Calculation of equivalent mass of acid

Given:
- Volume of caustic soda solution (V1) = 25 ml
- Normality of caustic soda solution (N1) = 10
- Volume of acid solution (V2) = 20 ml
- Concentration of acid solution (C2) = 7.875 g/L

Formula:
- Normality = (Weight of solute / Equivalent weight of solute) * Volume of solution in litres

Calculation:
- We know that the caustic soda is a strong base, and it reacts with an acid to form salt and water.
- The equation for the reaction is as follows:
NaOH + HCl → NaCl + H2O
- From the above equation, we can see that one mole of NaOH reacts with one mole of HCl.
- Therefore, the equivalent weight of NaOH is equal to its molecular weight, which is 40.
- Now, we can calculate the number of equivalents of NaOH in 25 ml of 10 N solution as follows:
Number of equivalents of NaOH = Normality * Volume of solution in litres
= 10 * 25 / 1000
= 0.25 equivalents
- Since the reaction is a neutralization reaction, the number of equivalents of acid in the 20 ml of acid solution is equal to the number of equivalents of NaOH.
- Therefore, we can calculate the equivalent weight of the acid as follows:
Equivalent weight of acid = Weight of acid / Number of equivalents of acid
- We know that the weight of the acid in 20 ml of solution is equal to its concentration multiplied by the volume of solution in litres, which is:
Weight of acid = Concentration * Volume of solution in litres
= 7.875 * 20 / 1000
= 0.1575 grams
- Therefore, the equivalent weight of the acid is:
Equivalent weight of acid = 0.1575 / 0.25
= 0.63 grams/equivalent

Conclusion:
The equivalent weight of the acid in the given solution is 0.63 grams/equivalent.