Required practical paper 2

Question 1

Describe how to investigate changes in concentration on the rate of a reaction

Answer 1

Use a measuring cylinder to put 10 cm³ of sodium thiosulfate solution into a conical flask
Place the Conoco flask into a printed black cross
Add 10 cm³ of hydrochloric acid into the conical flask
Swirl the solution and start the stopwatch
Look down through the top of the flask after some time the solution will go cloudy
Stop the clock when you can no longer see the Cross
Then repeat the experiment with lower concentration of sodium thiosulfate Solution
Then repeat the whole experiment and calculate the mean value
And do not include any anomalous results when calculating a mean

Question 2

What is reproducibility

Answer 2

A measurement is reproducible if it can be repeated by another person or using a different technique or equipment and still get the same results

Question 3

What is the problem with the disappearing cross experiment

Answer 3

Different people have different eyesight and some people can see the cross for longer than others

Question 4

How can you measure the volume of hydrogen gas produced

Answer 4

Use a measuring cylinder to place 50 cm³ of hydrochloric acid into a conical flask
Attach the conical flask to a bung and delivery tube
Place the delivery tube into a container filled with water
Place an upturned measuring cylinder also filled with water over the delivery tube
Add 3 cm strip of magnesium hydrochloric acid and start a stopwatch
the reaction produces hydrogen gas which is trapped in the measuring cylinder
every 10s measure the volume of hydrogen gas in the measuring cylinder and continue until no more hydrogen is given off
Repeat the experiment using different concentrations of hydrochloric acid

Question 5

Describe how paper chromatography can be used to separate substances

Answer 5

First we use a ruler to draw a horizontal pencil line on the chromatography paper (Should be around 2 cm from the bottom of the paper)
Mark 5 pencil spots at equal spaces across the line (at least 1cm)
Use a capillary tube to put small spots of each known food colorings and unknown into the pencil spots
(Capillary tube=Very thin glass tube)
Keep the spots small preventing the colors from spreading to each other
Pour water into a bigger (1cm)
Attach the paper to a glass rod and lower it into the beaker
Keeping the pencil line above the water
Then put a lid on the beaker



Question 6

How can you test for hydrogen

Answer 6

Using a burning splint at the open end of a test tube of gas.
If present hydrogen burns rapidly with a pop sound.

Question 7

How can you test for oxygen

Answer 7

Using a glowing splint insert into a test tube of the gas
If oxygen is present the splint real lights.

Question 8

How can you test for carbon dioxide

Answer 8

Carbon dioxide is shaken or bubbled through lime water
If present the lime water will turn milky (cloudy)

Question 9

What is lime water

Answer 9

An aqueous solution of calcium hydroxide

Question 10

How can you test for chlorine

Answer 10

Using damp litmus paper put into chlorine gas
If present the litmus paper turns white.

Question 11

Describe how to analyze a sample of water by destination

Answer 11

Test the pH of the water sample using universal indicator paper.
2. Accurately weigh and record the mass of an empty evaporating basin accurately to two decimal places.
3. Pour 50 cm³ of the water sample into the evaporating basin.
4. Heat the evaporating basin on a tripod and gauze using a Bunsen burner until all the liquid evaporates.
5. Allow the evaporating basin to cool, then weigh it again.
6. Calculate the mass of dissolved solids remaining in the evaporating basin. After this, record your findings in a table