Group 2, the alkaline earth metals Flashcards

1
Q

Describe and explain the general trend in atomic radius down the group 2 metals

A

Atomic radius increases down the group
More shells of electrons (stronger nuclear charge but more shielding ‘cancels out’)

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2
Q

Describe and explain the general trend in melting points down the group 2 metals

A

Melting points decrease down the group
Increased nuclear charge, but more shielding so weakened nuclear attraction between outer electrons and nucleus

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3
Q

Describe and explain the general trend in first ionisation energies down the group 2 metals

A

Decreases as you go down the group
Increased nuclear charge but more shielding (larger atom), so overall weaker attraction between the positively charged nucleus and negative outer electrons
Therefore easier to remove

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4
Q

How does the reactivity of group 2 metals change down the group?

A

Reactivity increases down the group

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5
Q

A student wants to test the reaction rate of Mg with an acid. What should they do to the Mg ribbon first, and why?

A

Clean it with sandpaper to remove oxide layer
Outer Mg will react with oxygen to form MgO
This will also react, but at a different rate, and so give a different result

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6
Q

Mg reacts with steam to give what products?

A

MgO (magnesium oxide) and H2 gas

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7
Q

Mg reacts with steam to give what products?

A

MgO + H2 gas

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8
Q

Give 2 differences between the reaction of Mg with water vs Mg with steam

A

Water reaction gives Mg(OH)2 and steam reaction gives MgO
Water reaction is far slower
Water reactions doesn’t give a flame

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9
Q

What would someone observe with the reaction between a group 2 element and cold water?

A

Fizzing
Metal dissolving
Solution heating up
The effects increase down the group
With Ca, formation of white ppt

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10
Q

Ti cannot be extracted using carbon. Why is this?

A

TiC (titanium carbide) formed instead

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11
Q

Describe how you would extract titanium

A

TiO2 (s) converted to TiCl4 (l) at 900C
TiCl4 purified by fractional distillation in an Ar atmosphere
Ti extracted by Mg in an Ar atmosphere at 500
C

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12
Q

Give a reaction to show the extraction of Ti by Mg

A

TiCl4 + 2Mg –> Ti + 2MgCl2

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13
Q

Give 2 reasons why Ti is expensive

A

Expensive cost of Mg
Batch process - slower, requires more energy, energy lost when reactor cooled after stopping
Use of Ar and need to remove moisture
High temperatures required in both steps

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14
Q

Why is TiO2 converted to TiCl4?

A

It can purified by fractional distillation
- TiCl4 molecular so (l) at room temp., TiO2 (s) as molecular

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15
Q

State the general trend in Group 2 hydroxide solubilities down the group

A

Generally become more soluble down the group

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16
Q

Is Mg(OH)2 soluble in water?

A

Technically classified as being insoluble in water

17
Q

What is Mg(OH)2 used for?

A

Used in medicine to neutralise excess acid in the stomach, and to treat constipation

18
Q

Why is Mg(OH)2 preferable for treating stomach acid than CaCO3?

A

CaCO3 would produce CO2

19
Q

What is Ca(OH)2 used for?

A

Used in agriculture to neutralise acidic soils
Aq soln. of it (lime water) can also be used to test for CO2 - mill go milky (CaCO3 produced)

20
Q

Describe the solubility of Ca(OH)2

A

Reasonably soluble in water

21
Q

Describe the solubility of Ba(OH)2

A

Easily dissolves in water

22
Q

Describe the general trend in Group 2 sulphate solubilities down the group

A

Sulphates become less soluble down the group

23
Q

Describe the solubility of BaSO4

A

Insoluble

24
Q

Give a use of BaSO4

A

Used in medicine as a ‘barium meal’ given to patients needing intestinal X-rays
Ba absorbs the X-rays - show up darker

25
Q

BaSO4 is toxic, yet is ingested before people have intestinal x-rays. Why?

A

BaSO4 is safe to use as its solubility is so low

26
Q

How could you test for the presence of a sulphate ion?

A

BaCl2 solution acidified with HCl
If sulphate ion present, white ppt of BaSO4 formed

27
Q

When testing for sulphate ions, why is the solution acidified?

A

Needed to react w/ carbonate impurities that are often found in salts which would give the white ppt BaCO3