To determine the energy change of a reaction, 25.0 cm³ of sodium hydroxide solution was poured into a polystyrene cup. Different volumes of hydrochloric acid were added and the maximum temperature reached was recorded (table 6.1). (Plot the graph on paper and draw two straight lines through the points.)

1. aUse your graph to find the temperature reached when 15.0 cm³ of hydrochloric acid was added. [1]
2. bWhat was the maximum temperature reached? [1]
3. cSuggest a reason why the temperature began to drop after a maximum was reached. [1]
4. dWhat volume of hydrochloric acid was required to neutralise the 25.0 cm³ of sodium hydroxide? [1]
5. eWrite an ionic equation for the reaction. [1]
6. fSuggest the pH of the mixture after the addition of 40 cm³ of hydrochloric acid. [1]
7. gIs the reaction endothermic or exothermic? Explain your answer. [1]
8. hDescribe an energy level diagram for the reaction between sodium hydroxide and hydrochloric acid (draw it on paper). [4]

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