Question

0.3M CH₃COONa solutions ka for acetic acid
is 2x10^-5 calculate its pH.​

Answer 1

Answer:

Buffer pH calculations – theoretical calculation of a buffer solution

6.4.1 Calculations involving a buffer made from a weak acid and its salt with a strong base.

Consider the mixture is made from a monobasic weak acid HA and an alkali metal salt M+A–

e.g. A = CH3COO, M = K or Na

it is reasonable to assume for simple approximate calculations that ..

[A–(aq)] = [salt(aq)] since salt fully ionised and M+ is a spectator ion, and

[HA(aq)]equilib., = [HA(aq)]initial since little of the weak acid is ionised.

Therefore the weak acid Ka expression is ...

(i) Ka =

[H+(aq)] [A–(aq)]

––––––––––––––––––––––––– mol dm–3

[HA(aq)]

becomes

(ii) Ka =

[H+(aq)] [salt(aq)]

–––––––––––––––––––––––––– mol dm–3

[acid(aq)]

therefore: [H+(aq)] = Ka [acid(aq)] / [salt(aq)] mol dm–3, and taking –log10 of both sides gives

(iii) pHbuffer = –log10(Ka x [acid(aq)] / [salt(aq)])

or (iv) pHbuffer = pKa + –log10([acid(aq)] / [salt(aq)])

or (v) pHbuffer = pKa + log10([salt(aq)] / [acid(aq)])

which is how the equation is usually quoted, sometimes called the Henderson Equation.

Note: For a given conjugate pair (HA and A–), the pH of the buffer is determined by the acid/salt ratio, though the more concentrated the buffer, the greater its capacity to neutralise larger amounts of added/formed in a reaction medium.

Explanation:

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Additional information ❤

How do you find the pH of a buffer solution with Ka?

To calculate the specific pH of a given buffer, you need to use the Henderson-Hasselbalch equation for acidic buffers: "pH = pKa + log10([A-]/[HA])," where Ka is the "dissociation constant" for the weak acid, [A-] is the concentration of conjugate base and [HA] is the concentration of the weak acid.

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What is the pH of a 0.2 M solution of sodium acetate?

pH 4.0 (0.2 M Sodium Acetate Solution): Weigh 27.20 g of Sodium Acetate Trihydrate into a one liter volumetric flask.

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