Chemistry - 7 Energy Changes - Required Practical 4: Temperature Changes

Aims:

  • investigate the variables that affect temperature changes in chemical reactions

Risk Assessment:

  • acid could be an irritant

  • acid could damage eyes

Safety:

  • wear safety goggles

  • stand cup in beaker to avoid spillage

Equipment:

  • 2 mol/dm³ hydrochloric acid

  • 2 mol/dm³ sodium hydroxide solution

  • expanded polystyrene cups & lids with thermometer holes

  • thermometers

  • measuring cylinder

  • beaker

Control variables:

  • volume of hydrochloric acid

  • concentrations of hydrochloric acid and sodium hydroxide solution

Independent variable:

  • volume of sodium hydroxide solution

Dependent variable:

  • maximum temperature reached

Method:

  1. Using a measuring cylinder, measure 30 cm³ hydrochloric acid - read from the bottom of the meniscus

  2. Transfer the acid into a polystyrene cup and stand the cup inside a beaker

  3. Using a thermometer, measure and record the starting temperature of the acid

  4. Using a measuring cylinder, measure out 5 cm³ of sodium hydroxide

  5. Transfer the sodium hydroxide into the polystyrene cup and fit the lid, pushing the bulb of the thermometer through the lid and into the solution

  6. Use the thermometer to gently stir the solution

  7. Observe the rise in temperature on the thermometer. When it stops changing, record the highest temperature reached

  8. Rinse out and dry the polystyrene cup

  9. Repeat steps 1-8, increasing the volume of sodium hydroxide by 5 cm³ until you reach a maximum of 40 cm³

  10. (optional) repeat the whole experiment again for accuracy and find a mean

Calculations/graphing:

  • plot a graph of maximum temperature reached (y-axis) against volume of sodium hydroxide solution (x-axis)

  • you will observe that the graph reaches a maximum (where HCl limits the reaction) and descends from then on. Why?

  • the energy released by the reaction is the same, but it is spread out through the whole solution. Since temperature is average kinetic energy of particles in a substance, the same amount will be spread thinner, so the reading in one area will decrease

  • Why use polystyrene? it is a good insulator!