How do you calculate equivalent weight of lactic acid?

First have a copy of the Periodic Table, showing atomic masses alongside you.

Next the name is 2-hydroxypropanoic acid. Its formula is CH3CH(OH)COOH

From the formula you will notice that there are :-

3 x carbon

6 x hydrogen

3 x oxygen.

Reading the periodic table

The Atomic Mass of carbon is '12' . So 3 x 12 = 36

The atomic mass of hydrogen is '1' . so 6 x 1 = 6

The atomic mass of oxygen is '16'. so 3 x 16 = 48

Adding

36 + 6 + 48 = 90 The relative molecular mass of lactic acis.

NB Equivalent weight is an old fashioned name for moles.

Hence moles = mass(g) / Mr

or

Equivalent weight = mass(g) /Mr

So 1 mole = 90g / 90 = 1

or

1 equivalent weight = 90 g/ 90 = 1

2 equivalednt weights = 180g / 90 = 2

et. seq.,