8.1 - 8.3 Flashcards
What ions do group 2 elements form when they react and how
- +2 ions by loosing 2 electrons
What is the electron configuration that all group 2 metals have
- s^2
What happens to the atomic radius as we go down group 2 and why
- IT INCREASES as there are extra shells added
What happens to ionisation energy as you go down group 2 and why
- IT DECREASES
SHIELDING: - extra shells so more shielding so a weak attraction between the nucleus and the electrons so easier to remove outer electrons
ATOMIC SIZE:
- the atom is radius also increases as the atom is getting bigger so the outer electron is further away from the nucleus which also weakens the attraction making the outer electron easier to remove
NUCLEAR CHARGE:
- there is an increase in the number of protons as you go down but shielding and atomic size override this
What happens to reactivity as you go down group 2 and why
- IT INCREASES
- because the atom gets larger and the electron is further away from the nucleus
- easier to remove so there are more reactive
- also there is more shielding
What are the products when group 2 elements react with water
- metal hydroxides + H2 (g)
How does Mg react with cold water
- slowly
How does Mg react with steam and what does it produce
- vigorously
- MgO
What are the products when group 2 elements react with oxygen
- metal oxides
What colour are group 2 oxides
- white solids
What product do you get when you react a group 2 oxide with water
- metal hydroxides
Describe the reactivity of MgO with water
- reacts very slowly
- hydroxide barely dissolves
What happens to the group 2 metal oxides reaction with water as you go down the group and why
- becomes more strongly alkaline
- as the hydroxides becomes more soluble
What are group 2 oxides and hydroxides
- bases
As group 2 oxides and hydroxides are bases what can they do
- neutralise acids
What is the neutralisation reaction of CaO with HCl
CaO(s) + 2HCl(aq) —> CaCl2(aq) + H2O(l)
What is the neutralisation reaction of Ca(OH) with HCl
Ca(OH)2 (s) + 2HCl(aq) —> CaCl2(aq) + 2H2O(l)
What are uses of group 2 compounds
- acidic soils= Ca(OH)2 (slaked lime) is used to neutralise acid is soils
- antacids= Mg(OH)2 is used to neutralise excess stomach acid
What is the ionic equation for neutralisation
H+(aq) + OH-(aq) —> H2O(l)
What are the halogens
- group 7 elements
What colour is fluorine and what state is it in
- pale yellow
- gas
What colour is chlorine and what state is it in
- pale green
- gas
What colour is bromine and what state is it in
- browny orange
- liquid
What colour is iodine and what state is it in
- grey
- solid
What are group 7 elements
- diatomic
State and describe the boiling point of group 7 as you go down
- INCREASES
- because the London forces increase due to increase in the atomic size and relative mass of the atom
State and describe the trend in electronegativity as you go down group 7
- DECREASES
- because the larger the distance between the nucleus and the electron the more shielding there is
What are displacement reactions
- where a halogen that is more reactive will displace a halogen that is less reactive
Describe what happens in a displacement reaction
1) add hexane do we see the colour change easily
2) halogen present will dissolve readily in the organic solvent which will form a layer above the aqueous layer
3) a coloured band will appear
What is the reaction when you react KCl with Cl2
- No reaction
- aqueous= colourless
- organic= colourless
- as chlorine water is colourless
What is the reaction when you react KBr and Cl2
- aqueous= yellow
- organic layer= orange
Cl2 + 2Br —> 2Cl- + Br2
What is the reaction when you react KI with Cl2
- aqueous= brown
- organic layer= purple
Cl2 + 2I- —> 2Cl- + I2
What is the reaction when you react KCl with Br2
- no reaction
- aqueous= yellow
- organic= orange
- as bromine water is orange
What is the reaction when you react KBr with Br2
- no reaction
- aqueous= yellow
- organic= orange
- as bromine water is orange
What is the reaction when you react KI with Br2
- aqueous= brown
- organic= purple
Br2 + 2I- —> 2Br- + I2
What is the reaction when you react KCl with I2
- no reaction
- aqueous= brown
- organic= purple
What is the reaction when you react KBr with I2
- no reaction
- aqueous= brown
- organic= purple
What is the reaction when you react KI with I2
- no reaction
- aqueous= brown
- organic= purple
How do we test for halide ions
- using silver nitrate and then confirm it with ammonia solution
Describe how we carry out the testing for halide experiment
1) put in unknown substance
2) add nitric acid (HNO3)
3) add silver nitrate solution
4) colour of precipitate helps you identity the halide ion
What colour precipitate to chloride ions form when silver nitrate is added
- white precipitate (silver chloride)
Ag+ (aq) + Cl- (aq) —> AgCl(s)
What colour precipitate to bromide ions form when silver nitrate is added
- cream precipitate (silver bromide)
Ag+ (aq) + Br- (aq) —> AgBr(s)
What colour precipitate to iodide ions form when silver nitrate is added
- yellow precipitate ( silver iodide)
Ag+(aq) + I- (aq) —> AgI(s)
Why do we add nitric acids before adding silver nitrate when testing for halides
- so it can react with any anions other than halide in your solution (e.g carbonates) as it could give a false result
What do we use to further test we do to confirm that we have the halide ions we think we have
- add ammonia solutions to the precipitates
What type of ammonia do you need to dissolve chlorine’s white precipitate
- DILUTE ammonia
What type of ammonia do you need to dissolve bromine’s cream precipitate
- CONCENTRATED ammonia
What happens when you use CONCENTRATED ammonia with iodine’s yellow precipitate
- the precipitate doesn’t dissolve it is INSOLUBLE
What type of reaction is done to make bleach made
- disproportionation reaction
What is a disproportionation reaction
- a reaction where an element is simultaneously oxidised and reduced
What is mixed to form bleach
- chlorine + sodium hydroxide
Write the equation for the formation of bleach and state how what has gone through disproportionation
2NaOH(aq) + Cl2(g) —> NaClO(aq) + NaCl(aq) + H2O(l)
*chlorine= 0 oxidised to +1 in NaClO
*chlorine= 0 reduced to -1 in NaCl
What is the uses of sodium chlorate(I)/bleach
- treating water
- bleaching paper and fabric
- cleaning agents (bleach)
What does adding chlorine to water do
- sterilises it by killing bacteria
What is water sterilisation useful for
- drinking water
- pools
Write the equation for water sterilisation
H2O (l) + Cl2(g) <=> HCl(aq) + HClO(aq)
What is the equation for water sterilisation an example of
- disproportionation of Cl
What are the advantages of chlorinating drinking water
- destroys microorganisms that cause disease
- long lasting so reduces bacteria build up
- reduces the growth of algae
What are the disadvantages of chlorinating drinking water
- toxic and irritates the respiratory system
- liquid chlorine causes severe chemical burns to the skin
- chlorine can react with organic compounds in the water to make chloroalkanes which are linked to causing cancer
- BENEFITS OUTWEIGH THE RISK
What is an ethical condition to chlorination drinking water
- occurs across the UK and we have no choice, some people object to this and claim it is forces medication
What are the two alternatives to chlorinating drinking water
- OZONE—> powerful oxidising agent that kills microorganisms but it has a short half life so treatment isn’t permanent and it is expensive to produce
- UV light—> damages DNA in microorganisms however it is ineffective in cloudy water and wont prevent water become contaminated further down the process
How do you test for ammonium compounds
- litmus paper
Describe how you would test for ammonium
1) add sodium hydroxide to unknown substance
2) gently heat
3) if ammonium is present ammonia gas will be produces
4) use damp red litmus paper
5) ammonia will turn it blue
How do you test for hydroxides
- using litmus paper
What is the observation if hydroxide ions are present
- turns red litmus paper blue
What is the problem with testing for hydroxide with only litmus paper
- it doesn’t confirm that you definitely have hydroxide as red litmus paper turns blue for any alkali
How do you test for carbonates
- use HCl
Describe how you test carbonates
1) HCL reacts with carbonates to make CO2 gas
2) this CO2 gas turns limewater cloudy
How do you test for sulfates
- uses HCl and BaCl (barium chloride)
Describe how you would test for sulfates
1) add HCl to remove any carbonates
2) add barium chloride
3) if sulfates are present a white precipitate forms
In what order do you test for ions
1) test from carbonates
2) test for sulfates
3) test for halides
