Test for halides: Reactions with Sulfuric Acid: ionic equations, observations, precautions, type of reaction (e.g what is red, what is ox)
Chloride: NaCl + H2SO4 —NaHS04 (s) + HCl(g) (same with ll halogens)
Bromide: 2Br- + 2H+ + H2S04(l)--- SO2(g) + 2H20 (1) + Br2(l) Redox Brown fumes Colourless gas Br- oxidised H2SO4 reduced
Iodide: Hydrogen iodide is produced in an acid-base
reaction as before.
Nal(s) + H S04(1) -> NaHS04 (s) + Hl(g)
H2SO4 + 8I- + 8H+ —- H2S + 4H2O
Rotten egg smell
Trends in atomic radius, electronegativity, melting and boiling points and 1st ionisation energy in group 7 and explain
AR:INCREASE as you go DOWN the group
- No. of energy levels INCREASES
- Outer electrons FURTHER AWAY
- INCREASE SIZE of atom
Electronegativity:-DECREASE as you go DOWN the group
-e-s distance from nucleus INCREASES
-LOWER attraction to positive nucleus
(As the halogen atoms get bigger, any bonding pair gets further and further away from the halogen nucleus, and so is less strongly attracted towards it. In other words, as you go down the Group, the elements become less electronegative.)
Melting and Boiling points:-INCREASE as you go DOWN a group
- Bigger molecs further down group, more electrons
- Greater d-d forces
- Greater VDW
- More energy req to overcome VDW
1st ionisation energy:-DECREASE as you go DOWN the group
- Outer e-s FURTHER AWAY from +ve nucleus
- Less attr btw +ve nuc and -ve e-s
- LESS en req to remove outer e-s
Fluorine, chlorine, bromine and iodine appearance at room temp, their vapours, other comments
Fl- yellow gas- poisonous
Cl- green gas- poisonous (greek word chloros)
Bromine- brown liquid- very easily forms orange vapour
often used as a solution in water ( yellow-orange bromine water)
Iodine- grey crystalline solid- very easily forms purple vapour
-often used as a (sort of) solution in water (brown ‘iodine solution’)
Cl2 + H20 —- H+ +Cl- + HClO
What species is responsible for the green colour
usie le chat’s princ to explain why the green colour disappears when sodium hydroxide solution is added to this solution
It neutralises the acidic products so the equilibrium shifts to the right to combat the change
Explain trends in atomic radius, 1st ionisation energy, melting points and reactivity (chem property) DOWN group 2
AR- no. of electron shells and energy levels INCREASES
-atoms are BIGGER
1st ionisation energy- AR and size of atoms INCREASES
- shielding INCREASES
- therefore weaker force of attr from +ve charged nuc to -ve charged e-s on outer shell- EASIER TO LOSE
Melting point–Group 2 elements are metals with high melting points, typical of a giant metallic structure.
- weaker metallic bonding (the electrons in the ‘sea’ of delocalised electrons arc further away from the positive nuclei. As a result, the strength of the metallic bonds decreases going down the group.)
- so lower MP
Reactivity- INCREASE DOWN GROUP
- larger atoms, e-s further away from nucleus AND
- more shielding
- more distance between +ve nuc and -ve e-s, less attr
- easier to lose
Reactions of metals (Mg to Ba) with water- observation and equations
Link intensity of reaction to trend in reactivity first
With water you see a trend in reactivity - the metals get more reactive going down the group. These are also redox reactions.
The basic reaction is as follows, where M is any Group 2 metal:
0 +l +2 0 (o states)
M(s) + 2H20(l) • M(OH)2 (aq) + H2(g)
Magnesium hydroxide is milk of magnesia and is used in indigestion remedies to neutralise excess stomach acid which causes heartburn, indigestion, and wind.
Magnesium reacts very slowly with cold water but rapidly with steam to form an alkaline oxide and hydrogen.
Mg(s) + H20(g) • MgO(s) + H2(g)
Calcium reacts in the same way but more vigorously, even with cold water. Strontium and barium react more vigorously still.
Describe the trend in solubility of Group 2 hydroxides (Mg(OH)2 to Ba(OH)2), solubility of EACH hydroxide and write ionic equation for precipitate formed, if precipitate is formed, and colour of (all group 2) precipitates
Solubility INCREASES down the group
Check on FCs/booklet
Describe the trend in solubility of Group 2 hydroxides (MgSO4 to BaSO4), solubility of EACH sulfate and write ionic equation for precipitate formed, if precipitate is formed, and colour of (all group 2) precipitates
Solubility DECREASES down the group
Check on FCs/booklet
Describe and name some uses of Group 2 compounds, why is…(OH)2 preferable to a carbonate?
Magnesium hydroxide is milk of magnesia and is used in indigestion remedies to neutralise excess stomach acid wh ich causes heartburn, indigestion, and wind. Better than carbonate as doesn’t release CO2
Calcium hydroxide is sometimes called slaked lime and is used to treat acidic soil.
BaSO4 is very insoluble so can be used as barium meal, causes contrast in x ray so image is clearer
Steps in the test for sulfate ions and why each step is necessary?
1) Add HCl(aq) to solution being tested
Reason: remove other ions that could give a precipitate with barium chloride
2) Add barium chloride (aq) to solution being tested
Reason: produce white precipitate with sulfate ions
What is a use of Mg metal? What type of reaction is extraction? Write out equation(s). What are the oxidation states in this reaction/reactions? What are the uses of the material extracted, and what properties make it good for these uses?
Extraction of Ti from the ore rutile (TiO2)
TiO2 + 2C + 2Cl2 →TiCl4 + 2CO o statesTi=4 Ti=4 TiCl4 + 2Mg →Ti + 2MgCl2 o states Ti=4 Mg=0 Ti=0 Mg=+2
Uses: artificial joints (lightweight and doesn’t wear out (corrode) easily)
marine motor vehicles (resistant to corrosion)