CH 142 Buffer Solutions 1. How do you prepare a buffer solution? Worksheet: Acid

Question

CH 142 Buffer Solutions 1. How do you prepare a buffer solution? Worksheet: Acid Base Equilibrium-Ch 14 Give two examples. 2. For each of the following, identify the conjugate base of the weak acid necessary to produce a buffer solution. (i) hydrofluoric acid (ii) acetic acid (CH COOH) (ii) formic acid (HCOOH) (iv) phosphoric acid (HyPO) (v) bicarbonate ion (HCOs) 3. For each of the following, identify the conjugate acid of the weak base necessary to produce a buffer solution. (i) ammonia t eby amie CHNib) What is the pH of a buffer solution that is 1.0S M acetic acid (CH,COOH) and 0.55 M sodium acetate (CH,COONa)? The K, for acetic acid is 1.8x 10 4. What is the pH of a buffer solution that consists of 0.12 M lactic acid and 0.10 M sodium lactate? [K, (lactic acid) -1.38 x 10 5. 6. What is the ratio of [HCOs [H CO] in blood of pH-7.4? [pK,i (carbonic acid)- 6.1 at physiological temperature) 7. ) Select the weak acid which would be suitable to prepare a buffer solution with a pH value of 5.2 (A) phthalic acid (pK, 2.9) (C) acetic acid (pK,-4.7) (B) lactic acid (pK,-3.9) (D) boric acid (pk, 9.2) ould be the pH range of the buffer solution prepared starting from each of the above? Sketch the titration curves for each of the following. Plot pH on y-axis, and Volume of titrant on a-axis. Clearly indicate whether the equivalence point occurs at pH -7, above 7, or below 7 (i) A strong base is titrated with a strong acid. 1. (ii) A strong acid is titrated with a strong base. (ii) A weak acid is titrated with a strong base. (iv) A weak base is titrated with a strong acid. What is an acid-buse indicator? Give two examples of common acid-base indicators

Explanation / Answer

1. A buffer solution is an aqueous solution that contains a weak acid and its conjugate base or a weak base and its conjugate acid.

When a small amount of strong acid or base is added to a buffer’s solution pH changes will be very small. Buffer solution is used to prevent any change in the pH of a solution that means of keeping pH at a nearly constant value.

To prepare a buffer solution of a specific pH, first prepare a solution with a weak acid and its conjugate base by dissolving the acid form of the buffer in water to get the final volume. Then, measure the pH of the solution. Using a strong base like NaOH, pH can be adjusted.

Similarly, the buffer is made with a base and its conjugate acid, the pH can be adjusted using a strong acid like HCl.

There are couple of other methods also available to prepare buffer solutions.

For example, A buffer of weak acid, carbonic acid (H2CO3) and and its conjugate base, bicarbonate (HCO3) is needed in blood plasma to maintain a pH=7.4.

2. Corresponding conjugate base of the weak acids are:

(1) F- (2) CH3COO- (3) HCOO- (4) H2PO4- (5) CO32-

3. Corresponding conjugate acid of the given bases are :

(1) NH4+ (2) CH3NH3+

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