Q: Which statement is true about buffers?

A buffer is most resistant to pH change when $$[\text{acid}] = [\text{conjugate base}].$$

Question 1

Which of the following best describes an Arrhenius base?

Accepted Answer

produces OH$$^- in $$water

Question 2

Which of the following species is amphoteric, meaning it can act as both an acid and a base?

Accepted Answer

H$$_2O$$

Question 3

What is the conjugate base of HNO$$_3$$?

Accepted Answer

NO$$_3^-$$

Question 4

Which of the following would you expect the concentration of acid to be nearly the same before and after dissociation?

Accepted Answer

A concentrated solution of a weak acid.

Question 5

Which of the following is true regarding the $$K_a$$ values of a diprotic acid?

Accepted Answer

$$K_{a1} \u003e K_{a2}$$

Question 6

Which of the following could act as a Lewis base?

Accepted Answer

Both H$$_2O $$and PCl$$_3$$

Question 7

What is the concentration of H$$_3O$^+ in a $$solution which has a concentration of OH$$^-$$ equal to $$8.9 	imes 10$$^{-9}$$ M? (K_w = 1.0$$ 	imes $$10^{-14})$$

Accepted Answer

$$1.1 	imes 10$$^{-6}$$ M

Question 8

The equilibrium constant $$K_c$$ for the reaction $$\mathrm{H_3PO_4 + NO_2$^- \rightleftharpoons H_2PO_4^- + $$HNO_2$$} is $$greater than 1. Which of the following is correct?

Accepted Answer

Phosphoric acid is a stronger acid than nitrous acid.

Question 9

Which of the following substances will give an aqueous solution with a pH closest to 7?

Accepted Answer

KNO$$_3$$

Question 10

Which statement is true about buffers?

Accepted Answer

A buffer is most resistant to pH change when $$[	ext{acid}] = [	ext{conjugate base}].$$

Question 11

What is the pH of a buffer that consists of 0.55 M HCOOH and 0.63 M HCOONa (p$$K_a of $$HCOOH = 3.74)?

Accepted Answer

3.80

Question 12

For a Na$$_2$$HPO$$_4/KH$_2PO$_4$$ buffer solution with pH 7.40, what is the buffer component concentration ratio $$\left( \frac{[	ext{base}]}{[	ext{acid}]} ight)$$? (For phosphoric acid $$K_{a1} = 7.2 	imes 10$$^{-3}$$, K$$_{a2} = 6.3 	imes $$10^{-8}$$, $$K_{a3} = 4.2 	imes 10$$^{-13}$$)

Accepted Answer

2.1

Question 13

The indicator thymolphthalein has $$K_a = 7.9 	imes 10$$^{-11}$$. Over what approximate pH range does it change color?

Accepted Answer

9.1 to 11.1

Question 14

Does any solid Cu(OH)$$_2$$ form when 0.075 g KOH is dissolved in 1.0 L of 1.0$$	imes10$^{-3} M Cu(NO$_3$$)$$_2$$?

Accepted Answer

Q \u003c K; precipitation will not occur

Question 15

Suppose a 45.00 mL sample of 0.240 M HOCl (p$$K_a = 7.54) is $$titrated with 0.250 M KOH. What is the pH at the equivalence point?

Accepted Answer

10.31

Question 16

Find the solubility of AgI in 2.5 M NH$$_3$$. ($$K_{sp} of $$AgI = $$8.3 	imes 10$$^{-17}$$; K_f$ of Ag(NH_3$)_2$$^+$$ = 1.7$$ 	imes $$10^7)$$

Accepted Answer

$$9.4 	imes 10$$^{-5}$$

Question 17

A 50.0 mL volume of 0.50 M Fe(NO$$_3$$)$$_3 is $$mixed with 125 mL of 0.25 M Cd(NO$$_3$$)$$_2. If $$aqueous NaOH is added, which ion precipitates first?

Accepted Answer

Iron(III)

Question 18

A 50.0-mL sample of 0.50 M HCl is titrated with 0.50 M NaOH. After 28.0 mL of NaOH have been added, which of the following statements is true?

Accepted Answer

The pH of the solution is less than 7.

Question 19

Which of the following titration mixtures will produce an equivalence point pH less than 7?

Accepted Answer

KOH + HClO$$_3$$

Question 20

What happens if we add NaC$$_2H$_3O$_2 to $$the following solution: $$\mathrm{HC_2H_3O_2 \rightleftharpoons H^+ + C_2H_3O_2^-}$$?

Accepted Answer

The pH will go up.

Question 21

HF is in solution with NaF. If HCl is added, which ion will react with the additional hydrogen ions from the HCl to prevent a change in pH?

Accepted Answer

F$$^-$$

General Chemistry Study Guide: Acids, Bases, Buffers, Equilibria, and Solubility

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