4. How many grams are in 54 moles H, O?

Explanation:1.8

×

10

24

 water molecules.

Explanation:

There are  

6.022

×

10

23

molecules in a mole.

There are  

18.01528

grams of water per mole of water.

These can be figured out using the concept of moles and molecular weight. I have attached a video that provides a good explanation.

Explanation of moles and molecular weight

Now you have all the information needed to solve the problem.

You start out with 54 grams of water. You want to convert that into molecules, but how can you do that? You can't go directly from grams to molecules because there is no easy unit conversion. However, you can go from grams to moles using

18.01528

grams of water per mole of water.

From there, you can go from moles to molecules using  

6.022

×

10

23

molecules in a mole.

A T chart is useful for this kind of problem.

54 g H

2

O

×

1 mol  H

2

O

18.0152 g H

2

O

×

6.022

×

10

23

molecules

1 mol H

2

O

54

g H

2

O

×

1 mol  H

2

O

18.0152

g H

2

O

×

6.022

×

10

23

molecules

1 mol H

2

O

Notice when you apply this T chart, the units cancel out, leaving molecules in the final answer, which is the correct units.

Now actually multiply everything out

54

×

6.022

×

10

23

18.0152

=

1.805

×

10

24

You are left with  

1.8

×

10

24

water molecules (rounded to two sig figs).

the answer is b & c i believe : )