Chapter 8 Flashcards
What is the reactivity trend as you down group 2, and why?
- Reactivity increases down the group
- The first and second ionisation energies decrease down the group
How do group 2 metals react with water? How does this change as you go down the group?
- They form a hydroxide and hydrogen, and dissolve
- The reaction becomes increasingly vigorous as you go down the group
How do group 2 metals react with dilute acid? How does this change as you go down the group?
- They form a salt and hydrogen
- The reaction becomes more vigorous as you go down the group
What happens when group 2 oxides react with water? Include equations.
- An alkaline solution of the metal hydroxide is formed, and hydroxide ions are released
- MO(s) + H2O(l) -> M2+(aq) + 2OH-(aq)
- When the solution becomes saturated, they start to form a precipitate
- M2+(aq) + 2OH-(aq) -> M(OH)2(s)
What trends are there in there in solubility as you go down group 2?
- It increases (more hydroxide ions are released)
- Alkalinity increases
- pH increases
What are 2 uses of group 2 metals? Give examples.
- Calcium hydroxide is used to neutralise acidic soil
- Magnesium hydroxide and calcium carbonate treat indigestion as they are used as antacids (they neutralise stomach acid)
What is the trend with boiling points in group 7? Explain it.
- They increase down the group
- This is because there are more electrons, so there are more London forces, and so more energy is required to overcome them
How does reactivity change down group 7, and how can you tell?
- Reactivity decreases down the group
- You can tell through displacement reactions; if a halogen displaces a halide, the solution changes colour to the colour of the displaced halogen; the halogen (not the halide) colours the solution
What colours do halogens turn in water?
- Chlorine: pale green
- Bromine: orange
- Iodine: brown
How can the colours of halogens in solutions be told apart more easily? How does this work?
- In water, bromine is orange and iodine is brown, which can be difficult to tell apart
- Cyclohexane can therefore be added as since it’s a non-polar solvent, the halogens dissolve more readily in it
- In cyclohexane, iodine is violet while chlorine and bromine remain the same colour
Why does reactivity decrease down group 7?
- The atomic radius increases
- Electron shielding increases
- Less nuclear attraction
- As it becomes harder to form a 1- ion, reactivity decreases
What is disproportionation? Required.
- A redox reaction in which the same element is both oxidised and reduced simultaneously
What are 2 reactions where disproportionation occurs?
- The reaction of chlorine with water
- The reaction of chlorine with cold, dilute sodium hydroxide
What is the equation for the reaction of chlorine and water?
- Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)
What is the reaction of chlorine with water useful for?
- The purification of water
- This is done by chloric (I) acid (HClO) and chlorate (I) ions (ClO-) as they kill bacteria
What is the equation for the reaction of chlorine and cold, dilute sodium hydroxide?
- Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
What is the reaction of chlorine with sodium hydroxide useful for?
- Making bleach
What is the benefit of the use of chlorine in water treatment?
- It kills bacteria
What are the risks of using chlorine in water treatment?
- Chlorine gas is toxic
- It can form chlorinated hydrocarbons, which may cause cancer
What is the difference between qualitative and quantitative analysis?
- Qualitative analysis relies on simple observations
- Quantitative analysis yields numerical results
How are carbonate ions tested for?
- They are reacted with H+ ions to form carbon dioxide
- This is done by reacting a carbonate with an acid (usually nitric)
- Bubble the gas produced through limewater, which will cause it to turn cloudy (carbon dioxide reacts with calcium hydroxide to form water and calcium carbonate, which is a white precipitate)
How are sulfate ions tested for?
- When they react with Ba2+, they form a white precipitate
- Barium ions are usually added as barium nitrate
- Most sulfates are soluble in water, but barium sulfate is very insoluble
How are halides tested for?
- Halides react with silver ions to form precipitates
- Silver nitrate is added to a solution containing halides
- Chloride, bromide and iodide ions form white, cream and yellow precipitates
- You then use aqueous ammonia to tell them further apart (as the colours can look similar); chloride ions are soluble in dilute ammonia, bromide ions are soluble in concentrated ammonia, and iodide ions are insoluble in ammonia
What is the correct order to test for anions in, and why?
- Carbonate, sulfate and halide
- Only carbonates form gas when reacted with acid, so since there is no possibility of a false result, this one goes first
- Barium carbonate is also a white precipitate, so you have to do the carbonate test first and ensure there is no carbonate present
- Silver carbonate and silver sulfate are both precipitates, so the halide test must be carried out last
How do you test a mixture of anions?
- You use nitric acid (so you’re not adding sulfate or chloride ions) in the carbonate test, and keep adding it until all of the bubbling stops
- In the sulfate test, add an excess of barium nitrate (don’t use barium chloride), then filter the solid out
How do you test for ammonium? Include an equation.
- You react it with aqueous sodium hydroxide and heat the mixture, which releases ammonia gas
- You can test for ammonia with damp pH indicator paper, which turns blue in its presence
- NH4+ + OH- -> NH3 + H2O
