I mean welcome back to three size lessons Cole you K by the end of this video you should be able to describe how to investigate the variables that affect temperature changes and chemical reactions under this is a required practical so you need to learn the details okay we've already seen that reactions can be exothermic or endothermic in this particle we're going to investigate the temperature change in an exothermic reaction this is the neutralization reaction between hydrochloric acid and the alkali sodium hydroxide we're going to add increasing volumes of sodium hydroxide solution to hydrochloric acid under Nietzsche experiment we'll measure the maximum temperature reached so in this practical the independent variable is the volume of sodium hydroxide solution and the dependent variable is the maximum temperature reached the control variables are the volume of hydrochloric acid and the concentrations of both the hydrochloric acid and the sodium hydroxide solution we start by using a measuring cylinder to measure 30 centimeters cubed of dilute hydrochloric acid we then transfer the acid into a polystyrene coke now we stand the polystyrene cup inside a beaker and this stops the cup from falling over next we use a thermometer to measure the temperature of the acid and we record this in a table now we use a measuring cylinder to measure 5 centimeters cubed of sodium hydroxide solution and we transfer this to the polystyrene cup at this point we fit a plastic lid to the coke and place at the monitor through the hole in the lid and the bulb of the thermometer must be in this solution we now use a thermometer to gently stir the solution now because this reactions exothermic it releases energy and this means that the temperature of the solution will increase so 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 we now lens out and draw the polystyrene cup and at this point we'll repeat the whole experiment using 10 centimeters cubed of sodium hydroxide solution we then carry out the experiment several more times on each time we increase the volume of sodium hydroxide solution by 5 centimeters cubed until we reach a maximum of 40 centimeters cubed of sodium hydroxide solution at this point we'll repeat the whole experiment one more time so we've got 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 at the end we can plot a graph of our results and I'm showing you a sample graph here as you can see as we increase the volume of sodium hydroxide solution the maximum temperature reached increases that's because when we add more particles of sodium hydroxide they react with hydrochloric acid as we saw this is an exothermic reaction so more Energy's released and the maximum temperature reached increases however at a certain volume of sodium hydroxide solution the maximum temperature reached starts to decrease at this point we're now adding so much sodium hydroxide that there's not enough hydrochloric acid this means that some of the sodium hydroxide is unable to react so because of this the amount of energy released by the reaction has reached a maximum so the question is why does the maximum temperature actually decrease from this point well you need to bear in mind that in each experiment we're adding a greater volume of solution so the energy released is now spread out into a greater volume so because of this when we add large volumes of sodium hydroxide solution the maximum temperature reached actually decreases now in the exam you could be asked the reason for using a polystyrene cup with a lid in this experiment we're measuring the temperature this means that we want to reduce any heat losses polystyrene is a good thermal insulator so this reduces heat loss through the sides and the bottom and the lid which is heat loss to the air remember you find plenty of questions on this required practical in my vision workbook and you can get that by clicking on the link above [Music]