# 8. When 15 grams of H2O decomposes how many grams of O2 are formed?

1. Nov 27, 2007

### BittersweetLove

[SOLVED] 8. When 15 grams of H2O decomposes how many grams of O2 are formed?

Here's the question:

When 15 grams of H2O decomposes how many grams of O2 are formed?

I have no idea how to even start that problem...I guess I missed that part in Chem class. *sighs*

2. Nov 27, 2007

### Staff: Mentor

You need to ratio the weights of the constituent parts of water. How much does a hydrogen atom weigh? How much does an oxygen atom weigh?

3. Nov 27, 2007

### ShawnD

Adding to this, the teacher will probably have the question on a test but it will be in pounds or ounces. Most people dick around with converting from grams to ounces, because they forget that ratios do not have units. Divide the units you know, which are probably grams, then apply that ratio to whatever units the question has. It could be grams, it could be pounds, it could be anything.

4. Nov 27, 2007

### symbolipoint

Each (1.008 + 1.008 + 16.00) mass of water contains (16.00) mass of oxygen. Now you have enough information for the ratio and the calculation for how much oxygen by mass is simple.

5. Nov 27, 2007

### BittersweetLove

Thanks everyone...I think I've got in now. I really appreciate you help. 8)