TEMPERATURE CHANGES Flashcards
What REACTION is taking place?
An EXOTHERMIC (neutralisation) reaction between hydrochloric acid and sodium hydroxide.
What is the INDEPENDANT variable?
Volume of sodium hydroxide solution
What is the DEPENDANT variable?
Maximum temperature reached.
What are the CONTROL variables?
Volume of hydrochloric acid and the concentration of both hydrochloric acid and sodium hydroxide solution.
Describe the PRACTICAL
- Use a measuring cylinder to measure 30cm^3 of DILUTE hydrochloric acid.
- Transfer acid to a polystyrene cup and stand cup inside a beaker for stability.
- Use a thermometer to measure temperature of acid and record in a table.
- Use a measuring cylinder to measure 5cm^3 of sodium hydroxide solution and transfer into the polystyrene cup.
- Fit a plastic lid to the polystyrene cup and place the thermometer through hole in lid.
- Gently stir solution with thermometer.
- Look at temp rise on thermometer - when it stops rising, record the highest temperature that is reached.
- Rinse out and dry polystyrene cup.
- Repeat experiment using 10cm^3 of sodium hydroxide - and then repeat several more times; increase volume of sodium hydroxide solution by 5cm^3 each time until you reach 40cm^3.
- Repeat experiment again - 2 sets of values are then acquired.
- Calculate a mean value for the maximum temperature reached for each volume of sodium hydroxide solution.
What OBSERVATIONS can you make from this practical?
As the volume of sodium hydroxide solution increases, the maximum temperature reached increases, HOWEVER, at a certain volume of sodium hydroxide solution, the maximum temperature starts to decrease as there is not enough HCl for the sodium hydroxide to react.
Why is a LID used on the cup?
To reduce any heat loss to the air.
Why is a polystyrene cup used?
Polystyrene is a good thermal insulator.
