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) 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 6th Edition
Q#78 p 172 Kotz 6th Edition