PH and indicators

Question 1

Define PH

Answer 1

Ph = -log10[H+]
or
Ph= -log10[ H3+O]

Question 2

What is the ph scale

Answer 2

a scale that runs from 0 to 14 that indicted its level of acidity or alkalinity

Question 3

Give three limitations of the pH scale

Answer 3

The pH is inly useful/valid in the 0-14 range
The pH scale only applies to aqueous solutions
The pH scale does not work with very concentrated solutions

Question 4

Arrhenious definition for an acid

Answer 4

dissociates in water to produce H+ or H3O+ ions

Question 5

Arrhenious definition for a stong base

Answer 5

dissociated fully in water to produce H+/ H3O+ ions

Question 6

Arrhenious definition for a weak base

Answer 6

dissociates only slightly in water to produce H+/H3o+ ions

Question 7

Arrhenious definition for monobasic acid

Answer 7

each molecule dissociated to produce one H+ ions in solution

Question 8

Arrhenious definition for dibasic acid

Answer 8

each molecule dissociates to produce one H+ ion in solution

Question 9

Arrhenious definition for tribasic acid

Answer 9

each molecule dissociated to produce three H+ ions in solution

Question 10

Arrhenious definition for a base

Answer 10

dissociated fully in water to produce OH- ions

Question 11

Arrhenious definition for strong base

Answer 11

dissociated only slightly in water to produce OH- ions

Question 12

Arrhenious definition for weak base

Answer 12

dissociates only slightly in water to produce OH-

Question 13

Arrhenious definition for monobasic base

Answer 13

each molecule dissociated to produce one OH- ion in solution

Question 14

Arrhenious definition for a dibasic base

Answer 14

each molecule dissociated to produce two OH- ions in solution

Question 15

Arrhenious definition for tribasic base

Answer 15

each molecule dissociated to produce three OH- ions in solution

Question 16

Two substances with the same pH

Answer 16

have the same [H+]
Have the same pOH
Have the same [OH-]

Question 17

do acids still have an [OH-]?

Answer 17

yes they do… just very low - if asked for the [OH-] of an acid, treat ‘as if’ it is a base

Question 18

Do Bases still have H+?

Answer 18

yes they do…just very low - if asked for the [H+] of an acid, treat it ‘as if’ it is an acid

Question 19

what are acid base inicators

Answer 19

substances which change colour according to the ph of the solution in which they are placed

Question 20

name a acid base indicator which change colour at 3-5 , 5-8 , 8-10

Answer 20

Methyl orange 3-5 yellow(base) to red(acid)
Litmus 5-8 Blue(base)to red(acid)
Phenolphthalein 8-10 Pink(base) to colourless (Acid)

Question 21

what is the ph of an indicator

Answer 21

indicators themselves are weak acids or weak bases and dissociate in solution

Question 22

HIn is an indicator that is itself a weak acid,Write a balanced equation to represent the dissociation of HIn in water/solution

Answer 22

Hln + H2O ⇌ ln- + H3O+

Question 23

HIn is an indicator that is itself a weak acid
Place the indicator in an acid

Answer 23

concentration of H3O+ increases
the equilibrium shiftfs to decrease concentration of H3O+ to the left to use it up
Reverse reaction favoured
colour A (left hand side) due to increased concentration of Hln

Question 24

HIn is an indicator that is itself a weak acid.
Place the indicator in a base

Answer 24

concentration of OH- increases, they will react with the H3O- ions to form H2O
concentration of H3O+ decreases
equilibrium shiftfd to increase concentration of H3O to produce more of it.
Foward reaction favoured to the right.
Colour B forms (RHS) to increase the concetration of ln-

Question 25

XOH is an indicator that is itself a weak base.
Write a balanced equation to represent the dissociation of XOH in water / solution

Answer 25

XOH ⇌ X+ + OH-

Question 26

XOH is an indicator that is itself a weak base.
Place the indicator in an acid

Answer 26

Concentration of H+ increases - they will react with OH- ions to from H2O. Concentration of OH- decreases.
Equilibrium shifts to increase concentration of OH- to produce more of it
Foward reaction favored to the right
Colour B forms due to increased concentration of OH- (RHS)

Question 27

Place the indicator in an acid