PRACTICAL: THE SOLUBILITY OF CALCIUM HYDROXIDE （Ye Yang)
Uncertainties
Pipette ±0.04cm3
%error= 0.04/10 x 100 = 0.4%
Burette ±0.1cm3
%error= 0.1/9.26 x 100 = 1.08%
Total %error = 1.48%
Calculation and procedures
1. Used Graduated Cylindar to measure 100cm3 of distilled water and placed it in a flask.
2. Added about spatula of solid calcium hydroxide.
3. Stoppered the flask and shook well for on minute.
4. Left to stand for at least 24 hours.
Ca(OH)2(s) + H2O(l) ==== Ca(OH)2( aq)
5. After 24hours took solution of Ca(OH)2 out and used thermometer to measure the temperature of it.
6. Made Filter Funnel lined with filter paper to keep extra Ca(OH)2 solid out and filtered saturated solution to a flask.
7. Used Pipet place 10cm3 of sample Ca(OH)2 solution in a beaker.
8. Dropped 2 drops methyl orange as indicator.
The colour of Ca(OH)2 solution changed from colourless to yellow.
9. Placed 0.05M HCL 50cm3 in burette and fixed ...
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3. Stoppered the flask and shook well for on minute.
4. Left to stand for at least 24 hours.
Ca(OH)2(s) + H2O(l) ==== Ca(OH)2( aq)
5. After 24hours took solution of Ca(OH)2 out and used thermometer to measure the temperature of it.
6. Made Filter Funnel lined with filter paper to keep extra Ca(OH)2 solid out and filtered saturated solution to a flask.
7. Used Pipet place 10cm3 of sample Ca(OH)2 solution in a beaker.
8. Dropped 2 drops methyl orange as indicator.
The colour of Ca(OH)2 solution changed from colourless to yellow.
9. Placed 0.05M HCL 50cm3 in burette and fixed burette on the iron support, and set a appropriate height.
10. Placed a flask with the iron support.
- Recorded the initial volume of 0.05M HCL, Turned on the tap, made HCL solution fell into the flask. Shook it slowly. When the colour from yellow became red. Turned off the tap, recorded the final volume of 0.05M HCL. This time is rough, for knowing the probable data and controling it well in next time.
Rough time: Added volume of 0.05M HCL= Final volume of 0.05M HCL - Initial volume of 0.05M HCL= 10.20cm3 -0cm3=(10.20 ±0.1)cm3
- Calculated the data of adding volume of HCL in rough time. Recorded the initial volume of 0.05M HCL. Turned on the tap, made HCL solution fell into the flask. Shook it slowly. Looked the degree of burette, when it close the data in the rough time, made HCL solution fell into the flask drop by drop. When Ca(OH)2 solution changed from yellow to red. Turned off the tap and recording the final volume of HCL.
No.1: Added volume of 0.05M HCL= Final volume of 0.05M HCL - Initial volume of 0.05M HCL= 29.38cm3 -20.05cm3=(9.33 ±0.1)cm3
- Repeated the step12 for twice.
NO.2:Added volume of 0.05M HCL= Final volume of 0.05M HCL - Initial volume of 0.05M HCL= 39.23cm3 -30.08cm3=(9.25 ±0.1)cm3
NO.3:Added volume of 0.05M HCL= Final volume of 0.05M HCL - Initial volume of 0.05M HCL= 48.53cm3 -39.23cm3=(9.3 ±0.1)cm3
- Calculated the average added volume of 0.05M HCL.
9.33cm3 + 9.25cm3 + 9.3cm3=(9.26 ±0.1)cm3
Ca(OH)2( aq) + 2HCL(aq) ==== CaCl2 + 2H2O(l)
Based on Formula c1v1n2=c2v2n1
v1=VCa(OH)2 = 10cm3 = 0.01dm3
v2=VHCL= 9.26cm3 = 0.00926dm3
c2=CHCL= 0.05 mol·dm-3
n1= 1
n2= 2
c1·0.01dm3·2 = 0.05（mol·dm-3 ）·0.00926dm3·1
cCa(OH)2= c1= (0.05（mol·dm-3 ）·0.00926dm3·1)/(2·0.01dm3) = 0.02315（mol·dm-3 ）
Because Total Error percentage is 1.48%
cCa(OH)2= 0.02315（mol·dm-3 ）± 1.48%·0.02315（mol·dm-3 ）
= 0.02315（mol·dm-3 ）±3.4262×10-4（mol·dm-3 ）
Conclusion
The literature value for the solubility of calcium hydroxide is 1.53×10-3 mol per 100g water at 298K.
V =100g/1000g·dm-3=0.1dm3
cCa(OH)2 =n·v=1.53×10-3/ 0.1dm3=0.0153（mol·dm-3 ）
So, the standard concentration is 0.0153M at 298k.
0.01530 0.02281 0.02315 0.02349
Limitations
Random errors:
- The temperature is different. The standard data is gotten at 25°C, but I measured the temperature is 22°C.
- Not easy to see the colour change, when I was seeing the degree of burette. So I can not turned off the tap immediately.
Improvement
For random error1: I can make this experiment at 25°C next time.
For random error2: When I make this experiment next time, I can watch the colour change of Ca(OH)2, and my partner can watch the degree of burette. When the degree close the rough data, my partner can control the tap and make it fall down drop by drop. When the colour change, I will tell my partner to turn off the tap.
