CHAPTER 8: Reactivity Trends Flashcards
What type of reaction is most common for Group 2 and Group 7 elements?
REDOX reactions
What name is given to GROUP 2 elements?
Alkaline metals
Group 2 elements are “reducing agents’ WHY?
They become OXIDISED and lose 2 electrons, meaning another element receives these electrons and becomes reduced.
When group 2 elements react with OXYGEN what is formed?
give general formula product
a METAL OXID
general formula = _O
When group 2 elements react with water what is formed? (give general formula of product)
an ALKALINE HYDROXIDE and hydrogen gas
general formula = _(OH)2
What is the reactivity trend of Group 2?
why?
Increases down the group.
Because the ionisation energies decrease down the group as the atomic radius increases and shielding increases so nuclear attraction for outer electron decreases.
What happens when OXIDES of group 2 elements react with water?
Hydroxide ions are released forming alkaline solutions.
What is the SOLUBILITY of HYDROXIDES trend of Group 2?
Solubility of group 2 hydroxides INCREASES down the group.
How can you measure solubility of hydroxides?
measure the PH.
More soluble = more hydroxide ions released so more alkaline.
How are group 2 compounds used in daily life?
AGRICULTURE = uses calcium hydroxide to increase the pH of acidic soils to form neutral water.
MEDICINE = used to neutralise acid indigestion.
What is the name given to group 7 elements?
Halogens
At room temperature in form do all halogens exist as?
DIATOMIC molecules
What is the boiling point trend of halogens? WHY?
Increases down the group.
More electrons so therefore stronger London Forces so more energy required to overcome the intermolecular forces.
What agent are halogens in a redox reaction?
OXIDISING agent
What reaction shows the reactivity of halogens?
displacement reaction
What happens during a halide displacement reaction?
You add a halogen solution to aqueous solutions of the other halides.
Whichever halogen is the more reactive will displace the halide from the solution and result in a colour change.
What is used to help distinguish the colours better during a displacement reaction? identify the colours.
CYCLOHEXANE
pale green = chlorine
orange = bromine
violet = iodine
What is the trend of reactivity of halogens? Why?
Decreases down the group because the atomic radius increases so more shielding therefore the nuclear attraction for an electron from another species is weaker
What is a DISPROPORTIONATION reaction?
a redox reaction where the same element is BOTH oxidised and reduced.
How are halogens used in daily life?
Chlorine is added to purify water.
It undergoes a disproportionation reaction and forms 2 acid products which kill the bacteria.
What is the disadvantage and advantage of using chlorine to purify water?
Chlorine is very toxic and can cause respiratory irritant however the advantage of clean water and preventing waterborne diseases outweighs this.
How can you test for carbonates?
React with acids and carbon dioxide gas should form.
-add dilute nitric acid and if u see bubbles, bubble the gas through lime water to see if it turns cloudy for the presence of CO2.
Why does lime water turn cloudy with carbon dioxide?
Carbon dioxide reacts to forms a fine white precipitate of calcium carbonate
How do you test for sulfates?
Most sulfates are soluble in water except BARIUM sulfate which is insoluble.
Add barium chloride/nitrate and a WHITE precipitate should form.
Why shouldn’t you use barium CHLORIDE for the sulfate test if you’re going to carry out a halide test afterwards?
Because the chloride ions would be detected.
How do you test for halide ions?
Halides are soluble in water except silver halides.
So aqueous silver nitrate is added and the solution should change colour.
Identify the colours for chloride, bromide and iodide when reacted with aqueous silver nitrate.
Chloride = White Bromide = Cream Iodide = Yellow
How else can you identify the halides if the colours aren’t very clear?
Add aqueous ammonia and test the solubility.
- Chlorine is soluble in DILUTE ammonia
- Bromide is soluble in CONC ammonia
- Iodide is insoluble in CONC ammonia
What is the sequence order of the qualitative test to identify a compound?
- Carbonate test - neither sulfate or halides produce gas with dilute acid.
(If you do see bubbles continue adding dilute nitric acid so all carbonate ions are removed) - Sulfate test - barium carbonate can form a white precipitate so if u carry it out after carbonate test, you can be sure that the precipitate is not because of carbonate.
(add EXCESS barium nitrate and filter out barium sulfate ) - Halide test - silver carbonate and silver sulfate form white precipitates so it is important halide test is last.
How can you test for ammonium ions?
Aqueous sodium hydroxide is added and if ammonium ions present, ammonia gas will be produced.
As ammonia is alkaline, you can test with litmus paper.
