Identification of gases

Question 1

If there is no change to the colour of litmus paper after testing for gases using the moist litmus paper, what does it mean and what do you then test it with?

Answer 1

It means the gas is neutral.

You test it with lighted splint and a glowing splint.

If it ‘pops’ with a lighted splint —> it means the gas is hydrogen

If it ‘relights’ with a glowing splint—> it means the gas is oxygen

Question 2

If, after testing for gases using the moist litmus paper and the moist red litmus paper turns blue, what does it mean

Answer 2

It means the gas is an alkaline

The gas is most likely ammonia, NH3

Question 3

If, after testing for gases using the moist blue litmus paper and it turns red, what does it mean and what do you do next?

Answer 3

It means the gas is acidic

We then pass the gas through limewater or pass the gas through aqueous acidified potassium manganate (VII)

If, after passing the gas through limewater and it gives a white precipitate with limewater, it means the gas is carbon dioxide. (CO2)

If, after passing the gas through aqueous acidified potassium manganate (VII) and it turns aqueous acidified potassium manganate (VII) from purple to colourless, it means the gas is sulfur dioxide (SO2)

Question 4

What should the blank be?

Na 2 SO 3 + 2 HCL—>

Answer 4

Na 2 SO 3 + 2 HCL —> 2NaCl + SO 2 + H2O

Question 5

What should the blank be?

Zn + H2SO4 —>____________

Answer 5

Zn + H2SO4 —> Zn SO4 + H 2

Question 6

What should the blank be?

2 H2O2 —> ___________

Answer 6

2 H2O2 —> 2H2O + O2

Question 7

What should the blank be?

CaCO3 + HCl —> ______________

Answer 7

CaCO3 + HCl —> CaCl2 + CO 2 + H2O

Question 8

What should the blank be?

NH4Cl + NaOH –> _____________

Answer 8

NH4Cl + NaOH –>NH3 + NaCl + H2O

Question 9

What should the blank be?

NaClO + 2 HCl –> ________________

Answer 9

NaClO + 2HCl –> NaCl + Cl2 + H2O

Question 10

What should you take note when heating something in a test tube?

Answer 10

• The test-tube holder should be clipped about 1cm below the mouth of the test-tube, NOT at the middle of the test-tube.
• When heating, move the test-tube gently, ensuring the whole mixture is heated, NOT just one spot.
• When heating, the test-tube should be held about 45 degrees to the flame and the mouth should be pointed away from others.
• When testing the gas with litmus paper, the paper should be held at the mouth of the test-tube, WITHOUT touching the test-tube.