3.2.2 Group 2, the alkaline earth metals Flashcards
What is the trend for melting points down group 2?
Melting points decrease down the group.
This is because metalling bonding weakens as atomic size increases.
This is because the distance between the positive ions and delocalised electrons increases, hence the electrostatic attractive forces between the ions and delcoalised electrons weaken.
How does the reactivity of group 2 change down the group?
The reactivity of group 2 is measured by their tendency to lose their 2 outer electrons. This means reactivity will increase down the group because:
1) more shells, hence more shielding
2) atomic radius increases
This makes it easier to remove an electron as the attractive force of the nucleus is weaker
How do the group 2 metals react with oxygen?
They will burn in oxygen to produce a metal oxide.
What’s important to note when experimenting with Magnesium?
Magnesium will react with oxygen without a flame, with means a Mg Ribbon will have a thin layer of Magnesium Oxide.
This needs to be cleaned off by emery paper before doing reactions with Mg Ribbon.
Otherwise, the ribbon would give a false result, since Mg and MgO react at different rates.
How does magnesium react with steam? (give an equation too)
Magnesium reacts with steam to produce magnesium oxide and hydrogen. The Mg would burn with a bright white flame.
Mg + H20 (g) –> MgO + H2
How does Magnesium react with warm water?
It will react to give a magnesium hydroxide product.
This is a much slower reaction and there is no flame.
Mg + 2H20 –> Mg(OH)2 + H2
How do group 2 metals (Ca, Sr, Ba) react with cold water?
Describe:
1) The trend in reactivity
2) Products
3) Observations
The other group 2 metals will react with cold water with increasing vigour down the group to form hydroxides.
Ca: Reacts steadily with cold water
Sr and Ba: React vigorously with cold water
Equation: M + 2H2O –> M(OH)2 + H2
Observations:
1) Fizzing (more vigorous down the group)
2) Metal dissolving (faster down the group)
3) Solution heating up (more down group)
What is the observation for calcium when it reacts with cold water? Why?
It produces a white precipitate as the product (Ca(OH)2) is sparingly soluble.
What is produced when group 2 metals react with cold water vs steam?
Cold Water - Metal Hydroxide
Steam - Metal Oxide
Why is titanium a very useful metal?
1) low density
2) corrosion resistant
3) abundant
What is titanium used for?
1) making strong, light alloys for use in aircrafts
Describe the steps in extracting titanium
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 Celcius.
What is the purpose of argon in the extracting of Titanium using magnesium?
The prevent the Magnesium from oxidising
Why is titanium expensive to extract?
1) Mg is expensive
2) Batch process means the process is slower / requires more labour / energy is lost when reactor is cooled down
3) Argon atmosphere is expensive to maintain
4) High temperatures
Why can’t titanium be extracted with carbon?
It would form titanium carbide - which is brittle.
Give the 2 equations for the extraction of Titanium
TiO2 + 2Cl2 + 2C –> TiCl4 + 2CO
TiCl4 + 2Mg –> Ti + 2MgCl2
Why is TiO2 converted to TiCl4 first in the extraction of titanium?
Such that it can be purified by fractional distillation, since TiCl4 is a molecular compound, hence liquid at room temperature
State the solubility of the Group 2 Metal Hydroxides
Mg(OH)2 - sparingly soluble
Ca(OH)2 - slightly soluble
Sr(OH)2 - soluble
Ba(OH)2 - soluble
State the solubility of the Group 2 sulfates
MgSO4 - soluble
CaSO4 - slightly soluble
SrSO4 - insoluble
BaSO4 - insoluble
What is Mg(OH)2 used for? Why is it preferred over methods? Give an equation.
It is used in medicine to neutralise excess acid in the stomach and to treat constipation.
Mg(OH)2 + 2HCl –> MgCl2 + 2H2O
It is weakly alkaline, hence safe to use. It is preferred to calcium carbonate as it will not produce carbon dioxide gas.
What is Calcium Hydroxide used for? (2)
It is used in agriculture to neutralise acidic soils as it has a pH of 11 and is sparingly soluble.
An aqueous solution of calcium hydroxide can be used as a test for CO2.
Ca(OH)2 + CO2 –> CaCO3 + H20
Explain the trend in pH of the metal hydroxides in group 2
Solubility increases down the group, hence pH will increase as there will be more hydroxide ions present in the solution.
What is BaSO4 used for?
It is used in medicine as a ‘‘barium meal’’ given to patients who need x-rays of their intestines. The barium absorbs x-rays, so the gut shows up on the x-ray image.
Why can BaSO4 be used in medicine despite it’s toxicity?
It’s low solubility means it is not absorbed into the blood
What is observed if barium metal reacts with sulfuric acid?
It will react slowly, as insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to further reaction.
This will occur to a lesser extent with metals going up the group as the solubility increases.
It doesn’t happen with other acids as they form solubles alts.
How do we test for the precense of sulfate ions?
We add BaCl2 solution, acidicfied with hydrochloric acid. If the solution contains sulfate ions, a white precipitate of barium sulfate forms.
HCl removes carbonate impurities which would give a false result due to the formation of Barium Carbonate.
What salts are generally soluble / insoluble?
SOLUBLE:
All sodium, potassium and ammonium salts. (including carbonates + hydroxides)
All nitrates.
Most chlorides, bromides and iodides.
Most sulfates.
INSOLUBLE:
Most carbonates + hydroxides
Silver + lead halides
Lead, strontium and barium sulfates
What are the two types of filtration and when do we use each? Draw each type.
Gravitational filtration. (use if small amount sof solid are formed)
Vacuum filtration - The apparatus is connected to a water pump whch will produce a vacuum. Use if larger amounts of solid are formed.
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