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Chemistry Titration/Moles Multiple Choice Question [PLEASE CHECK]

Hi,
This is a multiple choice question that I found and I wanted to check that my working was indeed correct.

When 0.28g of a basic oxide, MO, is reacted with 250cm3 of 0.05moldm–3 hydrochloricacid the excess acid required 50cm3 of 0.05moldm–3 sodium hydroxide solution forneutralisation. Which one of the following is the relative atomic mass of M?
A 12
B 28
C 40
D 56

My working for this question
First, I want to find out how many moles of HCl were excess.
I know that 50cm³or 0.05dm³ were excess and the concentration of NaOH (Sodium Hydroxide) needed was 0.05moldm^-3 so I did the following

0.05 x 0.05 = 0.0025 moles of NaOH were used.

The equation of this reaction is
HCl + NaOH → NaCl + H₂O
Where the NaOH and the HCl are in a 1:1 ratio, so the excess of HCl is also 0.025 moles.

I then referred back to the original question.
Since 250cm³ or 0.25dm³ of HCl was used of concentration 0.05moldm^-3, I needed to calculate the total number of moles involved in the reaction.

This was

\frac{0.25}{0.05} = 0.0125

moles.
I previously calculated the excess to being 0.0025 moles, so the total used were 0.0125 - 0.0025 moles = 0.01 moles.

I thought that MO was meant to be M^₂O due to the oxygen's oxidation number.

The equation of the reaction showed the following
M₂O + 2HCl → 2MCl + H₂O
The M₂O and the HCl are in a 1:2 ratio, so the M₂O moles used were

\frac{0.01}{2}

= 0.005

I also knew of the mass of the M₂O to being 0.28, so to calculate the M_r, I did

\frac{0.28}{0.005}

= 56.

Then I subtracted 16 to find the M_r of the Metal to be 40 (Calcium).
My answer was C.

Is this correct?

UPDATE - THE ANSWER HAS BEEN FOUND.

(edited 8 years ago)

Reply 1

mega.white

i think that MO in the question may indicate that M has an oxidation number of +2, like MgO and CaO.
in this case, the equation will be
MO + 2HCl --> MCl2 + H2O
but the mole ratio u used between HCl and MO is correct, C should be right
i might be wrong idk😂

Posted from TSR Mobile

(edited 8 years ago)

Reply 2

nwmyname