Redox and the Periodic Table

Question 0

What is a period?

Answer 0

A horizontal row of elements in the Periodic Table. Elements show trends in properties across a period.

Question 1

What is a group?

Answer 1

A vertical column in the Periodic Table. Elements in the same group have similar chemical properties and their atoms have the same number of outer shell electrons, and the same type of orbitals.

Question 2

What is periodicity?

Answer 2

A regular periodic variation of properties of elements with atomic number and position in the Periodic Table.

Question 3

What is the most important factor across a period?

Answer 3

Nuclear charge.

Question 4

What are the most important factors down a group?

Answer 4

Atomic radius and electron shielding.

Question 5

What are the general properties of Group 2 elements?

Answer 5

Reasonably high melting and boiling points; light metals with low densities; form colourless compounds.

Question 6

Why are the elements in Group 2 commonly called the alkaline earth metals?

Answer 6

They all have hydroxides that are alkaline.

Question 7

How does reactivity change down Group 2?

Answer 7

It increases, as it gets easier to lose electrons, because of the decrease in ionisation energies.

Question 8

Describe the reaction of a Group 2 elements with oxygen. What is the equation for the reaction of calcium with oxygen?

Answer 8

They react to form an ionic oxide, with the general formula MO. It is a redox reaction. They react vigorously.

2Ca(g) + O₂(g) → 2CaO(s)

Question 9

Describe the reaction of Group 2 elements with water. What is the equation for the reaction of calcium with water?

Answer 9

They react to form hydroxides with the general formula M(OH)₂ and hydrogen gas. Magnesium reacts slowly with water, but they get more vigorous down the group.

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Question 10

What is an oxidation number?

Answer 10

A measure of the number of electrons that an atom uses to bond with atoms of another element.

Question 11

What is the oxidation number of a uncombined element?

Answer 11

0

Question 12

What is the oxidation number of combined oxygen?

Answer 12

-2

Question 13

What is the oxidation number of combined hydrogen?

Answer 13

+1

Question 14

What is the oxidation number of a simple ion?

Answer 14

The charge on the ion.

Question 15

What is the oxidation number of combined fluorine?

Answer 15

-1

Question 16

How do metals generally form ions?

Answer 16

By losing electrons with an increase in oxidation number to form positive ions.

Question 17

How do non-metals generally react?

Answer 17

By gaining electrons with a decrease in oxidation number to form negative ions.

Question 18

Are Group 2 oxides and hydroxides acids, bases, or alkalis?

Answer 18

Bases.

Question 19

What will you observe when a Group 2 oxide or hydroxide reacts with hydrochloric acid?

Answer 19

The solid oxide or hydroxide dissolve.

Question 20

What do the Group 2 oxides form when reacted with water? Give the equation for this with magnesium. What is the typical pH of this product?

Answer 20

A solution of the metal hydroxide.

MgO(s) + H₂O(l) → Mg(OH)₂(aq)

The typical pH is 10-12.

Question 21

What do the Group 2 hydroxides form when reacted with water? Give the equation for this with calcium.

Answer 21

They form alkaline solutions.

Ca(OH)₂(s) + aq → Ca²⁺(aq) + 2OH⁻(aq)

Question 22

How does the solubility of Group 2 hydroxides change down the group? How do the resulting solutions change down the group?

Answer 22

Solubility increases down the group. The resulting solutions are more alkaline down the group.

Question 23

Give two uses of Group 2 hydroxides.

Answer 23

1) Calcium hydroxide is used as ‘lime’ to neutralise acid soils.
2) Magnesium hydroxide is used in ‘milk of magnesia’ to relieve indigestion, by neutralising excess acid in the stomach.

Question 24

What is thermal decomposition?

Answer 24

The breaking up of a chemical substance with heat into at least two chemical substances.

Question 25

What is formed when Group 2 carbonates are decomposed by heat? Give the equation for magnesium. How does this change down the group?

Answer 25

They form a metal oxide and carbon dioxide gas. MgCO₃(s) → MgO(s) + CO₂(g) The carbonates become more difficult to decompose down the group.

Question 26

What are the states at RTP of Cl₂, Br₂ and I₂?

Answer 26

Gas, liquid and solid.

Question 27

What is the trend in boiling points of Cl₂, Br₂ and I₂? Explain this.

Answer 27

Increases down the group. This is because the number of electrons increases, so there are more van der Waals' forces.

Question 28

What are the benefits of using chlorine in water treatment?

Answer 28

It kills bacteria in water supplies.

Question 29

What are the risks of using chlorine in water treatment?

Answer 29

Hazard of toxic chlorine gas; possible risk from formation of chlorinated hydrocarbons, which are suspected carcinogens.

Question 30

How does the reactivity of Group 7 elements change down a group?

Answer 30

It decreases.

Question 31

What is formed when Group 7 elements react with metals? Give an example.

Answer 31

Ionic halides with an X⁻ ion, i.e. NaCl.

Question 32

How do you test for halide ions?

Answer 32

1) Dissolve the halide substance in water. 2) Add an aqueous solution of silver nitrate, AgNO₃(aq). 3) Look at the colour of the precipitate formed (chloride is white, bromide is cream, iodide is yellow)

Question 33

What is a precipitation reaction?

Answer 33

The formation of a solid from a solution during a chemical reaction.

Question 34

What is a displacement reaction?

Answer 34

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter's ions.

Question 35

What is disproportionation?

Answer 35

The oxidation and reduction of the same element in a redox reaction.

Question 36

What are the colours of chlorine, bromine and iodine in cyclohexane?

Answer 36

Chlorine: pale green Bromine: orange Iodine: violet

Question 37

What are the colours of chlorine, bromine and iodine in water?

Answer 37

Chlorine: pale green Bromine: orange Iodine: brown

Question 38

What is the trend in reactivity of Group 7 elements down the group, and why?

Answer 38

Decreases, because of the increasing atomic radius and electron shielding, and the decreasing ability to gain an electron into the p sub-shell to form a halide ion.

Question 39

How do you differentiate between halide ions with ammonia?

Answer 39

Chloride ions are soluble in dilute NH₃, bromide ions are soluble in concentrated NH₃, and iodide ions see insoluble in concentrated NH₃.

Question 40

Give the equation for the reaction of chlorine with water as used in water purification. What type of reaction is this?

Answer 40

Cl₂(aq) + H₂O(l) → HClO(aq) + HCl(aq) Disproportionation reaction.

Question 41

Give the equation for the reaction of chlorine with cold, dilute aqueous sodium hydroxide, as used to form bleach. What type if reaction is it?

Answer 41

Cl₂(aq) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H₂O(l) Disproportionation reaction.