Module 3 section 1 Flashcards
What is the name given to the group 2 metals
The alkaline earth metals
What happens to the reactivity as you go down group 2 and why?
The reactivity increases.
This is because the group 2 elements react by forming 2+ ions. Their ionisation energies decrease as you go down the group because the atomic radius increases/the number of shells increase so the shielding increases
Why are group 2 metals sometimes referred to as reducing agents?
Because they cause other elements to be reduced in a reaction, while the alkaline earth metals are oxidised
How do group 2 elements react with water
The water releases hydroxide ions,
When the solution becomes saturated, metal hydroxide precipitate is formed
Hydrogen (H2) is formed also
What happens to the solubility of group 2 metal HYDROXIDES as you go down the group?
The solubility increases
pH increases
Alkalinity increases
The alkalinity increases because they get more soluble, so more aqueous metal hydroxide is made, making the solution more alkaline
Why are group 2 compounds useful (in terms of reacting with other things)?
The group 2 oxides, hydroxides and carbonates are able to neutralise acids, amongst other things, making them useful
How and why are group 2 compounds used in agriculture?
Calcium hydroxide is added to fields as lime water by farmers to increase the pH of acidic soils.
The calcium hydroxide neutralises the acid, making water.
Ca(OH)2 (s) + 2H+ (aq) -> ca2+ (aq) + 2H2O(l)
How and why are group 2 compounds used in medicine?
They are often used as antacids for treating indigestion.
Magnesium and calcium carbonates are often main ingredients, and ‘milk of magnesia’ is a suspension of magnesium hydroxide in water.
Stomach acid is mainly hydrochloric acid, so you can form the equations easily for them.
What do the group 2 elements naturally occur as?
They don’t naturally occur in a pure state. They are found as compounds with things like carbonates.
What do the halogens naturally occur on earth as
They occur as stable halide ions (ie Cl- or Br-) dissolved in sea water or combined with sodium/potassium as solid deposits, eg in salt mines
They also exist as diatomic molecules eg Cl2, I2, etc
What happens to the boiling point of the halogens as you go down the group and how does this affect the states of each of the halogens at RTP?
The boiling point increases as you go down the group as there are more electrons and stronger London forces, resulting in intermolecular forces which are more difficult to break.
Fluorine (yellow) and chlorine (green) are gases at RTP,
Bromine is a red-brown liquid and iodine is a grey-black solid
(Astatine has never been seen)
Why are halogens referred to as oxidising agents?
Because they oxidise other species in a reaction
What happens to the reactivity as you go down group 7
The reactivity decreases
The atomic radius increases
Shielding increases
Less nuclear attraction to attract an electron
What is the rule for halogen displacement reactions? What colours are formed when cyclohexane is added?
A more reactive halogen will displace a less reactive one from a compound
In cyclohexane:
If chlorine is displaced, the solution is pale green
If bromine is displaced, the solution is orange
If iodine is displaced, the solution is violet
In water:
Chlorine - pale green
Bromine - orange
Iodine - brown
What is a disproportionation reaction?
When the same element is both oxidised and reduced in a redox reaction.
Give 2 examples of disproportionation reactions
Chlorine with water
Chlorine with cold, dilute sodium hydroxide
What happens when you react chlorine with water?
A disproportionation reaction takes place.
For each chlorine molecule, one atom is oxidised and the other reduced.
Chlorine + water -> chloric(I) acid (HClO) + hydrochloric acid
2 acids are produced, which kill bacteria in the water
What happens during the reaction between chlorine and cold, dilute aqueous sodium hydroxide?
A disproportionation reaction occurs
Chlorine + sodium hydroxide -> sodium chlorate(I) (NaClO) + sodium chloride + water
What are the benefits and risks of chlorine use?
Benefits:
Makes water fit to drink, kills off waterborne diseases.
Risks:
Chlorine is a toxic, irritant gas.
Can react with organic hydrocarbons to make chlorinated hydrocarbons - these are suspected of causing cancer.
What is quantitative analysis?
An analysis technique that produces numerical results
What is qualitative analysis
An analysis technique which relies on simple observations, e.g. gas bubbles, colour changes etc.
They can often be carried out quickly on a test tube scale.
What do you do to test for carbonate ions (CO3)2-?
Carbonates react with acids to form CO2
You add the nitric acid to test substance.
If you see bubbles, it COULD be a carbonate
To prove whether it is or not, you add limewater (calcium hydroxide).
If a carbonate is present, the solution should turn cloudy (milky)
How do you test for sulfate ions?
Barium nitrate or barium chloride is added.
If a sulfate is present, barium sulfate forms, which is visible as a white precipitate
How do you test for Halide ions?
Adding silver nitrate to your test solution will show whether halide ions are present or not:
Chloride ions: white precipitate
Bromide ions: cream precipitate
Iodide ions: yellow precipitate
