| time
requ.: |
20 minutes. |
|
objective: |
Setting free
of carbon dioxide. The hydrocarbonate equilibrium. |
| material: |
- snap top vial 5ml or plastic bottle cap
- syringe needle
|
|
| chemicals: |
- calcium carbonate (limestone)
small pieces
- calcium carbonate (limestone)
powder
|
- calcium hydroxide solution (saturated)
- hydrochloric acid c~2mol/l
|
|
preparation: |
Prepare saturated calcium hydroxide
solution in a 1 liter bottle from distilled water and 50g of calcium
oxide. Shake from time to time with new distilled water. When required
filter the necessary volume for use. |
|
procedure 1: |
Insert a small
amount of limestone powser into the test tube and add 2ml of hydrochloric acid. |
|
observation: |
Gas bubbles
are emerging. The limestone disappears in about 3-5 min. |
|
interpretation: |
Limestone dissolves
in acids forming carbon dioxide:
CaCO3 + 2HCl(aq) --->
Ca2+(aq) + 2Cl-(aq) + CO2 + H2O
calcium carbonate hydrochloric acid calcium chloride carbon
dioxide water |
|
procedure 2: |
Use the
gas generator. Use hydrochloric acid with
small pieces of
limestone (d=2-3mm) to obtain carbon dioxide. Transfer 2-3 loads of gas
with syringe 2 of the gas generator and the extra needle in 1-1,5ml of saturated calcium
hydroxide solution in the extra snap top vial. |
|
observation 2: |
Soon a white
precipitation appears, but disappears after more than 5ml carbon dioxide
has been inserted. |
|
interpretation 2: |
1 CO2 + Ca2+(aq)
+ 2 OH-(aq) ---> CaCO3
+ H2O
carbon dioxide calcium hydroxide calcium carbonate water
CaCO3 + CO2
+ H2O ---> Ca2+(aq) + 2 HCO32-(aq)
calcium carbonate carbon dioxide water calcium
hydrocarbonateSum reaction:
2 CO2 + Ca2+(aq)
+ 2 OH-(aq) ---> Ca2+(aq) + 2 HCO32-(aq)
At high carbon dioxide
input the soluable hydrocarbonate is obtained. |
|
source: |
Barke, H.-D. et al.: One Hundred
Chemistry-Experiments to Avoid Chalk and Talk; University of Muenster,
2004. |
