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AQA A-Level Chemistry (new spec) 2.2 Group 2 - The Alkaline Earth Metals
Terms in this set (33)
Group 2 Trends: Atomic Radius
-Distance from nucleus increases
-Nuclear charge increases
Group 2 Trends: First Ionisation Energy
-Distances from nucleus increases (so attraction decreases)
-Nuclear charge increases
Group 2 Trends: Melting and Boiling Points (general)
-Metallic bonding weakens as the atomic size increases
-Distance between positive ions and delocalised electrons increases
-Electrostatic forces of attraction are weak
Group 2 Trends: Melting and Boiling Points (Mg)
Mg has fewer delocalised electrons, so metallic bonding is weaker
Reactivity with Oxygen (general)
Increases DOWN the group due to ease of cation formation
React with increasing vigour down the group
Reactivity with Oxygen (Ba)
Burns readily with an apple green flame
2Ba(s) + O2 (g) -> 2BaO(s)
Reactivity with Oxygen (Mg)
Burns with a bright white flame
2Mg(s) + O2(g) -> 2MgO(s)
It will also react slowly without a flame. Mg ribbon will have a layer of MgO which needs to be cleaned off before using it for reactions as it can cause a false result.
Reactivity with Water (Mg with warm water)
Will form a magnesium hydroxide product
Mg+2H2O -> Mg(OH)2 + H2
This reaction is slow and doesn't have a flame
Reactivity with Water (Mg with steam)
Produces magnesium oxide and hydrogen. The Mg will burn with a white flame.
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Reactivity with Water (Other metals with cold water)
Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
Sr(s) + 2H2O(l) -> Sr(OH)2(aq) + H2(g)
Ba(s) + 2H2O(l) -> Ba(OH)2(aq) + H2(g)
Observations of other G2 Metals in cold water
-Fizzing (with increasing vigour down the group)
-The metal dissolving (faster down the group)
-The solution heating up (more down the group)
-Less precipitate down the group (Ca has a white precipitate)
How is titanium extracted?
By reaction with a more reactive metal
What can't titanium be extracted with carbon?
Because titanium carbide is formed rather than titanium
Why can't titanium be extracted via electrolysis?
It has to be very pure
Steps to extracting titanium: 1
TiO2(s) is converted to TiCl4(l) at 900 degrees Celsius
TiO2 + 2CL2 + 2C --> TiCl4 + 2CO
Steps to extracting titanium: 2
The TiCl4 is purified by fractional distillation in an Ar atmosphere
Steps to extracting titanium: 3
The Ti is extracted by MG in an Ar atmosphere at 500 degrees Celsius
TiCl4 + 2Mg --> Ti + 2MgCl2
Reasons why titanium is expensive
-The cost of Mg
-Batch process - slower process and requires more labour, energy lost when the reactor is cooled down after stopping
- Ar and the need to remove water
What is TiCl4 susceptible to?
Why is TiO2 converted to TiCl4?
It can be purified by using fractional distillation as it is molecular, meaning it's liquid at room temperature, whereas TiO2 is ionic, so is solid at room temperature
Do group 2 hydroxides become more or less soluble down the group?
Is magnesium hydroxide insoluble or soluble in water?
Mg2+ + 2OH- -> Mg(OH)2
Magnesium hydroxide uses: Medicine
Is used in suspension to neutralize excess acid in the stomach and to treat constipation.
Mg(OH)2 + 2HCl --> MgCl2 + 2H2O
It doesn't produce CO2 so is preferred over calcium carbonate
Uses of Calcium Hydroxide: Agriculture
Used to neutralize acidic soils
Uses of Calcium Hydroxide: Test for CO2
In aqueous solution, calcium hydroxide is called lime water and can test for CO2. When CO2 is present, the lime water turns cloudy, as white calcium carbonate is formed
Ca(OH)2 + CO2 --> CaCO3 + H2O
Does barium hydroxide dissolve in water?
Yes, it would dissolve easily in water. The hydroxide ions make the solution strongly alkaline.
Ba(OH)2 + aq --> Ba2+ + 2OH-
Do Group 2 Sulphates become less or more soluble down the group?
Less soluble. BaSO4 is the least soluble
Full equation: SrCl2(aq) + Na2SO4(aq) --> 2NaCl(aq) + SrSO4 (s)
Ionic equation: Sr2+(aq) + SO42-(aq) --> SrSO4(s)
Use of BaSO4
Used as a barium meal, given to patients who need x-rays on their intestines. Barium absorbs x-rays so the gut shows up. It's safe because barium sulphate is insoluble
Use of BaCl2 (acidified with HCl)
Acidified BaCl2 is used as a reagent to test for sulphate ions, if sulphate ions are present, a white precipitate of barium sulphate is formed
Ba2+(aq) + SO42-(aq) --> BaSO4(s)
Why use HCl to acidify BaCl2?
The HCl reacts with carbon impurities found in salts which would form a barium carbonate precipitate, giving a false result.
Can be made by mixing appropriate solutions of ions so a precipitate is formed
Use if small amount of solids are formed
The apparatus is connected to a water pump which will produce a vacuum. Use if larger amounts of solid are formed
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