When aqueous solutions of potassium hydroxide and nitric acid are mixed together, an exothermic reaction occurs. The diagram shows the apparatus used in an experiment to measure the temperature increase.
This is the student’s method:
- use the larger measuring cylinder to add 25cm3 of aqueous potassium hydroxide to the polystyrene cup
- record the steady temperature
- use the smaller measuring cylinder to add 5cm3 of dilute nitric acid to the cup, stir the mixture with the thermometer
- record the highest temperature of the mixture
- continue adding further 5cm3 portions of dilute nitric acid to the cup, stirring and recording the temperature, until a total volume of 35cm3 has been added.
- the thermometer reading at the start of the experiment
- the temperature rise in the experiment.
thermometer reading at end / °C | 26.8 |
thermometer reading at start / °C | |
thermometer rise / °C |
Identify the volume of dilute nitric acid that exactly neutralises the 25 cm3 of aqueous potassium hydroxide.
[1]
volume = .............................................................. cm3
volume of aqueous potassium hydroxide | = | 20.0 cm3 |
starting temperature of aqueous potassium hydroxide | = | 18.5 °C |
maximum temperature of mixture | = | 30.0 °C |
volume of dilute nitric acid | = | 20.0 cm3 |
Calculate the heat energy released in this experiment.
c = 4.2 J /g/ °C |
mass of 1 cm3 of mixture = 1 g |
ΔH = .............................................................. kJ/mol
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