Required practical, Temperature changes Flashcards
What is the aim of the practical?
To investigate the variable that affect temperature changes in chemical reactions.
What type of reaction is it?
exothermic
What is the neutralisation reaction between?
hydrochloric acid and the alkali sodium hydroxide.
What is the first step?
Add increasing volumes of sodium hydroxide solution to hydrochloric acid.
What will we measure in each experiment?
The maximum temperature reached.
What is the independent variable?
The volume of sodium hydroxide solution.
What is the dependent variable?
The maximum temperature reached.
What are the control variables?
The volume of hydrochloric acid and the concentrations of both the hydrochloric acid and the sodium hydroxide solution.
What is the first step?
We start by using cylinder to measure 30cm*3 of dilute hydrochloric acid.
What is the second and third step?
Transfer the acid into a polystyrene cup. We then stand the cup inside a beaker to stop it from falling over.
What is fourth step?
We use a thermometer to measure the temperature of the acid and we record this in a table.
What is the fifth step?
We use a measuring cylinder to measure 5cm*3 of sodium hydroxide solution and we transfer this to the polystyrene cup.
What is the sixth step?
At this point we fit a plastic lid to the cup and place a thermometer through the hole in the lid. The bulb of the thermometer must be in the solution.
What is the seventh step?
We now use the thermometer to gently stir the solution. The temperature of the solution will increase.
What is the eighth step?
Now we look carefully at the temperature rise on the thermometer. When the reading on the thermometer stops changing we record the highest temperature reached.
What should we do to the polystyrene cup after we have recorded the highest temperature reached.
Rinse out and dry it
When we repeat the whole experiment what do we use?
10cm3 of sodium hydroxide solution. (Each time we increase the volume of sodium hydroxide solution by 5cm3… until we reach a maximum of 40cm*3 of sodium hydroxide solution.
How many times do we repeat the experiment?
Twice, so we have two sets of results. We can now use these to calculate a mean value for the maximum temperature reached for each volume of sodium hydroxide solution.
What do we do at the end?
Plot a graph of our results.
As we increase the volume of sodium hydroxide solution…
…the maximum temperature reached increases.
Why does the maximum temperature actually decrease at a point?
In each experiment we are adding a greater volume of solution so the energy released is now spread out into a greater volume. When we add large volumes of sodium hydroxide solution, the maximum temperature reached decreases.
What is the reason for using a polystyrene cup with a lid
We are measuring temperature, this means that we want to reduce any heat losses. Polystyrene is a good thermal insulator.. The lid reduces heat loss to the air.
