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MECH U3/4 > Acid and bases > Flashcards

Acid and bases Flashcards

1
Q

What is a hydrolysis reaction?

A

occurs when a molecule or ion in aqueous solution reacts with water, either accepting or donating a proton.

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2
Q

Alkali

A

soluble base

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3
Q

Amphiprotic substances

A

Substances that can act as an acid or a base, depending on the substance it reacts with

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4
Q

What is the Arrhenius definition for an acid?

A

substances that ionise (form ions) in water. They produce H+ ions

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5
Q

What is the Arrhenius definition for a base?

A

Bases dissociate in water to produce hydroxide ions

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6
Q

What is the Bronsted-Lowry definition for an acid?

A

Acids are proton donors

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7
Q

What is the Bronsted-Lowry definition of a base?

A

bases are proton accepters

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8
Q

Monoprotic acids (3 examples)

A

acids that can donate only one proton per molecule.

eg. HCL, HF, HNO3

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9
Q

Lavoiser (3)

A
  • define acid and bases on the basis of the nature of their constituent elements.
  • thought that acidic properties were due to the presence of oxygen
  • it didn’t apply to acids such as HCL
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10
Q

Davy

A

suggested that the acid properties of substances were associated with hydrogen and not oxygen, came to the conclusion that acids react with bases to form salts and water.

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11
Q

What does the bronsted lowry state about an acid’s and bases ability to donate H+ or OH-?

A

The strength of an acid is its ability to donate hydrogen ions to a base
The strength of a Base is a measure of its ability to accept hydrogen ions from a acid.

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12
Q

The smaller the acid ionisation constant

A

the weaker the acid (less products and more reactants) (hasn’t undergone a lot of ionisation)

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13
Q

The larger the acid ionisation constant

A

the stronger the acid (more products and less reactants) (there the acid must’ve ionised a great deal)

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14
Q

What is the equilibrium constant for acids?

A

(acidity constant) Ka= Products / reactants

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15
Q

What is the equilibrium constant for bases?

A

(basicity constant) Kb= Products / reactants

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16
Q

What is the difference between a strong acid and a weak acid?

A

A strong acid completely ionises in solution producing more H+ ions , while a weak acid only partially ionises in solution producing little H+ ions.

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17
Q

What is the difference between concentrated and dilute?

A

A concentrated solution contains a high proportion of acid, while a dilute acid solution is mainly water with a very small proportion of acid

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18
Q

What is the molar concentration of Water at 25C?

A

10-14 moL L

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19
Q

What is the concentration equilibrium for H2O?

A

Kc=[H+][OH-]=10-14

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20
Q

What occurs to the Kw if the temperature of a solution increases?

A

If the temperature increases the value of Kw increases.

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21
Q

What are 4 types of weak base?

A

Metal phosphates
Metal carbonates
Metal hydrogencarbonates
Ammonia

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22
Q

What are 6 examples of strong acids?

A 
HCl
HNO3
H2SO4
HBr
HI
HClO4
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23
Q

What are 7 examples of a weak acid?

A 
HF
H2CO3
H3PO4
CH3COOH
NH4Cl
NH4NO3
H2SO3
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24
Q

What are the 2 types of strong bases?

A

oxides of group 1 and 2 metals

hydroxides of group 1 and 2 metals

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25
Q

Is a salt from a strong acid and strong base, acidic or basic?(2)

A
  • It creates a neutral salt

- anion and cation of a neutral salt do not react with water by accepting or donating a proton.

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26
Q

Example of a salt from a strong acid and strong base

A

The salt of the strong acid, eg. HNO3 and a strong base, eg.NaOH sodium ions do not hydrolyse in water. Nitrate ions (conjugate base of the HNO3)are very weak bases and do not react with water, sodium nitrate therefore have a pH of 7

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27
Q

Is a salt from a strong acid and weak base, acidic or basic?

A

solutions of salts of a strong acid and a weak base are acidic as the conjugate acid of the weak base hydrolyses to form hydronium ions

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28
Q

Example of a salt from a strong acid and weak base.

A

NH₄Cl is the salt from NH₃, a weak base and HCl a strong acid
When ammonium chloride dissolves in water, ammonium ion is a weak acid that undergoes hydrolysis and donates a proton to water to form hydronium ions.

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29
Q

Is a salt from a weak acid and strong base, acidic or basic?

A

solutions of salts of a weak acid and a strong base are basic because the anions hydrolyse to form OH- ions.

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30
Q

Example of a salt from a weak acid and strong base

A

Weak acid ethanoic acid and strong base sodium NaOH, to form the salt CH₃COONa.
CH₃COONa dissociates into water to form Na⁺ and CH₃COO⁻ ions. CH₃COO⁻ ions accepts proton from water molecule to produce a hydroxide ion

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31
Q

Is a salt from a weak acid and weak base, acidic or basic?

A

The acidity of a salt produced by the reaction of a weak acid and weak base depends on the degree of hydrolysis (Kc) of anion and cation in the salt produced.

  • The conjugate base of the weak acid reacts with water to form hydroxide ions
  • The conjugate acid of the weak base reacts with water to form hydronium ions
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32
Q

Examples of a salt from a weak acid and weak base

A

NH₃ and HClO make NH₄ClO.
NH₄⁺ Kc=5.6x10⁻¹⁰
ClO⁻ Kc=3.3x10⁻⁸

Hydrolysis of ClO⁻ occurs to a greater extent than the hydrolysis of NH₄⁺, therefore NH4ClO is basic as more OH⁻ ions are produced than H₃O⁺

33
Q

What are buffer solutions?

A

solutions that are able to resist a change in pH when small amounts of acid or base are added

34
Q

What do buffer solutions consists of?

A

A weak acid and the weak conjugate base pair (one of its salts)(or vice versa), from the hydrolysis reaction that occurs between them.

35
Q

What is the aim to produce a buffering solution?

A

to produce a solution that contains high enough concentration of the substances to enable the system to shift in either direction

36
Q

What occurs if you add an acid/base to a buffer?

A

If a small amount of a strong acid/base, the pH will decrease/increase to a small extent, but not as much as if the buffer are not present.

37
Q

What is the buffering capacity?

A

Measure of the effectiveness of a buffer solution at resisting a change in pH when either a strong acid or strong base is added

38
Q

When is the buffering capacity greatest? (2)

A
  • There is a high concentration of weak acid and its conjugate base
  • The concentration of acid and its conjugate base are equal
39
Q

When is a buffer no longer effective?

A
  • when a large amount of acid or base consumes the buffer, and there will be a sharp decrease or increase in pH
40
Q

What are 4 applications of buffers?

A

Biochemical systems
agriculture
food industry
paper industry

41
Q

What are the two most important buffers in the body?

A

carbonic acid buffer

Phosphate buffer system

42
Q

How does the carbonic acid buffer work in the body?

A

It helps to oppose the acidic CO2 that is produced often in the respiration of cells

43
Q

Why does changes in soil pH affect agriculture?

A

Changes in soil pH can have large effects on nutrient availability and plant growth

44
Q

What is soil acidification? And how is it accelerated and how is it counteracted?

A

natural process that occurs very slowly as soil is weathered, it is accelerated by agricultural practises such as the use of nitrogen fertiliser
one chemical change is an increase in the solubility of Aluminium (Al) and manganese (Mn), which is toxic to plants.
To contract an increase in soil acidity, lime (calcium oxide) or limestone (calcium carbonate) can be added to the soil, neutralising the soil.

45
Q

How are buffers used in the food industry?

A

keeping acidity of food at the appropriate level, flavour and appearance can be maintain, by adding additives into food

46
Q

How are buffers used in the paper industry?

A

CO₂ is used to decrease calcium levels and to increase dewatering, helping with pulp brightness

47
Q

What are 6 characteristics of indicators?

A
  • indicators are large organic molecules whose colour changes in response to changes in the pH of the solution in which they are dissolved
  • weak acids or weak bases
  • solution, the acid form of indicator is in equilibrium with its conjugate base, shown in the following equation
  • the position of equilibrium depends on the pH
  • colour of the acid form of an indicator, HIn, the colour of its conjugate base, In- are different
  • acid or base colour of an indicator is visible at low indicator concentrations
48
Q

What is the equivalence point?

A

point during a neutralisation reaction when the amount of acid and base are in the stoichiometric ratio represented by the reaction equation in a process called titrations.

49
Q

Define pH

A

measure of the acidity of an acidic or basic solution through their concentration of H+ in solution

50
Q

How does Rain become acidic naturally?

A

Through the presence of CO₂ in the atmosphere, oxides of nitrogen formed in lightning strikes and SO₂ emitted by volcanic eruptions

51
Q

What is the main cause of acid rain?

A

SO₂ produced from burning sulfur-containing fossil fuels, which then reacts with water to create sulfuric acid which is a strong acid

52
Q

What are primary standard substances?

A

substances that are so pure that the amount of substance in moles can be calculated accurately from their mass

53
Q

What should primary standard be like? (4)

A
  • be readily obtained in a pure form
  • have a known chemical formula
  • be easy to store without deteriorating or reacting with the atmosphere
  • have a high molar mass to minimise the effect of errors in weighing
54
Q

How are standard solutions prepared? (2)

A
  • Dissolving a known mass of a primary standard in a known volume of solution (e.g anhydrous sodium carbonate)
  • standardisation of the solution (eg.NaOH) by titration against a standard solution (eg. HCl)
55
Q

Is water a weak or strong electrolyte?

A

weak as it partially ionises into H+ and OH-

56
Q

What are the two colours for bromothymol blue indicator?

A

yellow in acidic solutions and blue in basic solutions and green in neutral solutions

57
Q

Describe using bromothymol blue indicator how it connects with Le chatelier’s principle.

A

bromothymol blue indicator was added to HCl, the addition of H3O+ ions from HCl cause the indicator equilibrium system to shift to the left to oppose the increase in concentration of H3O+

58
Q

What is methyl orange indicator? (3)

A

it is synthetic and is often used in analysis of weak bases

red in acidic and yellow in basic solutions, indicator colour change between pH 3.1 and pH 4.4

it is a weak acid

59
Q

What is phenolphthalein indicator?

A
  • synthetic indicator used in analysis of weak acids
  • acidic solutions it is colourless, basic solutions it has a pink colour
  • changes colours between pH 8.3-10.0
60
Q

Difference between strong base and weak base

A

Strong base is a substance that readily accepts hydrogen ions
And a weak base accepts hydrogen ions to a limited extent

61
Q

Define conjugate acid of a base

A

The conjugate acid of a base contains one more hydrogen ion than the base

62
Q

What are the concentrations of H+ and OH- in pure water equal to?

A

1.0 X 10⁻⁷moL L⁻¹

63
Q

Define endpoint

A

when the indicator changes colour

64
Q

Why does universal indicator appear coloured across a range of pH values?

A

it is a mixture of several indicators and so it changes through a range of colours

65
Q

How many times more is pH 4 from pH 2?

A

100 times

66
Q

What happens to pH when temperature increases?

A

The pH decreases

67
Q

What pH of a strong acid and strong base at its equivalence point?

A

pH 7, as when a strong acid and strong base react they form a neutral salt

68
Q

Two reasons why using methyl orange wouldn’t good with a strong acid and strong base, where its equivalence point is at pH 9

A

Methyl orange changes colour between pH3-4.5 but the equivalence point occurs long after this at pH 9, so a small volume of the base than usual would a colour change

Fewer moles of added base results in a lower number of moles of acid being calculated so the calculated concentration of the acid would be lower than actual.

69
Q

If a titration curve were to show two acids, Acid 1 reached its equivalence point at 25mL of KOH, while Acid 2 reached its equivalence point at 37mL of KOH, which one is more concentrated?

A

As a larger volume of KOH is required to reach equivalence with Acid 2, therefore Acid 2 is more concentrated as there are more molecules for KOH to reach.

70
Q

What is the sharp end point?

A

One drop of acid will cause colour change

71
Q

What is a pipette?

A

Used to accurately measure a specific volume of the solution

72
Q

What is a Burette?

A

Delivers accurately known but variable volume of solution

73
Q

What are 3 examples of buffer solutions?

A

Acetic acid and sodium acetate
Carbonic acid and sodium bicarbonate
Ammonia and ammonium chloride

74
Q

What happens when the temperature of water is increased, would the pH be less than 7, equal to 7 or more than 7?

A

Self-ionisation of H2O is endothermic, therefore H⁺ would increase in warm water, making the pH less than 7

75
Q

If experiment a was repeat used 20.0mL of 0.04mol L-1 ethanoic acid instead of HCL, would the pH of the final solution be the same of different? (3)

A

It would be the same
ethanoic acid will totally ionise due to the presence of the strong base NaOH
- there will be same number of hydrogen ions present

76
Q

If experiment a was repeat used 20.0mL of 0.04mol L-1 sulfuric acid instead of HCL, would the pH of the final solution be the same of different? (3)

A
  • it would be different
  • sulphuric acid is a diprotic acid
  • number of moles of hydrogen ions provided to solution will be more so there will be an excess
77
Q

Is water acidic, basic or neutral at 50C? state a reason fro your answer,

A

Water is neutral at 50C

Regardless of temperature in pure water [H+] = {OH-] Therefore there is no excess of either H+ or OH-

78
Q

Could the sulfuric acid be replaced with hydrochloric acid in this breathalyser (instead of H2SO4) without affecting its reliability? Explain.

A

No- as the chloride ions form the HCl(aq) may be oxidised by the acidified dichromate solution. This means the Cr2O7-2 ions would change colour without presence of ethanol - false positive result.

MECH U3/4 (8 decks)

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