Chapter 8 - Reactivity Trends Flashcards
What is a reducing agent?
A species that donates its electrons to another species, reducing it.
Which group are reducing agents commonly found?
Group 2
Explain the trend in reactivity down group 2.
As you go down the group, atomic radius and shielding increases, so there is less attraction and ionisation energies decrease. Therefore it’s easier to lose electrons and reactivity increases.
What are the products of a group 2 element reacting with water?
Metal hydroxide + Hydrogen
What is the product of a group 2 element reacting with oxygen?
Metal oxide
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? Give an equation.
Increases pH of acidic soils.
Ca(OH)2(s) + 2H+(aq) —> Ca2+(aq) + 2H2O(l)
How are group 2 compounds used in medicine?
Used in indigestion tablets as antacids.
What is another name for group 2?
Alkaline earth metals
Explain the trend in boiling point down group 7.
Elements have more electrons as you go down the group, so there are increased London forces. So more energy is needed to overcome the intermolecular forces, so boiling point increases.
Explain the trend in reactivity down group 7.
As you go down the group, atomic radius increases, and there are more inner shells, causing shielding to increase. This causes nuclear attraction to decrease, so it is harder to capture an electron from another species. Therefore reactivity decreases.
What do more reacting halogens do to less reactive halide ions?
Displaces them
What can displacement reactions be used to identify?
Which halide is present in the solution
What compound is used to test for halides?
Aqueous silver nitrate
What is disproportionation?
A redox reaction in which the same element is both oxidised and reduced.
Describe the test for carbonates.
Add unknown compound to test tube and add dilute nitric acid.
If bubbling is seen, then it is a carbonate.
To make sure, bubble the gas through limewater and it will turn milky, indicating a positive test.
Describe the test for sulfates.
Add aqueous barium ions to unknown solution. If white precipitate forms, then sulfate is present.
Describe the test for halides.
Add aqueous silver nitrate to solution. Chloride - white precipitate Bromide - cream precipitate Iodide - yellow precipitate To make sure, add aqueous ammonia. If insoluble, then it is iodide. If soluble, then it is chloride or bromide.
What is the correct order for these anion halide tests?
Carbonate test, sulfate test, halide test
Why is the correct order for anion tests carbonate, sulfate, halide?
Carbonate first because it is the only test that produces bubbles, so it can be ruled out first.
Sulfate second because carbonate will also produce white precipitate, so it needs to be done after carbonate test.
Halide last because carbonates and sulfates are both insoluble in water and will both form precipitates in this test, so they need to be ruled out first.
Describe the test for cations (ammonium ion).
- Add sodium hydroxide to solution to provide hydroxide ions.
- Heat test tube to remove ammonia gas
- Smell for ammonia, and red litmus paper will turn blue
What are the benefits of chlorine use?
Disinfectant for water that kills all bacteria so it is safe to drink.
What are the risks of chlorine use?
Respiratory irritant
Toxic gas
Can cause cancer by formation of chlorinated hydrocarbons
What colours are the halogens in water?
Chlorine - pale green
Bromine - orange
Iodine - brown
What colours are the halogens in cyclohexane?
Chlorine - pale green
Bromine - orange
Iodine - violet
What is the trend in alkalinity of the solution formed when group 2 oxides are added to water?
Group 2 oxides react with water to form a metal hydroxide. Hydroxide ions in solution cause alkalinity.
Down group 2, solubility of the metal hydroxide increases, so pH and alkalinity also increase.
