# Chemistry f325 june 2010 question

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#1
The student diluted 25.0 cm3 of a solution of hydrogen peroxide with water and made the
solution up to 250.0 cm3. The student titrated 25.0 cm3 of this solution with 0.0200 mol dm–3
KMnO4 under acidic conditions. The volume of KMnO4(aq) required to reach the end-point was
23.45 cm3.
The overall equation for the reaction is given below.

2MnO4
– + 6H+ + 5H2O2 2Mn2+ + 8H2O + 5O2

• Calculate the concentration, in g dm–3, of the undiluted hydrogen peroxide solution.

I started by calculating the moles of KMnO4 23.45/1000 * 0.0200 = 4.69x10^-4

Then the moles of H2O2 in 25.0 by using the ratio 2:5 so moles of H2O2= 1.1725x10^-3 meaning there are 0.011725 moles in 250

How would you calculate the concentration in gdm-3? Don't understand this unit of concentraion?
0
6 years ago
#2
Hint = use moles equations,

hint 2 = use relative atomic mass
0
#3
(Original post by mattcandy3)
Hint = use moles equations,

hint 2 = use relative atomic mass
I don't understand because i thought to calculate concentration you just have to do moles/volume?
0
6 years ago
#4
multiply the mol dm-3 value by the relative molecular mass (Mr) of the chemical in solution to get the g dm-3 conc. value.
0
6 years ago
#5
Hi spaceboy, hope this helps.
0
#6
(Original post by James-King)
Hi spaceboy, hope this helps.
Thank you I understand now!
0
6 years ago
#7
(Original post by James-King)
Hi spaceboy, hope this helps.
you are not supposed to provide full answers to questions, just saying.
0
6 years ago
#8
in the mark scheme for this question it multiplies 40 by n(H2O2) and 34. I understand that 34 is the molecular mass but where does 40 come from?
1
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