From the graph of our results, temperature against volume of acid added, how do we find the point of neutralisation?

Draw a straight line of best fit for both the upward slope and the downward slope and extend them until they cross at the top. This point corresponds to the maximum temperature and to the volume of acid required for neutralisation.

So why is this maximum temperature higher on the graph than the maximum temperature that we measured?

The highest temperature will coincide with the exact neutralisation point. It's unlikely that you will add the exact quantity for neutralisation and measure the temperature at that point. There will also be some heat loss. Some heat is lost to the surroundings despite efforts to insulate the reaction vessel.

It's all colourless. How can we be sure that the highest temperature is really when the solution is neutral?

It may be helpful to add indicator to show students the colour changes and reinforce the ideas here. Or you could use a pH probe to allow the plotting of pH at the same time as temperature and show that the maximum temperature coincides with the pH being neutral.

Did we make a salt?

Yes, at the point of neutralisation, the salt is what's left over from the reaction in solution, from the acid when it has lost H⁺ and the alkali when it has lost OH^–. The soluble salt here is sodium chloride.