Practice Buffer in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A buffer is a solution that resists large changes in pH when small amounts of acid or base are added.

A buffer acts like a chemical shock absorber for pH.

Showing a random 20 of 50 problems.

Example 1

medium
Why does diluting a buffer with water barely change its pH?

Example 2

medium
Make a buffer at pH 5.04 using pKa=4.74pK_a = 4.74. What ratio [A−]/[HA][A^-]/[HA] is required?

Example 3

challenge
How many moles of NaANaA must be added to 1.0 L of 0.20 M HAHA (pKa=4.70pK_a=4.70) to reach pH 5.00? (Assume volume constant.)

Example 4

easy
Does a buffer work equally well at any pH?

Example 5

medium
A buffer is 0.300.30 M NH3NH_3 and 0.300.30 M NH4+NH_4^+. Given pKa(NH4+)=9.25pK_a(NH_4^+)=9.25, find pH.

Example 6

easy
Is a solution of pure HClHCl a buffer?

Example 7

hard
Adding 0.10 mol0.10\text{ mol} HCl to 1.0 L1.0\text{ L} pure water (initial pH 7) drops pH to about 1.0. The same 0.10 mol0.10\text{ mol} HCl in a 1.0 L1.0\text{ L} buffer (0.500.50 M HA / 0.500.50 M A−A^-, pKa=4.74pK_a = 4.74) gives what new pH?

Example 8

medium
Use Henderson-Hasselbalch to find pH of a buffer with [A−]=[HA][A^-]=[HA] and pKa=4.76pK_a=4.76.

Example 9

easy
In a buffer, what neutralizes added base (OH−OH^-)?

Example 10

medium
A formic-acid buffer has pKa=3.75pK_a = 3.75, [A−]=[HA]=0.20 M[A^-] = [HA] = 0.20\text{ M}. Find pH.

Example 11

medium
After adding 0.01 mol OH- to a buffer with 0.10 mol HA and 0.10 mol A-, find the new mole ratio A−/HAA^-/HA.

Example 12

challenge
Compare buffer capacity of (a) 0.50 M HA / 0.50 M A- and (b) 0.05 M HA / 0.05 M A-, same pKa. Which resists pH change more and why?

Example 13

easy
Use Henderson-Hasselbalch: [A−]=0.10 M[A^-] = 0.10\text{ M}, [HA]=0.10 M[HA] = 0.10\text{ M}, pKa=3.50pK_a = 3.50. Find pH.

Example 14

easy
Which pair forms a buffer: (a) HCl + NaCl, (b) CH3COOHCH_3COOH + CH3COONaCH_3COONa?

Example 15

easy
In a buffer made from CH3COOHCH_3COOH and CH3COO−CH_3COO^-, which component neutralizes added strong acid?

Example 16

hard
A 1.0 L1.0\text{ L} buffer has 0.20 mol0.20\text{ mol} HAHA (pKa=4.74pK_a = 4.74) and 0.20 mol0.20\text{ mol} A−A^-. After adding 0.30 mol0.30\text{ mol} HCl, is the buffer still functioning, and what is the approximate pH?

Example 17

hard
A buffer contains 0.40 M0.40\text{ M} phosphate as H2PO4−H_2PO_4^- (pKa2=7.21pK_{a2} = 7.21) and 0.40 M0.40\text{ M} HPO42−HPO_4^{2-}. After adding 0.10 mol0.10\text{ mol} HCl to 1.0 L1.0\text{ L}, find the new pH.

Example 18

easy
Which pair forms a buffer: (a) HNO3+NaNO3HNO_3 + NaNO_3, (b) HF+NaFHF + NaF?

Example 19

easy
Adding a buffer to pure water at pH 7 — does the buffer's pH always become 7?

Example 20

medium
Which buffer best holds pH 7.2: acetate (pKa=4.7pK_a=4.7), phosphate (pKa=7.2pK_a=7.2), or ammonia (pKa=9.2pK_a=9.2)?
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