Chapter 8 - Reactivity trends Flashcards
What is another name for group 2 ?
Alkaline earth metals
What is a reducing agent ?
- A species that donates its electrons to another species, thereby reducing that species
- It is known as an electron donor
Which group are reducing agents commonly found ?
Group 2
What is the trend in reactivity down group 2 ?
Reactivity increases as you go down group 2
Explain why reactivity increases as you go down group 2
- As you go down the group the atomic radius and shielding effect increase so ionisation energies decrease
- Therefore it is easier to lose electrons and they get more reactive down the group
What are the products of a group 2 element reacting with water ?
Metal hydroxide and hydrogen
What is the product of a group 2 element reacting with oxygen ?
Metal oxide
What is the trend of solubility like down group 2 ?
Solubility increases as you go down the group
Explain why solubility increases as you go down group 2
As you go down the group the solution has a greater concentration of hydroxide ions
Given that group 2 oxides, hydroxides and carbonates neutralise acids, what can they be referred to as ?
Bases
Given that most group 2 oxides, hydroxides and carbonates are soluble in water, what are they also besides bases ?
Alkalis
What is the use of calcium hydroxide in agriculture ?
- Increases the pH of acidic soils
- Ca(OH)(2) + 2H+ —> Ca2+ + 2H(2)O
How are group 2 compounds used in medicine ?
- Used as antacids in indigestion tablets
- They are often a suspension of a metal hydroxide in water
- Milk of magnesia is an example of this
What is the trend in boiling point down group 7 ?
The boiling point down the group increases
Explain why the boiling point increases down group 7
- There are more electrons as you go down the group
- Therefore stronger london forces are present
- More energy is required to break these intermolecular forces
- Therefore the boiling point increases down the group
What is the trend in reactivity down group 7 ?
Down the group the reactivity decreases
Explain why reactivity decreases as you go down group 7
- The atomic radius increases
- More inner shells so there is a greater shielding effect
- Nuclear attraction therefore decreases and it is harder to gain an electron
- This leads to reactivity decreasing down the groups
You have to remember that group 7 elements need to gain an electron, not lose one
What do more reactive halogens do to less reactive halogens ?
More reactive halogens displace less reactive halogen ions
What can chlorine displace ?
Iodine and bromine
What can bromine displace ?
Iodine only
What can iodine displace ?
It can’t displace chlorine or bromine
What can displacement reactions be used to identify ?
It allows you to identify which halide is present in the solution
Which compound is used to test for halides ?
Silver nitrate solution, AgNO3
How can the results for a halide test be further tested ?
For solubility in ammonia solution
What is disproportionation ?
It is a redox reaction in which the same element is both oxidised and reduced
Describe the test for carbonates
- Carbonates react with acids to form carbon dioxide gas
- Add dilute nitric acid (HNO3) to the testing solution
- If bubbles are observed a carbonate could be present
- To prove it is carbon dioxide, bubble it through lime water, a white precipitate will be formed
Describe the test for sulphates
- Aqueous barium ions are added to the solution.
- If a white precipitate forms, there is a sulphate.
- This is because barium sulphate BaSO4 is formed
In the halide tests, what happens to chloride with silver nitrate and then ammonia ?
- Silver nitrate - white precipitate
- Ammonia - soluble in dilute ammonia
In the halide tests, what happens to bromine with silver nitrate and then ammonia ?
- Silver nitrate - cream precipitate
- Ammonia - soluble in concentrated ammonia
In halide tests, what happens to iodine with silver nitrate and then ammonia ?
- Silver nitrate - yellow precipitate
- Ammonia - insoluble in concentrated ammonia
What is the correct order for the anion tests ?
- Carbonate test
- Sulphate test
- Halide test
Why is the correct order for anion tests carbonate, sulphate, halide ?
- Carbonates also form a white precipitate in the sulphate test but not vice versa.
- Carbonates and sulphates form precipitates with silver nitrate
Describe the test for ammonium ions
- Add aqueous NaOH to the solution
- Ammonia gas is produced
- Can be detected with moist indicator paper, the indicator paper will turn blue
What colour is chlorine in water ?
Pale green
What colour is bromine in water ?
Orange
What colour is iodine in water ?
Brown
What colour is chlorine in cyclohexane ?
Pale green
What colours is bromine in cyclohexane ?
Orange
What colour is iodine in cyclohexane ?
Violet
Describe the test for halides
- Add aqueous silver nitrate (AgNO3) to an aqueous solution or halide
- A silver halide precipitate will be formed
- Add aqueous ammonia to test the solubility of the precipitate
What is the ionic equation for testing for ammonium ions ?
NH4+ + OH- —> NH3 + H2O
What is the ionic equation for testing for halide ions ?
Ag + + X- —> AgX
What is the ionic equation for testing for sulphate ions ?
Ba + + SO42- —> Ba2SO4
