Group 7 Flashcards
Most electronegative element in group 7
Fluorine
What intermolecular forces exist in halogen molecules?
Van der Waals
State and explain the trend in boiling point down group 7 (5)
Increases
Simple molecular structure
Molecule gets bigger down group 7 so increased number of electrons so stronger van der Waals between molecules
Takes more energy to overcome
State and explain the trend in oxidising ability from F2 to I2 (4)
Going down the group the halogens become weaker oxidising agents
Oxidising agents are themselves reduced and, therefore, gain electrons.
Going down the group the halogens increase in size and atoms have more shielding, which makes the attraction to incoming electrons weaker
Accept electrons more easily
What colour is fluorine in an aqueous solution
Pale yellow gas
What colour is chlorine in an aqueous solution
Pale green
What colour is bromine in an aqueous/polar solution
Aqueous: yellow/brown
Non polar: orange/brown
What colour is iodine in an aqueous/polar solution
Aqueous: brown
Non polar: purple/solid black
State and explain the trend in reducing ability of the halide ions (4)
Going down the group, halides become stronger reducing agents
This is because the ions become larger and lose their electrons more easily as the outer electrons are more shielded and further from the nucleus
Write an equation for the reaction of solid sodium fluoride and concentrated H2SO4
NaF(s) + H2SO4(aq) —> NaHSO4 (s) + HF(g)
What is observed in the reaction between solid sodium fluoride and concentrated H2SO4
steamy white fumes of hydrogen fluoride gas released
Write an equation for the reaction of solid sodium chloride and concentrated H2SO4
NaCl(s) + H2SO4(aq) —> NaHSO4(s) + HCl(g)
What is observed in the reaction between solid sodium chloride and concentrated H2SO4
steamy white fumes of hydrogen chloride gas released
Write an equation for the reaction of solid sodium bromide and concentrated H2SO4
NaBr(s) + H2SO4(aq) —> NaHSO4 (s) + HBr(g)
Write the overall equation for the reaction of bromide ions in HBr and concentrated H2SO4
2H+ + H2SO4 +2Br- —> SO2 + 2H2O + Br2
What is observed in the reaction between solid sodium bromide and concentrated H2SO4
acidic gas/colourless, choking fumes of SO2 gas
brown fumes of bromine gas
Name the products formed when solid sodium iodide reacts with concentrated sulfuric acid and state the observations you would make upon their formation
Steamy fumes of HI
Black solid of iodine, I2
Bad egg smell caused by hydrogen sulphide, H2S gas
Yellow solid of sulphur, S
Colourless solution of sodium hydrogen sulphate, NaHSO4
Write the overall equation for the reaction of iodide ions reducing sulphur from (+6) in H2SO4 to (+4) in SO2
2H+(aq) + 2I-(aq) + H2SO4(aq) —> I2(s) + SO2(g) + 2H2O(l)
Write the overall equation for the reaction of iodide ions reducing sulphur from (+6) in H2SO4 to (0) in S
6H+(aq) + H2SO4(aq) + 6I- (aq) —> S(s) + 4H2O(l) + 3I2(s)
Write the overall equation for the reaction of iodide ions reducing sulphur from (+6) in H2SO4 to (-2) in H2S
8H+(aq) + H2SO4(aq) + 8I-(aq) —> H2S(g) + 4H2O(l) + 4I2(s)
Why is dilute nitric acid added before the silver nitrate?
Why not HCl?
To remove any carbonate and hydroxide ions which may be present in the sample which could form Ag2CO3. This is a white precipitate which would give a false positive
HCl would add Cl - ions giving a false positive
Describe the test for halide ions
Add nitric acid then silver nitrate
Add dilute ammonia to the mixture
Add concentrated ammonia to the mixture
Observation with fluoride ions with silver nitrate
No visible change
Observation with chloride ions with silver nitrate
White precipitate forms
AgCl
Observation with bromide ions with silver nitrate
Cream precipitate forms
AgBr
Observation with iodide ions with silver nitrate
Yellow precipitate forms
AgI
Observation with chloride ions with dilute ammonia
White precipitate dissolves
Observation with bromide ions with dilute ammonia
Cream precipitate remains
Observation with iodide ions with dilute ammonia
Yellow precipitate remains
Observation with chloride ions with concentrated ammonia
White precipitate dissolves
Observation with bromide ions with concentrated ammonia
Cream precipitate dissolves
Observation with iodide ions with concentrated ammonia
Yellow precipitate remains
Equation for reaction of chlorine with water
Cl2(g) + H2O(l) —> HClO(aq) + HCl(aq)
What is disproportionation?
Same species is both oxidised and reduced
Equation for reaction of chlorine with water in bring sunlight
2Cl2(g) + 2H2O(l) —> 4HCl(aq) + O2(g)
Equation for reaction of sodium chlorate with water
NaClO(s) + H2O —> Na+(aq) + OH-(aq) + HClO(aq)
Equation for reaction of chlorine with cold, dilute, aqueous NaOH
Cl2(g) + 2NaOH(aq) —> NaClO(aq) + NaCl(aq) + H2O(l)
What type of reaction occurs between sodium halide and sulfuric acid?
Acid-base reaction
Outline a test for ammonium ions.
Add sodium hydroxide solution to the sample and warm it
If the resultant gas turns damp red litmus paper blue it indicates ammonium ions were present in the initial sample
Outline a test for hydroxide ions
Universal indicator will turn dark blue or purple in the presence of hydroxide ions.
Outline a test for carbonate ions.
Add a dilute acid to the sample
Bubble the resultant gas through limewater
If it turns cloudy it indicates that carbonate ions were present in the initial sample
Even though chlorine is toxic, why do we add it to swimming pools?
Adding chlorine to swimming pools kills bacteria
The health benefits of adding very small amounts of chlorine to water outweigh the risks.
Give a common use of sodium hypochlorite.
Sodium hypochlorite is often used as a disinfectant as it kills bacteria.
