MODULE 3: Reactivity Trends Flashcards
How are group 2 metals and halogens related?
Group 2 have 2 electrons in their outer shell- two more than halogens have
What is a reaction common with group 2 metals?
Redox reaction
What is a reducing agent?
A substance that reduces another species
What is an oxidising agent?
A substance that oxidises another species
What products are formed when metals react with dilute acids?
Salt and hydrogen
In group 2, how does reactivity change?
Increases
In group 2, how does first ionisation energy change?
Decreases
In group 2, why does reactivity and first ionisation energy change?
Due to decreased attraction between the nucleus and outer shell electrons (increased atomic radius) and increased shielding
How does the solubility of group 2 metal hydroxides change down the group?
Increases down the group
How can you measure solubility of a group 2 metal hydroxide?
Add spatula of anhydrous metal oxide to water, observe for solid at the bottom and test pH (pH increases down the group)
What is calcium hydroxide used for?
Agriculture; increases pH of acidic soils (neutralises acid)
What is magnesium hydroxide used for?
Medicine; neutralise stomach acid for indigestion (milk of magnesia)
How do halogens exist at RTP?
Diatomic gas molecules (F2, Cl2)
How does fluorine exist at RTP?
Pale yellow gas
How does chlorine exist at RTP?
Pale green gas
How does bromine exist at RTP?
Red-brown liquid
How does iodine exist at RTP?
Shiny grey-black solid
What is a displacement reaction?
An atom or a set of atoms is displaced by another atom in a molecule
How can displacement reactions show reactivity in halogens?
A solution of the halogen is added to aqueous solutions of other halide ions (halogens with a negative charge)
How does reactivity change in halogens?
Decreases moving down the group
How can you tell that a halogen displacement has occured?
Added non-polar organic solvent (cyclohexane) to mix solution, if displacement has occurred colour change should take place; the solution will turn the colour of the halogen being displaced
What are the trends in group 17 (halogens)?
Down the group; stronger London forces, increased boiling and melting point, decreased reactivity
What is disproportionation?
A redox reaction where the same element has been both oxidised and reduced
Name 2 examples of disproportionation reactions
Chlorine with water and chlorine with cold, dilute sodium hydroxide
What are the benefits and risks of using chlorine in day-to-day life?
Benefits; ensure clean water, prevents devastating disease like cholera and typhoid
Risks; toxic, can bond with organic hydrocarbons from decaying vegetables to form chlorinated hydrocarbons (which may cause cancer)
What tests can you do for anions?
Carbonate test, sulfate test, halide test
What order should you carry out the tests for anions and why?
Carbonate, sulfate and halide; rule out possibilities of presence of other anions (think about the chemistry happening within the test)
Describe the carbonate test
Carbonates react with acids to form carbon dioxide gas, so; add nitric acid to solution being tested, if you see bubbles the unknown compound could be a carbonate but to be sure it is carbon dioxide gas the gas must be bubbled through lime water (if cloudy = carbon dioxide present)
Describe the sulfate test
Barium sulfate is insoluble, so; aqueous barium ions (usually as aqueous barium chloride or barium nitrate) are added to the sample being tested, if sulfate is present a white precipitate will form
Describe the halide test
Silver halide is insoluble, so; add aqueous silver nitrate, if precipitate forms halide is present (white = chloride, cream = bromide, yellow = iodide), then add aqueous ammonia to test solubility of precipitate (chloride = dilute ammonia, bromide = concentrate ammonia, iodide = insoluble)
Why is aqueous ammonia used in a halide test?
To easily distinguish the precipitate made as the colours are similar
How would you continue to test for anions if there were a mixture of ions?
Add excess and filter off precipitate (and use barium nitrate for sulfate test so no chloride ions are added to the solution for halide test)
What is the test for cations?
Ammonium ion test
Describe the ammonium ion test
Aqueous sodium hydroxide is added to solution, if ammonium is present ammonia gas will be produced, mixture is warmed to release ammonia gas, test with moist pH indicator paper (blue = ammonia present)
