Topic 8 & 18 Acids and Bases

Question 1

how does an indicator work

Answer 1

HIn <—> H+ + In-

HIn is a weak acid/base and dissociates into In- and H+, and the In- and H+ are different colors. the different concentrations of H+ ions shifts the position of equilibrium. depending on the relative concs of HIn and In-, the color of solution changes

Question 2

lewis bases

Answer 2

donate a lone pair of electrons

Question 3

lewis acids

Answer 3

accept a lone pair of electrons

Question 4

bronsted lowry acid

Answer 4

donates an H+

Question 5

bronsted lowry base

Answer 5

accepts an H+

Question 6

strong acid vs weak acid

Answer 6

strong
- dissociates completely in solution
- lower pH
- better conductor
- faster rate of reaction but NOT more products are produced

weak
- partially dissociates in solution
- higher pH
- not as good of a conductor

BUT BOTH:
- react with metal oxides, just s.a. react faster

Question 7

acid deposition

Answer 7

any process in which acidic substances leave the atmosphere to be deposited on the surface of the Earth. It can be divided into wet deposition (acid rain, fog and
snow) and dry deposition (acidic gases and particles) - pH BELOW 5.6 (rain has pH of 5.6)

Question 8

how is acid deposition formed

Answer 8

when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3

Question 9

effects of acid rain on buildings

Answer 9

limestone and marble are eroded by acid rain and dissolve away which exposes a new surface to react with more acid
CaCO3(s) + H2SO4(aq) → CaSO4(s) + H2O(l) + CO2(g)

Question 10

outline the formation of sulfuric acid and sulfurous acid in the environment

Answer 10

fossil fuels are contaminated with small amounts of sulfur impurities

when combusted, the sulfur is oxidized to SO2

S + O2 –> SO2

it may also be further oxidized to SO3

2SO2 + O2 <–> 2SO3

these compounds may then react with water to form sulfurous or sulfuric acidou

Question 11

outline the formation of nitric and nitrous acid in the environment

Answer 11

in internal combustion engines which reach high temps of 2000C cause the N2 and O2 to react (or lightning)

N2 + O2 <–> 2NO

or react further to produce

2NO + O2 <—> 2NO2

these can then react with water; contributing to acid rain

NO + H2O –> H2NO3 + HNO2

NO2 can be further oxidized to

4NO2 (g) + 2H2O (l) + O2 (g)→ 4HNO3 (aq)

and when clouds rise, temp decreases, droplets get bigger and the acid falls back down to earth

Question 12

effect of acid rain on plants

Answer 12

acid rain can fall on plants and kill them and the acid particulates can block stomata and prevent gaseous exchange. Mg2+ and Ca2+ K+ are washed out from soils so plants cannot use them

Question 13

effect of acid rain on water

Answer 13

pH decreases in the oceans, excessive algal growth causes depletion, aluminium is released from aluminium hydroxide in rocks which damages fish gills

Al(OH)3 (s) + 3H+ (aq) → Al3+ (aq) + 3H2O (l)

calcium carbonate shells breakdown of keystone species

Question 14

effect of acid rain on human health

Answer 14

when acid rain comes into contact with metal pipes, it increases the risk that toxic metal ions will be released into water supply;
acidic particles in air can increase risk of respiratory diseases

Question 15

outline pre-combustion methods to remove sulfur oxides emission

Answer 15

remove sulfur by reacting the sulfur with hydrogen in a process called hydrodesulfurization, the sulfur is then recovered and used in manufacture of sulfuric acid BUT this process is expensive

Question 16

what is the association between Ka and the strength of the acid

Answer 16

larger Ka means STRONGER acid, which also means stronger acids have lower pKa’s

Question 17

what is the association between Kb and pKb and the strenght of the base

Answer 17

higher Kb means STRONGER base, which also means stronger bases have lower pKb’s

Question 18

lewis acid

Answer 18

accepts a lone pair of electrons to form a dative covalent bond

Question 19

lewis base

Answer 19

donates a lone pair of electrons to form a dative covalent bond

Question 20

bronsted lowry base

Answer 20

accepts a proton

Question 21

bronsted lowry acid

Answer 21

donates a proton

Question 22

why does Kw increase with temperature

Answer 22

dissociation of water is endothermic so the position of equilibrium shifts to the right, so the concentration of H+ increases, so the numerator increases and hence so does Kw

Question 23

Kb expression

Answer 23

B + H2O <–> BH+ + OH-
([BH+][OH-])/[B]

Question 24

Ka expression

Answer 24

HA <–> H+ + A-
([H+][A-])/[HA]