Group 2, the Alkaline Earth Metals (AQA A Level Chemistry): Flashcards
Exam code: 7405
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Why do Group 2 elements act as reducing agents in their reactions?
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Why do Group 2 elements act as reducing agents in their reactions?
Group 2 metals lose their two outer electrons to form M2+ ions. Losing electrons is oxidation, so the metal is oxidised. A species that is oxidised donates electrons to another species, making it a reducing agent.
True or False?
Reactivity decreases down Group 2 because the nuclear charge becomes too large to allow electron loss.
False.
Reactivity increases down Group 2. The outer electrons become further from the nucleus and experience greater shielding, so they are more easily lost. Both first and second ionisation energies decrease down the group.
Down Group 2, the first and second ionisation energies both .......... because the outer electrons are .......... from the nucleus and experience .......... shielding from additional inner shells.
Down Group 2, the first and second ionisation energies both decrease because the outer electrons are further from the nucleus and experience greater shielding from additional inner shells.
What is the general trend in atomic radius down Group 2, and what causes it?
Atomic radius increases down Group 2.
Each successive element has an additional electron shell, placing the outer electrons further from the nucleus. Increased shielding also reduces the effective nuclear attraction on the outer electrons.
The melting points of Group 2 metals generally .......... down the group because the positive metal ions become .......... , weakening the .......... attraction in the metallic lattice.
The melting points of Group 2 metals generally decrease down the group because the positive metal ions become larger, weakening the electrostatic attraction in the metallic lattice.
True or False?
The density of Group 2 elements follows a perfectly regular increasing trend down the group.
False.
Density does not follow a perfectly smooth trend. It decreases from Be to Ca then increases from Ca to Ba. Differences in atomic mass, atomic radius, and metallic packing structures all influence density.
What is the second ionisation energy of a Group 2 element?
A standard state is the most stable physical state of a substance at 298 K and 100 kPa. It is the reference state used when defining standard thermodynamic quantities.
What is the trend in solubility of Group 2 hydroxides down the group?
The solubility of Group 2 hydroxides increases down the group. Mg(OH)2 is sparingly soluble, while Ba(OH)2 is soluble. As solubility increases, the concentration of OH− ions rises, so solutions become more alkaline.
True or False?
The solubility of Group 2 sulfates increases down the group.
False.
The solubility of Group 2 sulfates decreases down the group. MgSO4 is soluble, while BaSO4 is insoluble. This is the opposite trend to the Group 2 hydroxides.
When Group 2 oxides dissolve in water, the ionic equation is: O2− (aq) + H2O (l) → .......... . The more soluble the hydroxide, the more .......... the solution.
When Group 2 oxides dissolve in water, the ionic equation is: O2− (aq) + H2O (l) → 2OH− (aq). The more soluble the hydroxide, the more alkaline the solution.
How is the insolubility of barium sulfate used in a laboratory test for sulfate ions?
Add dilute HCl (or HNO3) to remove interfering anions such as carbonate, then add BaCl2 (aq) (or Ba(NO3)2 (aq)).
A white precipitate of BaSO4 confirms the presence of sulfate ions.
Group 2 hydroxides dissolve according to: X(OH)2 → X2+ (aq) + .......... . Going down the group, increasing solubility means a .......... concentration of OH− and a .......... pH.
Group 2 hydroxides dissolve according to: X(OH)2 → X2+ (aq) + 2OH− (aq). Going down the group, increasing solubility means a higher concentration of OH− and a higher pH.
True or False?
Calcium sulfate is classified as insoluble.
False.
Calcium sulfate is classified as sparingly (slightly) soluble. It sits between soluble MgSO4 and insoluble BaSO4 in the Group 2 trend. In equations where it forms as a product, it is represented as a solid (s).
Why is acid added before the barium chloride solution in the test for sulfate ions?
The acid (HCl or HNO3) removes interfering anions such as carbonate (CO32−), which could also form white precipitates with Ba2+. Adding acid first ensures that any white precipitate produced is specifically barium sulfate.
Sparingly soluble
A substance that dissolves only to a very limited extent in a solvent. For example, Mg(OH)2 and CaSO4 are sparingly soluble in water, dissolving sufficiently to produce a weakly alkaline or saturated solution but leaving most of the solid undissolved.
What is the general equation for the reaction of a Group 2 metal with oxygen?
2M (s) + O2 (g) → 2MO (s), where M is any Group 2 metal. Note that Sr and Ba can also form peroxides: M (s) + O2 (g) → MO2 (s).
True or False?
The observation for magnesium reacting with steam includes effervescence.
False.
The required observations are a bright white flame/light and a white (or grey) solid ash. Mark schemes explicitly do not accept 'effervescence' or 'fizzing' for this reaction.
When calcium reacts with dilute H2SO4, the reaction slows and stops because .......... forms on the surface of the metal, preventing further reaction.
When calcium reacts with dilute H2SO4, the reaction slows and stops because a sparingly soluble calcium sulfate (CaSO4) layer forms on the surface of the metal, preventing further reaction.
Write the equation for the reaction of calcium with water.
Ca (s) + 2H2O (l) → Ca(OH)2 (s) + H2 (g)
Calcium reacts moderately with cold water, forming calcium hydroxide and hydrogen gas.
The reaction of Group 2 metals with dilute HCl follows the general equation: M (s) + .......... → MCl2 (aq) + .......... .
The reaction of Group 2 metals with dilute HCl follows the general equation: M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g).
What happens when a Group 2 oxide reacts with water, and what general equation applies?
Group 2 oxides react with water to form the corresponding metal hydroxide. The general equation is: MO (s) + H2O (l) → M(OH)2. Going down the group, the reactions become more vigorous and the solutions formed are more alkaline.
True or False?
All Group 2 carbonates are soluble in water.
False.
All Group 2 carbonates except BeCO3 are insoluble in water. They do react with dilute acids to produce soluble chloride salts, water, and CO2 gas.
What is limewater and how is it formed?
Limewater is a solution of calcium hydroxide, Ca(OH)2, in water.
It is formed when calcium oxide (quicklime) reacts with water: CaO (s) + H2O (l) → Ca(OH)2 (s). The solution has a pH of approximately 11.
Limewater
A solution of calcium hydroxide, Ca(OH)2, in water. It is formed when calcium oxide (quicklime) reacts with water and is used as a test for carbon dioxide gas, which turns limewater milky.
What is quicklime?
A standard enthalpy change of neutralisation is the enthalpy change when one mole of water is formed from the reaction of an acid and an alkali under standard conditions (298 K, 100 kPa), with solutions at 1 mol dm-3.
True or False?
Calcium carbonate is preferred over calcium hydroxide in agricultural lime because it acts more quickly to neutralise soil acidity.
False.
Calcium carbonate acts more slowly than calcium hydroxide because it is largely insoluble. It is preferred because it is cheaper and safer to handle.
Ca(OH)2 (s) + 2H+ (aq) → .......... + ..........
Ca(OH)2 (s) + 2H+ (aq) → Ca2+ (aq) + 2H2O (l)
Why can barium sulfate be safely used in a barium meal despite barium being toxic?
Barium sulfate is insoluble, so it is not absorbed into the bloodstream. It passes through the digestive system without causing harm.
What is sulfur scrubbing (flue gas desulfurisation)?
A standard enthalpy change of reaction is the enthalpy change when a reaction occurs as written in the balanced equation, with all reactants and products in their standard states at 298 K and 100 kPa.
True or False?
Magnesium is used to extract titanium from TiCl4 by reducing it to titanium metal.
True.
Magnesium (or sodium) reduces TiCl4 to titanium metal: TiCl4 (g) + 2Mg (l) → Ti (s) + 2MgCl2 (l).
Milk of magnesia is a suspension of .......... in water used to neutralise excess stomach acid. It is safe because it is only .......... soluble, producing a mildly alkaline solution.
Milk of magnesia is a suspension of magnesium hydroxide (Mg(OH)2) in water used to neutralise excess stomach acid. It is safe because it is only partially soluble, producing a mildly alkaline solution.
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