group 7 Flashcards
what are a few properties of Halogens?
- non-metals
- exist as diatomic molecules
- flourine = pale yellow gas
- chlorine = pale green gas
- bromine = brown liquid
- iodide = black solid
explain the trend in boiling point as we go down group 7?
- the boiling and melting point increases as we go down group 7
- as molecules become larger down the group
- as they have a greater surface area and greater/ stronger Van der waals forces
explain the trend in electronegativity as we go down group 7?
- electronegativity decreases
- this is due to a greater atomic radii
- so there is greater shielding
- so therefore less able to withdraw electron density from a covalent bond
explain the trend in oxidising ability as we go down group 7?
- oxidising ability decreases as we go down group 7 elements
- due to increased atomic radii
- so there is greater shielding
- so the outer electron is attracted less strongly to the nucleus
Explain what happens in displacement reactions with halide ions?
- chlorine water displaces both potassium bromide to make an orange solution of bromine (Br2) and potassium iodide to make a brown solution of iodine (I2)
- bromine water has no reaction with sodium chloride but displaces potassium iodide to make a brown solution of iodine (I2)
- iodine has no reaction with the rest
describe the test for identifying halide ions?
Acidified silver nitrate
(nitric acid and silver nitrate)
describe the reaction when silver nitrate reacts with Cl-, Br- , and I-
Cl- = white precipitate
Br- = cream precipitate
I- = yellow precipitate
write an equation to show each equation
cl = Ag+ (aq) + Cl- —-> AgCl (s)
br = Ag+ (aq) + Br- ——> AgBr (s)
I = Ag+ (aq) + I- —-> AgI (s)
why is nitric acid added before the silver nitrate?
to remove any carbonate ions which may produce a false positive result
why is nitric acid instead of hydrochloric acid?
hydrochloric acid contains Cl- ions so may produce a false positive result
if we later added dilute ammonia to the test tubes what would be observed
sodium chloride - dissolves to form colourless solution
potassium bromide - sparingly soluble - add concentrated ammonia - would dissolve to form a colourless solution
potassium iodide - insoluble remains insoluble when conc. ammonia is added
why can acidified silver nitrate not be used to identify Fluoride ions?
because silver fluoride which is formed is soluble in water, so solutions containing fluoride ions remain colourless
reactions of halide ions
why does the reducing power of halide ions increase as we go down the group?
- reducing power of the halides increases as we go down the group
- due to increasing atomic radii
- there is greater shielding
- so more able to donate an electron
what do all halides react with?
concentrated sulphuric acid
but it depends on..?
the halide ion used and reflect the reducing power of the halide
what type of reaction do all halides undergo?
Acid-base reactions
write down an equation to show this acid base reaction
NaX (s) + H2SO4 (aq) —> NaHSO4 (s) + HX (g)
X = halide
what is formed?
NaX = white solid
forms
NaHSO4 = white solid and HX = steamy white fumes
some halides are strong enough to reducing agents to reduce sulphuric acid to…?
sulphur dioxide and water
show this reaction in an equation
2NaX (s) + 2H2SO4 (l) ——-> X2 (g) + SO2 (g) + 2H2O (l) + Na2SO4 (s)
what type of reaction is this?
a redox reaction
what has been reduced and what has been oxidised?
sulphur has been reduced, halide has been oxidised so the halide is the reducing agent
why can chloride not reduce sulphuric acid?
chloride is a weak reducing agent
chloride undergoes an …?
acid-base reaction
write an equation to show this reaction?
NaCl (s) + H2SO4 (l) —–> NaHSO4 (s) + HCL (g)
why is this not a redox reaction?
no change in the oxidation sate of any of the species
what happens when sodium bromide is reacted with concentrated sulphuric acid?
- undergoes an acid-base reaction
NaBr (s) + H2SO4 —-> NaHSO4 (s) + HBr (g)
ALSO - bromide is able to reduce sulphuric acid to sulphur dioxide
2NaBr (s) + 2H2SO4 ——> Br2 (g) + SO2 (g) + 2H2O (l) +Na2SO4 (s)
what happens when sodium iodide reacts with concentrated sulphuric acid?
- undergoes an acid-base reaction
- iodide is able to reduce sulphuric acid to sulphur dioxide
hydrogen iodide produced in the above reaction is able to reduce sulphuric acid to…?
sulphur and can also be reduced into hydrogen sulphide
Draw an equation to show how HI (hydrogen iodide) is able to reduce sulphuric acid to sulphur?
6HI (G) + H2SO4 (l) —> 3I2 (g) + S (s) + 4H2O (g)
sulphur is reduced (+6 -> 0)
iodine is oxidised (-1 –> 0)
show the oxidation of hydrogen Iodide to hydrogen sulphide (equation)
8HI (g) + H2SO4 (l) —–> 4I2 (g) + H2S (g) + 4H2O (g)
What is the overall equation when bromide reduces to sulphur dioxide
2NaBr (s) + 2H2SO4 (l) —-> Br2 (g) + SO2 (g) + 2H2O (l) + Na2SO4 (s)
what is this simplified to?
what is each oxidation sate?
2H+ + 2Br- + H2SO4 —> Br2 + SO2 +2H2O
-1 +6 0 +4
what is the oxidation half equation?
what is the reduction half equation?
oxidation - 2Br- —-> Br2 + 2e-
reduction - H2SO4 + 2e- + 2H+ –> SO2 + 2H2O
what is the overall equation when Hydrogen iodide reduced sulphuric acid to sulphur?
What is the oxidation states?
6HI + H2SO4 —> 3I2 + S + 4H2O
-1 +6 0 0
what is the oxidation half equation?
oxidation - 6I- —–> 3I2 + 6e-
reduction - H2SO4+ 6e- +6H+ —–> S + 4H2O
Overall equation when reduced to hydrogen sulphide?
what are the oxidation staes?
8HI + H2SO4 —> 4I2 + H2S + 4H2O
-1 +6 0 -2
what is the oxidation equation?
what is the reduction equation?
oxidation - 8I- —-> 4I2 + 8e-
reduction - H2SO4 + 8e- + 8H+ —-> H2S + 4H2O
Chlorine and water
chlorine dissolves in water to form..?
chlorine water
write the equation to show this reaction?
Cl2 (aq) + H2O (l) ⇌ HOCL (aq) + HCL (aq)
what is HOCL?
chloric acid, a colourless acidic solution
how has some of the CL been oxidised and some reduced?
some Cl2 has been oxidised to +1 (HOCL)
some of the Cl2 has been reduced to -1 (HCL)
what is the reaction called where the same element has been oxidised and reduced?
disproportionation reaction
what happens when universal indicator is added to chlorine water?
initially goes red as chlorine water is acidic then turns colourless as it’s bleached by HOCL
what is formed when chlorine water is left in sunlight. what is the equation?
2Cl2 (aq) + 2H2O (l) —–> 4HCL (aq) + O2 (g)
what type of reaction is this?
a redox reaction
how is this a redox reaction?
chlorine will oxidise water to oxygen gas in sunlight
what is the oxidising agent?
chlorine
How do we make bleach?
COLD DILUTED sodium hydroxide is added to chlorine water
what is the equation?
Cl2 (aq) + 2NaOH (aq) ——–> NaCl (aq) + NaOCl (aq) + H2O (l)
what is NaOCl?
sodium chlorate = bleach (colourless solution)
what is sodium chlorate/bleach used for?
used in water treatment, cleaning toilets, bleaching paper, bleaching textiles
what are the uses of Chlorine?
small amounts of chlorine is added to drinking water to kill bacteria which causes cholera and typhoid
what is an advantage to using chlorine in water?
saves thousands of lives every year, this outweighs the disadvantage
what is the disadvantage to using chlorine in water?
chlorine is toxic so must be added in low amounts to kill bacteria and not harm humas.
also some people are allergic to chlorine
what type of reaction is making bleach
reversible reaction
what is the colour change when NaOH (alkali) is added to chlorine water?
green to colourless (bleach formed)
what can we add to reform green chlorine water?
adding dilute acid, H2SO4 or HCL
show how adding acid can reform green chlorine water through an equation.
Cl- (aq) + CIO- (aq) + 2H+ —–> Cl2 (aq) + H2O
FINISH
