Chemistry

Question 1

Balance the following equation

C₂H₅N + O₂ → 8CO + H₂O + 4NO₂

Answer 1

4C₂H₅N + 13O₂ → 8CO + 10H₂O + 4NO₂

Question 2

Balance the following equation

Na (s) + O₂ → Na₂O

Answer 2

4Na (s) + O₂ → 2Na₂O

Question 3

What is the oxidation number of free elements such as N_2, P_4, H₂ and S₈

Answer 3

They all have oxidation numbers of zero

Question 4

Balance the following equation

C₂H₃Cl + O₂ → CO₂ + H₂O + Cl₂

Answer 4

4C₂H₃Cl + 12O₂ → 8CO₂ + 6H₂O + 2Cl₂

Question 5

Balance the following equation

C₄H₁₀ (l) + O₂ (g) → CO₂ + H₂O (l)

Answer 5

2C₄H₁₀ (l) + 13O₂ (g) → 8CO₂ + 10H₂O (l)

Question 6

a) Name elements in Group IA of the periodic table. b) What is their oxidation number?

Answer 6

a) Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr)
b) +1

Question 7

The oxidation number of a monatomic ion is equal to what?

Answer 7

The charge of the ion eg. Na⁺ the oxidation number is +1

Question 8

a) An oxidising agent causes another atom in a redox reaction to be reduced or oxidised?
b) Is the oxidising agent then reduced or oxdised?

Answer 8

a) An oxdising agent caused an atom in a redox reaction to undergo oxidation.
b) The oxdising agent in a redox reaction is reduced.

Question 9

What does the Mnemonic OIL RIG in terms of Redox reactions stand for?

Answer 9

OIL RIG

Oxidation is Loss, Reduction is Gain

Question 10

Define a Bonsted-Lowry Acid

Answer 10

A species that donates hydrogen [H⁺] ions

Question 11

Define a Bronsted-Lowry Base

Answer 11

A species that donates hydrogen [H⁺] ions

Question 12

Why do Bronsted-Lowry acids and bases always occur in pairs?

Answer 12

Becasue the defination requires a transfer of a proton from the acid to the base. These are conjugate acid-base pairs.

Question 13

When is a conjugate acid formed?

Answer 13

When a base gains a proton.

Question 14

When is a conjugate base formed?

Answer 14

When an acid loses a proton.

Question 15

Which is the base and which is its conjugate acid?

H₃O⁺(aq) ⇔ H₂O (aq) + H⁺ (aq)

Answer 15

H₃O⁺ is the conjugate acid of the base H₂O

Question 16

What is the conjugate base in this equation?

HNO₂ (aq) ⇔ NO₂^- (aq) + H⁺ (aq)

Answer 16

NO₂​^- is the conjugate base of HNO₂

Question 17

What are the conjugate base and acids in the following reaction?

HCO₃^- (aq) + H₂O (aq) ⇔ CO₃^2- (aq) + H₃O⁺

Answer 17

CO₃^2- is the conjugate base of HCO₃^-

H₃O⁺ is the conjugate acid of H₂O

Question 18

In aqueous solutions what happens to strong acids and bases?

In aqueous solutions what happens to weak acids and bases?

Answer 18

Strong acids and bases usually undergo complete ionisation (complete dissociation) in aqueous solutions.

Weak acids and bases only partially dissocate in the aqueous solutions.

Question 19

Strong Acid + Strong Base ⇒ ?

Answer 19

Strong Acid + Strong Base ⇒ Salt + Water

eg.

HCl + NaOH ⇒ NaCl + H₂O

Question 20

If you have a strong acid, what will the conjugate base be weak or strong?

Answer 20

The stronger the acid the weaker its conjugate base and vice versa.

Question 21

What is an amphoteric species?

Answer 21

An amphoteris species is a molecule that acts like an acid in the presence of a base, however acts like a base in the presence of an acid.

Question 22

How does water act like an amphoteris species?

Answer 22

H2O can act either as an acid or a base depending on reacting species. Water acts like an acid by donating one of its hydrogen ions, and it acts as a base by accepting a hydrogen ion. As an amphoteric compound, water can react with itself in a process called auto-ionsation.

H₂O (l) + H₂O (l) ⇔ H₃O⁺ (aq) + OH^- (aq)