Separation of a Mixture
NH4Cl, NaCl, and SiO2
NaCl and NH4Cl, Ionic Solids
• Ionic bonds are much weaker than covalent bonds
• Ionic Solids are Generally Soluble in water
Solvated Ions
The ions are happier in water than they are in NaCl(s)
NaCl – Rock Salt
• Melting point 801 °C
• Boiling point 1413 °C
• 2NaCl(l)  Na2(g) + Cl2(g)
NH4Cl – Ammonium Chloride
• Melting point 338 °C (decomposes) (sublimation)
• NH4Cl(s)  NH3(g) + HCl(g)
Silica
•
•
•
•
Periodic Covalent Solid (glass)
Insoluble
Melting point 1600-1725 °C
Boiling point
2230 °C
Separating NH4Cl from Salt and Sand
• A bunsen burner reaches around 1100oC in
the hottest part of the flame
• Ammonium chloride sublimes at 338oC
• NaCl(s) melts at 801oC
• SiO2 just gets hot!
• So remove NH4Cl by heating
Separating Salt from Sand
• Salt being an ionic solid is soluble in water, sand is not
• We can remove the salt by dissolving the salt in water and
decanting off the salt water (extraction)
Grams of NaCl w
Sand + 10 mL H2O
Pour out 9/10 of
the salt water
grams NaCl
removed in
extraction
Grams NaCl remain
with sand
1.0
0.9
0.1g
0.1
0.09
0.01g
0.01
0.009
0.001g
0.001
0.0009
0.0001g
Procedure
1.
2.
3.
4.
5.
Take an unknown and record the id number of the unknown in your notebook
Weigh the evaporating dish and record the mass to 4 decimal places m1
Transfer ALL of the sample into the dish and reweigh m2
In a fume cupboard heat the dish and its contents using a Meker Burner
When the sample stops exuding white smoke, stir it with a glass stirring rod – more
NH4Cl will probably be emitted. When no more smoke is seen and none deposits on the
stirring rod, turn off the burner and let the dish cool
6. Reweigh the dish m3
é m2 - m3 ù
7. Calculate the mass % of NH4Cl
ê m - m ú ´100%
ë 2
1û
8. Check with me before performing extraction
9. Add 10 mL of deionized water to the dish, stir with clean glass stirring rod
10. Being careful to not lose sand, pour out the water into a beaker, allowing water to flow
down a glass rod, keeping the rod pushed up against the lip of the dish to prevent sand
escaping
11. Repeat this last step 4 times in all. Dry sand with heat lamp, cool and re-weigh m4
1. Calculate the mass % NaCl
é m3 - m4 ù
ê m - m ú ´100%
ë 2
1 û