Solubility of Ca(OH)2

Equation of reaction:

2HCl + Ca(OH)2 → CaCl2 + 2H20

Moles = Concentration x Volume

Moles of HCl = 22.72 x (0.053/1000) = 0.0012

Moles of Ca(OH)x = 0.0012/2 = 0.0006     (/2 Because of the 2:1 ratio between HCl and Ca(OH)2

To be able to make a comparison between the limewater concentrations of our obtained value and the literature value, we need to change it into g/100cm3 since the literature values are given in g/100cm3.

Mass = moles x molar mass

Mass of Ca(OH)2 = 0.0006 x [40.1+2(16+1)]

                             = 0.0006 x 74.1

                             = 0.0445g

Since this is the value of the mass of Ca(OH) 2 in 25cm3, and we want to compare our value with a literature value that is in g/100cm3 t we multiply this value by 4.

Concentration of Ca(OH)2: 0.0445 x 4 = 0.1778g/100cm3 

                                            = 0.18g/100cm3 (2d.p)

Percentage Errors

Concentration of Ca(OH)2:  [(Estimated value – literature value) /literature value] x 100

                                             = (0.18 – 0.17)/0.17 x 100 = 5.9% (only 1 d.p. since % error is >2%)

Pipette: (+0.15/25) x 100 = +0.60%

(Uncertainty due to 25cm3 pipette is 0.05cm3 + The estimation of precision with which readings are taken is +0.1cm3) = +0.15 cm3

Burette: (+0.15 / 22.72) x 100 = +0.66%

(Uncertainty due to 22.7cm3 volume in burette is 0.05cm3 + The estimation of precision with which readings are taken is +0.1cm3) = +0.15 cm3

Total Percentage Error: Error on (Concentration of Ca(OH)2 + burette + pipette)

                                        = 5.9 + 0.60 + 0.66 = + 7.16%

                       

Range of uncertainty on the Ca(OH)2:7.16% of 0.18 = 0.012

The concentration of Ca(OH)2 should be 0.18 + 0.012  = 0.192g/100cm3
                                                          or   0.18 – 0.012 = 0.168g/100cm3

The concentration can therefore be expressed as 0.18 + 0.012 g/100cm3 

Conclusion

The aim of this experiment was to find the solubility of Ca(OH)2 from a titration with HCl(0.053mol/dm3.) The value of Ca(OH) 2 obtained in the experiment was 0.18 + 0.012 g/100cm3, which is approximately 0.1g off from the literature value of Ca(OH)2 that is 0.17g/100cm3. The total percentage error was relatively significant with a value of +7.16%. Inability to attain the exact literature value could have been due to several chemical, human, and equipment errors.