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science notes > [chem] acids, bases and salts > Flashcards

[chem] acids, bases and salts Flashcards

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1
Q

classes of acids

A

inorganic and organic

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2
Q

where are inorganic acids from

A

prepared in the laboratory from mineral elements or inorganic matter

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3
Q

where are organic acids from

A

obtained from plants and animals

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4
Q

examples of inorganic acids

A
  • hydrochloric acid (HCl)
  • nitric acid (HNO3)
  • sulfuric acid (H2SO4)
  • phosphoric acid (H3PO4)
  • carbonic acid (H2CO3)
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5
Q

examples of organic acids

A
  • ethanoic acid
  • citric acid
  • ascorbic acid
  • tartaric acid
  • lactic acid
  • tannic acid
  • formic/methanoic acid
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6
Q

what are acids

A

an acid is a substance which dissociates in water/aqueous solutions to give hydrogen ions. all acids contains H+ ions

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7
Q

what do pure acids exist as

A

simple covalent molecules, they react with water to give hydrogen ions

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8
Q

when is reversible and normal arrow used (for dissociation equation of acid)

A

normal arrow used for complete dissociation
reversible reaction arrow used for partial dissociation

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9
Q

what gives the properties of the acids

A

hydrogen ions

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10
Q

nature of solution when hydrogen chloride dissolved in an organic solvent and why

A

neutral solution, in absence of water, hydrogen chloride still exists as simple molecules, and no hydrogen ions are formed

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11
Q

nature of solution when hydrogen chloride dissolved in water and why

A

acidic solution. hydrogen chloride dissociates in water to produce hydrogen ions and chloride ions, the hydrogen ions are responsible for the acidic property

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12
Q

what is basicity of an acid

A

basicity of an acid is the maximum number of hydrogen ions produced by one molecule of the acid when the acid molecule dissociates in water

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13
Q

what are the 3 basicity of acids

A

monobasic, dibasic, tribasic

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14
Q

examples of monobasic acids

A

hydrochloric acid, nitric acid, ehtanoic acid

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15
Q

examples of dibasic acid

A

sulfuric acid, carbonic acid

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16
Q

examples of tribasic acids

A

phosphoric acid

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17
Q

what does strength of acid depend on

A

the extent of dissociation/ionisation of the acid molecule in water/aqueous solution

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18
Q

what is strong acid, and examples

A
  • a strong acid is one that completely dissociates in water to give hydrogen ions
  • hydrochloric acid, sulfuric acid, nitric acid
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19
Q

what is a weak acid and examples

A
  • a weak acid is one that partially dissociates in water to give hydrogen ions
  • ethanoic acid, carbonic acid, phosphoric acid
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20
Q

what is concentration of solution

A

concentration of a solution is a measure of how much solute has dissolved in 1dm3 of the solution

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21
Q

unit for concentration

A

mol/dm3

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22
Q

why can aqueous acids conduct electricity

A

in the presence of water, acid molecules are able to dissociate to form ions. these ions can move freely in water to conduct electricity.

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23
Q

how to explain for strong or weak acid

A
  1. ___ is a strong/weak acid
  2. which completely/partially dissociates in water to form hydrogen ions
    - thus, there is a high/low concentration of hydrogen ions in the solution to react with ____
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24
Q

properties of acids (physical)

A
  • sour
  • ph<7
  • turns blue litmus paper red
  • conducts electricity
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25
Q

chemical properties of acids

A
  1. acids react with:
    - metals above hydrogen in the reactivity series
    - metal carbonates/metal hydrogen carbonates
    - bases (metal oxides/hydroxides)
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26
Q

memorise the solubility table

A

refer to notes

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27
Q

observation for reaction between acid and metal

A
  • effervescence of colourless, odourless gas observed
  • gas extinguishes a lighted splint with a pop sound
  • gas is hydrogen
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28
Q

metals above the reactivity series

A

K
Na
Ca
Mg
Al
Zn
Fe
Sn
Pb

29
Q

metals under reactivity series

A

Cu
Ag
Au
Pt

30
Q

why will some reactive metals have no apparent reaction with acids?

A
  • lead metal appears not to react with hydrochloric acid or sulfuric acid
  • the initial reaction produces a layer of lead(II) chloride or lead (II) sulfate. this layer is insoluble in water and forms a layer around the metal, which prevents from further reaction between the metal and the acid
31
Q

observation for metal carbonate and acid

A
  • effervescence of colourless, odourless gas observed
  • gas forms white precipitate when passed into limewater
  • gas is co2
32
Q

why will a white precipitate be seen

A

carbon dioxide gas reacts with limewater to give calcium carbonate, an insoluble salt which appears as a white precipitate

33
Q

what is a base

A

a base is a substance that reacts with an acid to form salt and water only

34
Q

what are bases made of and exceptions

A

bases are usually metal oxides or metal hydroxides
exception is aqueous ammonia is also a base

35
Q

what are alkalis

A

alkalis are bases that dissociate in water to produce hydroxide ions (OH-)

36
Q

what are alkalis usually

A

metal hydroxides, exception is aqueous ammonia is also an alkali

37
Q

what is strong alkali

A

a strong alkali completely dissociates in water to give hydroxide ions

38
Q

what is weak alkali

A

a weak alkali partially dissociates in water to give hydroxide ions

39
Q

why is ammonia gas a weak alkali when dissolved in water

A
  • when ammonia gas dissolves in water, only a small fraction of ammonia molecules react with water to produce ammonia and hydroxide ions
  • most ammonia will still remain as simple molecules in the solution
40
Q

physical properties of alkalis

A
  • bitter
  • soapy
  • turns red litmus paper blue
  • ph>7
  • can conduct electricity
41
Q

chemical properties of alkalis

A
  1. alkalis react with
    - acids
    - ammonium salts
    - some metal cations to form precipitate
42
Q

observation for alkali with ammonium salt

A
  • colourless and pungent gas is produced
  • gas turns moist litmus paper blue
  • gas is ammonia
43
Q

why must litmus paper be moist? (ammonia)

A

ammonia reacts with water to produce hydroxide ions which turn the red litmus paper blue

44
Q

what does test for cations (precipitation) reaction produce

A

it produces insoluble metal hydroxide, which appears as precipitate.

45
Q

commonly used alkalis to test for cations

A

aqueous sodium hydroxide and aqueous ammonia

46
Q

definition of precipitation

A

precipitation is a chemical reaction between which an insoluble produce is formed when two aqueous solutions are mixed

47
Q

what is ph

A

ph is a measure of acidity or alkalinity in aqueous solution

48
Q

what does ph measure

A

the concentration of hydrogen ions in the aqueous solution

49
Q

number range of ph scale

A

0 to 14

50
Q

ph ranges to types of acids

A
  1. 0-2 strongly acid
  2. 4-6 weakly acid
  3. 7 neutral
  4. 8-10 weakly alkaline
  5. 12-14 strongly alkaline
51
Q

examples of neutral substances

A

water, aqueous sodium chloride

52
Q

examples of weak alkali

A

aqueous sodium carbonate, aqueous sodium bicarbonate, aqueous ammonia

53
Q

examples of strong alkalis

A

aqueous sodium hydroxide, aqueous potassium hydroxide

54
Q

what is indicator

A

an organic compound which changes in colour in accordance with the ph of the solution

55
Q

what are indicators made of

A

can be made from natural living organisms, like parts of plants such as leaves and flowers

56
Q

5 common indicators

A
  • litmus
  • phenolphthalein
  • methyl orange
  • screened methyl orange
  • bromothymol blue
57
Q

colour of solution in litmus and ph at which colour changes

A

red and blue, 7

58
Q

colour of solution in phenolphthalein and ph at which colour changes

A

colourless, pink, 9

59
Q

colour of solution in methyl orange and ph at which colour changes

A

red, yellow, 4(turns orange)

60
Q

colour of solution in screened methyl orange and ph at which colour changes

A

purple, green, 4(turns grey)

61
Q

colour of solution in bromothymol blue and ph at which colour changes

A

yellow, blue, 7(turns green)

62
Q

what is universal indicator

A

contains a mixture of dyes and can come in the form of a solution or ph paper, can give a spectrum of different colours across ph values

63
Q

what is ph meter

A

an electrical method of measuring the ph of a solution

64
Q

how to measure using ph meter

A

it consists of a ph electrode connected to a meter, the ph electrode is dipped into the solution and the ph value is then shown on the meter

65
Q

advantages of ph meter

A
  • more reliable and accurate
  • can be used in data logging to record rapid changes in ph
66
Q

problem of ph in agriculture

A

soils tend to become acidic from acid rain and extensive use of chemical fertilisers

67
Q

solution for problem in agriculture

A

adding of slaked lime (calcium hydroxide) to the soil to neturalise the acids, which is also known as ‘liming the soil’

68
Q

why cannot add slaked lime and chemical fertiliser (ammonia nitrate) at the same time?

A

other than neutralising the soil, the slaked lime will react with ammonium nitrate to produce ammonia gas which will escape into the air. this will result in the loss of nitrogen content from the fertiliser added to the soil

science notes (15 decks)

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