3.2.2 - Group 2, the Alkaline Earth Metals

Question 1

How do the group 2 metals react with oxygen?

Answer 1

They will burn in oxygen to produce a metal oxide.

Question 2

How does magnesium react with steam? (give an equation too)

Answer 2

Magnesium reacts with steam to produce magnesium oxide and hydrogen. The Mg would burn with a bright white flame.

Mg + H2O (g) → MgO + H2

Question 3

Why is titanium a very useful metal?

Answer 3

1) low density
2) corrosion resistant
3) abundant

Question 4

What is titanium used for?

Answer 4

Making strong, light alloys for use in aircraft.

Question 5

Describe the steps in extracting titanium.

Answer 5

1) TiO2 is converted to TiCl4
2) TiCl4 is purified by fractional distillation in an argon atmosphere
3) The Ti is extracted by Mg in an argon atmosphere at 500 degrees Celsius.

Question 6

Why can’t titanium be extracted with carbon?

Answer 6

It would form titanium carbide - which is brittle.

Question 7

Give the 2 equations for the extraction of Titanium.

Answer 7

TiO2 + 2Cl2 + 2C → TiCl4 + 2CO

TiCl4 + 2Mg → Ti + 2MgCl2

Question 8

Explain the trend in pH of the metal hydroxides in group 2.

Answer 8

Solubility increases down the group, hence pH will increase as there will be more hydroxide ions present in the solution.

Question 9

Explain what BaSO4 is used for.

Answer 9

1) Used in medicine as a barium meal
2) Given to patients who need x-rays of their intestines.
3) The barium absorbs x-rays, so the gut shows up on the x-ray image.

Question 10

Explain how we test for the presence of sulfate ions.

Answer 10

1) We add BaCl2 solution, acidified with hydrochloric acid.
2) If the solution contains sulfate ions, a white precipitate of barium sulfate forms.
3) HCl removes carbonate impurities which would give a false result due to the formation of Barium Carbonate.

Question 11

After an insoluble salt has been formed in a precipitation reaction, how can we remove it?

Answer 11

1) Filtration
2) Wash with distilled water to remove soluble impurities
3) Dry on filter paper.

Question 12

What happens to the solubility of the elements when reacting them with sulfates?

Answer 12

Solubility decreases down the group when reacting with sulfates, becoming less soluble.

Question 13

Explain how you test for sulfates.

Answer 13

1) Add HCl to remove any carbonate, which could form a white precipitate and cause a false reading.
2) Add Barium Chloride.
3) White precipitate forms, indicating sulfates are present.

Question 14

Explain barium meals.

Answer 14

1) Barium sulfate
2) Patient drinks suspension of barium sulfate - which coats the lining of soft tissue e.g the stomach.
3) Helps identify problems with the digestive tract.
4) X-rays are absorbed by barium sulfate so will show up on x-ray.
5) Barium sulfate is insoluble so cannot get absorbed.

Question 15

Explain the extraction of titanium.

Answer 15

Mg is used to extract titanium from its ore.
1) Titanium ore (TiO2) is converted to titanium (IV) chloride TiCl4, by heating with carbon and chlorine gas.
2) TiCl4 is passed through a fractional distillation column, increasing its purity.
3) Purified TiCl4 is reduced using magnesium in a 1000 degree furnace.

Question 16

What are the uses of titanium?

Answer 16

Light weight but strong and common use in planes.

Question 17

Explain the process of wet scrubbing (flue gas desulfurization).

Answer 17

1) Spray calcium carbonate onto sulfur dioxide as it leaves a chimney.
2) Forms calcium sulfide which can be used for the production of plaster boards.

Question 18

What are plaster boards made of?

Answer 18

Calcium sulfide.

Question 19

Explain in terms of bonding, why magnesium chloride has a high melting point.

Answer 19

1) Giant ionic lattice, with strong electrostatic forces of attraction between its molecules.
2) Requiring lots of energy to break.

Question 20

Why doesn’t Beryllium react?

Answer 20

Beryllium has a thick oxide layer on the surface of the metal.

Question 21

Explain how to carry out a flame test to identify Group 2 ions.

Answer 21

1) Dip nichrome wire loop in concentrated HCl.
2) Then dip a wire loop into an unknown compound.
3) Hold the loop clear blue part of the Bunsen flame.
4) Observe the colour change.

Question 22

When testing for ammonia gas, why does the litmus paper have to be damp?

Answer 22

In order for ammonium gas to dissolve.

Question 23

How do you test for Ammonium ions?

Answer 23

1) Add hydroxide ions to a solution containing ammonium ions (NH4+).
2) NH4+ + OH- → NH3 + H2O.
3) Add dilute sodium hydroxide.
4) If ammonia is given off, ammonium ions are present.

Question 24

How would you test for sulfate ions?

Answer 24

1) Add HCl and barium chloride.
2) If a white precipitate forms - it means the compound contains sulfates.

Question 25

How would you test for Hydroxide ions?

Answer 25

1) You can use a pH indicator.
2) e.g. add red litmus paper.
3) If the red litmus paper turns blue, hydroxide ions are present.

Question 26

How would you test for carbonate ions?

Answer 26

1) Add dilute HCl, where solutions containing carbonate ions will fizz.
2) This is because carbonate ions react with the hydrogen ions in the acid to give off carbon dioxide.
3) Test for CO2 using lime water.
4) Lime water turns cloudy if carbon dioxide is present.

Question 27

How do you test for sulfates?

Answer 27

Add BaCl2. A white precipitate is formed.

Question 28

Describe the observation and provide the equation when magnesium reacts with steam.

Answer 28

Observation: Bright/white light and white powder/ash are produced.

Mg(s) + H2O(g) → MgO(s) + H2(g)

Question 29

Group 2 metals reacting with cold water.

Answer 29

Observation: Varies with each metal, producing respective hydroxides and hydrogen.

Question 30

Explain why titanium cannot be extracted by electrolysis.

Answer 30

1) Titanium cannot be extracted by electrolysis.
2) As it has to be very pure.

Question 31

Suggest one reason why a sample of magnesium appears to be stable in air at room temperature.

Answer 31

Forms a protective layer of MgO.

Question 32

Why is Titanium expensive?

Answer 32

1) Due to the expensiveness of Mg.
2) Being a batch process which makes it expensive because the process is slower and requires more labour.
3) The energy is lost when the reactor is cooled down after stopping.
4) Also expensive due to argon, and the need to remove moisture.

Question 33

Describe the trend in atomic radius across Group 2 elements.

Answer 33

The atomic radius increases down the group due to the addition of electron shells, which causes the outer electrons to be further from the nucleus.

Question 34

Explain why first ionisation energy decreases down Group 2.

Answer 34

The first ionisation energy decreases down the group as the atomic radius increases, resulting in outer electrons being further from the nucleus and more shielded by inner shells.

Question 35

Discuss the trend in melting points down Group 2.

Answer 35

Melting points generally decrease down the group as the metallic bonds weaken due to the increasing distance between the positive ions and the delocalized electrons.

Question 36

How does the reactivity of Group 2 metals with oxygen change down the group?

Answer 36

The reactivity increases down the group. Magnesium reacts slowly with oxygen at room temperature but more rapidly when heated, while metals lower down the group react more readily.

Question 37

Describe how Group 2 metals react with water.

Answer 37

1) Magnesium reacts very slowly with warm water, while calcium, strontium, and barium react more vigorously with cold water, producing their respective hydroxides and hydrogen gas.

Question 38

How does the solubility of hydroxides change down Group 2?

Answer 38

1) The solubility of Group 2 hydroxides increases down the group.
2) Magnesium hydroxide is barely soluble, whereas barium hydroxide dissolves easily, making the solution strongly alkaline.

Question 39

Explain why magnesium hydroxide is used in medicine.

Answer 39

Magnesium hydroxide is used as milk of magnesia to neutralise excess stomach acid and treat constipation. It’s favored because it is mild and less likely to cause side effects like gas compared to more soluble hydroxides.

Question 40

What happens when barium chloride solution is added to a solution containing sulfate ions?

Answer 40

A white precipitate of barium sulfate forms, indicating the presence of sulfate ions.

Question 41

Describe the trend in solubility of sulfates down Group 2.

Answer 41

The solubility of Group 2 sulfates decreases down the group, with barium sulfate being notably insoluble.

Question 42

How is calcium oxide used to reduce sulfur dioxide emissions?

Answer 42

Calcium oxide reacts with sulfur dioxide in flue gases to form calcium sulfite, a method known as flue gas desulfurization.

Question 43

What happens with the ionisation energies down group 2?

Answer 43

They decrease down the group as the electrons are further from the nucleus and have shielding.

Question 44

Describe the bonding in magnesium.

Answer 44

1) Magnesium has metallic bonding characterized by a lattice of positively charged Mg2+ ions surrounded by a sea of delocalized electrons.
2) This electron sea facilitates the strong electrostatic attraction between the ions and electrons.

Question 45

Explain why magnesium chloride has a high melting point.

Answer 45

1) Magnesium chloride forms a giant ionic lattice with strong electrostatic forces of attraction between oppositely charged Mg2+ and Cl− ions.
2) Requiring substantial energy to overcome these forces.

Question 46

What is a common use for barium sulfate?

Answer 46

Barium sulfate is used in medicine to produce an X-ray image due to its high density and opacity to X-rays.

Question 47

Explain why magnesium has a higher melting point than sodium.

Answer 47

1) Magnesium has a higher melting point than sodium due to stronger metallic bonding resulting from magnesium’s higher charge density and more delocalized electrons.
2) This enhances the electrostatic attractions within the metal.

Question 48

Explain why magnesium is used as a reducing agent in the extraction of titanium from titanium(IV) chloride.

Answer 48

1) Magnesium acts as a reducing agent because it donates electrons.
2) Reducing titanium by changing its oxidation state from +4 in TiCl4 to 0 in titanium metal.

Question 49

What are the observations when dilute aqueous sodium hydroxide is added to solutions of magnesium chloride and barium chloride?

Answer 49

1) With magnesium chloride, a slight white precipitate forms.
2) With barium chloride, there is no visible change; the solution remains colorless.

Question 50

What role does magnesium play in the reaction with titanium(IV) chloride?

Answer 50

Magnesium acts as the reducing agent, donating electrons to reduce the titanium from its +4 oxidation state to metallic titanium.

Question 51

What property would you expect radium, Ra, to possess?

Answer 51

Radium, being a Group 2 element, is a good conductor of electricity due to the presence of delocalised electrons in its metallic structure.

Question 52

Which property of the Group 2 elements from calcium to barium increases with increasing atomic number?

Answer 52

The atomic radius increases with increasing atomic number from calcium to barium.

Question 53

Which salt gives a white precipitate with aqueous silver nitrate and dilute sulfuric acid?

Answer 53

The salt that reacts to give a white precipitate with both reagents is BaCl2.

Question 54

Which substance is used to reduce titanium(IV) chloride in the extraction of titanium metal?

Answer 54

Magnesium is used as the reducing agent in the extraction of titanium from titanium(IV) chloride.

Question 55

Which compound is used to treat the symptoms of indigestion?

Answer 55

Mg(OH)2, magnesium hydroxide, is used to treat symptoms of indigestion due to its ability to neutralize stomach acid.