GASES IN THE ATMOSPHERE [lyceum]

What is the approximate percentage by volume of carbon dioxide in unpolluted, dry air?

• 78.1

• 21.0

• 0.9

• 0.04

Answer explanation

NITROGEN 78.1%

OXYGEN 21.0%

ARGON 0.9%

CARBON DIOXIDE 0.04%

Magnesium burns in oxygen with an extremely bright white flame to give a white, powdery ash what is this compound?

• MgO₂

• MgO

• MgCO₃

• Mg₃N₂

Answer explanation

Magnesium burns in oxygen with an extremely bright white flame to give a white, powdery ash of magnesium oxide:

2Mg(s) + 0₂(g) --->2Mg0(s)

When Sulfur burns in oxygen with a blue flame a poisonous, colourless gas is produced. What is this gas?

• SO₃

• SO₂

• O₂ 

• H₂S

Answer explanation

Sulfur burns in oxygen with a blue flame.

Poisonous, colorless sulfur dioxide gas is produced.

S(s) + 0₂(g) -+ S0₂(g)

What is produced when sulfur dioxide gas dissolves in water?

• Sulfuric acid

• Sulfur

• Sulfurous acid

• Hydrogen sulfide

Answer explanation

The sulfur dioxide dissolves in water to form an acidic solution of sulfurous acid: S0₂(g) + H₂0 (I) ---> H₂S0₃(aq)

What is produced when Hydrogen burns in oxygen with a pale blue flame?

• H₂O

• H₂O₂

• ArH

• CO₂   

Answer explanation

Hydrogen burns in oxygen with a pale blue flame. The product is water:

2H₂(g) + 0₂(g)-+ 2H₂0(I)

Select the most appropriate answers for (a) and (b) respectively;

Metal oxides are usually (a) ___________ oxides while non-metal oxides are usually (b)___________ oxides.

• (a) basic

  (b) basic

• (a) acidic

  (b) acidic

• (a) acidic

  (b) basic

• (a) basic

  (b) acidic

Answer explanation

Metal oxides are usually basic oxides, which means that they react with acids to form salts.

Non-metal oxides are usually acidic oxides, which react with alkalis/bases to form salts.

What is the colour change that occurs in the following reaction

CuCO₃(s) --, CuO(s) + C0₂(g)

• Black to green

• Green to black

• Green to colourless

• Colourless to green

Answer explanation

copper (II) carbonate is a green powder which decomposes on heating to produce black copper (II) oxide:

CuCO₃(s) ---->CuO(s) + C0₂(g)

Which of the following can be used to produce CO₂

• CaCO₃

  (marble chips)

• CaO

• Coal

• CaCl₂  

Answer explanation

Carbon dioxide is most easily made in the laboratory by the reaction between dilute hydrochloric acid and calcium carbonate in the form of marble chips:

CaC0₃(s) + 2HCl(aq)------>CaCl₂(aq) + CO,(g) + H₂0(1)

Carbon dioxide is also produced when fossil fuels (coal, oil and gas) burn. For instance, when coal, which is mostly carbon, burns in excess oxygen:

C(s) + 0₂(g) --, C0₂(g)

Many people believe that the increase in the level of carbon dioxide in the atmosphere may contribute to climate change. Which of the following is not an effect of climate change?

• polar ice caps could melt

•  sea levels could rise

•  there could be more extreme weather (such as floods, droughts and heat waves).

• deforestation

Answer explanation

Deforestation is considered to be one of the contributing factors to global climate change. But it is not effect of climate change.

What is produced when petrol is burnt in air?

• CO₂ and H₂O

• CH₄ and H₂O

• CO₂ and H₂O

• CH₄ and H₂

Answer explanation

Petrol is a mixture containing many different hydrocarbons. An example of a reaction that occurs when petrol burns is: 2C₈H₁₈(l) + 250₂(g) ---> 16C0₂(g) + 18H₂0(1)