Question

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

a
54 grams
b 40 grams
C
30 grams
d 20 grams

Answer 1

54 grams

Step-by-step 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

Answer 2

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

Step-by-step 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.

`(18.015 \ g \ H_2 O)/( 1 \ mol \ H_2 O)`

Multiply by the given number of moles.

`3 \ mol \ H_2O*(18.015 \ g \ H_2 O)/( 1 \ mol \ H_2 O)`

The moles of water will cancel.

`3 *(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.