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Chemistry > Acid-Base > Flashcards

Acid-Base Flashcards

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1
Q

At what point does an Indicator change colour?

A

When the pH of the solution changes past the pKa of the indicator

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2
Q

How are weak bases defined?

A

Weak bases are defined as having a low Kb

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3
Q

How are strong acids defined?

A

Strong acids are defined fully ionising/dissociating (Ka > 1)

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4
Q

How does the Brønsted-Lowry model define an acid and a base?

A

Acid as any species that can donate protons (H+). Bases as any species that accept protons (H+)

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5
Q

How are strong bases defined?

A

Strong bases are defined as having a high Kb

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6
Q

How do we calculate concentration?

A

C = n / v

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7
Q

How are the acid and its conjugate base different in indicators?

A

They are different colours

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8
Q

How do we calculate Kw?

A

Kw = Ka x Kb

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9
Q

How are weak acids defined?

A

Weak acids are defined as having a Ka < 1

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10
Q

How do you calculate Ka?

A

Ka = [H3O+] X [A-] / [HA]

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11
Q

How do you calculate Kb?

A

Kb = [BH+ ] x [OH-] /
[B]

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12
Q

How often should a titration be performed?

A

Until you have obtained three titres that differ by less than or equal to 0.1mL

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13
Q

How is the [H+] calculated?

A

[H+ ]= 10^(-pH)

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14
Q

Identify the conjugate acid produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O

A

H2O

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15
Q

How is [OH-] calculated?

A

[OH-] can be obtained using the pH or pOH value: pH + pOH = 14 pOH = 14 - pH pOH= –log10 [OH- ] [OH-] = 10^(-pOH)

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16
Q

Identify the conjugate base produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O

A

NH3

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17
Q

How is pH calculated?

A

The pH of a solution can be calculated from the concentration of hydrogen ions using the relationship
pH = -log10 [H+ ]

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18
Q

If an acid or a base completely ionises in water what is it called?

A

Strong acid or base

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19
Q

How is pOH calculated?

A

pOH = -log10 [OH-]

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20
Q

If an acid or a base only partially ionises in water what is it called?

A

A weak acid or base

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21
Q

Is a base strong or weak if its pKb is large?

A

Weak

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22
Q

Name an example of a monoprotic acid

A

HCl - hydrochloric acid
HBr - hydrogen bromide
HNO3 - nitric acid
CH3COOH - ethanoic acid

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22
Q

Is an acid strong or weak if it has a low pKa?

A

Strong

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22
Q

Is Kw temperature dependent?

A

Yes

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22
Q

Name an example of a triprotic acid

A

H3PO4 - Phosphoric acid

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22
Q

pH + pOH = ?

A

14 or Kw (at just below 25oC)

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22
Q

The strength of an acid is explained by the degree of …

A

dissociation of the acid at equilibrium in an aqueous solution

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22
Q

Is the conjugate base of a weak acid, stronger or weaker?

A

Stronger

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23
Q

Name an example of a diprotic acid

A

H2SO4 - sulphuric acid
H2CO3 - carbonic acid

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23
Q

Under what circumstances could the numerical value of Kw differ?

A

Different temperatures. Kw is 10-14 at just below 25oC

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23
Q

What are acid-base indicators?

A

Weak acids or bases, which dissociate slightly in water and form ions

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24
Q

What can be tested experimentally to determine the strength of an acid or base?

A

The electrical conductivity of the acid or base

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24
Q

What are examples of Strong Acids?

A

Hydrochloric Acid (HCl)
Nitric Acid (HNO3)
Sulfuric Acid (H2SO4)

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24
Q

What does amphiprotic mean?

A

A molecule or ion that can donate of accept a proton. Therefore it acts as both an acid and a base.

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24
Q

What are examples of Strong Bases?

A

All group 1 hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Barium hydroxide (Ba(OH)2)

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25
Q

What does it mean if an acid is concentrated?

A

It means it has a large number of moles of the acid in a litre of water

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26
Q

What are examples of Weak Acids?

A

Carboxylic acid (R-C(=O)-OH), carbonic acid (H2CO3), aqueous carbon dioxide (CO2 (aq))

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27
Q

What does it mean if an acid is dilute?

A

It means it has a small number of moles of the acid in a litre of water

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28
Q

What are examples of Weak Bases?

A

Ammonia (NH3), amines

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29
Q

What does Ka represent?

A

The equilibrium constant for the dissociation of an acid in an aqueous solution

30
Q

What does the buffer region look like on a weak acid or base titration curve?

A

It is the (almost) horizontal area that occurs before the equivalence point.

31
Q

What is a conjugate acid?

A

An acid formed when a base accepts an H+

32
Q

What happens when the pH of a solution is equal to the pKa of an indicator?

A

The indicator will change colour

33
Q

What is a conjugate acid?

A

An acid formed when a base accepts a proton (H+) B: + H2O → B:H+ + OH- (B:H+ is the conjugate
acid)

34
Q

What impact does having water in the burette have in a titration?

A

It will decrease the concentration of the titrant and therefore a greater volume will be needed to neutralise the analyte

35
Q

What is a conjugate base?

A

A base formed by removing a proton (H+) from an acid

36
Q

What impact does having water in the flask holding the analyte have in a titration?

A

No impact as the number of moles of the substance remains the same

37
Q

What is a conjugate base?

A

A base formed by removing a proton (H+) from an acid

38
Q

What is a buffer solution?

A

A solution that resists changes in pH when small quantities of acids or bases are added to it

39
Q

What is a conjugate pair?

A

Two species that differ by a proton (H+)

40
Q

What is an indicator?

A

A chemical substance that changes colour at
particular pH values

40
Q

What is a diprotic acid?

A

An acid that can donate two protons per molecule

41
Q

What is a monoprotic acid?

A

An acid that can donate one proton per molecule

42
Q

What is a polyprotic acid?

A

An acid that can donate more than one proton per molecule

43
Q

What is an aliquot?

A

A fixed volume of liquid measured by a pipette

43
Q

What is a titration?

A

A technique used to determine the unknown concentration of a solution

44
Q

What is an amphiprotic substance?

A

A substance that can act as either an acid or a base

45
Q

What is hydronium?

A

H3O+

45
Q

What is an example of a common amphiprotic
substance?

A

Examples could include - water, amino acids and hydrogen carbonate ions (HCO3-)

46
Q

What is Kw?

A

Kw is the ionic product constant of water. It is the equilibrium constant for the self-ionisation of water. Kw can be used to calculate the concentration of
hydrogen ions from the concentration of hydroxide ions in a solution

46
Q

What is pKb a measure of?

A

The strength of a base

46
Q

What is meant by a standard solution in a titration?

A

A solution whose concentration is accurately known

47
Q

What is meant by the “strength” of an acid or a base

A

The level of dissociation that occurs in the acid or base.

48
Q

What is self-ionisation of water?

A

Self-ionisation of water refers to the reaction in which a water molecule loses a hydrogen ion (leaving OH-)
and the hydrogen ion immediately reacts with another water molecule to form a hydronium ion (H3O+ )

49
Q

What is parallax error?

A

When the volume of a liquid is read when the eye level is above or below the meniscus. It leads to inaccurate volumes being determined

49
Q

What is the analyte?

A

The solution in a titration whose concentration is unknown

49
Q

What is pH?

A

pH is a figure expressing the acidity or alkalinity of a
solution on a logarithmic scale

49
Q

What is the Bronsted-Lowry definition of an acid?

A

A proton donor

49
Q

What is pKa a measure of?

A

The strength of an acid

50
Q

What is the Bronsted-Lowy definition of a base?

A

A species that accepts protons

51
Q

What is the buffer point on a weak acid or weak base titration curve?

A

It is the point where pH = pKa. It is at half the equivalence volume.

52
Q

What is the definition of a strong acid in terms
of its Ka?

A

Ka > 1 is a strong acid

53
Q

What is the conjugate acid of hydroxide (OH-)?

A

H2O

54
Q

What is the definition of a strong base in terms of its Kb?

A

High Kb - Strong bases

55
Q

What is the conjugate acid of the following base: OH-?

A

H2O

56
Q

What is the definition of a weak acid in terms of its Ka?

A

Ka < 1 Weak acids

57
Q

What is the conjugate base of ammonium (NH4+)?

A

NH3

58
Q

What is the conjugate base of CH3COOH?

A

CH3COO

58
Q

What is the definition of a weak base in terms of its Kb?

A

Low Kb - Weak bases

59
Q

What is the dissociation expression for a base?

A

Kb = [products] / [reactants]

60
Q

What is the dissociation expression for an acid?

A

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

61
Q

What is the “end point”?

A

The point in a titration when the indicator changes colour

62
Q

What strength is an acid or base that is used as an indicator?

A

They are weak acids and bases

63
Q

What substances make up a buffer?

A

A weak acid and its conjugate base or a weak base and its conjugate acid

64
Q

What is the equivalence point?

A

The point in a titration when neutralisation is reached (i.e. when moles H+ = moles OH-)

65
Q

What substance states are included in a dissociation expression?

A

Aqueous (aq)

66
Q

What is the relationship between the pH range of an acid-base indicator and its pKa value?

A

A higher pKa correlates to a higher end point of the indicator

67
Q

What type of substance does this equation represent? BOH → B+ (aq) + OH-(aq)

A

A strong base

68
Q

What is the titrand?

A

The solution in a titration whose concentration is known

69
Q

What type of substance does this indicator represent? HIn ⇌ H+ (aq) + In-(aq)

A

A weak acid

70
Q

What type of substance has a pH of 1?

A

A strong acid

71
Q

Which have better electrical conductivity, strong or weak acids (or bases)?

A

Strong acids (or bases)

72
Q

What type of substance has a pH of 7?

A

A neutral substance

72
Q

Why are acids and bases good electrolytes?

A

They can dissociate into positive and negative ions
which means they can conduct an electrical charge

73
Q

What type of substance has a pH of 13?

A

A strong base

74
Q

Why is water a weak electrolyte?

A

It can self-ionise, but equilibrium lies to the left H2O ⇌ H+(aq) + OH-(aq)

75
Q

When choosing an indicator for a titration what are you looking for?

A

An indicator whose end point is close to the equivalence point.

76
Q

Which Acid and Bases (strong or weak) completely ionise in water?

A

Strong acids and bases

Chemistry (9 decks)

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