CH3.9 Acid-base equilibria

Question 1

concentrated

Answer 1

means that there’s a large amount of acid or base dissolved in a set volume of water

Question 2

Dilute

Answer 2

means that there is a small aount of acid or base dissolved in a set volume of water

Question 3

Lowrt-Bronsted definition

Answer 3

An acid is a substance that releases or provides H+ ions (H+ donar)

A base is a substance that removes or accepts H+ ions (H+ acceptor)

Question 4

strong acid

Answer 4

Is one that almost totally dissociated (splits up) into H+ ions and negative ions in solution in water

Question 5

A weak acid

Answer 5

is one that partially dissociates into H+ ions and negative ions in water. The free ions are in equilibrium with unidissociated acid molecules

Question 6

ph of a weak acid

Answer 6

about 4

Question 7

ph of a weak alkali

Answer 7

about 9

Question 8

definition of pH

Answer 8

pH=-log(H+(aq)

Question 9

what does one chagne in pH mean

Answer 9

a multilple of 10 e.g 10,100 ,, 1000, 100000

Question 10

Ka equation for the equation Ha H+ + A-

Answer 10

Ka = (H+)(A-)/(HA)

Question 11

kW equation

Answer 11

kW = (H+)(OH-)

Question 12

kW at 25 degrees c

Answer 12

is approximately 10-14 mol^2dm^-6

Question 13

buffers

Answer 13

resists chagne in pH as small amounts of alkali are added to a a acid or acid added to a alkali.

Question 14

what is a buffer typically made up of

Answer 14

weak acid, a salt of the same acid with a strong base

Question 15

when acid is added to the buffer

Answer 15

THe amount of H+ ions increases and this causes the equilibrium to shift to the lefft removing the H+ ions by reacting with the negative ion.

Question 16

when alkali is added to a buffer

Answer 16

The amount of OH- ions is increase and this removes some of the H+ ions present. This causes the equilibrium to shift to the right producing H+ ions. The H+ ions replace those removed by reaction with the hydroxide ions.

Question 17

buffers are used as (2)

Answer 17

• stoing enzymes to ensure pH remains at the optmum value

- storing of biological molecules, such as pharmacceuticals, which will be denatured at the incorrect pH

Question 18

Henderson-Hasselbach equation

Answer 18

pHbuffer=pKa + log(SALT)/(ACID)

Question 19

a salt produced from a stron acid and strong alkali will form …

Answer 19

neutral solutions

Question 20

a salt produced from a strong acid and weak alkali will be …

Answer 20

an acidic salt

Question 21

a salt produced by a weak acid and strong alkalie wil be a…

Answer 21

basic salt

Question 22

vertical region on acid-base titration cuves

Answer 22

vertical region happens when the number of moles of alkali added equals the number of moles of acid in the original solution. This is calle

Question 23

indicator

Answer 23

is a substance that has different colours in low and high pH solutions. This can be used to differentiate between an acid and an alkali but cannnot distiniguish between acids of different pH or alkali of differen pH

Question 24

universal indicator

Answer 24

is a solution that shows a range of colours as the pH changes, so it can be used to find the pH of a particular solution.

Question 25

phenolphthalien approximate colour chagne range

Answer 25

8.3-10.0

Question 26

bromothylmol blue approximate colour change

Answer 26

6.0-7.5

Question 27

Litumus approximate colour change

Answer 27

4.0-6.5

Question 28

Methyl orange approximate colour change

Answer 28

3.2-4.4