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# Chemistry AS4 Course Work

Extracts from this document...

Introduction

AS4 Finding and enthalpy change using Hess's Law Results Experiment 1: Mass of weighing bottle and potassium hydrogen carbonate: 25.75g Mass of weighing bottle: 18.75g Mass of potassium hydrogen carbonate: 4.00g Time(min) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 Temperature(C) 25.0 25.0 25.0 25.0 25.0 25.0 25.0 15.0 14.0 14.0 14.0 14.0 14.0 14.0 Potassium hydrogen carbonate and hydrochloric acid: KHCO3(S) + HCl (aq) KCl (aq) + H2O (l) + CO2 (g) Fall in temperature for complete reaction: 25-14=11 = 11C, Mass= 30g, C= 4.18Jg-1K-1 H1= MxCx T =30x4.18x (+11) ...read more.

Middle

26.5 24.5 24.5 24.5 24.5 24.5 24.5 30.0 30.0 30.0 29.5 29.5 29.5 29.5 Magnesium carbonate and hydrochloric acid: MgCO3(S) + 2 HCl (aq) MgCl2 (aq) +H2O (l) + CO2 (g) Rise in temperature for complete reaction: 24.5-30.0= (-5.5C) H= -5.5C, Mass= 50g, C= 4.18Jg-1K-1 H2= MxCx T = 50x4.18x (-5.5) = -1149.51J/1000 = -1.1495KJ Number of moles of acid = (50/100) x2 = 1 mole in excess Molar mass of potassium hydrogen carbonate Mr= 24+12+48 = 84g mol-1 Number of moles= m/Mr = 2/84 = 0.02381 mol H for 1 mole= -1.1495KJ/0.02381mol = -48.3KJmol-1 H MgCl2 (aq) +KHCO3 (g) +H2O (l) + CO2 (g) MgCO3(S) + 2KCl (aq) + 2H2O (l) + 2CO2 (g) ...read more.

Conclusion

* A cm of the solution was assured to be equal to a gram of the solution. * The specific heat capacity of water was taken as the specific heat capacity of the solution/ liquid. * The heat lost to the surrounding was accounted for by extrapolating the graph of the temperature change against time. * The accuracy of the burette was not accurate. * The specific heat capacity of the cup was not accounted. How the errors could be minimised? * Use temperature sensors instead of the thermometer * Use a vacuum flask rather than polystyrene cup and keep the lid shut. So the heat doesn't escape. ...read more.

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