Acidic Environment 3

Question 1

acids as proton donors

Answer 1

an acid is a substance that in solution, produces hydrogen ions (H+). Hydrogen ions in solution do not occur free but attach themselves to water molecules to form Hydronium ions (H3O+)

Question 2

Bronsted lowry theory

Answer 2

Acids are proton (H+) donors. The formation of ions by acids explains why they are good conductors of electricity. The behaviour of acids is due to H+.

Question 3

acetic acid

Answer 3

• Acetic / ethanoic acid (CH3COOH) pungent colourless liquid used to make acetates such as vinegar.
  Can preserve foods and produced by bacterial action on alcohol in air and industrially by oxidation of ethanol.

Question 4

Citric acid

Answer 4

(2-hydroxypropane- 1,2,3-tricarboxylic)
C6H8O7
Colourless crystalline solid, a carboxylic acid which is widespread in plant and animal tissue.
Formed in our bodies during cellular respiration.
Used as an antioxidant and added to canned foods to prevent microbial growth .
Made commercially by fermenting crude sugar with Aspergillus fungus.

Question 5

Hydrochloric acid

Answer 5

HCl is produced in the linings of our stomachs to aid digestion of foods.
Sold under the name muriatic acid and used to clean brickwork.

Question 6

sulfuric acid

Answer 6

H2SO4 widely used to manufacture explosives and fertilisers. Present in car batteries.

Question 7

Ascorbic acid

Answer 7

C6H8O6
AKA Vitamin C
present in fresh fruit and veg.
Involved in a # of metabolic pathways and has important role in healing, blood cell formation and bone and tissue growth.
As an antioxidant it is added to foods to prevent microbial growth.

Question 8

strong acids and bases

Answer 8

completely (or almost completely) ionises in solution.
E.g. HCl Strong acid which in solution, completely forms H+ and Cl- (ions).
HCl (aq) –> H+ (aq) + Cl-(aq)
HCl(aq) + H20 (l) –> H3O+(aq) + Cl- (aq)
Forward reaction goes completely

Question 9

Weak acids and bases

Answer 9

ionise to a small extent releasing relatively few H+ ios in solution.
e.g. acetic acid
CH3COOH H+ (aq) + CH3COO-(aq)

Question 10

concentrated vs. dilute

Answer 10

terms referring to the amount of solute dissolved.
Concentrated solution has relatively large amount of solute dissolved in a given volume of solvent.
Dilute solution has a relatively small amount of solute dissolved in a given volume of solvent.

Question 11

equation for pH

Answer 11

acids release H+ ions into solution
As H+ ion conc. can vary and is small, the negative logarithm of the H+ conc is taken.
pH= -log10[H+]
[ ] refers to concentration of.

Question 12

relative strengths of = conc. of acids

Answer 12

pH of a solution is determined by conc. of H+ ions in it.
pH change of 1 unit means a ten fold change in [H+].
STRONG ACIDS
HA –> H+ + A- (HA is strong acid) [HA]= [H+]
WEAK ACIDS
HB H+ + B- (HB is weak acid, degree of ionisation is less) [HB] > [H+]

strength of an acid depends on how readily it can donate a proton.
Degree of ionisation for a weak acid, HB:
[H+] / [HB] X 100%

Question 13

Measuring pH of identical conc. of strong and weak acids

Answer 13

CaVa / a = CbVb / b

Question 14

Acids as food additives

Answer 14

improve taste and/or preserve them.
Many bacteria cannot survive in acid conditions.
Acid must be weak enough and not harmful for human consumption.
Acetic, citric, tartaric