Chemistry Practical WAEC EXAM 2026

 In this post, I am going to show you how you can calculate the endpoint and concentration of acid in mole per dm³. so , if you are preparing to write WAEC 2026 chemistry practical exam, this post is for you. this year’s examination, you are going to titrate tetraoxosulphate (VI) acid and relative density(R.D) of the acid is given as 1.84 and its percent purity is 98% while volume of the acid to make up to 1000cm³ is 5.6cm³.

 Note:

R.D = 1.84

This means that for every  1cm³ of the acid contains 1.84g

So, 1000cm³ will be 1.84 x 1000 = 1840g

Now, we have the mass of the acid in 1000cm³  next:

 

Percentage Purity of the acid

98/100 x 1840  = 1803.2g of pure acid next

 

Concentration in mole of the acid

Mole = mass/molar mass

 

Mole = 1803.2/98 = 18.4 mole

Note : molar mass of H₂SO₄ is 98g/mole now , we can use dilution formula to find out the concentration in mole of the acid to be used in the titration.

                                              C₁V₁ = C₂V₂

C₁   =  18.4mole

V₁ = 5.6cm³

C₂  = unknown

V₂ = 1000cm³  then

                                              18.4 x5.6 =  1000 x C₂ =

                                          C₂ = 18.4 x 5.6/1000 = 0.103mol/dm³

Calculation of Endpoint of the Titration

Since the volume of pipette = 25  or 20 cm³ , we are using 25cm³

Concentration of NaOH in grams = 4g

The mole concentration  = 4/40  = 0.1mole per dm³

Mole concentration of the acid = 0.103mole per dm³

Volume of the acid  = Va unknown

      

                              CaVa/CbVb = a/b ( note : a and b = mole ratio of acid and base)

From the equation

H₂SO₄ + 2NaOH ----> Na₂SO₄  + 2H₂O

So

                        0.103 x Va/ 0.1 x 25  =1/2

                        Va = 0.1 x 25x2/0.103    = 12.13cm³    

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