1. Redox calculations 1

2. Steps….. Find the number of moles of the substance you know the most about Multiply by the stoichiometric ratio to get the number of moles of the other substance Convert to mass or concentration or whatever of that substance

3. Try this on your own! Two iron tablets total mass 1.30 g were dissolved in dil sulphuric acid and made up to 100 cm 3 10 cm 3 of this solution needed 12.00 cm 3 of a 0.005 mol dm -3 solution of manganate to produce a pink tinge. Find the % by mass of iron in the tablets.

4. Answer = 12.9% n MnO 4 - = 12.00x0.005 = 6.0x10 -5 1000 n Fe 2+ =6.0x10 -5 x5= 3.0x10 -4 (in 10cm 3 ) n Fe 2+ = 3.0x10 -4 x10= 3.0x10 -3 (in 100cm 3 ) mass Fe = 3.0x10 -3 x55.8=0.1674g % Fe=0.1674x100= 12.88 1.3

5. 100 cm 3 of bleach was diluted up to 1000 cm 3 with water and 10 cm 3 of this was placed in a conical flask with an excess of KI. The iodine produced was titrated with 0.1 mol dm -3 sodium thiosulphate solution giving a mean titre of 26.60 cm 3 1.Write a half equation for iodide to iodine 2.Write a half equation for thiosulphate to tetrathionate 3.Work out the moles of thiosulphate used in the titre 4.Convert this into the moles of iodine 5.1 mole of bleach needs 2moles of electrons to react with iodide so you can work out how many moles of bleach there were in the 10 cm 3 6.Convert this into a concentration of bleach in the original.

6. 1.2I- → I 2 + 2e 2.2S 2 O 3 2- → S 4 O 6 2- + 2e- 3.n thiosulphate= 0.1 x 26.6/1000 =2.6x10 -3 4.n iodine= 2.6x10 -3 x ½ = 1.3x10 -3 5.n bleach= 1.3x10 -3 x 1000/10= 0.13 (in the 1000cm 3 ) then x10 (for the reverse of the dilution) c=0.13x10 =1.3 moldm -3

7. Stochiometric relationships across equations. Given 2A+3B→4C 3C+3D→9E If 1 mole of A is reacted, what is the maximum number of moles of E that will form?

8. Answer 6

9. Given 5A+ B→C 3C+D→5E+F E+G→2H If 0.5 moles of A react what is the maximum number of moles of H that will form?

10. 0.333moles

11. N 2 +3H 2 →2NH 3 4NH 3 +5O 2 →4NO+6H 2 O Given these two equations what volume of nitrogen reacted to make 0.5moles of Nitrogen Oxide ( assume complete conversions)

12. Answer 6dm 3