Group 2 Flashcards
(27 cards)
Describe the trend in atomic radius going down group 2
Increases as you go down the group
As you go down the group the number of filled main energy levels of electrons increases with each element
Describe the trend in first ionisation energies going down group 2
Decreases as you go down the group because the outer valence electrons are a further distance away from the positivley charged nucleus as atoms get bigger and the nucleus is also shielded by the repulsive force of inner energy levels of electrons
Overall electrostatic force of attraction is decreased so it is easier for the atom to loose their 2 valence electrons
Give equations for the trend in first ionisation energies going down group 2
All of the group 2 electrons lose two outer electrons to form ions with two positive charges
M(g) = M(g)+ +2e-
1st- M(g) = M+(g) + e-
2nd- M+(g) = M2+(g) +e-
Amount of energy equal to the sum of the first and second ionisation energies is needed for complete ionisation
Describe the trend in mp and bp of elements going down group 2
-Decrease as you go down the group because metallic bonding weakens as the atomic size increases
Distance between the positive ions(nuclei) and the sea of negative delocalised electrons increases
This means the electrostatic attractive forces between positive ions and delocalised electrons weakens
However Mg has lowest bp but this is an anomaly
Describe the electron arrangement of the elements going down group 2 of the periodic table
-All elements have 2 electrons in their outer s orbital, s orbital becomes further away from the nucleus going down the group
This means the group 2 elements act as reducing agents as they are oxidised
Describe the trend in reactivity of the group 2 elements with water going down the group
The metals get more reactive with water as you go down the group
Mg(s)+ 2H2O(l) = Mg(OH)2(aq) + H2(g)
Ca(s)+2 H2O (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)
If the hydroxide is soluble it makes the water alkaline
Describe the trend in observations when group 2 elements react with water as you go down the group
-Fizzing gets more vigarous as you go down the group
-The metal dissolves faster down the group
-The solution heats up more as you go down the group
- Less precipitate is formed down the group with other metals
Describe the reaction of magnesium with steam
Mg(s) + H2O(G) = MgO(s) + H2(g)
This produces magnesium oxide plus hydrogen
Mg would burn with a bright white flame
Describe the difference in reaction of magnesium with water compared to that of steam
Water = Mg(s)+ 2H2O(l) = Mg(OH)2 (aq)+ H2(g)
Magnesium hydroxide is formed in water conditions, this is a much slower reaction than the one with steam, no flame will be given off, however when Mg reacts with steam a flame is given off
Describe the reaction of group 2 metals with oxygen
Burn in oxygen e.g Mg burns with a bright white flame
2Mg+ O2= 2MgO
MgO is a white solid with a high melting point due to its ionic bonding
Describe why titanium is a useful material
- Abundant
-Low density
-Corrosion resistant
Used for making strong,light alloys used in aircraft
Describe the use of Mg(OH)2
Give eq and why its safe
Used in medicine as a suspension of milk of magenisa
To neutralise excess stomach acid in the stomach and to treat constipation
Mg(OH)2(s) + 2HCL(aq)= MgCl2(aq)+ 2H2O(l)
Safe because it is weakly alkaline, preferred to calcium carbonate as it will not produce carbon dioxide gas
Give the ionic equation for the production of Mg(OH)2
Classed as insoluble in water
Mg2+ (aq)+ 2OH- (aq)= Mg(OH)2(s)
Describe the steps and equations for extracting titanium
TiO2(s) is converted to TiCL4(l), reacted with chlorine gas and carbon at 900 degrees because TiCl4 is liquid at room temp so it can be purified by frac distil
TiO2(s)+ 2Cl2(g) + 2C(s) = TiCl4(l)+ 2CO(g)
The TiCl4 is then purified by fractional distillation in an argon atmosphere
The Ti is then extracted by Mg in an argon atmosphere at 500 degrees celcius ( extracted by reaction with a more reactive metal)
TiCl4(g) + 2Mg(s) = Ti(s) + 2MgCl2(s)
Why is titanium expensive
- 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
Describe the trend in solubilities of group 2 hydroxides down the group
Increases down the group
Mg(OH)2 is sparingly soluble( basically insoluble in water), sold in a suspension in water rather than a solution
Ca(OH)2 is more soluble, solution is used as lime water
Sr(OH)2 is more soluble than the above
Ba(OH)2 is very soluble and dissolves to form a strongly alkaline solution
Give eq and uses of calcium hydroxide in water
- Partially soluble in water, appears as a white ppt
Used to neutralise acidic soils in agriculture
Suspension of Ca(OH)2 will be more alkaline than a suspension of Mg(OH)2 because it is more soluble as there is more hydroxide ions present in the solution
Aq solution of Ca(OH)2 is called lime water and can be used as a test for carbon dioxide, limewater turns cloudy as white calcium carbonate is formed
Ca(OH)2(aq) + CO2(g) =CaCO3(s) + 2OH-(aq)
Give detail of Ba(OH)2 in water
Easily dissolves in water
Hydroxide ions present would make the solutions strongly alkaline
Ba(OH)2(s) +aq = Ba2+ (aq) + 2OH- (aq)
aq represents an unspecified amount of water
Describe the trend in solubility of the sulfates going down group 2
Become less soluble down the group
BaSO4 is the least soluble
Write the full and ionic equations for the formation of group 2 sulfates e.g strontium chloride plus sodium sulfate
E.g strontium chloride plus sodium sulfate forms sodium chloride and strontium sulfate
Full equation : SrCl2(aq) + Na2SO4 (aq) = 2NaCl (aq) + SrSO4 (s)
Ionic equation: Ionic equation: Sr2+(aq) + SO42-(aq) = SrSO4(s)
Describe the use of BaSO4 in medicine
Used as a barium meal given to patients who need an xray of their intestines
Barium absorbs the x rays so the gut shows up on the x ray image
Even though barium compounds are toxic, they are safe to use for this because their low solubility means they are not absorbed into the blood
Describe what happens when a barium metal reacts with sulfuric acid
Will only react slowly because the insoluble barium sulfate produced will cover the metal and act as a barrier to any further attack
Ba+ H2SO4 = BaSO4 + H2
Same effect happens with the other group two metals going up the group to a lesser extent
Same effect does not happen with any other acids as they form soluble group 2 salts
Describe the test, eq and result observed when we are testing for the presence of a sulfate ion
BaCl2 solution acidified with HCl is used as a reagent to test for sulphate ions.
If there is sulphate ions present we get a white ppt of barium sulfate
Ionic eq= Ba2+ (aq) + SO42-(aq) = BaSO4(s)
Describe why the reagent used to test for sulphate ions needs to be acidified
Needs to be acidified so the acid added (HCL) added can be reacted with carbonate impurities that are often found in salts which would form a white barium carbonate ppt and so give a false result
2HCL(aq) + Na2CO3(s) = 2NaCl (aq)+ H2O(l)+CO2(g)
Sulphuric acid cannot be used as this contains sulphate ions which may give a false positive result
Fizzing due to CO2 would be observed if a carbonate was present
