# Limiting Reagents Determine the mass of P 4 O 10 formed if 25g P 4 and 50g O 2 are combined. P 4 + 5O 2  P 4 O 10 What is the given? We have to find the.

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Limiting Reagents Determine the mass of P 4 O 10 formed if 25g P 4 and 50g O 2 are combined. P 4 + 5O 2  P 4 O 10 What is the given? We have to find the limiting reagent! 1 Mole P 4 5 Mole O 2 32 g O 2 25 g P 4 X X X = 32.26 g O 2 124 g P 4 1 Mole P 4 1 Mole O 2

Limiting Reagent 32.26 O 2 was what we got when we used up all of our P 4. We have to now compare how much we used, to how much we had. We had 50 g O 2. We used 32.26 g O 2. We therefore had 17.74 g O 2 left over, in other words, in excess. Since we have O 2 left over, but have used up all of our P 4, we now know that O 2 is our excess reagent. This means that P 4 is our limiting reagent.

Limiting Reagent We now know to use P4, our limiting reagent as our given. This is because we can only produce as much product as our limiting reagent will allow. Think of it this way: We have 5 bicycle frames, and 20 wheels, how many bicycles can we produce? Frames: 5 bikes Wheels: 10 bikes We can only make 5 bikes, because frames are our limiting reagent!

Limiting Reagents Determine the mass of P 4 O 10 formed if 25g P 4 and 50g O 2 are combined. P 4 + 5O 2  P 4 O 10 The limiting reagent was P4, therefore we use P4 as our given to solve. 1 Mole P 4 1 Mole P 4 O 10 284 g P 4 O 10 25 g P 4 X X X = 57.26 g P 4 O 10 124 g P 4 1 Mole P 4 1 Mole P 4 O 10

Percent Yield Calculations If 100 g of Na and 100 g of Fe 2 O 3 are used in this reaction, how much Na 2 O, can be made? 6Na + Fe 2 O 3  Na 2 O + 2Fe 1 Mole Na 1 Mole Fe 2 O 3 160 g Fe 2 O 3 100 g Na X X X = 115.94 g Fe 2 O 3 23 g Na 6 Mole Na 1 Mole Fe 2 O 3 Fe 2 O 3 is limiting

Percent Yield Calculations If 100 g of Na and 100 g of Fe 2 O 3 are used in this reaction, how much Na 2 O, can be made? 6Na + Fe 2 O 3  Na 2 O + 2Fe 1 Mole Fe 2 O 3 1 Mole Na 2 O 62 g Na 2 O 100 g Fe 2 O 3 X X X = 38.75 g Na 2 O 160 g Fe 2 O 3 1 Mole Fe 2 O 3 1 Mole Na 2 O This is the theoretical yield!

Percent Yield Calculations Calculate the percent yield if the reaction actually yields 28.6 g of Na 2 O. 38.75 g Na2O was our theoretical. It is our theoretical because we had to do the math on paper. Actual 28.6 Theoretical 38.75 X 100 =X 100 = 73.81%

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