ES From Sep 2015

Question 1

What are the three key features of oxidation?

Answer 1

1. Gain of oxygen.
2. Loss of electrons
3. An increase in oxidation number.

Question 2

What are the three key features of reduction?

Answer 2

1. Loss of oxygen.
2. Gain of electrons.
   3 A decrease in oxidation number.

Question 3

What is meant by a ‘systematic name’?

Answer 3

A named element with a Roman numeral in brackets e.g. iron(III).

Question 4

What does the Roman numeral signify in a systematic name?

Answer 4

The numeral shows the oxidation state of a preceding element. e.g. In iron(II) the oxidation state is +2, whereas in potassium nitrate(V) the nitrogen has an oxidation state of +5.

Question 5

What is an oxyanion?

Answer 5

A negative ion with oxygen in it.

Question 6

What are halogens?

Answer 6

They are all the elements in group 7 of the periodic table

Question 7

What do all halogens have in common?

Answer 7

• 7 electrons in the outer shell
• very reactive so are never found in their elemental form
• occur as diatomic particles, the two atoms are linked by a covalent bond

Question 8

How can halogens become stable?

Answer 8

1. gaining an electron from a metal atom, forming a halide anion in an ionic compound
2. sharing an electron from another non-metal atom in a covalently bonded compound

Question 9

What are the physical properties down group 7?

Answer 9

• become darker in colour
• melting and boiling points increase
• change from gases to liquids to solids at room temperature
• become less volatile

Question 10

Which halogen is most reactive?

Answer 10

Elements at the top of the group are most reactive and the strongest oxidising agents.
E.G fluorine atoms have fewer shells, so the attraction between the core and the electron that completes its outer shell is very strong.
Whereas in chlorine the outer shell is further from the core and the attraction for the extra electron is therefore weaker.
It is also because there is more shielding due to a larger number of electrons as you move further down the group

Question 11

What are spectator ions?

Answer 11

They are ions left out of ionic equations because they are unchanged

Question 12

What happens when you react halogens with halide ions?

Answer 12

Displacement reactions occur; a halogen displaces the less reactive halide from a compound.
It is an example of a redox reaction because both oxidation and reduction occurs in the same reaction.

Question 13

How do halide ions react with silver ions? What precipitates do they form and how can we distinguish between the colours of precipitate?

Answer 13

(X represents a halide)
Ag+ (aq) + X- (aq) –> AgX (s)
Silver halides are precipitated when a solution of silver ions is added to a solution containing chloride,bromide or iodide ions;

Silver chloride = White
Silver bromide = Cream
Silver iodide = Pale yellow.

It is sometimes difficult to distinguish between colours of precipitate, so ammonia solution can be added. After ammonia solution is added:

• Solubility of silver chloride is greater than that of silver bromide
• Silver iodide is insoluble in ammonia solution.

Question 14

What is dynamic equilibrium?

Answer 14

The point in a reversible reaction where the forwards and backwards reaction are occurring at the same rate, causing the concentrations of reactants and products to stay constant.

Question 15

What does the value of the equilibrium constant tell you about the position of equilibrium?

Answer 15

If Kc > 1 then equilibrium lies to the right.

If Kc = 1 then equilibrium lies in the middle

If Kc

Question 16

For the reaction H2 + I2 —> 2HI

what would the expression for Kc be?

Answer 16

[H2] [I2]

Question 17

What value for reactants and products in the equation would you use to calculate Kc?

Answer 17

The concentration at equilibrium

Question 18

Why can’t HBr or HI be made using sulfuric acid?

Answer 18

They are strong enough reducing agents to reduce the sulfuric acid.

Question 19

What are the balanced equations for the reaction of the following with Sulfuric acid:

Sodium Chloride
Sodium Bromide
Sodium Iodide

Answer 19

NaCl(s) + H2SO4(l) ==> NaHSO4(s) + HCl(g)

2NaBr(s) + 2H2SO4(l) ==> NaHSO4(s) + Br2(g) + SO2(g) + 2H2O(l)

8NaI(s) + 5H2SO4(l) ==> 4Na2SO4(s) + 4I2(g/s) + H2S(g) + 4H2O(l)

Question 20

What do hydrogen chloride, hydrogen bromide and hydrogen iodide dissolve in water to form?

Why is this different with Hydrogen fluoride?

Answer 20

They all create strong acids because the molecule dissociates to release a H+ ion.

However hydrogen fluoride creates a weak acid because it does not fully dissociate when dissolved in water.

Question 21

What happens at the cathode/anode?

Answer 21

At the cathode, positive ions are reduced (gain electrons), whereas at the anode, negative ions are oxidised (loss of electrons). Typically, metals are found at the cathode and non-metals at the anode in metal-nonmetal compounds.

Question 22

Name two frequent uses of chlorine.

Answer 22

1/ Water treatment -> Killing bacteria and other pathogens.
2/ Household cleaning products -> Bleach (killing bacteria/other pathogens on surfaces)
3/ Washing clothes -> Removing stains via bleach.

Question 23

What oxidation state are Group 7 elements usually in (when in a compound comprised of other elements)?

Answer 23

Group 7 elements in a compound usually have an oxidation state of -1. This is an exception when they are combined with oxygen, or a more reactive halogen. Fluorine, being the most reactive, is always -1.

Question 24

How are oxyanions easily identified?

Answer 24

Oxyanions always have names ending in ‘ate’ e.g. Phosphate

Question 25

Which redox reaction occurs at the cathode and at the anode?

Answer 25

At the cathode, reduction occurs and at the anode, oxidation occurs.