Chapter 8 - Reactivity Trends Flashcards
Group 2, The halogens and Quantitative analysis.
What is a reducing agent?
A species that donates its electrons to another species, thereby reducing that species
Which group are reducing agents commonly found?
Group 2
What (and why) is the trend in reactivity down group 2?
• Reactivity increases
• Greater atomic radius, more electron shielding, less attraction to the nucleus
• Easier to lose electrons and form bonds
What is the general equation for a group 2 element reacted with water?
Metal + Water → Metal hydroxide + Hydrogen
What is the general equation of a group 2 element reacted with oxygen?
Metal + Oxygen → Metal oxide
What is the general equation for a group 2 oxide reacted with water?
Metal oxide + Water → Metal hydroxide
What (and why) is the trend of solubility down group 2?
• Solubility increases
• Down group 2, metal ions become larger and so the attraction between ions in the solid lattice decreases
• So polar solvents can attract ions in lattice easier and dissolve the solid
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?
To increase the pH of acidic soils
Ca(OH)2 + 2[H]+ -> [Ca]2+ + 2H2O
How are group 2 compounds used in medicine?
Used in indigestion tablets such as antacids, often a suspension of a metal hydroxide in water
What is another name for group 2?
Alkaline Earth Metals
What is another name for group 7?
Halogens
What (and why) is the trend in boiling point down group 7?
• Boiling point increases
• Atomic size increases (more electrons)
• Greater ability to form London forces
• Requiring more energy to overcome and thus higher boiling points
What (and why) is the trend in reactivity down group 7?
• Reactivity decreases
• Atomic size increases
• Therefore a greater effect of electron shielding and weaker nuclear attraction
• So it’s harder to gain an electron and react
What do more reactive halogens do to less reactive halide ions?
Displace them
What can displacement reactions be used to identify?
Which halide is present in a solution
What substance is used to test for halides?
Silver nitrate solution, AgNO3(aq)
How can the results for a halide test be further tested?
• Check solubility in ammonia solution
• AgCl is soluble in dilute ammonia
• AgBr is soluble in concentrated ammonia
• AgI is insoluble in both dilute and concentrated ammonia
What is disproportionation?
A redox reaction in which the same element is both oxidised and reduced
Describe the test for carbonates:
• Add dilute nitric acid to the testing solution
• Effervescence indicates a possible carbonate
• To confirm, bubble the gas through lime water, to which it will turn cloudy
Describe the test for sulfates:
• Add aqueous barium nitrate to the testing solution
• A white precipitate will form
Halide test results:
• Chlorine - White precipitate
• Bromine - Cream precipitate
• Iodine - Yellow precipitate
What is the correct order for anion tests?
• Carbonate
• Sulfate
• Halide
Why is there a correct order for anion tests?
• Carbonates also form a white precipitate in the sulfate test but not vice versa
• Carbonates and sulfates form precipitates with silver nitrate
Describe the test for ammonium ions:
• Add aqueous sodium hydroxide to the testing solution
• Ammonia gas is produced
• Gas can be detected with moist indicator paper as it will turn blue (paper must be moist to form the base NH4OH)
What are the halide solutions’ colours when added to cylcohexane?
• Chlorine - Pale green
• Bromine - Orange
• Iodine - Violet
Table for halogen-halide displacement reactions:
What is the reaction (and what type) between chlorine and cold, dilute, aqueous sodium hydroxide?
Cl2(aq) + 2NaOH(aq) → NaClO(aq) + NaCl(aq) + H2O(l)
• Disproportionation reaction, as chlorine is both oxidised and reduced
