Question

0.250g of phthalic acid is dissolved in 40.00cm^3 of 0.100 mol dm^-3 NaOH. It requires 11.80 cubic centimeters of 0.100 mol\dm^-3 HCL fo neutralisation( to phenolphthalein) The mole ratio in which phthalic acid reacts with sodium hydroxide ihn 1:2

(a) Calculate the moles of excess NaOH reacted with HCL
(b)Calculate the moles of phthalic acid used
(c) Calculate the molecular mass of phthalic acid

p.s-urgently need help to solve this before my lab today :'( (22.09.11)

Answer 1

Phthalic acid = H2T
H2T + 2NaOH ==> Na2T + 2H2O
(a1)moles NaOH initially = M x L = 0.1 x 0.004000 L = ??
(a2)moles HCl reacted = 0.0118 x 0.100M = ??
(a3)mole excess NaOH = moles NaOH initially-moles HCl (a2-a1)=a3
(b)moles H2T used = 1/2 moles NaOH used
(c)molar mass = 0.250g/moles H2T. I get something like 166. The actual molar mass is about 177.

Answer 2

hey thanx heaps for your help much appreciated :)



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