# chemistry

If you add 5.0 mL of 0.50 M NaOH solution to 20.0 mL to Buffer C, what is the change in pH of
the buffer?
(where buffer C is 8.203 g sodium acetate with 100.0 mL of 1.0 M acetic acid)

I have calculated the pH of buffer C to be 4.74.
Now what? =\

1. 👍
2. 👎
3. 👁
1. NEVERMIND
I am a , I have figured this out

1. 👍
2. 👎
2. couple someone please still explain? and explain how the 4.74 pH was found? thanks

1. 👍
2. 👎
3. could someone please still explain? and explain how the 4.74 pH was found? thanks

1. 👍
2. 👎
4. pH = pKa + log ([A-]/[HA])
We ned to determine the concentration of the sodium acetate:
Molar mass CH3COONa = 82.0340 g/mol
Therefore you are adding 1mol CH3COOH per litre = 1.00M
pKa CH3COOH = 4.75
pH = 4.75 + log (1/1)
pH = 4.75 as you got - OK.

Question 2: If you add 5 ml of 0.50M NaOH solution to 20ml of the buffer, what is the change in pH?

The answer should be that the pH does not change very much - that is what a buffer solution is all about. I am sure that there is a simple way to make this calculation - but I do not know it. So let us try and do it from first principles:

You have a buffer solution that is 1.00M in CH3COOH and 1.00M in CH3COONa.
If you add some NaOH you react with the CH3COOH , reducing its concentration and increasing the concentration of CH3COONa

Mol CH3COOH in 20 mL of 1.00M = 20/1000*1 = 0.02mol CH3COOH
Mol CH3COONa in 20mL of 1.00M = 0.02mol CH2COONa
Mol NaOH in 5.0mL of 0.50M = 5/1000*0.5 = 0.0025mol NaOH
The NaOH reacts with the CH3COOH to form 0.0025 mol CH3COONa and 0.0025 mol CH3COOH is removed
You end up with
CH3COOH = 0.02mol - 0.0025 mol = 0.0175mol CH3COOH in 25mL total solution:
Molarity of CH3COOH = 0.0175/25*1000 = 0.70M CH3COOH
CH3COONa = 0.02mol + 0.0025mol = 0.0225 mol CH3COONa in 25mL total solution
Molarity of CH3COONa = 0.0225/25*1000 = 0.9M CH3COONa

pH = pKa + log([A-]/[HA])
pH = 4.75 + log( 0.9/0.7)
pH = 4.75 + log 1.286
pH = 4.75 + 0.11
pH = 4.86

1. 👍
2. 👎

## Similar Questions

1. ### Chemistry

Which of the following pairs would make a good buffer solution in an aqueous solution? A) H2SO4 and NaHSO4 B) Ca(NO3)2 and HNO3 C) HCl and NaCl D) HF and NaOH E) none of them I know the answer is D but I don't understand why. I

2. ### CHEMISTRY

HOW CAN U TELL IF HNO3 +KNO3 IS A BUFFER SOLUTION A buffer solution must contain a weak acid and its conjugate base OR a weak base and its conjugate acid. HNO3 is a strong base and KNO3 is the salt of a strong base (KOH) and a

3. ### Chemistry Help! Thank you :)

Assuming the final solution will be diluted to 1.00 , how much more should you add to achieve the desired pH? Information: Imagine that you are in chemistry lab and need to make 1.00 L of a solution with a pH of 2.80. You have in

4. ### chemistry

Consider a buffer solution consisting of CH3NH3Cl and CH3NH2. Which of the following statements are true concerning this solution? (Ka for CH3NH3+ = 2.3 x 10 -11). 1. A solution consisting of 0.1 M CH3NH3Cl and 0.1 M CH3NH2 would

1. ### Chemistry

A 500 mL buffer solution is 0.1 M benzoic acid and 0.10 M in sodium benzoate and has an initial pH of 4.19. What is the pH of the buffer upon addition of 0.010 mol of NaOH?

2. ### Chemistry

You are asked to prepare 500. mL of a 0.150 M acetate buffer at pH 5.00 using only pure acetic acid, 3.00 M NaOH, and water. Calculate the quantities needed for each of the following steps in the buffer preparation. 1. Add acetic

3. ### Chemistry

What would happen if you add HCl to a buffer solution of HNO2 and KNO2 and result. WHat about adding NaOH?

4. ### chemistry

2. A 350 mL buffer solution containing 0.15 M HF and 0.150 M NaF is reacted with sodium hydroxide. What mass of NaOH can this buffer neutralize before the pH rises above 4.0? If the same volume of buffer was 0.35 M in HF and 0.35

1. ### chemistry

Chemist needs a buffer with pH of 4.5. how many milliliters of pure CH3COOH (density;1.049g/ml) must be added to 500ml of 0.1M NaOH solution to obtain such a buffer?

2. ### Chemistry

You need to prepare 1.0 L of a buffer with a pH of 9.15. The concentration of the acid in the buffer needs to be 0.100 M. You have available to you a 1.00 M NH4Cl solution, a 6.00 M NaOH solution, and a 6.00 M HCl solution.

3. ### Quantitive Analysis

You are asked to prepare 500. mL of a 0.250 M acetate buffer at pH 4.90 using only pure acetic acid (MW=60.05 g/mol, pKa=4.76), 3.00 M NaOH, and water. Answer the following questions regarding the preparation of the buffer.

4. ### chemistry

Prepare 500mL of a 0.200 M acetate buffer at pH 4.90 using only pure acetic acid, 3M NaOH, and water. 1) Add acetic acid to ~400mL of water in a 500 mL beaker. How many grams of acetic acid are needed? 2)Add 3 M NaOH solution