Chapter 20 - Acid-base Equilibria

Question 1

what was the Arrhenius model of an acid

Answer 1

Acids dissociate and release H+ ions in aqueous solutions

Question 2

What was the Arrhenius model of an alkali

Answer 2

Alkalis dissociate and release OH- ions in aqueous solutions

Question 3

What is the Bronsted Lowry model for an acid

Answer 3

Acids are proton donors

Question 4

What is the Bronsted Lowry model for an alkali

Answer 4

Alkalis are proton acceptors.

Question 5

Define conjugate acid-base pairs

Answer 5

They contain 2 species that can be interconverted by transfer of a proton

Question 6

What is a Conjugate acid

Answer 6

If it has lost a H+.

Question 7

What is a Conjugate alkali

Answer 7

If it has gained a H+

Question 8

Define monobasic, dibasic, tribasic

Answer 8

They refer to the number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction.

Question 9

What plays an active role in an acid

Answer 9

the H+ ion

Question 10

acid + metal

Answer 10

salt + H2

Question 11

acid + carbonate

Answer 11

salt + water + CO2

Question 12

acid + base

Answer 12

salt + water

Question 13

acid + alkalis

Answer 13

salt + water.

Question 14

Equation for pH

Answer 14

ph = -log [H+]

Question 15

Equation for [H+]

Answer 15

[H+] = 10^ -pH.

Question 16

What is neutral on the pH scale

Answer 16

7.

Question 17

What is acid on the pH scale

Answer 17

Anything below 7.

Question 18

What is alkali on the pH scale

Answer 18

Anything above 7.

Question 19

pH of strong acids

Answer 19

In aqueous solutions, a strong mono basic acid will complete dissociate.
So, for any strong acid, the [H+] is equal to the concentration of the acid [HA].

Question 20

Define a strong acid

Answer 20

One that completely dissociates in aqueous solutions

Question 21

Define a weak acid

Answer 21

One that partially dissociates in aqueous solutions.

Question 22

What is the Ka

Answer 22

The acid dissociation constant for weak acids only.

It is equal to the Kc in some ways, but for an equilibrium equation

Question 23

The larger the Ka

Answer 23

The further the equilibrium has shifted to the right side, so the greater the dissociation and the acid strength

Question 24

Equation for pKa

Answer 24

pKa = -log Ka

Question 25

Equation for Ka

Answer 25

10 ^ -pKa

Question 26

Strong acid =

Answer 26

Large Ka = Small pKa

Question 27

Weak acid =

Answer 27

Small Ka = Large pKa

Question 28

What does a strong acid do in water

Answer 28

Completely dissociate

Question 29

What happens when a weak acid in mixed with water

Answer 29

It will only partially dissociate and instead, an equilibrium will take place. [HA] [A-] + [H+]

Question 30

What does the [H+] depend on?

Answer 30

Concentration of the acid, [HA] | And the acid dissociation constant, Ka.

Question 31

What are the 2 important approximations to make for the calculation of the Ka?

Answer 31

1. You can assume that the concentration of H+ = Concentration of A-, because they are equal at first. 2. The equilibrium concentration of HA is smaller than the undissociated concentration. As the dissociation of weak acids is small, you can assume that it is so small, it's negligible, so that [HA] start = [HA] eqm

Question 32

Equation to calculate Ka for a weak acid

Answer 32

Ka = [H+]^2 / [HA]

Question 33

Experimentally, how can you calculate Ka (2 ways)

Answer 33

1. Preparing a standard solution of a weak acid of known concentration. 2. Measuring the pH of the standard solution using a pH meter.

Question 34

What are the approximations made when calculating with weak acids?

Answer 34

1. The dissociation of water is negligible. | 2. The concentration of the acid is much greater than the H+ concentration at equilibrium

Question 35

What is Kw

Answer 35

Ionic product of water. The ions in water multiplied together. At 25 degrees C, it is 1 x 10^-14.

Question 36

For whole number pH values, ensure that the indices for [H+] and [OH-] add up to:

Answer 36

-14

Question 37

Define an alkali

Answer 37

A soluble base that releases OH - ions in aqueous solutions.