Group 2 Flashcards
atomic radius trend down G2
increases down the group, the atoms gain an extra electron shell making the atom bigger
Melting Point trend down the group
It decreases down the group, this is cos as the atomic radius increases the strength of the metallic bonding decreases. Also the distance between the positive ions and the delocalised electrons increases meaning the electrostatic attractive forces weakens.
Ionisation energy Trend
Decreases down the group. this is cos the outermost electrons are held weakly as they go successively further away from the nucleus in additional shells. also the outer shells become more sheilded from the attraction of the nucleus by the repulsive forces of the inner shells.
Explain why there is a dip at the melting point of Mg
the crystal structure of Mg changes and weakens the metallic bonds between the positively charged ions and the delocalised electrons.
Reactivity trend down the group
Reactivity increases down the group cos of the outer electrons get further away from the nucleus so the attraction is weaker and the shielding is greater. resulting in it being lost easily/reacting easily.
Explain the structure of group 2 metals
Metallic structures with the positive ions in a crystal strucutre and the delocalised electrons from the outer electron shells.
Reactions with oxygen
G2 metals burn in oxygen,
eg - 2Mg + o2 ->2MgO
Beryllium and Oxygen
Reluctant to burn, white flame
Magnesium and Oxygen
Burns easily, bright white flame
Calcium and Oxygen
Difficult to ignite, with a red flame
Strontium and Oxygen
Difficult to ignite with a red flame.
Barium and Oxygen
difficult to ignite with a green flame.
Magnesium and steam
this forms Magnesium oxide and hydrogen, with a bright white flame.
Mg(s) + H2O(g) -> MgO(s) + H2(g)
Magnesium with warm water
Magnesium hydroxide and hydrogen produced.
Mg(OH)2 . This is a much slower reaction than with steam and doesnt give off a flame.
What does Ca, Sr and Ba react with and what happens ?
which metal in the group doesnt react with it
they react with cold water and will form metal hydroxides and hydrgoen, (calcium hydroxide, strontium hydroxide and barium hyroxide). these hydroxides- if soluble - make water alkaline.
Be doesnt react with water.
What observation are made when the Ca, Sr and Ba react with water
- effervescence - increasing down the group.
- the metal dissolves - - more down the group.
- the solution becomes hotter. - more down the group.
- with calcium a white ppt appears.
- they react more readily down the group cos the ionisation energy decreases
what is the role of water in the reactions with G2 metals
water is the oxidising agent (it itself gets reduced) cos it increasing the OS of metals from 0 to 2+ (the metals get oxidised)
why is titanium extracted
useful cos it it abundant, has a low density and is corrosion resisitant. so can be used to make strong, light alloys for use in aircrafts.
What is used to extract titanium
with a more reactive metal like Mg (sometimes even Na).
Step - 1 - of extraction -
TiO2 -> TiCl4
Ti is extracted from it’s ore as TiO2 (solid), which is then converted to TiCl4 (liquid for the fractional distillation purifying) at 900 degrees.
TiO2 + 2Cl2 + 2C -> TiCl4 + 2C0
Step - 2 - of extraction of Ti
TiCl4 is purified by fractional distillation in an argon atmosphere.
Step - 3 - of extraction of Ti
TiCl4 is reduced by Mg to Ti, in an argon atmosphere at 500 degrees.
TiCl4 + 2Mg -> Ti + 2MgCl2
What is done to make the Ti obtained in the end is pure
once cooled the mixture is crushed and dilute HCL is added to react with any excess Mg to form MgCl2. this is soluble in water so can be further purified
What makes Titanium expensive ?
- the expensive cost of Mg.
- the batch process of extracting the Ti makes it £££ cos the process is slower and needs more labour. the energy is lost when the reactor is cooled after finished.
- the need for argon also makes it expensive. also the need to remove moisture is £££ - cos TiCl4 is susceptible to hydrolysis.
- also high temps in both processes are needed.
trend of Solubility of G2 Hyrdoxides
More soluble down the group. usually the singly charged negative ions (OH-) increase in solubility.
Magnesium Hydroxide
is sparingly soluble
- simplest ionic equation Mg2+(aq) + OH-(aq) -> Mg(OH)2 (s).
- A suspension of Mg(OH)2 in water will apear slightly alkaline so some of the hydroxide ions must have been produced hence why Mg(OH)2 is ‘sparingly soluble’
Uses of Mg(OH)2 in medicine
It is alkaline so is used as an antiacid to neutralise stomach acids and assist with indigestion and constipation.
- ionic equation -
H+ (aq) + OH-(aq) -> H2O(l)
- it is safe to use as it is so weakly alkaline and deosnt rpoduce C02
Calcium Hydroxide
More Soluble in water than Mg(OH)2, so produces a more alkaline solution ( with more hydroxide ions present in the solutions) and appears as a white ppt.
Use of Ca(OH)2
Neutralises acidic soils in agriculture.
Aqueous solutions of Ca(OH)2 is called what and what is it used for??
called lime water and is used to test for carbon dioxide. if CO2 preesent then the limewater turns cloudy as calcium carbonate is produced.
Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O(l)
Barium Hydroxide
Highly soluble and produces a strongly alkaline solution.
trend of Solubility of G2 sulfates
they become less soluble down the group, cos they are compounds with a double negative charge (SO4 2-)
Example of Strontium chloride and sodium sulfate, give the full and ionic equation
- Full equation : SrCl2(aq) + Na2SO4 (aq) -> 2NaCl (aq) + SrSO4 (s)
- Ionic equation: Sr2+ (aq) + SO4 2-(aq) -> SrSO4 (s)
Uses of BaSo4 in medicine
used as Barium Meals. they are given to patients who need x-rays of theur intestines. they absorb the x-rays and so the gut shows an image up on the x-ray.
- even tho they are toxic they are used as they are insoluble so are safe to use as they won’t be absorbed into the blood.
what happens when a barium metal is reacted with sulfuric acid
it reacts slowly(with a white ppt) as the insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to prevent any further attack.
what happens when a barium metal is reacted with sulfuric acid. does this happen to the other metals (as youi go up the group) and other acids (like HCl and nitric acid) as well??
it reacts slowly as the insoluble barium sulfate produced will cover the surface of the metal and act as a barrier to prevent any further attack.
- Ba + H2SO4 ->BaSO4 + H2
- the same effect happens but at a lesser extent with metals as you go up the group as the solubility increases up the group.
- this same effect doesnt happen with other acids like HCl and nitric acid as they form soluble group 2 salts.
what is used to test for sulfate ions, and what does using other anions result in?
BaCl2 solution which is acidified with hydrochloric acid is used as the reagent to test for sulfate ions.
- using other anions will give a negative result with no ppt formed.
what happens if there is sulfate ions present, and give the simplest ionic equation.
when the acidified barium chloride is added to the solution containing the sulfate ions a white precipitate of barium sulfate ions forms.
Ba2+ (aq) + SO4 2-(aq) -> BaSO4 (s).
Why is the BaCl2 acidified with HCl ? and why can’t you use sulfuric acid to acidify
the HCl reacts with any carbonate or sulafte impurities in the salts that could form a white barium carbonate ppt with CO2 fizzing, to give a false result.
- sulfuric acid can’t be used as it contains sulfate ions so would give a false possitive result.
what is the process of removing flue gases - SO2 - from exhausts, and what is used
wet scrubbing - powdered Calcium oxide (lime - Cao) and calcium carbonate (CaCO3) are used. to prevent flue gases being released in tho the atmosphere.
explain the test for carbonates
add some di;ute HCl to the sample, bubble the gas into limewater. if carbonate present then the limewater turns cloudy.
