**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, NaHCO _{3} can** be decomposed quantitatively by heating:

**2 NaHCO _{3} (s) **

A 0.682 g sample of
impure NaHCO_{3} yielded a solid residue (consisting of Na_{2}CO_{3}
and other solids) with a mass of 0.467 g.
What was the mass percent of NaHCO_{3} in the sample?

1. Let x = mass of
pure NaHCO_{3} 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 Na_{2}CO_{3} can be produced from x grams of NaHCO_{3}

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

**0.631x** *g Na _{2}CO_{3} +*

**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**