Group 7 (halogens) tests - RP

Question 1

test for halogens

Answer 1

add dilute nitric acid and then add silver nitrate solution

Question 2

why do you add dilute nitric acid before silver nitrate

Answer 2

to prevent false positive results from carbonate ions precipitating out with silver ions

Question 3

equations for silver nitrate and halide ions

Answer 3

Ag+ (aq) + X- (aq) → AgX (s)

Question 4

results of adding dilute nitric acid and silver nitrate

Answer 4

-silver chloride –> white precipitate
-silver bromide –> cream precipitate
-silver iodide –> pale yellow precipitate

Question 5

results after adding dilute ammonia to precipitate

Answer 5

-Cl- colourless as dissolves
-Br- remains cream as insoluble
-I- remains pale yellow as insoluble

Question 6

results of adding concentrated ammonia solution to precipitate

Answer 6

-Cl- dissolves so colourless
-Br- dissolves so colourless
-I- pale yellow as insoluble

Question 7

test for Cl- ions

Answer 7

-dilute nitric acid and silver nitrate –> white precipitate

-dilute ammonia solution to precipitate –> dissolves so colourless

-adding concentrated ammonia solution to precipitate –> dissolves so colourless

Question 8

test for I- ions

Answer 8

-dilute nitric acid and silver nitrate –> pale yellow precipitate

-dilute ammonia solution to precipitate –> remains pale yellow as insoluble

-adding concentrated ammonia solution to precipitate –>remains pale yellow as insoluble

Question 9

test for Br- ions

Answer 9

-dilute nitric acid and silver nitrate –> cream precipitate

-dilute ammonia solution to precipitate –> remains cream as insoluble

-adding concentrated ammonia solution to precipitate –> dissolves so colourless

Question 10

what is produced when halide ions react with concentrated sulfuric acid

Answer 10

-produce toxic gases
-equation
H2SO4(l) + X-(aq) → HX(g) + HSO4-(aq)

Question 11

where should reaction of halide ions with concentrated sulphuric acid be carried out

Answer 11

fume hood as toxic gas is produced

Question 12

reaction of chloride ions with concentrated sulphuric acid
(NaCl)

Answer 12

-concentrated sulfuric acid is added dropwise to sodium chlorine crystals to produce hydrogen chloride gas
-HCl gas produced is seen as white fumes
- H2SO4 (l) + NaCl (s) → HCl (g) + NaHSO4 (s)

Question 13

reaction of bromide ions with concentrated sulfuric acid (NaBr)

Answer 13

-H2SO4 (l) + NaBr (s) → HBr (g) + NaHSO4 (s)
-bromine seen as reddish-brown gas

Question 14

reaction of bromide ions with concentrated sulfuric acid (HBr) –> SO2

Answer 14

-concentrated sulfuric acid oxidises HBr which decomposes into bromine and hydrogen gas and sulfuric acid itself is reduced to sulfur dioxide gas
-2HBr (g) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)
-bromine seen as reddish-brown gas

Question 15

sodium iodide with concentrated sulfuric acid

Answer 15

H2SO4 (l) + NaI (s) → HI (g) + NaHSO4 (s)

Question 16

reaction of concentrated sulfuric acid and hydrogen iodide (HI) –> (SO2)

Answer 16

-hydrogen iodide decomposes readily
-sulfuric acid oxides the hydrogen iodide to form several products
-the concentrated sulfuric acid oxidises HI and itself reduces to sulphur dioxide gas
-2HI (g) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (l)
-iodine is seen as violet/purple vapor

Question 17

observations of concentrated sulfuric acid and hydrogen iodide (HI)

Answer 17

-iodine is seen as violet/purple vapor

Question 18

reaction of concentrated sulfuric acid and hydrogen iodide (S)

Answer 18

-concentrated sulfuric acid oxides HI and itself is reduced to sulpher
-6HI (g) + H2SO4 (l) → 3I2 (g) + S (s) + 4H2O (l)
-sulfur seen as a yellow solid

Question 19

observation of concentrated sulfuric acid and hydrogen iodide (S)

Answer 19

-Sulfur is seen as a yellow solid

Question 20

reaction of concentrated sulphuric acid and hydrogen iodide (H2S)

Answer 20

-The concentrated sulfuric acid oxidises HI and is itself reduced to hydrogen sulfide
-8HI (g) + H2SO4 (l) → 4I2 (g) + H2S (s) + 4H2O (l)
-hydrogen sulfide has strong smell of bad eggs

Question 21

observation of of concentrated sulphuric acid and hydrogen sulfide (H2S)

Answer 21

hydrogen sulfide has strong smell of bad eggs