ACIDS, BASES AND SALT PREPARATIONS [dchemlc]

Which of the following will not react with dilute acids?

• aluminium

• copper

• zinc

• iron

Answer explanation

Simple dilute acids react with metals depending on their positions in the reactivity series. (Higher the reactivity, the more vigorous the reaction)

• Metals below hydrogen in the series don't react with dilute acids.

• Metals above hydrogen in the series react to produce hydrogen gas and the corresponding salt.

What will be the products of the reaction between magnesium and sulfuric acid?

• O₂

• H₂

• MgSO₄

• H₂O

Answer explanation

There is rapid fizzing and a colourless gas is evolved, which pops with a lighted splint (the test for hydrogen). The reaction mixture becomes very warm as heat is produced. The magnesium gradually disappears to leave a colorless solution of magnesium sulfate.

Mg_(s) + H₂SO_4(aq) ----->

MgSO_4(aq) + H_2(g)

The reaction between zinc and HCl acid is slower than the reaction between Magnesium and HCl acid. This is because;

• Zinc is less reactive than magnesium

• Zinc is more reactive than magnesium

• HCl is more reactive than zinc 

• Zinc is more reactive than HCl

Answer explanation

The reactions between zinc and the two acids look exactly the same. The reactions are slower because zinc is lower down the reactivity series than magnesium.

Which of the following is not a base?

• Metal oxide

• Metal hydroxide

• Ammonia

• Metal nitrates

Answer explanation

Bases are substances that neutralize acids by combining with the hydrogen ions in them to produce water. When we are referring to a base at this level, we usually mean a metal oxide, a metal hydroxide or ammonia.

The copper(II) oxide reacts with hot dilute sulfuric acid to produce a blue solution. What are the products of this reaction?

• CuSO₄ and H₂O

• CuSO₄ and H₂

• CuSO₄ and H₂SO₄

• CuO and H₂O

Answer explanation

The copper(II) oxide (black powder) reacts with hot dilute sulfuric acid to produce a blue solution of copper(II) sulfate. CuO(s) + H₂SO₄(aq) -----> CuSO₄(aq) + H₂0(I)

Which of the following is not soluble in water?

• AgCl

• K₂O

• Na₂CO₃

• CuCl₂

Answer explanation

All the Group 1 oxides are soluble in water. (K₂O)

Sodium carbonate is soluble in water. (Na₂CO₃)

Copper chloride is also soluble in water. (CuCl₂)

Which of the following reactions will not produce alkalis?

• NH_3(aq) + H₂O_(l)

• CaO_(s) + H₂O_(l)

• Na₂O_(s) + H₂O_(l)

• AgNO_3(aq) + NaCl_(aq)

Answer explanation

we can define alkalis as solutions that are a source of hydroxide (OH-) ions, so we can see that;

NH_3(aq)+ H₂0_(l) <--->NH₄⁺_(aq)

+ OH^-_(aq)

CaO_(s) + H₂0_(l) ---> Ca(OH)_2(aq)

Na₂O_(s) + H₂O_(l) --> 2NaOH_(aq)

Mixing sodium hydroxide solution and dilute hydrochloric acid produces a colourless solution. However, the temperature of the solution rises several degrees. What will be the products of this reaction?

• NaCl

• H₂O

• H₂

• NaOH

Answer explanation

The rise in temperature shows that there has been a chemical change. Sodium chloride solution will be formed:

NaOH_(aq)+ HCl_(aq)--->NaCl_(aq) + H₂0_(l)

Give the products resulting from the following reaction?

Na₂CO₃ + 2HCl ----->

Answer explanation

Sodium carbonate is soluble in water. The equation for the reaction of sodium carbonate with hydrochloric acid is: Na₂CO_3(aq) + 2HCl_(aq)---->

2NaCl_(aq) + CO_2(g) + H₂O_(l)

What will be the colour change observed in the following reaction?

CuCO_3(s) + H₂SO_4(aq) -->CuSO_4(aq) + CO_2(g) + H₂O_(l)

• Green to blue

• Black to blue

• Blue to green

• Blue to black

Answer explanation

Green copper(II) carbonate reacts with the common dilute acids to give a blue or blue-green solution of copper(II) sulfate.

Carbon dioxide gas is given off. You can recognize this because it turns limewater milky.