Group 2. Flashcards
Describe and explain the change in atomic radius going down group 2.
Atomic radius increases down the group.
As one goes down the group, the atoms have more shells of electrons each further from the nucleus making the atom bigger.
Describe and explain the trend in melting point going down group 2.
Melting points decrease down the group. The metallic bonding weakens as the atomic size increases. The distance between the positive ions and delocalized electrons increases. Therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken due to distance and shielding.
Describe and explain the trend in 1st ionisation energy moving down group 2.
The outermost electrons are held more weakly because they are successively further from the nucleus in additional shells.
In addition, the outer shell electrons become more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons.
What is the trend in reactivity down group 2 and why.
Reactivity of group 2 metals increases down the group. Reactivity is dependent in the ease with which the metal atom can lose two outer electrons and so as the ionisation energy decreases down the group the metals get more reactive down the group.
Describe the appearance of MgO and also its melting point.
MgO is a white solid with a high melting point due to its ionic bonding.
State what the group 2 metals will do in oxygen and give the equation and observation for this happening with magnesium.
The group 2 metals will burn in oxygen.
For magnesium burning in oxygen :2Mg + O2 —-> 2MgO
Mg burns with a bright white flame.
State the reaction that will occur naturally with Mg ribbon and why this can be a source of error when testing for reaction rates with Mg and an acid and what can be done to prevent this from happening.
Mg will also react slowly with oxygen without a flame, in addition to bright light with one.
Mg ribbon will often have a thin layer of magnesium oxide on it formed by reaction with oxygen.
2Mg + O2 —> 2MgO
This needs to be cleaned off by emery paper before doing reactions with Mg ribbon.
If testing for reaction rates with Mg and acid, an un-cleaned Mg ribbon would give a false result because both the Mg and MgO would react but at different rates. Two different reactions.
Mg + 2HCl—>MgCl2 + H2 (being cleaned with emery paper)
MgO + 2HCl—>MgCl2 + H2O. (Not being cleaned with emery paper)
State the two forms of H20 that Mg can react with and write the resulting reaction in each case. Compare the two reactions.
1) Reaction with WARM WATER to give the standard reaction of all group 2 metals with water:
Mg + 2H2O—>Mg(OH)2 + H2
2) Magnesium reacts in STEAM to produce magnesium oxide and hydrogen. The Mg would burn with a bright white flame. (Exception type reaction)
Mg (s) + H2O (g) –> MgO (s) + H2 (g)
Note:The reaction with warm water is a much slower reaction than the reaction with steam and there is no flame.
What type of water do all group 2 metals excluding Mg react with as their only reaction with water and give a general form of this reaction including state symbols.
The other group 2 metals will react with COLD WATER with increasing vigour down the group to form hydroxides.
General reaction: X + 2H2O (l)—>. X(OH)2 (aq) + H2 (g) where X is Ca, Sr or Ba.
Mg will also take part in this reaction is Warm water is used.
State how the group 2 metals , excluding Mg , will react with cold water to produce Hydroxides moving down the group and refer to the observations moving down the group.
Moving down the group they will react with Increasing vigour to form their hydroxides.
The main three changes in observations are as follows:
1)Fizzing- more vigorous down the group.
2)The metal dissolving - will dissolve faster down the group.
3)Heating up of the solution (due to exothermic reaction) - will heat up more down the group.
In addition a white precipitate of calcium hydroxide will be seen and there is less precipitate seen as you move down the group for other metals E.g Sr and Ba.
State two reasons why titanium is a useful metal and also one use of titanium.
Titanium is a very useful metal because it is abundant, has a low density and is corrosion resistant – it is used for making strong, light alloys for use in aircraft for example.
State why Titanium is unable to be extracted by electrolysis or by reduction using carbon and then state how it is actually extracted.
Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium .
Titanium cannot be extracted by electrolysis because it has to be very pure.
Titanium is extracted by reaction with a more reactive metal (e.g. Mg). Reduced by Magnesium.
State why , despite being an abundant metal, Titanium is expensive and so can only be used in limited amounts.
Titanium is expensive because
- The expensive cost of the Mg
- This is a batch process which makes it expensive because the process is slower (having to fill up and empty reactors takes time) and requires more labour and the energy is lost when the reactor is cooled down after stopping
- The process is also expensive due to the argon, and the need to remove moisture (because TiCl4 is susceptible to hydrolysis).
- High temperatures required in both steps.
Give , with the aid of balanced chemical equations, the three steps that are carried out to extract titanium.
TiO2 (solid) is converted to TiCl4 (liquid) at 900 degrees Celsius : TiO2 +2Cl2 +2C—> TiCl4 +2CO -This is called reacting the Naturally occurring TiO2 with Coke.
The TiCl4 is purified by fractional distillation in an argon atmosphere ( being molecular and all)
The Ti is extracted by Mg in an argon atmosphere at 500 degrees Celsius: TiCl4 + 2Mg —> Ti + 2MgCl4
Why is it necessary to add in the extra step of reacting the naturally occurring TiO2 with coke ( 2Cl and 2C) to form Titanium tetrachloride as opposed to just reducing the Titanium Oxide as it is there and then.
TiO2 is converted to TiCl4 as it can be purified by fractional distillation, TiCl4 being molecular (liquid at room temperature) rather than ionic like TiO2 (solid at room temperature). The naturally occurring TiO2 needs to be purified before its extracted and this can’t happen in its solid ionic state so needs to be converted into a liquid.
State what happens to the group 2 hydroxides moving down the group. And state how any group 2 hydroxide would appear if it where not soluble in solution.
Group II hydroxides become more soluble down the group.
All Group II hydroxides when not soluble appear as white precipitates.
