How was chemistry practical 2015 paper 32

[qwertypoiu]

Titre value around 14.45 for me. Can't remember exactly. I used 13.20cm^3 of FB1 for dilution.
Moles of HCl = 0.1*14.45/1000 = 0.001445mol
Moles of Na2CO3 in 25cm^3 of FB3 = 0.001445mol/2 = 0.0007225 moles
Concentration of Na2CO3 in FB3 = 0.0007225mol/(25/1000)dm^3 = 0.02890mol/dm^3
Concentration of Na2CO3 in FB1 = 0.02890mol/dm^3 * 250/13.20 = 0.5473mol/dm^3
Concentration in g/dm^3 of FB1 = 106g/mol * 0.5473mol/dm^3 = 58.01g/dm^3
It was supposed to be 125g/dm^3 however...
Therefore purity = 58.01/125*100% = 46.4%

Enthalpy change:
My mass = 2.1g
Temperature rise = 13.0 degrees.

Heat produced = 40cm^3 * 4.2J/cm^3/degree * 13.0degree = 2184J = 2180J
I forgot what the standard enthalpy was. Let's say -471kJ
Moles = 2184J / 471,000J/mol = 0.00467mol
Mass = 0.00467mol * 24.3g/mol = 0.113g
Purity = 0.113g/2.1g*100% = 5.4%

Assumption was that there is no heat lost.
Uncertainty = 0.5*2/13 * 100% = 7.69%
Experiment could be improved by using more precise thermometer with 0.1 degree division.

Qualitative analysis:
FB6 had Zn2+ and NH4+
FB7 had iodoalkane
Reaction was hydrolysis
FB8 and FB9 contained: H+, CO3 2-, SO4 2- (Wasn't sure about this one actually)

 

[shazmina]

Even i wrote H* ,,, not sure though......
My titre values was 28.00