Plan an investigation into the impact of concentration on temperature change when Mg reacts with HCl

Indexed: 2026-05-17

[00:00:00]How would you investigate how the concentration of an acid affected the temperature change when you added some magnesium to it?

[00:00:07]Hi, my name's Dr. De Bruin. I'm a GCSE and A-level science teacher, and I also make revision videos on YouTube.

[00:00:13]There are many possible reactions that you can use as part of the Unit 5 required practical, but the reaction of an acid with some metal like magnesium is a pretty common one. For any kind of reaction where you're measuring the temperature change, you need to be doing this in some kind of insulated vessel like a polystyrene cup.

[00:00:28]Polystyrene is a good material, not just because it's an insulator, but crucially because it's a better insulator than a glass beaker. If we're investigating the impact of concentration, then that's our independent variable, which we need to change. And we can do this by taking some acid and gradually diluting it to give us different concentrations.

[00:00:45]Typically, you're going to want about five different values for that independent variable. So, maybe concentrations of 1, 0.8, 0.6, 0.4, and 0.2.

[00:00:53]For the temperature change required practical, you need to calculate a temperature change. So, that means you're going to need to take the temperature at the start of the reaction and the end. The independent variable should be the only thing that's changing. So, that means that you should describe that you're always going to use the same volume of acid and the same mass of magnesium. The fastest way to write this down is just to say, "Take 10 cm cubed of acid and 1 g of magnesium."

[00:01:15]The actual numbers here aren't important. It's just much faster to state a number than it is to explain that you're going to do it again, but not change those things.

[00:01:22]So, measure the volume of the acid and the mass of the magnesium, take the temperature of the acid, then add the magnesium to the acid, and record the highest temperature reading.

[00:01:30]Dilute your acid to make a new concentration and do the whole thing again. You might also want to describe how, now that you have your five concentrations, you're going to do the entire experiment three times, and that will then allow you to calculate a mean temperature change for every concentration. Remember, in GCSE science, there's never a mark for just saying repeat. It needs to be repeat and calculate a mean.