Group 2 Flashcards by eleanor g

Atomic Radius trend of Group 2

Increases down the group
-> there are more occupied energy levels
-> therefore the atoms are bigger

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1st IE trend of Group 2

Decreases down the group
-> outer electron is further from the nucleus
-> therefore there’s less attraction between the nucleus and outer electron
-> increase in shielding
-> therefore less energy required to remove outer electron
-> even though there’s increase in nuclear charge the effect of shielding and distance is greater

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Melting Point trend of Group 2

Generally decreases down the group
-> increase in ionic radius (of the metal ions)
-> therefore the delocalised electrons are further away from the nucleus
-> less attraction between nucleus and delocalised electrons
-> therefore lesson energy required to break the metallic bonding

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General equation for reaction of Group 2 with water

M(s) + 2H20(l) -> M(OH)2 (aq) + H2 (g)

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Solubility of Group 2 Hydroxides

Solubility of hydroxides increase down

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Solubility of Group 2 Sulfates

Solubility of sulfates decreases down

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Observation of Group 2 in adding sodium hydroxide solution

Mg2+ : thick white precipitate
Ca2+ : white precipitate
Sr2+ : thin white precipitate
Ba2+ : very thin white precipitate

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Observation of Group 2 on adding sodium sulfate solution

Mg2+ : no precipitate
Ca2+ : thin white precipitate
Sr2+ : white precipitate
Ba2+ : thick white precipitate

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Oxidising agent

Something that causes oxidation by reduction (gaining by electrons)

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Reducing agent

Something that causes reduction by oxidising itself (losing electrons)

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What is significant about BaSO4

It’s insoluble

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Is Mg(OH)2 soluble

It’s sparingly soluble

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Why is group 2 more reactive going down the group

Even though the nuclear charge increases going down, factors such as an increased shielding and a larger distance between the outermost electron and nucleus outweigh it
- as a result it gets easier for the atoms to lose 2 electrons and become 2+ ions

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Reaction of group 2 with dilute HCl

Bubbles of hydrogen gas are given off much faster going down indicating the reactions become more vigorous

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Equation for group 2 metals with water

X(s) + 2H2O(l) -> X(OH)2(aq) + H2 (g)

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Are group 2 hydroxides soluble

Not really but they more soluble as you go down the group
-> CaOH shows up as a white precipitate
-> you get less precipitate as you go down the group as more of the OH dissolves in the water

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Equation for group 2 metals with oxygen

2X(s) + O2 (g) -> 2XO(s)

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Formation of group 2 peroxides

Barium and strontium will react with oxygen to form their peroxides

Eg. Ba(s) + O2(g) -> BaO2(s)

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Solubility of group 2 hydroxides

Get more soluble as you go down the group

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Solubility of group 2 sulfates

They become less soluble as you go down the group

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Solubility of the group 2 carbonates

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Become less soluble as you go down

Melting point trend of group 2

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Decreases down as the outer electrons get further away from the nucleus
-> this means that the attraction between the nucleus and the outermost electrons decreases causing a decrease in melting point

Reaction of magnesium with steam vs wager

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With steam (H2O(g))
• forms MgO and H2
• the Mg burns with a bright white flame

With warm water
• forms Mg(OH)2 and H2

What type of water do the rest of group 2 react with

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Cold water

What would you observe when group 2 react with water

• fizzing (more vigorous down) • the metal dissolving (faster down) • solution heating up (more down) • with calcium a white precipitate appearing

Why is titanium useful

It is abundant, has a low density and is corrosion resistant

How is titanium extracted

1. TiO2 is converted to TiCl4 at 900*C 2. The TiCl4 is purified by fractional distillation in an argon atmosphere 3. The Ti is extracted by Mg in an argon atmosphere at 509*C

Why can’t Ti be extracted by carbon

Because TiC is formed rather than Ti

Why can’t Ti be extracted by electrolysis

Because it has to be very pure

Equations for Ti extraction

1. TiO2 + 2Cl2 + 2C -> TiCl4 + 2CO 2. TiCl4 + 2Mg -> Ti + 2MgCl2

Why is the TiO2 converted to TiCl4

As it can be purified by fractional distillation, TiCl4 being molecular rather than ionic like TiO2

Why is titanium expensive

1. Mg is expensive 2. It’s extraction is a batch process which makes it expensive as the proxies is slower and requires more work and the energy is lost when the reactor is cooled down 3. The process is also expensive due to the argon 4. High temperatures required in both steps

What is Mg(OH)2 used in medicine for

To neutralise excess acid in the stomach and to treat constipation -> it’s safe to use as its weakly alkaline

Why is mangneisum hydroxide preferred to calcium carbonate in medicine

Because it won’t produce CO2

What is calcium hydroxide used for in agriculture

To neutralise acidic soils

What is an aqueous solution of calcium hydroxide called

Limewater

Why does limewater turn cloudy in the presence of CO2 and what is the equation

• because white CaCO3 is produced Ca(OH)2(aq) + CO2 -> CaCO3(s) + H2O

Example of iconic equation for sulfate solubility

Sr2+ + SO42- -> SrSO4

How is BaSO4 used in medicine

• as a ‘barium meal’ given to patients who need X-rays of their intestines • the barium absorbs X-rays and so the gut shows up on the X-ray • even though barium compounds are toxic it’s safe to use because it’s low solubility means it’s not absorbed into the blood

Testing for sulfate ions

• barium chloride solution acidified with HCl added forms a white precipitate

Iconic equation for sulfate test

Ba2+ + SO42- -> BaSO4

Why is HCl needed in the sulfate ion test

To react with carbonate impurities that are often found in salts which would form a white barium carbonate precipitate and so give a false result • fizzzing due to CO2 would be seen if a carbonate was present

What are soluble salts

• all sodium, potassium, and ammonium salts • all nitrates • most chlorides, bromides, iodides • most sulfates • sodium, potassium and ammonium carbonates • sodium, potassium and ammonium hydroxides

What are insoluble salts

• silver, lead chlorides, bromides and iodides • lead, strontium and barium sulfate • most other carbonates • most other hydroxides

How is the salt removed when making an insoluble salt

The salt would be removed by filtration, washed with distilled water to remove soluble impurities and then dried on filter paper

Spectator ions are ions that are..

• not changing state • not changing oxidation number

Equation for conversion of TiO2 into TiCl4

TiO2 + 2Cl2 + 2C -> TiCl4 + 2CO

Equation for reduction of the titanium(IV) chloride

TiCl4 + 2Mg -> Ti + 2MgCl2

What is TiCl4 reduced by

Magnesium

Problems with extraction of Ti

• Traces of oxygen or nitrogen in the titanium tend to make the metal brittle -> the reduction has to be carried out in an inert argon atmosphere rather than in air • Titanium is made by a batch process

Group 2 Flashcards

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