Group 7

What is the trend in boiling point down Group 7?

Increases down the group. Size of atom increases as more occupied electron shells, stronger Van der Waals forces of attraction between molecules take more energy to break

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What is the trend in electronegativity down Group 7?

Decreases because more occupied electron shells greater atomic radius and outer electrons are further from the positive charge of the nucleus lower force of attraction between the nucleus and electron pair in the covalent bond

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What do you use to test for halide ions?

Acidified AgNO3

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Why add HNO3 not HCl?

To remove Co32-. Adding HCl would add Cl- ions giving a false positive result

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Result and equation for Cl- test?

White ppt Ag+ + Cl- -----> AgCl(s)

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What is the result and equation for the test for Br?

Cream ppt Ag+ + Br- -----> AgBr(s)

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What is the result and equation for the test for I-?

Yellow ppt Ag+ + I- -----> AgI(s)

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What happens to each of the silver halide ppt when dilute/conc NH3 are added?

AgCl- dissolves in both dilute and conc AgCl (s) + 2NH3 (aq) --> [Ag(NH3)2]+ + Cl- AgBr- only dissolves in conc AgBr (s) + 2NH3 (aq) --> [Ag(NH3)2]+ + Br- AgI- will not dissolve in either

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What is the trend in oxidising ability down the group?

Decreases down the group (Cl best) Cl has fewest occupied shells greatest force of attraction between outer electrons and nucleus easiest to gain electrons and be reduced so best oxidising agent

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Write the equation for Cl2 oxidising 2I-

Cl2 + 2I- ---> 2CL- + I2

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What is the trend in reducing ability of the halides down the group?

Increases down the group (Cl- worst) because I- has the most occupied electron shells so outer electrons are further from the nucleus weakest force of attraction between outer electrons, positive charge of nucleus easiest to be oxidised lose electron

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What products are formed when I- reduces H2SO4?

H2SO4 + 2I- ---> 2HI

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What products are formed when I- reduces H2SO4?

H2SO4 + 2H+ + 2I- ---> SO2 + I2 + 2H2O (SO2 is a choking gas with a pungent odour)

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What products are formed when I- reduces H2SO4?

H2SO4 + 6H+ + 6I- ----> S+ 3I2 + 4H2O (S is a yellow solid)

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What products are formed when I- reduces H2SO4?

H2SO4 + 8H+ + 8I- ---> H2S + 4I2 + 4H20 (H2S smells of rotten eggs)

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What are the products of Br- + H2SO4

HBr and SO2

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Does Cl- reduce H2SO4?

No not a powerful enough reducing agent only HCl is formed

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Why is Chlorine added to drinking water? Why is it safe?

Forms ClO- ions which oxidise/kill all the microorganisms in water. Once it has its job little remains, and the health benefits outweigh the risks of using it

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What are the potential risks of adding Chlorine to drinking water?

Chlorine is toxic and damages the respiratory system in large enough quantities; can form carcinogens with hydrocarbons

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Why is ozone not used to purify water in the UK?

More expensive than chlorine evaporates from water more quickly

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What is the equation for the reaction of Cl2 with water?

Cl2 (g) + H2O (l) ----> HClO (aq) + HCl (aq)

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What type of reaction is the reaction of Chlorine with water?

Disproportionation; Chlorine is oxidised and reduced

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What are the two forms of the Chlorate ion?

ClO- is Chlorate (I) ClO3- is Chlorate (V)

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What is the equation for making bleach?

Cl2 + 2NaOH ---> NaCl + NaClO + H2O

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Give the equation for the reaction of Chlorine and water in the presence of sunlight

2Cl2 + 2H2O ----> 4HCl + O2 (g)

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What is desalination

Converts saltwater into clean water either by reverse osmosis using smart membrane or by vacuum distillation at low pressue and low temperature

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Group 7

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