31.998 g/mol
• CO₂= 12.011 + 31.998=44.009 g/mol

Set up a conversion factor using the molar mass.

$\frac {44.009 \ g \ CO_2}{ 1 \ mol \ CO_2}$

We are converting 85.0 grams of carbon dioxide to moles, so we multiply by this value.

$85.0 \ g \ CO_2 *\frac {44.009 \ g \ CO_2}{ 1 \ mol \ CO_2}$

Flip the fraction so the units of grams of carbon dioxide cancel.

$85.0 \ g \ CO_2 *\frac { 1 \ mol \ CO_2}{44.009 \ g \ CO_2}$

$85.0 *\frac { 1 \ mol \ CO_2}{44.009}$

$\frac {85.0}{44.009} \ mol \ CO_2$

$1.931423118 \ mol \ CO_2$

The original measurement of grams (85.0) has 3 significant figures, so our answer must have the same. For the number we found, that is the hundredth place. The 1 in the thousandth place tells us to leave the 3.

$1.93 \ mol \ CO_2$

There are approximately 1.93 moles of carbon dioxide in 85.0 grams.

Answer 2

N=m(g)/m.wt
n=85/12(1)+16(2) =1.93 moles