Difficult stuff Flashcards
Pale pink trans element ions
Mn^2+ and Co^2+
Lilac trans element ions
Ti^2+ and V^2+
Purple trans element ions
Ti^3+ and MnO^4+
Green trans element ions
V^3+ and Cr^3+ ad Ni^2+ and MnO4^2-
Pale green trans element ions
Fe^2+
Pale blue trans element ions
Cu^2+
Blue trans element ions
VO^2+ and Cr^2+
Yellow trans element ions
VO2^+1 and Fe^3+ and CrO4^2-
Orange trans element ions
Cr2O7^2-
Precipitation rct of Cu^2+
Cu2+ (aq) + 2OH- –> Cu(OH)2 (s)
Blue solution –> Blue ppt
Precipitation rct of Mn^2+
Mn^2+ (aq) + 2OH- –> Mn(OH)2 (s)
Pale pink solution –> Pale brown ppt
Precipitation rct of Fe^2+
Fe^2+ (aq) + 2OH- –> Fe(OH)2 (s)
green solution –> green ppt
Precipitation rct of Fe^3+
Fe^3+ (aq) + 3OH- –> Fe(OH)3 (s)
yellow solution –> brown ppt
Reaction of Cu(H20)6^2+ (aq) with NH3
Cu(H20)6^2+ (aq) + 4NH3 (aq) –> Cu(NH3)4(H2O)2^2+ + 4H2O
Blue solution –> Dark blue solution
Reaction of Co(H20)6^2+ (aq) with NH3
Co(H20)6^2+ (aq) + 6NH3(aq) –> Co(NH3)6^2+ + 6H2O
Reaction of Cu(H2O)6^2+ with Cl-
Cu(H2O)6^2+ + 4Cl- —> CuCl4^2- + 6H2O
Blue solution –> Yellow/Green solution
Reaction of Cu(H2O)6^2+ with Cl-
Co(H2O)6^2+ + 4Cl- –> CoCl4^2+ + 6H2O
Pink solution to blue solution
Reaction of Cu and Cr with excess NH3
Cr(OH)3(H2O)3 (s) + 6NH3 (aq) –> Cr(NH3)6^3+ + 3H2O (l) + 3OH- (aq) Purple solution
Cu(OH)2(H2O)4 (s) + 4NH3 (aq) —> Cu(NH3)4(H2O)2 + 2H2O (l) + 2OH-(aq) Deep blue solution
Precipitation rct of Cr3+
Cr(H20)6^3+ + 3OH- –> Cr(OH)3(H2O)3 (s) + 3H2O (l)
Green solution –> Grey-green ppt
How is Fe2+ oxidised to Fe3+
MnO4^- + 8H+ + 5Fe2+ –> Mn^2+ + 4H2O + 5Fe^3+
Pale green –> Yellow
How is Fe3+ reduced to Fe2+
2I- + 2Fe^3+ –> 2Fe^2+ + I2
Yellow –> Pale green
How is Cr^3+ oxidised to CrO4^2-
3H2O2 + 2Cr(OH)6^3- –> 2OH- + 2CrO4 ^2- + 8H2O
Dark green to yellow
Warm H2O2 in alkaline conditions
Oxygen is reduced and Chromium is oxidised
How is Cr2O7^2- reduced to Cr^3+
Cr2O7^2- + 14H+ +3Zn –> 2Cr^3+ + 7H2O + 3Zn^2+
Orange to Green
Acidified zinc
ZInc is oxidised and chromium is reduced
How can trans elements be identified
- Add sodium hydroxide (aq) Cu^2+ = blue ppt Fe^2+ = green ppt Fe^3+ = Yellow/orange ppt Mn^2+ = pink/buff ppt Cr^3+ =grey/green ppt
How do you calculate a pH of a strong acid
- conc of H+ is same as conc of acid
How to calculate pH of water
- Use Kw and square root as [H+] = [OH-]
How to calculate pH of strong base
- Work out [H+] using kw expression (Kw = 1x10-14
How to calculate pH of a weak acid
- use Ka = [H+] + [A-] / [HA]
- assume: [H+] = [A-] and [HA] (initial) = [HA] (eqm)
- simplify Ka to Ka = [H+] ^2/HA
How to calculate pH of diluted strong acid
- [H+] = [H+] (old) x old volume/new volume
- pH = -log(H+)
How to calculate pH of diluted strong alkali
- [OH-] = [OH-] (old) x old vol/new vol
- [H+] = Kw / [OH-]
- pH = -log(H+)
How to calculate the pH of buffer solution
Ka = [H+] [A-] / [HA]
Assume the initial conc of the acid remained constant as the amount that has dissociated is small
Rearrange to [H+] = Ka x [HA] / [A-]
How to calculate change in ph of buffer on addition of small amount of acid/alkali
- Work out moles of acid and salt in initial buffer solution
- Work out moles of acid and salt after addition of acid/alkali by taking away/adding conc of acid/alkali to initial moles of acid and salt
- Sub in values into Ka expression
