3.1.12 Acids and bases

Question 1

the point that represents the solution is acting as a buffer

Answer 1

the straight part of the graph - no change in pH

Question 2

what is a Bronsted - Lowry acid

Answer 2

proton donor

Question 3

strong acid definition

Answer 3

completely ionising to give H+ ions in water

Question 4

what do you use when calculating the HA

Answer 4

use the equivalence point

Question 5

HA ->

Answer 5

H+ + A-

Question 6

Ka =

Answer 6

conc H+ x conc A-

divided by
conc ACID HA

Question 7

pH

Answer 7

-Log10 H+conc

Question 8

pka

Answer 8

-Log 10 ka

Question 9

kw

Answer 9

CONC H+ x conc OH-

Question 10

what assumption can you make in weak acid calculations but not in buffer calculations

Answer 10

H+ conc = A- conc at eqm

Question 11

p =

Answer 11

• P = - log

Question 12

pure water

Answer 12

• Pure water = conc of H+ = conc of OH-

Question 13

• Dilution questions

Answer 13

• Strong acid and water - conc H+ final = conc H+ initial x ( initial volume/ final volume)

just use OH- for bases

Question 14

half neutralization point

Answer 14

• Half neuralization point
• Conc HA = conc A-
• Meaning pH = pKa

Question 15

• Buffer calculations

Answer 15

• Initial to final
  1. Start with mols of initial HA and A- ( and H+ / OH- from substance added)
  2. Draw out the weak acid dissociation equation and the equation of the substance added
  3. Workout mols of final
• If an acid is added – then add h+ mols to the acid and take them away form the A-
• If a base is added – Oh- mols take away from acid and add them to A-
  4. Rearrange Kw and wat not to workout what needed

Question 16

why is pure water not acidic

Answer 16

as conc OH- = conc H+ by definition

Question 17

what to do with a di basic and diprotic acid

Answer 17

• Di basic / di protic – have to multiple the conc of H+ or OH- by 2
• Example of a di protic acid = sulfuric acid – example of a di basic = group 2

Question 18

working out the end poInt Ha

Answer 18

• Color change of the indicator = the end point
  Alkali added
• n(end point ) = (concentration x volume at the eq point)
• n end point HA = n point (oh-)

Question 19

workout the pH of a neutralization Acid + Base

Answer 19

• workout the pH of a neutralization Acid + Base
  1. workout which is in excess between the Oh- and the H+
  2. use the leftover to calculate the pH

Question 20

relation between H+ and pH

Answer 20

• as the concentration of H+ increases pH decreases

Question 21

explain why H2O is not shown in the Kw equation

Answer 21

• explain why H2O is not shown in the Kw equation – the concentration of water is (almost) constant

Question 22

• suggest why the Ph probe is washed with distilled water before new reading

Answer 22

– different solutions must not contaminate each other

Question 23

• why volume added of base to acid decreases as the end point get closer –

Answer 23

to avoid missing the end point

Question 24

why indicator is suitable

Answer 24

all have color change within the vertical/ steep part of the titration curve

Question 25

if a sample is diluted

Answer 25

* if a sample is diluted – have to workout moles and then scale to the correct size (use the new volume) to workout correct concentration

Question 26

to workout the mass of salt

Answer 26

* to workout the mass of salt – sort it out as an ice table ( initial – final )

Question 27

the highest pH at the equivalence point

Answer 27

* the highest pH at the equivalence point = weak acid and strong base

Question 28

* a buffer solution has a constant pH even when diluted show mathematically

Answer 28

ratio between conc HA/ conc A- = as the H+ conc is irrelevant at constant pH

Question 29

WHAT IA TRUE ABOUT H+ conc at a concstant pH

Answer 29

it is irelevent

Question 30

half neutralisation point important

Answer 30

I was also told that the half-equivalence point is when the concentration of a weak acid equals concentration of conjugate base: [HA]=[A−]. conjugate bace = proton acceptor

Question 31

difference between the half neutralization point and the equivalence point

Answer 31

The equivalence point is where the amount of moles of acid and base are equal, resulting a solution of only salt and water. If you are titrating an acid against a base, the half equivalence point will be the point at which half the acid has been neutralized by the base

Question 32

End point

Answer 32

The volume of alkaline or acid added when the indicator has changed colour

Question 33

Properties of a suitable indicator

Answer 33

The colour change must be sharp - no more than one drop needed to give a complete colour change The endpoint of titration must be the same as the equivalence point - change colour in the vertical section of the graph The indicator should give a distinct colour change

Question 34

strong acid important point

Answer 34

mol of h+ and A- are the same

Question 35

buffer solution made when base is added to weak acid

Answer 35

OH- mols = A- mols as 1:1

Question 36

how to make a buffer

Answer 36

weak base and its salt (chloride) must be mixed together, for example, ammonia and ammonium chloride. To prepare acidic buffer solution, weak acid and its salt must be mixed.

Question 37

example of a weak alakali

Answer 37

nh3

Question 38

what does a beurette allow

Answer 38

variable volumes to be added more easily