Question

What would be the mass of 3 moles of water molecules?

Answer 1

Answer:

$\boxed {\boxed {\sf A. \ 54 \ grams }}$

Explanation:

To convert from moles to grams, we must use the molar mass.

Recall that water's molecular formula is H₂O. It contains hydrogen and oxygen. Look up the two elements masses on the Periodic Table.

• Hydrogen (H): 1.008 g/mol
• Oxygen (O): 15.999 g/mol

Now, use these masses to find water's mass. The subscript of 2 tells us there are 2 atoms of hydrogen, so we multiply hydrogen's mass by 2 and add oxygen's.

• H₂O= 2(1.008 g/mol) + 15.999 g/mol = 18.015 g/mol

Use the molar mass as a ratio.

$\frac{18.015 \ g \ H_2 O}{ 1 \ mol \ H_2 O}$

Multiply by the given number of moles.

$3 \ mol \ H_2O*\frac{18.015 \ g \ H_2 O}{ 1 \ mol \ H_2 O}$

The moles of water will cancel.

$3 *\frac{18.015 \ g \ H_2 O}{ 1 }$

$3 *{18.015 \ g \ H_2 O}$

$54.045 \ g \ H_2O$

Round to the nearest whole number. The 0 in the tenth place tells us to leave the number as is.

$54 \ g \ H_2O$

There are about 54 grams of water in 3 moles.

Answer 2

Answer:

54 grams

Explanation:

First step is to find what one mole of water is in grams.

Water is H2O so that means we have two moles of Hydrogen.

H - 2 grams (on periodic table)

We have one mole of Oxygen.

O - 16 grams (on periodic table)

Add 2 and 16 to get 18 total grams in one molecule of H2O

Now multiply 3 times 18 to know how many grams in 3 moles of H2O

You end with

3x18=54 grams