Tests for ions/compounds

Question 1

Test for oxygen?

Answer 1

Put a glowing splint in a test tube filled with the gas. The splint will re-light.

Question 2

Test for hydrogen?

Answer 2

Put a lit splint at the open end of a test tube containing the gas. A “squeaky pop” noise will be produced.

Question 3

Test for chlorine?

Answer 3

Put a piece of litmus paper into a test tube containing the gas so that it becomes damp. The litmus paper will be bleached.

Question 4

Test for carbon dixoide?

Answer 4

Bubble gas through limewater (calcium
hydroxide solution). The solution will turn
cloudy.

Question 5

How to prepare solid food for a food test?

Answer 5

1) Get a piece of food and break it up using a pestle and mortar
2) Transfer the ground up food to a beaker and add distilled water
3) Give the mixture a good stir, with a glass rod, to dissolve some of the food
4) Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food

Note: you do not have to filter the sample for the Sudan III test

Question 6

Test for reducing sugars?

Answer 6

Benedict’s test:

1) Prepare a food sample and transfer 5 cm3 to a test tube
2) Prepare a water bath so that it is set to 75 degrees Celcius
3) Add ~10 drops of Benedict’s solution to the test tube, using a pipette
4) Place the test tube in the water bath, using a test tube holder
5) Leave it for 5 minutes, with the tube pointing away from you
6) If the sample contains ‘it,’ there will be a colour change from blue to green, yellow or brick-red, depending on how much of ‘it’ it contains

Question 7

Test for starch?

Answer 7

1) Prepare a food sample and transfer 5 cm3 to a test tube
2) Add a few drops of iodine solution and gently shake the tube to mix the contents
3) If the sample contains ‘it,’ there will be a colour change from browny-orange to black or blue-black

Question 8

Test for proteins?

Answer 8

Biuret test:

1) Prepare a food sample and transfer 2 cm3 to a test tube
2) Add 2 cm3 of biruet solution and gently shake the tube to mix the contents
3) If the sample contains ‘it,’ there will be a colour change from blue to purple

Question 9

Test for lipids?

Answer 9

Sudan III test:

1) Prepare an unfiltered food sample and transfer 5 cm3 to a test tube
2) Using a pipette, add 3 drops of Sudan III stain solution to the test tube and gently shake the tube to mix the contents
3) If the sample contains ‘it,’ the mixture will separate into 2 layers, whereby the top layer will be bright red

Question 10

Test for acidic/neutral/alkaline solution?

Answer 10

Add a few drops of universal indicator and observe the colour change:

• Strongly acidic: red
• Weakly acidic: orange-yellow
• Neutral: green
• Weakly alkaline: blue
• Strongly alkaline: purple

Question 11

Test for alkenes?

Answer 11

1) Add to a test tube containing the compound you want to test
2) If there is a colour change from orange to colourless, ‘it’ is present