Chapter 11. Group 17

Question 1

What are characteristics of the halogens at room temperature?

Answer 1

Fluorine is a pale yellow gas, chlorine is a greenish gas, bromine is a red-brown liquid, and iodine a black solid.
-All the halogens have a characteristic swimming pool smell

Question 2

Note

Answer 2

The genral bond strength of the molecules of halogens, decreases as we descend down the group because the shared electrons in the bond get further from the nuclei of the bonded atoms, i.e atomic radius increases
-Fluorine is a bit untypical because the size of its atoms are small, so the non-bonding electrons will repel each other as they are close together making the bond weaker than expected

Question 3

Note

Answer 3

Electronegativity decreases down the group.
-The halogens get less volatile down the group, meaning boiling point and melting point increases dwon the group. This is because of london dispersion forces, they get stronger with increase proton number as there are more electrons to create the instantaneous dipole.

Question 4

Note

Answer 4

The oxidising ability of halogens decreases down the group.

Question 5

Note

Answer 5

The hydrogen halide bond decreases down the group so thermal decomposition is easier for iodine than for fluorine as hydrogen fluoride is more stable.

Question 6

Note

Answer 6

Halide ions can act as reducing agents, reducing power increasing down the group because of the ionic radius, the further the electron to be removed is from the nucleus the easir it is to remove it.
-The following reactions require <b>solid</b> sodium halides and <b>concentrated</b> sulfuric acid
-NaCl + H₂SO₄ –> NaHSO₄ + HCl – steamy fumes of the acid meaning gaseous state same for fluorine as they are both weak reducing agents
-NaBr + H₂SO₄ –> NaHSO₄ + HBr but then 2HBr + H₂SO₄ –> SO₂ + 2H₂O + Br₂ – steamy white fumes of HBr then brown fumes of Br
-NaI + H₂SO₄ –> NaHSO₄ + HI(steamy fumes) but then 8H⁺ + 8I^- + H₂SO₄ –> H₂S_(g)(bad egg smell) + 4H₂O + 4I₂(black solid)
-This occurs in stages though
-2HI + H₂SO₄ –> SO₂(colourless) + I₂ + 2H₂O
-4HI + SO₂ –> S(yellow solid) + 2I₂ + 2H₂O
-2HI + S –> H₂S + I₂

Question 7

Test for halides

Answer 7

First add nitric acid to remove carbonate and hydroxide impurities from the solution.
-2AgOH –> Ag₂O(brown ppt) + H₂O
-Add a few drops of silver nitrate to the solution
-With Silver fluoride, no ppt is formed
-With Silver chloride, white ppt is formed, dissolves in dilute ammonia
-With Silver bromide, cream ppt is formed, dissolves in concentrated ammonia
-With Silver iodide, pale yellow ppt is formed, insoluble in concentrated ammonia

Question 8

Chlorine reactions

Answer 8

-Cl_2(g) + H₂O_(l) <–> HClO_(aq)(chloric(I) acid) + HCl_(aq)
-In sunlight, 2Cl_2(g) + 2H₂O_(l) –> 4HCl_(aq) + O_2(g), from pale green to colourless
-NaClO_(s)(sodium chlorate(I)/hypochlorite) + H₂O _{<–> Na⁺(aq) + OH^-(aq) + HClO(aq)
-Cl2(g) + 2NaOH(aq)(cold and dilute) –> NaClO(aq) + NaCl(aq) + H2O(l)
-3Cl2(g) + 6NaOH(aq)(hot and concentrated) –> NaClO3(aq)(sodium chlorate(V)/chlorate) + 5NaCl(aq) + 3H2O(l)
-Similar hydroxide reactions for bromine and iodine}