melly713

WOW! AWesome avatar =) =) =) good luck on your exams =) =)

Read the posts from bottom to top. Separated it because of word limit.

In part iii you again consider the mole ratio of Cu(2+) ions and I2 (not I- ions) which is 2 Cu ions to 1 I2.

So u multiply the ans of c(ii) by 2

IN part iv you use n = cv So u just calculated n (moles) in the previous part. and v (volume) is 25 cm3 or 0.025 dm3. Use these to calculate c (concentration)

So in part ii it asks "how many moles of I2 reacted with the Na2S2O3 run from the burette."

So u see The mole ratio of Na2So3(2-) ions and Iodine (I2) are in 2:1

So the moles u calculated in part i you just divide it by 2 according to the ratio.

For your first paper 9701_s09_qp_31

In part c(i) you would have calculated moles of Sodium Thiosulphate (Na2S2O3).

The 2 equations in part ii are ionic equations meaning only the ions that reacted are given.
For this you just combine the 2 equations. Reactants together and products together.

The S2O3(2-) ions are actually of the Sodium thiosulpate.