ch20 - acids, bases & ph

Question 1

what is the bronsted - lowry definition of an acid and base

Answer 1

acid - proton donor
base - proton accepter

Question 2

what is the arrhenius definition of an acid and base

Answer 2

aicds - dissociate and release h+ ions in aq solution
alkali - soluble bases releases oh- ions

Question 3

HCl (aq) + OH- (aq) <–> H2O (l) + Cl- (aq)

what are the conjugate acid-base pairs

Answer 3

HCl (A1) -> proton donor -> Cl- (B1)

OH- (B2) -> proton acceptor
-> H2O (A1)

Question 4

what are monobasic acids and give examples of them

Answer 4

monobasic: one H+ in acid that can be replaced in acid-base reactions per molecule

(H)Cl
CH3COO(H)

Question 5

what are dibasic acids and give examples of them

Answer 5

dibasic: two H+ in acid that can be replaced in acid-base reactions per molecule

H2CO3

Question 6

what are tribasic acids and give examples of them

Answer 6

tribasic: three H+ in acid that can be replaced in acid-base reactions per molecule
H3BO3

Question 7

write the ionic eq for:

H2SO4 (aq) + Mg (s) -> MgSO4 (aq) + H2 (g)

Answer 7

H2+ (aq) + Mg (s) -> Mg2+ (aq) + H2 (g)

Question 8

acid + metal -> ?
eg?

Answer 8

acid + metal -> salt + h2
2H+(aq) + Zn(s) -> Zn2+(aq) + H2 (g)

Question 9

acid + carbonate ->?
eg?

Answer 9

-> salt + water + co2
2H+ (aq) + CO32- (aq) -> H2O (l) + CO2 (g)

Question 10

acid + base -> ?
eg?

Answer 10

-> salt + water
2H+ (aq) + MgO (s) -> Mg2+ (aq) + H2O (l)

Question 11

acid + alkali ->
eg?

Answer 11

-> salt + water
H+ (aq) + OH- (aq) -> H2O (l)

Question 12

what is the relationship b/w pH value and [H+]

Answer 12

low [H+] -> high pH value
high [H+] -> low pH value

Question 13

whats the mathematical realtionship bwteen pH and [H+]

Answer 13

pH = -log[H+(aq)]

[H+ (aq)] = 10^-pH

Question 14

a change of one ph number is equal to a *x difference in [H+]

Answer 14

• ten times

Question 15

what is the pH of a solution with a H+ (Aq) concentration of 2.45*10^-3 moldm-3

Answer 15

pH = -log(2.45*10^-3)
2.61 dp

Question 16

What is the [H+ (aq)] of a solution with a pH of 8.75

Answer 16

[H+ (aq)] = 10^(-8.75)

Question 17

for a …… acid [H+ (aq)] is equal to the concentration of the acid [HA(aq)]

Answer 17

strong

the pH of a strong acid can calculated directly from the conc. of the acid

Question 18

a pH of 1 has x times the conc. of H+ ions as a solution with a pH of 2

Answer 18

x = 10

Question 19

Ka?

Answer 19

Acid dissociation constant %

Question 20

The higher the Ka the …….. the acid

Answer 20

Stronger the acid
High Ka -> high dissociation

Question 21

What is the logarithmic equation for Ka

Answer 21

pKa = -logKa

Ka = 10^-pKa

Question 22

A stronger acid would have a …….pKa value

Answer 22

Smaller

Question 23

what is a weak acid

Answer 23

an acid that partially dissociates in solution

Question 24

what is the Ka equation for a weak acid

Answer 24

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

Question 25

what are the two approximations that we make when simplifying the Ka equation for weak acids

Answer 25

HA dissociates to produce ‘equal’ equilibrium conc. of H+ and A- (we neglect the small h+ released by water)

neglect any decrease in conc. of HA from dissociation (assume [HA]&raquo_space;> than [H+] eq

Question 26

how can we determine the Ka for a weak acid experimentally

Answer 26

prepare standard solution of weak acid of known conc
measure pH of solution w/ pH meter

Question 27

what is Kw and what is its equation

Answer 27

ionic product of water
Kw = [H+(aq)] [OH-(aq)]

Question 28

what is the importance of having Kw as a set value

Answer 28

sets a neutral point in the pH scale

Question 29

what is the value of Kw at 298K give the units

Answer 29

1 * 10^-14 mol2dm-6

Question 30

what is the relationship b/w [H+] and [OH-] when solution:

acid
neutral
alkali

Answer 30

[H+] > [OH-]

[H+] = [OH-]

[H+] < [OH-]

Question 31

what is the [H+] and [OH-] for a acid solution of pH = 3

Answer 31

[H+] = 10^-3 moldm-3
[OH-] = 10^-11 moldm-3

Question 32

for monacidic bases each mole of NaOH (eg) releases …. mole of OH- ions

Answer 32

one

Question 33

What is a buffer solution

Answer 33

A solution that minimises pH changes when small amounts of an acid or base are added.