Group 2: Physical/ Chemical Properties

Question 1

Trend for atomic radius as you go down group from Mg- Ba. Explain.

Answer 1

• Atomic radius increases as you go down the group.
• More electron shells between the nucleus and the outer electron.

Question 2

What are group 2 metals referred to as?

Answer 2

• Alkaline- earth metals.

Question 3

How does the melting point change as you go down the group from Mg- Ba? Explain

Answer 3

• OVERALL, melting point decreases.
• Positive ions get bigger as you go down group, increased distance between positive nucleus/ sea of delocalised electrons means weaker force of attraction between positive nucleus/ sea of delocalised electrons.
• Less energy is required to break these forces.

Question 4

What is the exception to the melting point decreasing as you go down the group from Mg- Ba? Briefly explain why this exception occurs…

Answer 4

• Exception = Mg.
• Mg melting point significantly less than others due to its structure (don’t need to know any more than that!)

() - extra info for clarification.

Question 5

Trend in first ionisation energy as you go down group from Mg- Ba? Explain?

Answer 5

• First ionisation energy decreases.
• As you go down group, atom has more shielding/ outer electrons are further away from the nucleus.
  -Two factors means: weaker force of attraction between positive nucleus/ outer electrons.
• So, outer electron is lost more easily/ less energy needed to remove outer electron.

Question 6

What block elements are group 2 metals?

Answer 6

• S block elements.

Question 7

What type of bonding do these alkaline earth metals have?

Answer 7

• Metallic bonding.

Question 8

How does barium react with water? Give balanced symbol equation (include state symbols.)
Which other group 2 elements react in this way with water?

Answer 8

Ba (s) + 2H₂O (l) –> Ba(OH)₂ (aq) + H₂ (g)
All group 2 elements react with water in this way other than magnesium.

Question 9

How does magnesium react with water when it is in a liquid state vs a gas state (ie. steam?)

Answer 9

• Magnesium will react with cold water (liquid) very slowly.
• But, if magnesium reacts with steam, it will react a lot more vigorously and form magnesium oxide (instead of hydroxide) and hydrogen.

Question 10

Write balanced symbol equation for reaction of magnesium with steam?

Answer 10

Mg (s) + H₂O (g) –> MgO (s) + H₂ (g)

Question 11

How do the solubility of group 2 metal sulphates and hydroxides change as you go down group?

Answer 11

• Sulphates (and any double-charged ions): as you go down the group, solubility of these compounds decreases.
• Hydroxide (singly charged ions): as you go down the group, solubility of these compounds increases.

Question 12

How can you test for sulphate ions in an unknown solution?

Answer 12

• Add HCl to substance - to remove any carbonates in the solution.
• Then, add barium chloride to the substance.
• If sulphate ions exist in substance, a white precipitate of barium sulphate should be formed (because barium sulphate is insoluble.)

Question 13

True or False

Barium sulphate is NOT VERY SOLUBLE in water.

Answer 13

• False.
• Barium sulphate is insoluble in water.

Question 14

What is Mg(OH)₂ solubility like?

Answer 14

• Sparingly soluble (ie. has low solubility.)

() - extra info for clarification.

Question 15

What can group 2 compounds neutralise? Give specific examples?

Answer 15

• Group 2 compounds can neutralised acids.
• Ca(OH)₂ used in agriculture to neutralise acidic soils.
• Mg(OH)₂ neutralises excess stomach acid.

Question 16

Use of BaSO₄?

Answer 16

• Used in “barium meal.” -identify problems in digestive tract.
• Patient takes barium sulphate. This coats the soft tissues in digestive tract.
• X- rays are absorbed by barium sulphate and will be seen on the image. (to show any blockages/ issues. normally X rays go straight through soft tissue.)

() - extra info for clarification.

Question 17

Why can BaSO₄ be taken in barium meal to outline the gut in X rays if Barium is toxic?

Answer 17

• Because BaSO₄ is insoluble so won’t be absorbed into the blood.

Question 18

Why do we acidify the sample we are testing for sulphate ions?

Answer 18

• Acidifaction removes any carbonate ions (in solution ie. from water) that may lead to formation of white precipitate (ie. ensures formation of white precipitate is due to sulphate ions.)

Question 19

Why does reactivity of group 2 elements with water increase as you go down the group?

Answer 19

• Atoms get larger –> outer electron is further away from the positive nucleus ALSO More shielding.Easier for the outer electron to be lost (weaker attraction between positive nucleus/ outer electron), so reactivity increases.

Question 20

What substances do group 2 elements form when they react with water?

Answer 20

• Bases.

Question 21

Steps in extraction of titanium from its ore.

Answer 21

• Titanium ore (TiO₂) is heated with carbon and chlorine gas, forming titanium (- 4- IV - chloride)
• Titanium 4 chloride is purified by fractional distillation.
• Purified TiCl₄ (titanium 4 chloride) is reduced using magnesium in a 1000⁰C furnace - forming pure Ti (titanium.)

Question 22

What is titanium used in and why?

Answer 22

• Aircrafts.
• Because it is light yet strong.

Question 23

Equation to show reaction between TiCl₄ and Mg.

Answer 23

TiCl₄+ 2Mg –> Ti + 2MgCl₂

Question 24

How can CaO or CaCO3 be used to remove sulphur dioxide from flue gases (when burning fossil fuels?)

Answer 24

• CaO or CaCO3 are dissolved in water and then sprayed on acidic sulphur dioxide gas.
• The CaO or CaCO3 (dissolved in water) neutralise the sulphur dioxide in flue gases.

Question 25

Write balanced equation (inc state symbols) for reaction of calcium carbonate with sulphur dioxide.

Answer 25

CaCO₃(s) + SO₂(g) –> CaSO₃(s) +CO₂(g)

Question 26

Write balanced equation (inc state symbols) for reaction of calcium oxide with sulphur dioxide.

Answer 26

CaO(s) + SO₂(g) –> CaSO₃(s)

Question 27

What is product of reaction between CaO or CaCO₃ and sulphur dioxide in flue gases? What can this product be used in?

Answer 27

CaSO₃ (s) - calcium sulphite.
Can be used in production of plasterboard.

Question 28

How can we tell that TiCl₄ is reduced in its reaction with magnesium to form pure titanium?

Answer 28

• TiCl₄+ 2Mg –> Ti + 2MgCl₂
• Ti goes from having oxidation state of 4+ (in compound) to 0 in element. Has gained electrons to do this - so, TiCl₄ is reduced.

Question 29

Why is BaCl₂ specifically added to solution to test for presence of sulphate ions?

Answer 29

• The barium in BaCl₂ will react with SO₄²⁻ ions in solution to form insoluble BaSO₄ –> forming white precipitate.
• The Cl₂ in BaCl₂ is useful as it means the BaCl₂ will not react with the HCl (because both have same element - generally, two compounds with same element won’t react!)

() - extra info for clarification.

Question 30

Which has a higher pH value, Mg(OH)₂ or Ba(OH)₂?

Answer 30

• Ba(OH)₂ as it is more soluble than Mg(OH)₂ so, it will release a higher concentration of OH- ions into solution it is dissolved in (so pH would be greater.)