Inorganic chemistry Flashcards
Why ionisation energy decreases down group 2
- more electron shielding
- larger atomic radius
- less attraction between nucleus and outer shell
Why reactivity increases down group 2
- metals lose electrons in reactions
- shielding and atomic radius increase
- it becomes easier to lose electrons
Group 2 reaction with oxygen
Group 2 + oxygen»_space; group 2 oxide
Group 2 reaction with chlorine
Group 2 + chlorine»_space; group 2 chloride
Group 2 reaction with water
Group 2 + water»_space; group 2 hydroxide + hydrogen
Group 2 oxide reaction with water
Group 2 oxide + water»_space; group 2 hydroxide
Group 2 oxide / hydroxide reaction with dilute acid
Group 2 oxide / hydroxide + acid»_space; group 2 salt + water
Solubility of group 2 sulfates down the group
Decreases (remember insoluble barium sulfate precipitate from the test for sulfates)
Solubility of group 2 hydroxides down the group
Increases (magnesium hydroxide can be used as medicine because of its low solubility)
Explain the trend in thermal stability of metal carbonates and nitrates
- thermal stability decreases as polarising power of the cation increases (size decrease, charge increase)
- as the anion’s electrons are distorted, its covalent bonds become weaker
How flame tests work
- electrons absorb energy from the flame
- they move into a higher energy level
- as they move back down, they release the energy as specific wavelengths of light
How to do a flame test
- dip nichrome wire into concentrated HCl then into the solid sample
- hold the wire over a flame and observe the colour
How to test thermal stability of nitrates
- heat the nitrate
- normal decomposition gives no observation
- greater decomposition (so a less stable nitrate) produces brown fumes (nitrogen dioxide)
How to test thermal stability of carbonates
- weigh the sample of carbonate
- heat it
- weigh the sample again
- if mass decreased, decomposition occurred (so a less stable carbonate)
Lithium flame
Red
Sodium flame
Yellow
Potassium flame
Lilac
Rubidium flame
Purple
Caesium flame
Blue
Calcium flame
Orange
Strontium flame
Crimson
Barium flame
Apple green
Why boiling point increases down group 7
- amount of electrons increases
- london forces become stronger
Why electronegativity decreases down group 7
- electron shielding increases
- atomic radius increases
- less attraction between nucleus and bonding electron pairs
Why reactivity decreases down group 7
- halogens want to gain electrons in a reaction
- shielding and atomic radius increase
- it becomes harder to gain electrons
Displacement redox reactions of halogens
A more reactive halogen displaces and oxidises a less reactive halide ion
Why is cyclohexane added to identify halogens?
- it is hard to tell the difference between halogens in aqueous solution
- halogens are more soluble in organic solvent and the colour difference is clearer
Chlorine in cyclohexane
Pale green (same as in water)
Bromine in cyclohexane
Orange (same as in water)
Iodine in cyclohexane
Purple (changed from brown in water)
Disproportionation of chlorine with water
- chlorine + water»_space; hydrochloric acid + chloric(i) acid
- Cl reduced from 0 to -1 in HCl
- Cl oxidised from 0 to +1 in HClO
- reaction is used to disinfect water
Reduction of halogens with metal
- metal + halogen»_space; metal halide
- halogen reduced from 0 to -1 in the metal halide
Disproportionation of chlorine with cold, dilute sodium hydroxide
- chlorine + sodium hydroxide»_space; sodium chloride + sodium chlorate(i) + water
- Cl reduced from 0 to -1 in NaCl
- Cl oxidised from 0 to +1 in NaClO
- reaction is used to make bleach (NaClO)
Disproportionation of chlorine with hot, concentrated sodium hydroxide
- chlorine + sodium hydroxide»_space; sodium chloride + sodium chlorate(v) + water
- Cl reduced from 0 to -1 in NaCl
- Cl oxidised from 0 to +5 in NaClO3
- reaction is used to make weed killer (NaClO3)
Oxidation number of sulfur in sulfuric acid
+6
Oxidation number of sulfur in sulfur dioxide
+4
Oxidation number of sulfur in hydrogen sulfide
-2
Reactions of halide ions with sulfuric acid
Halide ions act as reducing agents for sulfur:
Chloride - sulfur dioxide produced
Bromide - sulfur dioxide and sulfur
Iodide - sulfur dioxide, sulfur, and hydrogen sulfide
Reducing power increases down the group
Test for chloride ions
Add silver nitrate - white precipitate
Add dilute ammonia - solid dissolves
Test for bromide ions
Add silver nitrate - cream precipitate
Add dilute ammonia - solid does not dissolve
Add concentrated ammonia - dissolves
Test for iodide ions
Add silver nitrate - yellow precipitate
Add dilute ammonia - solid does not dissolve
Add concentrated ammonia - still does not dissolve
Reactions of hydrogen halides
- hydrogen halide + water»_space; acidic solution
- hydrogen halide + ammonia»_space; ammonium halide salt
Test for carbonate / hydrogencarbonate ions
- react with dilute acid
- colourless gas (carbon dioxide) is produced
- white precipitate when gas is bubbled through limewater
Test for sulfate ions
- react with acidified barium chloride
- white precipitate (barium sulfate) produced
Test for ammonium ions
- heat with dilute sodium hydroxide
- colourless gas (ammonia) is produced
- gas causes damp red litmus paper to turn blue
