sample questions 1.5

(answers are at the bottom)

1. How many moles of oxygen do you need to make one mole of nitric acid: HNO3?

2. How many moles of oxygen do you need to make 2 moles of nitric acid: HNO3?

3. How many grams would a mole of nitric acid (HNO3) weigh?

4. How many grams would a half mole of citric acid (C6H8O7) weigh?

5. If you have 2 grams of ethyl acetate (C4H8O2), how many moles of this substance do you possess?

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ANSWERS

1. 3 moles because there are three oxygen atoms for each nitric acid (HNO3) molecule.

2. 6 moles of oxygen. Each nitric acid (HNO3) molecule carries 3 oxygen. So, you will always multiply the number of oxygen by 3 for every nitric acid molecule you need to create. So if you have 2 moles of HNO3 you need 2 x 3 = 6 moles oxygen.

3. 63.012 grams. One mole of HNO3 requires 1 mole of hydrogen (H) which weighs 1.008 grams, 1 mole of nitrogen (N) which weighs 14.007 grams and 3 moles of oxygen (O) each weighing 15.999 each. If you add that all up you get 63.012 grams.

4. 96.062 grams. To get to this answer, we first had to figure out how many grams one mole of citric acid weighs, and then divide that in half. A mole of citric acid (C6H8O7) is comprised of 6 moles of carbon weighing 12.011 grams each, 8 moles of hydrogen weighing 1.008 grams each and finally, 7 moles of oxygen weighing 15.999 grams each. All in all, one mole of citric acid weighs 192.123 grams. Therefore, a half mole of citric acid will weigh 96.0615 grams. Because we have only 3 significant figures to the right of the decimal, we have to round the answer up to 96.062.

5. 0.023 mole. To get this answer, we had to first figure out how many grams one mole of ethyl acetate (C4H8O2) weighs. A mole of this substance is comprised of 4 moles of carbon weighing 12.011 grams each, 8 moles of hydrogen weighing 1.008 grams each and finally, 2 moles of oxygen weighing 15.999 grams each. All in all, this adds up to 88.106 grams. Now we know that one mole of ethyl acetate weighs 88.106 grams. But we only have 2 grams of this substance. How can we determine how many moles that is? By using the following formula, we determine how much of a mole of ethyl acetate 2 grams are:
mole equations 5What this formula does is divide the number of grams you actually possess by the number of grams per mole of that substance. This will give you the actual number of moles represented by the grams you have.

CONGRATULATIONS! NOW FEEL FREE TO DO THE NEXT TUTORIAL.

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