Titration calculation questions (urgent help needed)

[aerialsprite]

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Could someone please help me with either of these two questions?

1) Pthalic acid is a weak diprotic acid for which we can write the formual as H2(C8H4O4). Potassium hydrogen phtalate KH(C8H4)4) is a good primary standard for standardising alkali solutions. It contains one acidic hydrgoen per formual unit. 0.917g potassium hydrogen phtalate was dissolved in water and titrated with approximately 0.2 mol/L sodium hydroxide solution; 27.2 mL hydroxide solution was needed to reach the end point. Calculate the molatrity of the hydroxide solution.

2) 'Cloudy ammonia' is often used in the home as a cleaning agent. To determine the concentration of ammonia in the solution, a chemist first accurately diluted 25mL (by pipette) to 500 mL (volumetric flask) then titrated 25Ml (by pipette) of the dilute solution with 0.151 mol/L nitric acid solution; it required 27.2 mL. Calculate the molarity of the original ammonia solution.

(ref: conquering chem p 155 q17 and 19)

[Jumbo Cactuar]

H(C8H4O4)- + OH- -> C8H4O4 2- + H20

For KH(C8H4O4);
m = 0.917 g
M = 204.2 g/mol
n = 0.00449 mol

For NaOH;
n = 1/1 * 0.00449 mol
V = 0.0272 L
c = 0.00449/0.0272 = 0.165 M

[aerialsprite]

What does it mean when it says it has "one acidic hydrogen per fomulat unit"?

[Jumbo Cactuar]

NH3 + HNO3 -> NH4+ + NO3-

For HNO3;
c = 0.151 M
V = 0.0272 L
n = 0.151 * 0.0272 = 0.00411 mol

For diluted NH3;
n =1/1 * 0.00411 mol
V = 0.025 L
c = 0.00411/0.025 = 0.164 M
dillution factor is 500/25 = 20

For undiluted NH3;
c = 0.164 * 20 = 3.29 M

[Jumbo Cactuar]

It means it is monoprotic.

[Dreamerish*~]

Jumbo, you are really the chemistry king.

[Jumbo Cactuar]

Might as well be bored and productive!

[aerialsprite]

Wow. Thanks - I think I get it now ^^

[Jumbo Cactuar]

Kind of on topic!

http://www.newscientist.com/article.ns?id=dn7440