Chem Class - January 22, 2010

More Stoichiometry today! We did a few examples on problems that involved converting from mass to moles and involving volume at STP.

Here are the examples we did in class:
1) When 1.5 g of oxygen reacts with nitrogen monoxide, how many moles of nitrogen dioxide are produced?
1.5 g x 1 mol O2/32.0 gx 2 mol NO2/1 mol O2 = 0.094 mol of NO2

2) If 2.0 g of O2 reacts with nitrogen monoxide, what volume of nitrogen dioxide is present at STP?
2.0 g x 1 mol O2/ 32 g x 2 mol NO2/ 1 mol O2 x 22.4 L/ 1 mol NO2 = 7.8 L of NO2

3) In the formation of Copper (II) oxide, 3.5 g of copper react. How many moles of copper oxide are produced?
3.5 g x 1 mol Cu/63.5 g x 2 mol CuO/ 2 mol Cu = 0.055 mol CuO

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Mr. Doktor also gave us 2 questions to do on our own and when were were finished we were to show him our answers to get our homework in return:

4) What mass of water is produced when 3.5 L of hydrogen is burnt (reacted with O2)?
2H2 + O2 -----> 2H2O
3.5 L of H2 x1 mol/22.4 L x 2 mol H2O/2 mol H2 x 18 g/ 1 mol = 2.8 g of H2O

5) Lead (IV) Nitrate reacts with 2.5 g of potassium iodide. How many molesof Lead (V) Nitrate are needed?
Pb(NO3)4 + 4KI -----> PBI4 + 4KNO3
2.5 gKIx 1 mol/166 g KI x1 mol Pb(NO3)4/4 mol KI = 0.0038 mol of PBI4

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For further help on solving problems involving stoichiometry, there are a lot of youtube videos. Here's one example: