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Chemistry > Group 2 - The Alcohol Earth Metals > Flashcards

Group 2 - The Alcohol Earth Metals Flashcards

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1
Q

What are group 2 metals and where are they found and which are the most common?

A

They are all metals with a shiny silvery white appearance and their compounds are all found in the Earths crust and are widely distributed in rock structures. Calcium and magnesium are the most common

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2
Q

What does the name alkaline earth metals come from?

A

Their metal oxides

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3
Q

What is the electron configuration of group 2 elements?

A

They have two electrons in their outer s sub-shell and moving down the group each element has an extra shell of electrons

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4
Q

What is the bonding in group 2 elements?

A

They have metallic bonding where each metal atom transfers two electrons to create the sea of delocalised electrons

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5
Q

What is the trend in atomic radius of the group 2 elements and why?

A

The atomic radii increase moving down group 2. Each successive element has an extra shell of electrons and a larger nuclear charge. The additional shell of electrons shield the outer 2s electrons from the nuclear charge. The outer electrons are attracted less strongly and move further away from the nucleus. The atomic radius increases

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6
Q

What is the trend in first ionisation energies moving down group 2?

A

They decrease down group 2 as extra electron shells are added successfully shielding the outer 2s electrons from the nuclear charge making it easier to remove and electron

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7
Q

What is the first ionisation energy?

A

The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state

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8
Q

What is the general trend in melting points for group 2 elements?

A

They generally decrease

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9
Q

What does the melting point of a metal depend on?

A

The strength of the bonds formed when the elements atoms join together to make giant structures with metallic bonding

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10
Q

What is the melting point an indication for and why?

A

The energy that must be transferred to the metal for it to melt because when metals melt they gain sufficient kinetic energy to break free from their fixed positions in the surrounding sea of delocalised electrons

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11
Q

Why does the melting point decrease down group 2?

A

Because moving down group 2 there are more electron shells sheilding the metal ion nucleus from the delocalised electrons reducing the attraction. It becomes easier to break the metallic bonds and the melting point is lower

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12
Q

Why is the melting point of magnesium lower than predicted in the trend?

A

Because the strength of the metallic bond depends not only on the charges and radii of the metal ions but also on the pattern in which the metal ions pack together

Magnesium and Beryllium have hexagonal close packed structures

Calcium strontium and barium have cubic structures. These are not as close packed as hexagonal.

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13
Q

What does magnesium’s low melting point make it useful as?

A

A reducing agent in the extraction of titanium metal

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14
Q

What’s tintaniums similarity to steel and what makes it advantageous to steel?

A
  • they both have high tensile strength
  • titanium density is half of steel
  • it does not corrode because it forms a layer of protective oxide on its surface when exposed to air
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15
Q

What ores are titanium extracted from and why cant this be done by reduction by carbon?

A
  • the ores are: titanium rule, TiO2 and ilmenite FeTiO3

* reduction with carbon produces titanium carbide which makes the metal brittle and useless

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16
Q

Desribe what happens in the extraction of titanium

A

• titanium (IV) oxide is converted to titanium (IV) chloride, TiCl4, by heating with carbon in a stream of chlorine gas:
TiO2 +2Cl2 + 2C -> TiCl4 + 2CO
•Titanium (IV) chloride is then reduced using magnesium metal as the reducing agent.
TiCl4 + 2Mg -> Ti + 2MgCl2
• This is called the Kroll process. Magnesium is oxidised from oxidation state 0 to +2 in magnesium chloride
• Titanium (IV) chloride and liquid magnesium are heated to about 1200 °c in an inert atmosphere of helium or argon gas

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17
Q

How long does the Kroll process take and why is it a batch process?

A
  • It takes 36-50 hours plus 4 days to cool

* it’s a batch process because the furnace does not operate continuously

18
Q

Why are group 2 metals good reducing agents?

A

Because they have two electrons in their outer shells which are readily transferred to other elements and compounds

19
Q

What is the general equation, the full redox equation and the half equations for the reduction of water to hydrogen? Where M represents a group 2 metal

A

M + 2H20 -> M(OH)2 +H2

M + 2H2O -> M2+ + 2OH- + H2

M -> M2 + 2e-

2H2O + 2e- -> 2OH- + H2

20
Q

What does the ease that the metal can transfer electrons depend on?

A

It depends on the first and second ionisation energies. They decrease going down the group so as you go down the group it becomes easier to transfer two electrons.

Therefore the energy needed to oxidise group 2 metals is less as you go down the group

21
Q

What happens when magnesium reacts with cold water and steam

A
  • cold water: magnesium reacts very slowly to form magnesium hydroxide and hydrogen has. It takes several days to produce noticeable amounts of hydrogen gas because the magnesium hydroxide formed is almost insoluble and formes a layer on the magnesium metal
  • if steam is passed over heated magnesium an exothermic reaction occurs and the magnesium hydroxide initially formed is decomposed into magnesium oxide and hydrogen gas
22
Q

How does calcium react with water?

A

It has lower ionisation energies so it reacts more easily. Calcium reacts with cold water to form calcium hydroxide and hydrogen gas. The resulting solution is commonly called limewqter and is used to test for carbon dioxide gas

23
Q

How do strontium and barium react with waterM

A

With increasing vigour to produce a metal hydroxide and hydrogen

24
Q

What is a solute?

A

A substance that is present in a solution

25
Q

What is a solution and how is it made?

A

It is a homogenous mixture of a solute and solvent made by dissolving the substance in a solvent

26
Q

What does the solubility of a substance measure?

A

The maximum concentration of the solution possible

27
Q

Who do I love

A

Theo

28
Q

What categories of solubility do chemists often group substances into?

A
  • insoluble: doesn’t dissolve
  • sparingly soluble: only small quantities of the substance dissolve
  • soluble: the substance dissolves
29
Q

What is the trend in the solubility of the hydroxide as you go down group 2?

A

It increases

30
Q

What is the general equation for the dissolution of group 2 hydroxides

A

M[OH]2 + aq -> M2+ +2OH-

31
Q

What is solubility?

A

The maximum amount of solute that will dissolve in a solvent at a stated temperature

32
Q

What is magnesium hydroxide used for?

A

• in medicine for digestive upsets and as a laxative
• milk of magnesia (an 8 % aqueous suspension)
• to neutralise excess acid in the oesophagus:
Mg(OH)2 + 2HCl -> MgCl2 + 2H2O
• in toothpastes to neutralise acidity

33
Q

What is calcium hydroxide commonly known as and where does this name come from?

A

Slaked lime

The name comes from the highly exothermic reaction that happens when water is added to calcium oxide

34
Q

What is calcium oxide used for?

A

• in agriculture to neutralise soil acidity. Most plants grow best in a pH between 6 and 7
• many of the uses of calcium hydroxide involve neutralisation reactions:
H+ + OH- -> H20

35
Q

What is the trend of solubilities of the group 2 sulfate going down the group?

A

They decrease

36
Q

How does a ‘barium meal’ work and how comes it doesn’t harm your body seeing as barium is poisonous

A

A barium meal is comprised of barium sulfate which is insoluble so can pass through the body without dissolving in body fluids and being absorbed.

Barium sulfate absorbs X Rays so is given to patients when X-ray images of their digestive system are needed. As the barium meal fills the digestive tract an X ray image shows any abnormalities

37
Q

What is a precipitate?

A

When ions in a solution combine to form an insoluble compound

38
Q

What are precipitates useful for?

A

Identifying anions (negatively charged ions)

39
Q

How do you test for a sulfate?

A
  • If two solutions are mixed, one containing barium ions and the other containing sulfate ions then a barium sulfate precipitate will form
  • Barium chloride can be mixed with the solution to be tested. If a white precipitate forms then it probably is a sulfate
  • however if a solution being tested contains carbonate ions then a white precipitate of barium carbonate forms and the results can be misleading. So dilute hydrochloric or nitric acid is added to the barium chloride solution. The acid reacts with any carbonate ions producing carbon dioxide and water and removing them from the solution
  • so a white precipitate of barium sulfate when an acidified solution of barium chloride is added confirms the presence of sulfate ions

Ba2+ + SO42- -> BaSO4

40
Q

What are the reactions that take place to remove sulphur dioxide from waste gases or flue gases using calcium oxide or calcium carbonate?

A

•SO2 + CaCO3 -> CaSO3 + CO2
then
2CaSO3 + O2 -> 2CaSO4

• SO2 +CaO -> CaSO3
Then
2CaSO3 + O2 -> 2CaSO4

41
Q

What solubility is calcium sulfate and why is this useful?

A

It is sparingly soluble

Most forms calcium sulfate which is removed and used in the building industry after being produced in the removal of sulfur dioxide

Chemistry (15 decks)

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