Q: Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[\text{conjugate base}]}{[\text{weak acid}]} \right)$$

Q: Which weak acid-conjugate base pair would be most suitable for preparing a buffer with a pH of $$4.74$$?

Cyanic acid and Potassium cyanate ($$K_a = 4.9 \times 10$$^{-4}$$)

Question 1

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[	ext{conjugate base}]}{[	ext{weak acid}]} ight)$$

Question 2

A buffer solution is made by mixing 0.500 M $$\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2$$ and 0.450 M $$\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_3^+. If$$ $$K_b$$ for $$\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2 is$$ $$5.6 	imes 10$$^{-10}$$, what is the pH of the solution?

Accepted Answer

$$9.45$$

Question 3

Which weak acid-conjugate base pair would be most suitable for preparing a buffer with a pH of $$4.74$$?

Accepted Answer

Cyanic acid and Potassium cyanate ($$K_a = 4.9 	imes 10$$^{-4}$$)

Question 4

If a buffer solution is diluted to one-fourth of its original concentration, what will happen to the pH?

Accepted Answer

The pH will increase

Question 5

What is the buffer component concentration ratio $$\dfrac{[\mathrm{Pr}^-]}{[\mathrm{HPr}]} of a $$buffer that has a pH of $$5.11$$? ($$K_a of $$HPr is $$1.30 	imes 10$$^{-5}$$)

Accepted Answer

$$8.13$$

Question 6

Over what pH range will an oxalic acid ($$\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4) / $$sodium oxalate ($$\mathrm{NaHC}_2\mathrm{O}_4) $$buffer work most effectively? ($$K_a of $$oxalic acid is $$6.0 	imes 10$$^{-2}$$)

Accepted Answer

$$1.00 - 3.00$$

Question 7

A solution is prepared by mixing $$2.75 M $$sodium phenolate ($$\mathrm{C}_6\mathrm{H}_5\mathrm{ONa}) $$and $$3.0 M $$phenol ($$\mathrm{C}_6\mathrm{H}_5\mathrm{OH}). If$$ $$K_a of $$phenol is $$1.0 	imes 10$$^{-10}$$, what is the pH of the solution?

Accepted Answer

$$9.32$$

Question 8

Which of the following best describes the role of a buffer in a biological system?

Accepted Answer

It maintains a relatively constant pH when small amounts of acid or base are added.

Question 9

How many grams of sodium acetate ($$\mathrm{NaCH}_3\mathrm{CO}_2$$, MW = $$82.05 g/$$mol) are needed to prepare $$3.2 L of a $$buffer with $$0.065 M $$acetic acid ($$\mathrm{CH}_3\mathrm{CO}_2\mathrm{H}$$, MW = $$60.05 g/$$mol) and a pH of $$4.58$$? ($$K_a of $$acetic acid is $$1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$16.99 g$$

Question 10

A buffer is made from $$0.20 M $$acetic acid and $$0.20 M $$sodium acetate. If $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$4.74$$

Question 11

Which of the following statements about buffer capacity is correct?

Accepted Answer

Buffer capacity increases as the concentrations of the acid and its conjugate base increase.

Question 12

A hospital needs to prepare a buffer solution with a pH of $$7.4$$ for intravenous fluids. Which acid/base pair would be most appropriate?

Accepted Answer

Dihydrogen phosphate and hydrogen phosphate ($$pK_a \approx 7.2)$$

Question 13

If the ratio $$\dfrac{[	ext{conjugate base}]}{[	ext{weak acid}]} in a $$buffer is $$1$$, what is the relationship between pH and $$pK_a$$?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a$$

Question 14

A buffer solution is prepared using $$0.10 M $$ammonia ($$\mathrm{NH}_3) $$and $$0.10 M $$ammonium chloride ($$\mathrm{NH}_4\mathrm{Cl}). If$$ $$K_b$$ for ammonia is $$1.8 	imes 10$$^{-5}$$, what is the pOH of the solution?

Accepted Answer

$$4.74$$

Question 15

Which of the following will NOT affect the pH of a buffer solution?

Accepted Answer

Adding a small amount of water to dilute the buffer

Buffer Solutions and pH Calculations in GOB Chemistry

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