posted by linda .
I dissolved 4g of solid NaOH in 200mL of water. I converted grams of NaOH to moles by 4g/40g/moles= 0.1moles.
I calculated the concentration of NaOH by 0.1/(200mL/1000L)= 0.5 moles/L.
I now have to record the expected mass of benzoic acid required to react in stoichiometric proportion with 20mL of the NaOH solution. Not sure about this part.
First, you write the equation.
PhCOOH + NaOH ==> PhCOONa + H2O
So you used 20 mL of 0.5 mole/L which means you used 0.50 x 0.02 = 0.01 mole NaOH.
Since the reaction is a 1:1 mole ratio, it will require 0.01 mole benzoic acid. How many grams is 0.01 mole benzoic acid? You know benzoic acid is about 122 g/mol so 0.01 moles would be about 1.22 g. You can do it exactly.