STOP IN THE NAME OF STOICH?!?!?!?!

           Percent Yield
Percent Yield is used when you cannot recover the whole product or when the reactants haven't been used up yet.

The actual boring definition of Percent Yield - the ratio amount of product obtained to amount of product expected by calculation, expressed as a % blah blah blah.

Mrs. PinchOfKCN will enlighten you by giving you the ancient formula for percent yield.

%

Now an example, 

2 C(s) + 1O₂(g) --- > 2 CO(g)

What is the percent yield of CO2 if 44g was predicted to be formed, and 34g actually formed?

Step. 1 USE THE FORMULA.

Step.2  DO THE MATH.

Percent yield = 100 x ( 34 grams CO₂ actual / 44 grams CO₂ predicted ) = 77 %

Moving on.... Percent Purity.

Reactants are sometimes impure and we must calculate the pure parts.

Boring Definition - ratio of the mass of the pure substance to the mass of impure.

Of course Mrs. PinchOfKCN has a formula for everything(love does not count).

Easy Example, If there was 121.2 g of solid was obtained, but showed that only 109.2g of it was aspirin. Calculate the percent purity of the product.

Percent purity = 109.2 ÷ 121.2 × 100% = 90.0%

Harder Example, 

Chalk is almost pure calcium carbonate. We can work out its purity by measuring how much carbon dioxide is given off. 10 g of impure chalk was reacted with an excess of hydrochloric acid. 2.128 liters of carbon dioxide gas was collected at standard temperature and pressure (STP).

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

Step 1 Calculate the molar mass of CaCO3 = 100g.

Step 2 Calculate the amount of grams CaCO₃ from the volume of CO₂

(hint: convert to moles)

2.128L CO₂(22.4 L/mol CO₂)* 1 mol CaCO₃/1 mol CO₂*100gCaCO₃/1 mol CaCO₃=9.5g CaCO₃

Step.3 Use the formula and find the percent purity.

Percent purity = 9.5 ÷ 10 × 100% = 95%

If you did not look at any of my examples, I'm not going to be mad at you. Just watch the videos =.= ........

WOAH AP CHEM!!!