required pracfical 4: Temperature changes

Question 1

briefly describe the practical to investigate the temperature change in an exothermic reaction
recap

Answer 1

it’s a neutralisation reaction between hydrochloride acid and the alkali sodium hydroxide

Question 2

what are the 2 chemicals used to investigate temperate change in an exothermic reaction

Answer 2

hydrochloric acid

sodium hydroxide

Question 3

in an exothermic reaction we investigate the temperate change.
We add increasing amounts of sodium hydroxide solution to hydrochloric acid
In each experiment we measure the maximum temperature reached.
what is the independent variable?
what is the dependant variable?
what is the control variables?

Answer 3

the independent variable is the volume of sodium hydroxide solution

The dependant 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

Question 4

what is the first step of the practical?

Answer 4

use a measuring cylinder to measure 30cm^3 of dilute hydrochloric acid

Question 5

in the first round,

how much dilute hydrochloric acid is used?

Answer 5

30cm^3

Question 6

after using a measure cylinder to measure 30cm^3 of hydrochloric acid, whats next?

Answer 6

we add the acid into a polystyrene cup and stand the polystyrene cup inside a beaker to stop the cup from falling over

Question 7

after pouring the acid into the polystyrene cup and standing the cup inside a beaker, what do we do next?

Answer 7

we use a thermometer to measure the temperature of the acid and record it in a table

Question 8

after measuring the temperature of the acid and recording it on a table, what do we then do?

Answer 8

we use a measuring cylinder to measure 5cm^3 of sodium hydroxide solution and transfer this to the polystyrene cup

Question 9

in the first round, how much sodium hydroxide solution is used ?

Answer 9

5cm^3

Question 10

after using a measuring cylinder to measure 5cm^3 of sodium hydroxide solution, what do we do next

Answer 10

transfer it into the polystyrene cup with the 30cm^3 of hydrochloric acid

Question 11

what do we do after transferring the sodium hydroxide solution into the polystyrene cup with the hydrochloric acid?

Answer 11

we then fit a plastic lid to the cup and place the thermometer through the hole in the lid
the bulb of the thermometer must be in the solution
we use the thermometer to gently stir the solution

Question 12

what must be in place to measure the temperatures of the acids

Answer 12

the bulb of the thermometer must be in the solution

Question 13

because this is an exothermic reaction, what happens to the energy
what does this mean for the solution

Answer 13

energy is released meaning the temperature of the solution will increase

Question 14

after using the thermometer to gently stir the solution, what next?

Answer 14

we look carefully at the temperature rise on the thermometer, when the reading on the thermometer stops changing, we record the highest temperature reached

Question 15

after recording the highest temperature reached, what do we do

Answer 15

we rinse out and dry the polystyrene cup to repeat the whole experiment using 10cm^3 of sodium hydroxide solution
after every time we repeat the experiment, we add 5cm^3 more of sodium hydroxide solution

Question 16

when the neutralisation experiment between hydrochloric acid and sodium hydroxide solution is repeated, how much sodium hydroxide solution is used this time?

Answer 16

10cm^3 of sodium hydroxide solution

Question 17

when repeating the experiment, each time, how much more sodium hydroxide solution is added?
when does this stop?

Answer 17

the volume of sodium hydroxide solution is increased by 5cm^3 each time until we reach a maximum of 40cm^3 of sodium hydroxide solution

Question 18

after repeating the experiment a number of times until we add 40cm^3 of sodium hydroxide solution,
what needs to happen to get a good result

Answer 18

we repeat the whole experiment one more time so that we have 2 sets of results

Question 19

what do we do with the 2 sets of results?

Answer 19

we use them to calculate a mean value for the maximum temperature reached for each volume of sodium hydroxide solution

Question 20

what do we do after getting a mean value of the maximum temperature reached for each volume of sodium hydroxide solution?

Answer 20

we can plot a graph of our results

Question 21

what does our results graph show us?

Answer 21

as we increase the volume of sodium hydroxide solution, the maximum temperature reached increases
at a certain volume of sodium hydroxide solution, the maximum temperature reached starts to decrease

Question 22

why is the maximum temperature reached on a graph increased as the volume of sodium hydroxide solution increases?

Answer 22

that is because when we add more particles of sodium hydroxide, they react with hydrochloric acid, more energy is released (exothermic reaction) and the maximum temperature reached increases

Question 23

at a certain point the maximum temperature starts to decrease, why?

Answer 23

we are now adding so much sodium hydroxide that there isn’t enough hydrochloric acid meaning
some of the sodium hydroxide is unable to react,
because of this, the amount of energy released by the reaction has reached a maximum.

Question 24

at a certain volume of the sodium hydroxide solution, the MTR decreases because there isn’t enough hydrochloric acid so some sodium hydroxide is unable to react, why does the temperature decrease?

Answer 24

the amount of energy released by the reaction has reached a maximum,
in each experiment, a greater volume of solution is added so the energy released is now spread out into a greater volume

Question 25

what is the reason for using a polystyrene cup with a lid?

Answer 25

polystyrene is a good thermal insulator so it reduces any heat losses through the sides and the bottom
the lid reduces heat loss to the air