AQA GCSE Chemistry Paper 2 Practicals

Exothermic and Endothermic Reactions

Variables

  • Independent - concentration of HCl
  • Dependent - temperature change
  • Control - HCl and NaOH must be same amount and same temperature

Steps

1. Measure 25 cm³ of 0.25 mol/dm³ of HCl and NaOH in seperate beakers

2. Place beakers in water bath set to 25 °C until both are 25 °C

3.Add the HCl followed by the NaOH to a polysterene cup with a lid

4.Take temperature every 30 seconds and record highest temperature

5.Repeat steps 1-4 with 0.5 mol/dm³ and 1 mol/dm³ of hydrochloric acid

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Measuring Rates of Reaction - Experiment 1

Variables

  • Dependent - colour change
  • Control - amount of liquid, person determining colour change point

Steps

  • Black cross on paper placed underneath conical flask
  • Add reactants
  • Use timer to attempt to compare when the colour changes 

Advantages

  • Can visibly see chanmge through precipitates forming and clouding the solution or the colour change

Disadvantages

  • Exact point not clear as different people argue different time of colour change
  • Cannot plot a rate of reaction graph
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Measuring Rates of Reaction - Experiment 2

Variables

  • Dependent - rate of reaction

Steps

  • Place conical flask on mass balance
  • Mass balance mesaures mass disappering
  • Quicker reading means faster rate of reaction

Advantages

  • Most accurate as mass balance is very accurate
  • Rate of reaction graph can be plotted if measurements taken at regualr intervals

Disadvantages

  • Gas released into room
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