Group 7 Flashcards
Explain the trend in volatility of the halogens down the group
As the group is descended, volatility decreases as atomic number increases which increases the forces of attraction between the electrons and the nucleus. This increases the amount of energy required to change the element to a gas
Use the E^0 (e north) values and the sodium thiosulfate reagent to explain the relative reactivity of the halogens as oxidizing agent.
As group 7 is descended, E^0 values decrease which indicate a decrease in oxidizing ability.
F, Cl and Br oxidize the thiosulfate ion to the sulfate ion while I oxidizes the thiosulfate ion to the tetrathionate ion
Describe the reactions of the halogens with hydrogen
Fluorine- reacts explosively with hydrogen even in the dark at -200°C (H2(g) +F2(g) —> 2HF(g))
Chlorine- less reactive than fluorine. Reacts explosively with hydrogen in the sunlight at room temp. (H2(g) +Cl2(g) —> 2HCl(g))
Bromine- even less reactive. Only reacts with hydrogen if heated and in the presence of a platinum catalyst. (H2(g) + Br2(g) —> 2HBr(g))
Iodine- least reactive. Reacts very, very slowly (H2(g) + I2(g) —> 2HI(g))
Explain the trend in relative stabilities of the group 7 hydrides
H-X bond lengths increase as group 7 is descended. Therefore bond strength decreases down the group (shorter bond length= stronger bond). From this it can be said that stability decreases as group 7 is descended as stronger bonds would be more stable.
What is disproportionation?
This is a chemical reaction in which a species undergoes simultaneous oxidation and reduction
What is the trend in colours of the halogens?
Colour deepens as group 7 is descended
F2- pale yellow gas
Cl2- pale green gas
Br2- reddish brown gas
I2- shiny black solid w/ a purple sheen
What is meant by the term ‘volatility’ ?
This describes how readily a substance vaporizes
Why does melting and boiling point increase as group 7 is descended?
This is because atomic number increases so there are more electrons. This means that there will be a greater positive dipole and a greater negative dipole. As a result the strength of Van der Waal forces increase and molecules are harder to break apart.
Describe the reaction of the halogens with silver nitrate followed by ammonia
Fluoride ions- no ppt
Chloride ions- white ppt for AgNO3
Ppt is purple in sunlight
Ppt is soluble in NH3
Bromide ions- cream ppt for AgNO3
ppt is yellow green in sunlight
Ppt is slightly soluble in NH3
Iodide ions- pale yellow ppt for AgNO3
no change in sunlight
ppt is insoluble in NH3
Describe the reaction of the halide ions in concentrated sulphuric acid
Fluoride ions
- White fumes of HF and acidic gas that turns blue litmus red
Chloride ions
- white fumes of HCl and acidic gas that turns blue litmus red
Bromide ions
- white fumes of HBr and acidic gas. HBr gas is oxidised to BR2 gas which is reddish brown
2Br- (s) + H2SO4(l) = SO42-(s) + 2HBr(g)
2HBr(g) = H2(g) + Br2(g)
Iodide ions
Colourless fumes of HI and acidic gas
HI is oxidized to I2 gas which is deep purple and readily sublimes into a black solid with a purple sheen
2I-(s) + H2SO4(l) = SO42-(s) + 2HI(g)
2HI(g) = H2(g) + I2(g)
Describe the reactions of chlorine with cold and hot aqueous solutions of sodium hydroxide
@ 15°C room temp (cold)
Cl2(g) +2NaOH(aq) = NaCl(aq) + NaClO(aq) + H2O(l)
NaClO and NaCl is packaged together and sold as bleach
Upon hearing 70°C (hot)
3NaClO(aq) = 2NaCl(aq) +NaClO3(aq)
NaClO3 is used as weed killer
