A solution containing 4.2 g of KOH and Ca(OH)2 is neutralised by and a...
First of all, always remember that 1 equivalent of an acid always reacts with 1 equivalent of a base. It doesn’t matter which acid or base we’re taking.
Step 1: First let’s find the equivalent weights of KOH and Ca(OH)2
(a) KOH: Molar mass of KOH= 39 + 16 + 1 = 56. Valency factor of KOH = 1. So, equivalent weight of KOH = 56
(b) Ca(OH)2: Molar mass of Ca(OH)2= 40 + 2*(16+1) = 74. Valency factor of Ca(OH)2= 2. So, equivalent weight = 74/2 = 37
Step 2: We’ve been given 0.1 equivalent of acid. So, some of this will react with KOH and some will react with Ca(OH)2
Let the number of equivalents of acid that react with Ca(OH)2 = x. So, the number of equivalents of acid that react with KOH = 0.1 - x
Step 3: Let the mass of Ca(OH)2 = y, and so the mass of KOH= 4.2 -y
Step 4: Time for some math. 1 equivalent of acid will react with 1 equivalent of Ca(OH)2. That means 1 equivalent of acid will react with 37 g of Ca(OH)2.
So, by proportion, 1/37 = x/y
or, y = 37x
Similarly for KOH, 1/56= 0.1-x/4.2-y
Putting value of y as 37 x and cross multiplying
4.2–37x=5.6–56x
x= 0.0737
So, y = 37x = 37*0.0737 = 2.73 g (approx)
so, 4.2 - y = 4.2 - 2.73 = 1.47 g (approx)
So, mass of Ca(OH)2 = 2.73 g and mass of KOH= 1.47g