energy changes - required prac

Question 1

what is the independent variable in this practical

Answer 1

the volume of sodium hydroxide solution

Question 2

what is the dependent variable in this practical

Answer 2

the maximum temperature reached

Question 3

what are the control variables

Answer 3

• volume of hydrochloric acid
• concentration of hydrochloric acid
• concentration of sodium hydroxide

Question 4

method

Answer 4

1. start by using a measuring cylinder to measure 30cm3 of dilute hydrochloric acid
2. Then transfer the acid to a polystyrene cup
3. Then, stand the polystyrene cup inside a beaker
4. Next, use a thermometer to measure the temperature of the acid, and record it in a table
5. then, use a measuring cylinder to measure 5cm of sodium hydroxide solution, then transfer it to a polystyrene cup
6. Place a plastic lid on the cup, and place a thermometer through a hole in the lid (the bulb of the thermometer must be in the solution)
7. use the thermometer to gently stir the solution
8. The temperature of the solution will increase as the reaction is exo, so record the highest temperature reached
9. Rinse out and dry the polystyrene cup
10. Carry out the experiment again, increasing the volume of sodium hydroxide solution until you get to 40cm3
11. Repeat the whole experiment again, find a mean and draw a graph

Question 5

why do we stand the polystyrene cup inside a beaker

Answer 5

to stop if from falling over

Question 6

what happens as we increase the volume of sodium hydroxide and why

Answer 6

• the maximum temperature reached increases

why? - because when we add more particles of sodium hydroxide, they react with hydrochloric acid, and since this is an exothermic reaction, more energy is released, therefore the maximum temp increases

Question 7

at a certain volume of sodium hydroxide, the maximum temperature reach begins to decrease, why is this

Answer 7

because we are now adding so much sodium hydroxide, that there is not enough hydrochloric acid to react with it, this means that some of the sodium hydroxide does not react, so the amount of energy released by the reaction has reached a maximum

Question 8

why does the maximum temperature decrease from a point

Answer 8

• in each experiment, we are adding a greater volume of solution
• so the energy released is now spread out into a greater volume
• because of this, when we add large volumes of sodium hydroxide, the maximum temperature reached decreases

Question 9

why is a polystyrene cup with a lid used in experiments

Answer 9

• in the experiment we want to reduce heat loss as were measuring the temperature, and polystyrene is a good thermal insulator, reducing heat loss from the sides and the bottom
• lid reduces heat lost by evaporation

Question 10

simple method

Answer 10

1 . measure 50cm3 of