# Percent yield questions

1. May 8, 2013

### Originaltitle

% yield questions (URGENT)

1. The problem statement, all variables and given/known data
We have 3 equations:

1.64 g of an impure NaNO3-containing substance is reacted with Devarda's alloy. The amount of NH3 got from this reaction is reacted with 25cm3 1.00 moldm-3 H2SO4. The H2SO4 left over is reacted with 16.2 cm3 2.00 moldm-3 NaOH. Calculate the percentage yield of NaNO3 in the impure substance.

2. The attempt at a solution

1. Amount of H2SO4 reacted with NaOH = (2.00 x 16.2 x 10-3) / 2 = 0.0162 moles.
2. Amount of H2SO4 reacted with NH3 = 0.025 - 0.0162 = 0.0088 moles.
3. Amount of NH3 reacted = (0.0088 x 2) = 0.0176 moles.
4. Amount of NaNO3 reacted = 0.0176 x (3/2) = 0.0264.
5. Mass of NaNO3 reacted = 0.0264 x 85 = 2.244 g.

% yield = 2.244/1.64 = 137 %.

It's wrong because the final mass can't be more than the initial. HELP!!!

2. May 8, 2013

### Staff: Mentor

Why 3/2?

% yields over 100% do happen. They usually mean something is wrong, but it is not necessarily a math error. For example in this case it could mean that the impurity is some other nitrate.

3. May 8, 2013

### Staff: Mentor

The error is in the line:

4. May 8, 2013

### Staff: Mentor

Edit: But Borek already told you that...