CHM 2045C Module Five Sample Name:_______________

 

Module Four Part N Mixture Problem 4 points

 

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

 

 

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

 

2 NaHCO3 (s) 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 6th Edition

Q#78 p 172 Kotz 6th Edition