Chemistry : Acids And Bases

Front 1

HX + H2O ->

Back 1

H3O+ + X-

Front 2

What is a Brønsted-Lowry Acid?

Back 2

A hydrogen ion (proton) donor

Front 3

What is a Brønsted-Lowry Base?

Back 3

A hydrogen ion (proton) acceptor

Front 4

What is a strong acid?

Back 4

An acid 100% dissociated in solution e.g. HCl, H2SO4 and HNO3

Front 5

What are weak acids?

Back 5

Acids that only slightly dissociate in solution e.g. CH3COOH

Front 6

HA + water ->

Back 6

H+ + A-

Front 7

What are strong bases?

Back 7

Bases that fully (100%) dissociate in solution e.g. NaOH

Front 8

What are weak bases?

Back 8

Bases that only slightly dissociate in solution e.g. NH3

Front 9

H20 <=>

Back 9

H+ + OH-

Front 10

KC =

Back 10

[H+][OH-] ÷ [H2O]

Front 11

How much does 1 mole of water weigh?

Back 11

18

Front 12

What type of process is dissociation of water?

Back 12

Endothermic as bonds are broken

Front 13

pH =

Back 13

-log [H+]

Front 14

Why is the pH value used to express concentration of hydride ions?

Back 14

As there is such a wide range in values

Front 15

pH =

Back 15

-log10 [H+]

Front 16

What is complete dissociation?

Back 16

All the acid molecules have dissociated into hydrogen ions

Front 17

HCl + water ->

Back 17

H+ + Cl-

Front 18

How does H+ concentration affect pH value?

Back 18

As H+ value decreases, pH value increases

Front 19

What does complete dissociation mean we can conclude?

Back 19

In a monoprotic acid such as HCl, H+ is equal to the original concentration of the acid

Front 20

What is difference from HCl from sulfuric acid?

Back 20

Sulfuric acid is diprotic so each acid molecule produces 2 hydrogen ions in solution

Front 21

H2SO4 + water ->

Back 21

2H+ + SO4²-

Front 22

What will all aqueous solutions contain?

Back 22

H+ ions and OH- ions which are derived from the partial dissociation of water

Front 23

Acidic solution

Back 23

[H+ (aq)] > [OH-(aq)]

Front 24

Alkaline solution

Back 24

[OH-(aq)] > [H+ (aq)]

Front 25

Neutral solution

Back 25

[H+(aq)] = [OH-(aq)]

Front 26

(using KW) pH =

Back 26

-log√kw

Front 27

Why is water still neutral?

Back 27

The concentration of hydrogen ions is the same as the concentration of hydroxide ions

Front 28

NaOH + H2O ->

Back 28

Na+ + OH-

Front 29

[H+] =

Back 29

kW / [OH-(aq)]

Front 30

What are the 5 stages of calculating the pH after mixing strong acids and strong alakalis?

Back 30

Mol of H+

Mol of OH-

Mol of H+ in excess (H+ - OH-)

Calculate [H+] (c = n/v)

pH = -log c

Front 31

How do you calculate pH after dilution?

Back 31

Calculate moles of acid

Divide by total volume in dm³

pH = -log10 (ans)

Front 32

Why can we not use the same method to work out the pH of a weak acid that we used for a strong acid?

Back 32

In weak acids, the hydrogen ion concentration is not the same as the concentration of the acid

Front 33

HA(aq) + H2O <=>

Back 33

H3O+(aq) + A-(aq)

Front 34

HA(aq) <=>

Back 34

H+(aq) + A-(aq)

Front 35

Ka =

Back 35

[H+][A-] / [HA]

mol dm-³

Front 36

[H+] =

Back 36

√(Ka × [HA(aq)])

Front 37

How do you find the pH of a weak acid?

Back 37

Insert into √(Ka × [HA(aq)]

-log10(ans)

Front 38

What is the relationship between the strength of an acid and it's pKa?

Back 38

The lower the pKa values, the stronger the acid.

Front 39

What is the purpose of an indicator in an acid base titration?

Back 39

To show when the exact amount of acid and alkali are mixed to 'neutralise' each other

Front 40

What is the 'end-point' of a titration?

Back 40

When the indicator changes colour

Front 41

What is the equivalence point?

Back 41

Equal quantities of acid and base

Front 42

What is the pH curve of strong acid-strong base?

Back 42

Equivalence point = pH 7.00

Front 43

What is the pH curve of weak acid-strong base?

Back 43

Equivalence point = pH more than 7

Front 44

What is the pH curve of strong acid-weak base?

Back 44

Equivalence point = pH less than 7

Front 45

What is the pH curve of weak acid - weak base?

Back 45

Difficult to detect accurate equivalence point as pH change is more gradual

Front 46

What is on the X and Y axis of a pH curve?

Back 46

Y = pH

X = Volume of base added

Front 47

When do indicators change colour?

Back 47

Over a narrow pH range approximately centred around the pKa of the indicator

Front 48

What are the features of phenolphthalein?

Back 48

Pink in any solution with a pH greater than 10.0 and colourless at a pH of 8.4 or less

Front 49

Colour of methyl orange in acid

Back 49

Red

Front 50

Colour of methyl orange in alkali

Back 50

Yellow

Front 51

Colour of phenolphthalein in acid

Back 51

Colourless

Front 52

Colour of phenolphthalein in alkali

Back 52

Pink

Front 53

What must the pH range of the indicator lie between?

Back 53

The equivalence range, for it to work as an indicator

Front 54

Why type of indicator is suitable for a strong acid-strong base titration?

Back 54

Phenolphthalein and methyl orange

Front 55

Why type of indicator is suitable for a weak acid-strong base titration?

Back 55

Phenolphthalein

Front 56

Why type of indicator is suitable for a strong acid-weak base titration?

Back 56

Methyl orange

Front 57

Why type of indicator is suitable for a weak acid-weak base titration?

Back 57

You would never titrate a weak acid and a weak base in presence of an indicator

Front 58

What is the equivalence range of phenolphthalein?

Back 58

8.4-10.0

Front 59

What is the equivalence range of methyl orange?

Back 59

3.0 - 4.4

Front 60

At half equivalence, [HA (aq)] =

Back 60

[A-(aq)]

Front 61

What is a buffer?

Back 61

A buffer solution opposes change in pH when small quantities of acid or base are added

Front 62

What does an acidic buffer consist of?

Back 62

A weak acid (HA)

A salt of the weak acid (A-)

Front 63

What does a basic buffer consist of?

Back 63

Weak base (B)

Salt of the weak base (BH+)

Front 64

What must an acidic buffer contain to work effectively?

Back 64

Large concentration of the weak acid and it's salt

Front 65

What happens to the position of equilibrium if OH- ions are added to acidic buffer?

Back 65

Removes H+ (aq) ions so equilibrium shifts right to oppose change, producing H+ so solution doesn't become acidic

Front 66

What happens to the position of equilibrium if H+ ions are added to acidic buffer?

Back 66

Equilibrium shifts left to oppose change and CH3COO-(aq) react with H+ (aq) ions, salt remove any H+, so small change to pH

Front 67

What must a basic buffer contain to work effectively?

Back 67

Large concentration of the weak base and it's salt

Front 68

What happens to the position of equilibrium if OH- ions are added to basic buffer?

Back 68

Removes H+ ions so equilibrium shifts left to oppose change so more H+ produced so solution doesn't become alkaline

Front 69

What happens to the position of equilibrium if H+ ions are added to basic buffer?

Back 69

Equilibrium shifts right to oppose change so if there's a large concentration of both the weak base and it's salts then addition of small quantities of an acid/base will have little effect upon the [H+]

Front 70

Why are buffers important in the body?

Back 70

The pH of the blood must remain constant for the chemical reactions that occur

Front 71

Blood equilibrium

Back 71

HCO3- + H+ <=> CO2 + H2O

Front 72

How does the blood remove excess hydroxide/hydrogen ions to keep pH constant?

Back 72

HCO3- + H+ -> CO2 + H2O

H+ + OH- -> H2O

Front 73

How can the pH of an acid buffer be made and calculated?

Back 73

Add salt to weak acid, add strong base to excess of weak acid.

[H+] = Ka × [HA(aq)] / [A-(aq)]

Front 74

How can the pH of an acid buffer after the addition of acid be calculated?

Back 74

Mol of H+

Mol of A- / Mol of HA

A- - H+

HA + H+

Insert into equation for [H+]

PH = -log [H+]

Front 75

How can the pH of an acid buffer after the addition of base be calculated?

Back 75

Mol of OH-Mol of A- / Mol of HA A- + H+ HA - H+Insert into equation for [H+]PH = -log [H+]