Acids and Bases

Question 1

why arrhenius’ theory is not solid

Answer 1

1. it cannot explain why substances without OH- like NH3 act as bases
2. does not take account the role of solvent
3. does not describe accurately the H+ ion state as it does not exist but exists as H3O+

Question 2

what is the name of the compound that results from the reaction of a Lewis base and a Lewis acid?

Answer 2

lewis adduct

Question 3

amphoteric substances

Answer 3

substances that can act as both acids and bases

Question 4

water as an amphoteric substance

Answer 4

water donates H+ when it reacts with a stronger base
water accepts H+ when it reacts with a stronger acid

Question 5

dissociation of carbonic acid

Answer 5

carbonic acid is a diprotic acid

H2CO3 + H20 –><– H3O+ + HCO3-

HCO3- is a weak acid a second dissociation can take place:

HCO3- + H20 –><– H3O+ + CO3 2-

Question 6

dissociation of sulfuric acid

Answer 6

H2SO4 + H2O –> H3O+ + HSO4-
HSO4- + H20 –><– H3O+ + SO4 2-

Question 7

what happens to the conjugate base as the strength of the acid decreases

Answer 7

the strength of the conjugate base increases

Question 8

how can we determine the direction of the reaction

Answer 8

in any acid-base reaction, we have 2 acids and 2 bases; however, one acid is stronger than the other base. by comparing their relative strength, we can determine the direction of the reaction

Question 9

why is water omitted from the expressions involving dissociation?

Answer 9

because the concentration of water in water is 55.5 mol and when we add acid, the conc of water barely changes

Question 10

what does the equilibrium constant depend on?

Answer 10

temperature

Question 11

antacids

Answer 11

substances that are used to neutralise excess acid. they are made up of Al(OH)3 and Mg(OH)2 mixtures. these hydroxides are not very soluble in water so the levels of OH- are not damaging to the intestinal tract

Question 12

equation for strong acids

Answer 12

[H3O+] = Ca (initial)

Question 13

equation for weak acids

Answer 13

H3O+ = square root( Ka x Ca)

Question 14

equation for weak base

Answer 14

OH- = square root( Kb x Cb)

Question 15

ionisation energies for polyprotic acids

Answer 15

1st ionization energy is the strongest because once you have a negative charge on an ion, pitting another negative charge on that ion by releasing a proton is more difficult

Question 16

what happens to the acid-base equilibria as you add acid?

Answer 16

when adding acid, the equilibrium shifts to the left.

Question 17

what happens to the acid-base equilibria as you add OH-?

Answer 17

the equilibrium shifts to the right

Question 18

acid-base titration

Answer 18

a known volume of acid is placed in a flask with an indicator and titrated with a measured volume of a base solution, such as NaOH, to the neutralization endpoint

Question 19

the endpoint of the titration

Answer 19

1. the moles of the base= moles of the acid
2. concentration of the base is known
3. The volume of the base used to reach the endpoint is measured
4. molarity of the acid is calculated using the neutralisation equation for the reaction

Question 20

buffer

Answer 20

a solution that resists changes in pH when small amounts of acid or base are added

Question 21

why are buffers important for proteins

Answer 21

because proteins lose their 3D structure as they are sensitive to pH changes because of an interruption of hydrogen bonds, dipole-dipole, and van der Waals.

Question 22

what are the constituents of a buffer solution?

Answer 22

of a weak acid and a conjugate base in similar concentrations or a weak base and its conjugate acid.

Question 23

addition of a base to a buffer solution

Answer 23

the small amount of base that is added is neutralised by the weak acid shifting the equilibrium in the direction of the products

Question 24

addition of an acid to a buffer

Answer 24

the additional H3O+ combines with the conjugate base ion causing the equilibrium to shift in the direction of the reactants

Question 25

Henderson Hasselbach Equation

Answer 25

pH = pKa + log [base]/[acid]

Question 26

blood pH

Answer 26

7.35- 7.45

Question 27

example of a buffer in biological fluids

Answer 27

carbonic acid/bicarbonate system:
CO2 + H2O ⇌ H2CO3
H2CO3 + H2O⇌ HCO3- + H3O+

Question 28

describe the presence of CO2 in our cells

Answer 28

CO2 is continually produced as an end product of cellular metabolism. it is carried to the lungs for elimination and the rest is dissolved in body fluids forming carbonic acid

Question 29

what happens when excess H3O+ enters the body fluids?

Answer 29

it reacts with HCO3-
H2CO3 + H2O⇌ HCO3- + H3O+
equilibrium shifts to the left

Question 30

what happens when excess OH- enters the body fluids?

Answer 30

H2CO3 + OH- ⇌ HCO3- + H2O

reacts with H2CO3 and the equilibrium shifts to the right

Question 31

how does our body maintain normal blood plasma pH?

Answer 31

the ratio of [H2CO3]/[HCO3-] needs to be about 1 to 10

Question 32

what happens to the concentration of carbonic acid when carbon dioxide levels increase?

Answer 32

carbonic acid increases and the equilibrium shifts to produce more H3O+ which lowers the pH: acidosis

Question 33

what happens to the concentration of carbonic acid when carbon dioxide levels decrease?

Answer 33

blood pH increases: alkalosis