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 OH- ions

Question 6

Arrhenious definition for a weak base

Answer 6

dissociates only slightly in water to produce OH- 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 two 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 in water to produce OH- ions

Question 11

Arrhenious definition for strong base

Answer 11

dissociates fully 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

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

Answer 27

Concentration of OH- increases Equilibrium shifts to decrease conc of OH-, to the left to use it up. The reverse reaction is favoured, Colour A forms due to increased conc of XOH

Question 28

What is a pH titration

Answer 28

An acid base titration where a pH meter is placed in the acid in a beaker. ALL OF THE BASE is added.Changes in PH are recorded A pH curve is plotted The Endpoint can be found from the vertical part of the graph. Endpoint if the volume of base required for neutralisation.

Question 29

In pH titrations,why is a beaker used instead of a concial flask

Answer 29

a beaker is more suitable to place the ph meter probe and stir

Question 30

In pH titrations,Why is the acid in a beaker and base in a burette

Answer 30

Allows us to start with a low ph value and work upwords

Question 31

In pH titrations,Why is a indicator not required

Answer 31

Ph is directly measured by pH meter

Question 32

Decribe a pH titration between a strong acid and a strong base, and list a potential indicator and explain

Answer 32

End point between 3 -11, The vertical part of the titration is the volume of base required for neutralsation. Methyl orange or Phenohphtalein the vertial part of the titration- end point between pH 3-11 Methyl orange or Phenolphtalein changes colour according to the vertical part of the graph

Question 33

Decribe a pH titration between a stong acid and a weak base and list a potential indicator and explain

Answer 33

the end point is between ph 3-7 a potential indicator is methyl orange. The vertical part of the titration is the volume of base required for neutralsation.Shown by the vertical part. The end point is between3-7, Methyl orange changed colour according to the vertical part of the graph

Question 34

Decribe a pH titration between a weak acid and a strong base and a potential indicator, explain

Answer 34

the end point is between ph 7-11. potetial indicator is phenophothalein.The vertical part of the titration is the volume of base required for neutralsation. as shown by the vertical graph- the end point occours between a PH of 7-11. Phenophthalein changes colour coinciding with the vertical part of the graph

Question 35

What is the formula for Vb?

Answer 35

Ma x Va / na =Mb x Vb/ nB

Question 36

Write a equation for the dissociation of water

Answer 36

2H2O ⇌ H3O+ + OH-

Question 37

what is the only thing that affects Kw

Answer 37

temperture

Question 38

Is the self ionisation of water endothermic or exothermic, explain

Answer 38

As the temperture increases, Kw increases. Equilibrium shifts to decrease temperture in the endothermic direction. Kw: the foward reaction if favoured.The foward reaction if endothermic, the self ionisation of water is endothermic

Question 39

what is unique about pure water

Answer 39

[H3O+]=[OH-]