Reqired Practical 4 -> Temperature Changes Flashcards
What is the independent variable?
Volume of sodium hydroxide solution.
What is the dependent variable?
Maximum temperature reached
What are the control variables
The volume of hydrochloric acid and the concentrations of both the hydrochloric acid and sodium hydroxide solution
What is the method of measuring the temperature change of exothermic?
1) use a measuring cylinder to measure 30cm cubed of dilute hydrochloric acid.
2) transfer the acid to a polystyrene cup and place it in a beaker (which stops it from falling over)
3) put a thermometer into the cup and measure the temperature and record it in a table
4) use a measuring cylinder to measure 5cm cubed of sodium hydroxide solution
5) transfer it into a polystyrene cup and immediately put a plastic lid on with a thermometer in the hole.
6) gently stir the solution with a thermometer.
7) record the maximum temperature reached
8) clean the cup and wait for it to cool down and repeat with 10cm cubed of sodium hydroxide solution
9) repeat the method and every time with 5cm cubed added until a maximum of 40cm.
10) repeat all of the steps again and calculate the mean of each volume and then draw a graph.
What is the reaction?
The neutralisation reaction between hydrochloric acid and sodium hydroxide (alkali)
What is the overall method?
Adding increasing volumes of sodium hydroxide solution to hydrochloric acid and in each experiment we will record the maximum temperature reached.
Why does the maximum temperature stop increasing (exothermic)
There isn’t enough hydrochloric acid to reach with all of the sodium hydroxide solution we are adding. So some is left unreacted. It decreases because the heat is spread out across a larger volume the more we add of sodium hydroxide.
We use polystyrene and a lid because?
Reduce heat lost because that is what we are measuring. Polystyrene is thermal insulating. The lid reduced heat lost to the air
