CHM 2045C Module Five Sample Name:_______________

Module Four Part N Mixture Problem 4 points

Problem #77 p 172 Kotz 6^th Edition (5^th Edition Problem 65 with different numbers)

Sodium hydrogen carbonate, NaHCO₃ can be decomposed quantitatively by heating:

2 NaHCO₃ (s) à Na₂CO₃ (s) + CO₂ (g) + H₂O (g)

A 0.682 g sample of impure NaHCO₃ yielded a solid residue (consisting of Na₂CO₃ and other solids) with a mass of 0.467 g. What was the mass percent of NaHCO₃ in the sample?

1. Let x = mass of pure NaHCO₃ in the original sample

2. Let y = mass of impurities in the original sample

3. Therefore: x + y = 0.682 g mixture or y = 0.682 - x

4. Calculate how much Na₂CO₃ can be produced from x grams of NaHCO₃

5. Assuming the impurities before the heating remain as solid impurities after heating,

0.631x g Na₂CO₃ + y g impurities = 0.467 g after heating mixture or

0.631x + y = 0.467

6. From #3 y = 0.682- x and substituting in #5 yields the equation:

0.631x + (0.682 – x) = 0.467

0.631x – x = 0.467 – 0.682

- 0.369x = - 0.215

X = - 0.215 / - 0.369 = 0.583 g pure NaHCO3

0.583 g pure/0.682g impure x 100 = 85.4 % pure

Additional Mixture Problems:

Q# 75 p 171 Kotz 6^th Edition

Q#78 p 172 Kotz 6^th Edition