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Yr 12 Chemistry > The Acidic Environment > Flashcards

The Acidic Environment Flashcards

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1
Q

oxides of non-metals are usually?

A

acidic (covalent bond)

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2
Q

oxides of metals are usually?

A

basic (ionic bonds)

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3
Q

litmus indicates?

A

turns red in acid(5)
purple as neutral
blue as base (8)

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4
Q

Phenolphthalein indicates?

A

it turns from colourless to pink at a basic pH (9 approx.)

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5
Q

Bromothymol blue indicates

A

it turns from yellow to blue at pH of around 7

around neutral

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6
Q

methyl orange indicates?

A

it turns from red to yellow at a pH of 3-4

tests for more acidic pH

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7
Q

household substances that are acidic, basic and neutral?

A

acidic: vinegar
neutral: methylated spirits/ethanol
basic: oven cleaner/detergents

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8
Q

What was the historical development of ideas about acids?

A

Lavoisier: defined an acid as a non-metal compound containing oxygen (couldn’t explain why metal oxides weren’t acidic)

Davy: defined acids as substances containing replaceable hydrogen

Arrhenius:

  • acids ionise in solution to produce H+
  • a base is a substance producing OH- (excludes metal oxides)

Bronsted-Lowry

  • an acid is a proton donor
  • a base is a proton acceptor
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9
Q

Outline Bronsted-Lowry theory of acids and bases?

A
  • an acid is a protoon donor
  • a base is a proton acceptor
  • an acid base reaction needed one species (the acid) to donate protons and another (the base) to accept protons
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10
Q

identify oxides of non-metals which act as acids & describe the conditions under which they act as acids?

A

Oxides of non-metals are: acidic, acting as acids when dissolved in water
*CO, nitrous oxide and nitric oxide are neutral

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11
Q

Acidity and the periodic table, what happens?

A
  • moving left: increasing basicity
  • moving right, increasing acidity until Grp 7
  • moving down: elements become more metallic/basic
  • semi metals form: amphiprotic oxides
  • metal oxides are basic
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12
Q

What is Le Chatelier’s principle?

A

When a system at equilibrium is changed, the equilibrium shifts to minimise the disturbance of that change.

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13
Q

what are the properties of equilibrium?

A
  1. the system is closed
  2. observable properties are constant, stay the same (colour, concentration, pressure)
  3. the concentration of reactions and products are constant
  4. The rate of the forward reaction equals the rate of the reverse reaction
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14
Q

What are the rules for the comparative strength of conjugates?

A
  1. strong acids & bases have very weak conjugates (can’t accept or donate protons)
    2.Weak acids and bases have relatively strong conjugates (can accept/donate protons)
    3.
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15
Q

What do buffers contain?

A
  • a weak acid which contains equal concentrations of its conjugate base (or weak base and conjugate acid)
  • resists change in pH when acids/bases added to them
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16
Q

Uses of esters related to their properties

A

fragrant-used in perfumes
have fruity flavours-used in food flavouring
-good solvent -used in nail polish remover

**also naturally occur eg. flower scents,

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17
Q

What are 2 esters and their uses?

A

ethyl butanoate: -pineapple flavoured ester used as a food additive and in making rum

-ethyl ethanoate: nailpolish remover dueto its solvent properties as well as in foods with a pear flavour.

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18
Q

Why do we reflux in esterification?

A

the contents of the reactant mixture are volatile and dangerous, they will evaporate when heated .all the reactants would escape.

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19
Q

What is refluxing

A

the process of heating liquids in a flask that has a condensor attached to it.

  • refluxing cools vapours so they condense and fall back down into the reaction.
    1. it avoids the loss of reactants/products
    2. avoids afety issues with evaporated alkanols (combustion)

*refluxing apparatus has an open top, to stop build up of pressure. a hot plate with a water bath is used to heat the mixture.

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20
Q

What are the differences between alkanols and alkanolic acids?

A

alkanols:

  • polar due to the hydroxyl group
  • relatively high MP & Bp due to H bonding
  • *as molecule increases however, dispersion forces become stronger than H bonding
  • soluble in water and non-polar substances
  • neutral molecule

alanoic acids

  • polar due to carboxylic acid group aswell as H bonding, therefore morepolar than alkanols.
  • this means that higher Mp/Bp with stronger intermolecular bonding, and greater dispersion forces
  • more soluble in water, with higher polarity
  • alkanoic acids are weak acids
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21
Q

what are the intermolecular forces of esters?

A

-have no H bonding, they bond mainly over weak dispersion forces, meaning they have much lower BP/MP than alkanols & alkanoic acids

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22
Q

how do you define an acid?

A

donates protons to form hydronium ions in solution

bases accept protons from water to form hydroxide ions

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23
Q

What is the difference between strong,weak and concentrated and dilute acids?

A

strong acid: completely ionises, all H+ are donated
weak acid: only partially ionised (only some H+ donated) (equilibrium)

  • *more dilute weak acid - greater ionisation
  • *not all H atoms on molecule are acidic

Concentrated: lots of acid molecules comapred to water volume
dilute: few acid molecules compared to water volume

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24
Q

What are HCl and H2SO4?

A

both strong acids
HCl is the strongest!!
HCl 100% ionises
HCL + H2O –>H3O+ + Cl-

Sulfuric acid 100% ionises:
H2SO4 +H2O –>H3O+ +HSO4-
2. 99% HSO4- +H2O –> H3O + SO42-

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25
Q

What are citric acid and ethanoic (acetic acid)

A

weak acids

citric acid ionises 10-20%
ethanoic acid: ionises 1%

all depend on concentrations however

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26
Q

What is a standard solution?
What is a primary standard solution?
What is a secondary solution?

A

solutions whose concentrations are known

  • a standard solution prepared from a solid
  • a standard solution whose concentration was determined through titation
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27
Q

What are good acid and base standards?

A

-oxalic acid
-Na2CO3 sodium carbonate (base)
(NaOh is bad primary standard quickly absorbs moisture from air, increasing mass)

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28
Q

How to prepare a standard solution?

A
  1. rinse volume flask with distiled H2O
  2. weigh primary standard in small beaker
  3. Dissolve primary standard in small volume of distilled H2O
  4. Pour solution into volumetric fask.
    i. uuse fulter funnel
    ii. rinse beaker and funnel several times with distilled H2O and add rinsings to flask
    ii. Invert to mix the solution
  5. Add distilled H2O until bottom of meniscus reaches line. Place lid ont op and mix into solution you want
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29
Q

What is the method for titration?

A
  1. Pour standard solution into a clean burette using a clean funnel. Ensure solution goes above ml line.
  2. rinse excess solution out of burette
  3. rinse a cleanconical flask with distilled water.
  4. Add the unknown solution to the flask and place it under the burette
  5. Slowly add the standard solution in the burette to the flask, swirling continuously until the indicator just changes colour (end point)
  6. Read volume of burette.
    Repeat 3 times. Calculate average
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30
Q

Describe the relationship between an acid and it’s cingulate and a base and it’s conjugate acid

A

An acid gives up a proton to form its conjugate base

A base accepts a proton to form its conjugate acid

Eg. Water acts as an acid, OH- is conjugate base
H2O + CH3COO- CH3COOH + OH-
CH3COOH is an acid with CH3COO- acting as its conjugate base

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31
Q

What is an example of a conjugate base

A

ACID +H2O
—->
H3O+ +CONJUGATE BASE
HCl + H2O —–> H3O+ + Cl-

CH3COOH + H2O —-> H3O+ + CH3COO-

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32
Q

What is an example of a conjugate acid

A

BASE + H2O
—–>
conjugate acid + OH-

NH3 + H2O—-> NH4+ + OH-

CO32- + H2O—-> HCO3- + OH-

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33
Q

What are example of amphiprotic substances?

A

C6H8O7

HCO3-

H2PO4-

HSO4-

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34
Q

Identify a range of salts which form acidic basic or neutural solutions and explain their acidic, basic or neutral nature

A

Acidic:
Ammonium sulfate
Ammonium nitrate

Basic:
Calcium carbonate
Calcium acetate

Neutral:
Sodium chloride
Sodium sulfate

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35
Q

oxides of non-metals are acidic or basic in water?

A

acidic

eg. CO2 + H2O —> H2CO3(aq)

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36
Q

identify factors which can affect the equilibrium in a reversible reaction?

A
  • conc.
  • temp
  • pressure (if gas)
  • volume (if gas)
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37
Q

does a catalyst have an effect onn an equilibrium reaction?

A

no it doesn’t change equilibrium position

-it increases the rate of forward and reverse reactions

38
Q

describe the solubility of carbon dioxide in water as an equilibrium reaction

A

co2 solubility increases when temperature decreases

39
Q

What does the change in pressure have on the solubility of CO2 in water?

A

CO2(g) + H2O(l) ——–> H2CO3 (aq)

increasing pressure favours reaction with fewer gas molecules

  • therefore increasing pressure favours the forward direction, causing more CO2 to dissolve ->H2CO3
  • decreasing pressure shifts equilibrium left to produce more CO2
40
Q

What does the change in CO2 in a system have on the solubility of CO2 in water?

A

increased CO2 conc. causes equilibrium to reduce CO2 conc, pushing reaction to the right

-decrease CO2 concentration moves reaction to the left

41
Q

What does the change in temperature have on the solubility of CO2 in water?

A
  • increased temperature favours the endothermic direction (reverse direction),meaning less CO2 is dissolved
  • decreased temperature favours exothermic direction (forward), causing more CO2 to become dissolved
42
Q

What does the change in pH have on the solubility of CO2 in water?

A

Adding (OH-) NaOH to the equilibrium will neutralise the carbonic acid, and the system moves to the right to compensate the change

-Adding H+ will cuase the equilibrium to shift to the left

43
Q

What is a mole

A

quantity of a substance that contains 6.022 x 10 to the 23 particles (Avogadro’s number)

44
Q

What is an example of a monoprotic acid?

A

HCl

acetic acid CH3COOH

45
Q

What is an example of a diprotic acid?

A

H2SO4

46
Q

What is an example of a triprotic acid?

A

citric acid C6H8O7

phosporic acid H3PO4

47
Q

What are examples of strong acids?

A

Ionise close to 100%

H2SO4 (di)
HNO3 nitric acid (mono)
HCl (mono)

48
Q

What are examples of weak acids?

A 
H2CO3 carbonic acid
H3PO4 phosphoric acid
NH4 ammonium
CH3COOH acetic acid 
C6H8O7 citric acid
49
Q

Weak acid
strong acid
concentrated acid
dilute acid

A

strong -completely ionises in H+
weak -only partially ionises (less than 10%) to form H+
concentrated -high no. moles per liter (generally more than 0.1mol/L)
dilute -has a low no.moles per litre

50
Q

identify examples of naturally occurring acids and their chemical composition

A
  • HCl (produced by glands in lining of stomach, acidic enviro for enzymes)
  • Acetic acid (ethanoic acid), present in vinegar and rotting fruit
  • Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) occurs in citrus fruit
  • C6H8O6 (vitamin C), fruits and veggies
51
Q

identify examples of naturally occurring bases and their chemical composition

A

CaCO3 present in limestone and marble

calcium magnesium carbonate -found as dolomite

52
Q

use of acids as food additives?

A
  • citric and tartaric acid (C4H6O6) added to jams to give sharp taste
  • phosphoric acid is added to soft drink eg. colas as it increases the sharpness of taste and prevents spoilage
  • acetic acid in vinegar helps to preserve food and enhance flavour eg. pickles and chutneys, by lowering the pH, making enzyme reactions slow down, slowing the spoilage of food
  • ascorbic acid (vitamin C6H8O6) prevents the spoilage of food by oxidation

-weak acids are used so they don’t corrode the food and they are also safe to ingest

53
Q

describe the use of the pH scale in comparing acids and bases

A

number line from 0 to 14 which measures the concentration of H+ ions and therefore the acidity or basicity of a substance

54
Q

how would you investigate measuring the pH of identical concentratinos of strong and weak acids?

A
  1. make up mixtures of ethanoic acid and HCl in test tubes of exactly 0.1M
  2. Add drops of universal indicator to find the pH of the soutions

-it was found that the HCl had a higher acidity than the ethanoic acid (weak)

55
Q

Lavoisier

A

In 1776 Lavoisier defined an acid as a non-metal compound containing oxygen (couldn’t explain why metal oxides weren’t acidic)

ADV: recognised acidic properties were a result of the composition of a substance
DIS: many acidic compounds eg. HCl didn’t meet this definition

56
Q

Davy

A

in 1810 defined acids as substances containing replaceable hydrogen

ADV: recognised H was important to the activity of acids
DIS: some substances contained replaceable Hydrogen but weren’t acids (eg. sugar reacted with metals & bases –>H2)

57
Q

Arrhenius:

A

in 1884 Arrhenius defined:

  • acids ionise in solution to produce H+
  • a base is a substance producing OH- (excludes metal oxides)

ADV: explained why acidic solutions conduct electricity
DIS: definition requires that water be a solvent, excluding some acid/base reactions
-not applied to amphiprotic substances
-only applied to aqueous solutions

58
Q

Bronsted-Lowry

A

in 1923 Bronsted-Lowry defined:

  • an acid is a proton donor
  • a base is a proton acceptor
59
Q

What is a natural buffer?

A

H2CO3 (carbonic acid) and HCO3- in the blood

CO2 + H2O –> H2CO3
H2CO3 + H2O –> HCO3- + H3O+

  • adding an acid shifts equilbrium left to absorb excess H3O+
  • adding a base (OH-) effectively removes H3O+, therefore shifts equilibrium to the right to produce/replace H3O+
60
Q

neutralisation reaction?

A

acid + base —> salt + water exothermic!

61
Q

In chemical spills what is used to minimise damage?

A

weak amphiprotic substances such as NaHCO3 (sodium hydrogen carbonate)

62
Q

What are the advangtages of using NaHCO3 ?

A
  1. as it is amphiprotic, it isnt necessary to know the nature of the spill
  2. cheap, so easy to be stored in large quantities
  3. solid and relatively stable = stored for long periods of time
  4. can be used in excess, as adding extra solid wont worsen spill
  5. non-hazardous so won’t make spill more dangerous
63
Q

NaHCO3 reacting with an acid & base

A

with an ACID: NaHCO3(s) + H+ –> Na+ + CO2 +H2O

with a BASE: NaHCO3(s) +OH- –> Na+ + CO32- + H20

64
Q

What are the disadvantages of NaHCO3?

A
  1. If the spill is acidic, CO2 can build up, and if the area isnt ventilated could cause asphyxiation
  2. Reactions with acids/bases are exothermic meaning there is a potential for large amounts of heat to build up
65
Q

before acidic waste is discharged from factories into waterways what needs to happen?

A
  • must be neutralised and diluted

- ensures that thermal pollution doesn’t occur and that a high concentration of ions isnt discharged

66
Q

what are the advantages of the bronsted lowry theory over Arrhenius?

A
  1. BL theory applies to non-aqueous aswell as aqueous solutions,
  2. explaining why salts act as acids and some as bases even if they don’t have H+ or OH- ions
  3. also explains amphiprotic substances
67
Q

What are the rules for comparative strength of conjugates?

A
  1. strong acids and bases have weak conjugates (can’t accept or donate protons)
  2. weak acids and bases have relatively strong conjugates (can accept/donate protons)
68
Q

what is an example of amphiprotism?

A

H2CO3 –> HCO3-

as a BASE: HCO3- + H3O+ —-> H2CO3
as an ACID: HCO3- + OH- —–> CO32- + H2O

69
Q

describe the proton transfer in neutralisation reactions

A

a proton is transferred from the hydronium ion to the hydroxide ion forming 2 molecules of water

70
Q

what are natural sources of sulfur dioxide?

A
  • geothermal hot springs

- volcanoes

71
Q

What are natural sources of oxides of nitrogen (NOx)

A
  • lighting: O2(g) +N2(g) –>2NO(g)

- N2O(nitroyus oxide) formed by bacterial action on nitrogenous materials

72
Q

What are oxides of nitrogen (NOx)?

A

nitrous oxide: N2O
nitric oxide: NO
nitrogen dioxide: NO2

73
Q

NO

A

nitric oxide

74
Q

N2O

A

nitrous oxide

75
Q

NO2

A

nitrogen dioxide

76
Q

what are industrial sources of sulfur dioxide?

A
  • processing or burning fossil fuels (eg. coal containing sulfur) S(s) + O2(g) –> SO2(g)
  • extracting metals from sulfide ores
    eg. 2ZnS(s) + 3O2(g) –> 3ZNO(s) + 2SO2(g)
77
Q

What are industrial sources of oxides of nitrogen?

A
  • high temperatures of combustion chambers (cars/power stations)
  • burning fossil fuels and vegetation
  • further reaction of 2NO + O2 –> 2NO2
78
Q

what are reasons for concern about the release of SO2 and NOx into the enviro?

A
  • since industrial revolution there has been an increase in air poluttion and levels of acidic oxides
  • SO2 and NOx don’t have a significant build up in the atmosphere (like CO2) as they are predominately washed out of the atmosphere by rain
  • direct health effects
  • acid rain
  • photochemical smog
79
Q

What are the direct health effects of SO2 and NOx?

A

-nitric oxide, nitrogen dioxide and sulfur dioxide irritate respiratory tract and cause breathing difficulties, exacerbating asthma and emphysema

80
Q

What are the effects of acid rain?

A
  • lowers the pH of waterways and soil, death of aquatic organisms and fish eggs (wont hatch), stunt plant growth and kill microorganisms in soil
  • damage to the human built enviro: buildings and statues that contain calcium carbonate eg. marble
81
Q

What is the equation to represent the damage to marble structures from acid rain?

A

Marble statue: CaCO3(s) + H2SO4(aq) —–> CaSO4(aq) +H2O(l) + CO2(g)

82
Q

What are the effects of photochemical smog?

A

issue with Nitrogen dioxide

  • it combines with other gases to produce toxic photochemical smog
  • photochemical smog causes breathing difficulties and can also produce more toxic gases such as ozone (toxic to life in the troposphere)
83
Q

explain the formation of acid rain?

A
  • occurs when SO2 and NOx dissolve in rain making it acidic

- has a pH below 5

84
Q

formation of acid rain through SO2?

A

SO2 + H2O –> H2SO3 (sulfurous acid)

2H2SO3 + O2 –> 2H2SO4

85
Q

formation of acid rain through NO?

A

2NO + O2 –> 2NO2
2NO2 + H2O –>HNO2
2HNO2 +O2 –> 2HNO3

86
Q

What are the effects of acid rain?

A
  1. defoliation, destroying crops and forests
  2. lowering soil pH, stunting plant growth and solubilising toxic ions eg Al3+ which can move into food chain
  3. lowering pH of waterways, preventing aquatic animals from reproducing (eggs won’t hatch), death of aquatic plants and sometimes animals
  4. destruction of human built eviro eg. sandstone, limestone, marble, metals
    eg. Zn + 2H+ –> Zn2+ + H2(g)
87
Q

examples of chemical reactions which release SO2?

A

-metal refining process produces SO2 directly:
2ZnS(s) + 3O2(g) –> 2ZNO(s) + SO2(g)

-sulfur in fossil fuels converted to SO2 during combustion process

S(s) + O2(g) –> SO2(g)

88
Q

examples of chemical reactions which release NOx?

A

-high temperatures of internal combustion engines or lighting

N2 + O2 –> 2NO

2NO + O2(g) –> 2NO2

89
Q

what evidence is there that indicates increases in atmospheric concentration of oxides of sulfur and nitrogen?

A
  • measurement on bubbles of ancient air trapped in ice sheets in antarctica and greenland.
  • this is then compared to modern levels, successfully showing increase in atmospheric oxides of Sulfur and nitrogen
  • burning of coal and petroleum aswell as smelting minerals has led to sig. increase in acidic oxides in atmosphere
  • BUT these are continually washed out by rain and thus concentrations don’t build as much
  • therefore measuring soil pH and waterway pH could be monitored and compared also
90
Q

how to prepare an ester

A

 substances used: alkanol (1-pentanol), alkanoic acid (ethanoic/acetic acid), concentrated H2SO4
 mix 1-pentanol with ethanoic acid to round bottom flask, add H2SO4
 add anti-bumping granules, grease opening and fit to condenser
 heat using electric heater, reflux for 30 mins
 risk: conc. H2SO4-> corrosive, added by teacher, everyone wearing gloves and glasses. Flammable reactants and products-> electric heater to avoid open flame. Volatile, smelly chemicals-> good ventilation (windows/door)

Yr 12 Chemistry (11 decks)

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