[imsushi92]

1. The problem statement, all variables and given/known data
Do not understand the question.


2. My Lab Results

Topic : Volumetric analysis - Acid base
purpose : To determine the exact concentration of a mineral acid, HXO4, and to determine the relative atomic mass of the element X.
Materials : KA1 is a mineral acid, HXO4
KA2 is a solution containing 1.70g of OH- ions per dm3.
Phenolphthalein as indicator.

Procedure : Pipette 25.0cm3 of KA2 into the titration flask. Add two or three drops pf phenolphthalein indicator and titrate this solution with KA1. Record your readings in the table.
Repeat the titration as many times as you think necessary to achieve accurate results.

My result up.

My problems is here the question.
a. Calculate the concentration, in mol dm-3, of solution KA2
b. Write a balanced ionic equation for the reaction between solution KA1 and the solution KA2.
c. Calculate the concentration, in mol dm-3, of mineral acid HX04 in solution KA1.
d. If the concentration of mineral acid HXO4 in solution KA2 is 20.1g dm-3, calculate the relative molecular mass of HXO4.
e. Using the answer to (d), determine the relative atomic mass of the element X.
f. Suggest and identity for element X.

Please guide me. Thx

In question (a) i tried with
mol=mass/mm
=1.7/17 = 0.1mol

mol=mv/1000
0.1=m(250)/1000
m=0.4
concentration of KA2 is 0.4moldm-3?

[Schrödinger]

I don't know if this level of accuracy is acceptable by the standards of your experiment, but it looks like there is a lot of difference between the volumes of KA1 in the 3 trials.

The calculations are quite simple.

a. moles = mass/molecular mass.
So moles of OH^- = 1.7/17 = 0.1 moles
We have 1.7 grams OH^- in 1 dm³. So concentration of OH^- = 0.1mol dm^-3. It is from this solution that you are taking an aliquot of 25cm³. The concentration remains unchanged. It doesn't depend on how much you are pipetting out. It has already been determined.

c. Since you have a monoacidic base and a monobasic acid, you can use M₁V₁ = M₂V₂

M₁ = molarity of KA1
V₁ = volume of KA2
M₂ = molarity of KA2
V₂ = volume of KA2

[imsushi92]

(C)
M₁V₁=M₂V₂
M₁(27.3)=0.1x25
M₁=0.09158mol dm^-3
For (d),

What does it mean by concentration of mineral acid HXO4 in solution KA2 is 20.1g dm-3?
I try to do it..

M₁V₁=M₂V₂
M₁(27.3)=20.1x(27.3+25)
M₁=38.51g mol^-1

how do i continue?

[sjb]

I'm not 100% sure what your calculations here are meant to show.

But, for instance, if you have 0.09158 mol dm^-3, and 20.1 g dm^-3 in the exact same solution, what is the molecular weight of the compound?

[imsushi92]

but it states 20.1g dm^-3 of KA1 in KA2. does that means mass of KA1 over Volume of KA1+KA2?