# chemistry

posted by .

i need help solving this

Benzoic acid is a weak, monoprotic acid
(Ka = 6.3 × 10−5). Calculate the pH and the percent dissociation of each of the following solutions of benzoic acid. Then use Le Châtelier’s principle to explain the trend in percent dissociation of the acid as the solution becomes more dilute.
(a)1.0mol/L (b)0.10mol/L (c)0.01mol/L

• chemistry -

I'll show you how to do a and I expect you can do the rest but I can help you through them if necessary. Call benzoic acid HBz.
..........HBz ==> H^+ + Bz^-
I.........1.0M....0......0
C..........-x.....x......x
E........1.0-x....x......x

Then 6.3E-5 = (x)(x)/(1.0-x)
You can do the math but I get x = approx 8E-3M = (H^+) and convert that to pH.
Then %dissoc = [(H^+)/(HBz)]*100 = approx [(8E-3)/1]*100 = about 0.8%

You can do b and c. (H^+) becomes less as (HBz) becomes smaller ( as you would expect) BUT % dissoc increases. Why? Because HBz + H2O ==> H3O^+ + Bz^-
As H2O is added (making the solution more dilute) Le Chatelier's Principle says the reaction will shift to the right and of course that means it is dissociated more in more dilute solutions.

## Similar Questions

1. ### chemistry

A 0.25 mol/L solution of benzoic acid, KC7H5O2 and antiseptic also used as a food preservative, has a pH of 2.40. Calculate the Ka of benzoic acid at SATP How does the benzoic acid ionization go?
2. ### Chem

I am having the following problem: I need to calculate 2 Keq values based on the experiment that I conducted. I reacted 0.082 moles of benzoic acid with 0.618 moles of methanol and obtained 0.055 moles of methyl benzoate. When I calculate …
3. ### Chemistry

Calculate pH of a solution by mixing 15.0 mL of .50 M NaOH and 30.0 mL of .50 benzoic acid solution (benzoic acid is monoprotic, its dissociation constant is 6.5 x 10^ -5). I am not sure whether I am supposed to do it by acid-base …
4. ### Chemistry

You have 150 ml of a solution of benzoic acid in water estimated to contain about 5 g of acid. The distribution coefficient of benzoic acid in benzene and water is approx 10. Calculate the amount of acid that would be left in the water …
5. ### Chemistry

Benzoic acid (C6H5COOH)is a monoprotic weak acid with Ka=6.30*10^-5. What is the pH of a solution of benzoic acid that is 0.559M and has 2.25*10^-2M NaOH added?
6. ### Organic Chemistry

How to find the crude percent, percent recovery, and percent composition of benzoic acid and acetanilide if 2 grams of a mixture of benzoic acid and acetanilide was separated through separatory funnel and recrystallize and purified, …
7. ### Chemistry (Acid/Base)

Consider a solution made by mixing 100 mL of 2.0 M acetic acid (Ka= 1.8e-5) with 100 mL of 0.00020 M benzoic acid (Ka= 6.4e-5). How many moles of solid NaOH must be added to the solution so that half of the benzoic acid is protonated …
8. ### chemistry

Given 20g of benzoic acid contaminated with 0.4g of salicytic acid. 1)Determine the volume of hot water required to dissolve the mass of acid. 2)Calculate the mass of benzoic acid which participates when the solution is cooled to 20°C. …
9. ### organic chemistry

How to find the volume of hot water required to dissolve the mass of acid, if we have 20g of benzoic acid contaminated with 0.4g of salicylic acid?
10. ### Chemistry

References Chapter 17: EOC Assume you dissolve 0.178 g of the weak acid benzoic acid, , in enough water to make mL of solution and then titrate the solution with 0.187 M . ( for benzoic acid = .) What was the pH of the original benzoic …

More Similar Questions