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Chemistry > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

pH scale

A
  • measure of how acidic or alkaline a solution is

- neutral substances have a pH of 7

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2
Q

What pH does an acid have?

A

Below 7

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3
Q

What pH would an alkali have?

A

Above 7

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4
Q

Give two examples of strong acids

A
  • car battery acid
  • stomach acid (hydrochloride)
  • vinegar
  • lemon juice
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5
Q

Give two examples of weak acid

A
  • acid rain
  • lemon juice
  • normal rain
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6
Q

Give two examples of strong alkalis

A
  • caustic soda (drain cleaner)

- bleach

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7
Q

Give two examples of weak alkalis

A
  • pancreatic juice

- washing-up liquid

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8
Q

Indicator

A
  • a dye that changes colour depending on acidity or alkalinity of substance
  • wide range indicators have a mixture of dyes that gradually change colour over a broad range of pH
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9
Q

Neutralisation

A
  • reaction between an acid and a base
  • react to form a salt and water
  • pH 7
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10
Q

Acid + base =>

A

Salt + water

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11
Q

Ionic equation for neutralisation (acid + base)

A

H+ + OH- => H2O

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12
Q

Titration

A
  • used to find the exact volume of acid required to neutralise a measured volume of alkali (or vice versa)
  • data used to work out concentration of the alkali
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13
Q

Titration method to find concentration of alkali

A
  • add a set volume of alkali to a conical flask (using pipettes and pipette filler)
  • add two or three drops of indicator
  • use a funnel to fill a burette with an acid of known concentration - record initial volume of acid
  • add the acid slowly to the alkali; go especially slowly when you think the end-point is about to be reached
  • indicator changes colour when alkali has been neutralised
  • record final volume of acid and use in concentration calculation
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14
Q

Why must you repeat titrations?

A
  • repeat the experiment to increase accuracy and spot any anomalous results
  • several consistent readings
  • first is a rough titration to get an approximate idea of end-point
  • calculate a mean of results (ignoring any anomalous results)
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15
Q

Phenolphthalein colour in acid and alkali

A
  • colourless in acid

- pink in alkali

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16
Q

Litmus colour in acid and alkali

A
  • red in acid

- blue in alkali

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17
Q

Methyl orange colour in acid and alkali

A
  • red in acid

- yellow in alkali

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18
Q

Difference between strong and weak acids

A
  • strong acids ionise completely in water
  • all acid particles dissociate to release H+ ions
  • weak acids do not fully ionise in solution
  • small proportion of acid particles dissociate to release H+ ions
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19
Q

Difference between strength and concentration of acids

A
  • strength tells you proportion of acid molecules that ionise in water
  • concentration measures how much acid there is in a certain volume of water; how pure or dilute it is
  • pH affected by concentration and strength of acid
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20
Q

Acid + metal oxide =>

A

Salt + water

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21
Q

Acid + metal hydroxide =>

A

Salt + water

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22
Q

Acid + metal carbonate =>

A

Salt + water + carbon dioxide

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23
Q

Soluble salts from insoluble bases

A
  • right acid + insoluble base
  • gently warm dilute acid with Bunsen burner, then turn off burner
  • add base slowly until no more reacts (it is in excess)
  • filter out excess to get just salt solution
  • evaporate remaining water to get pure, solid crystals
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24
Q

Reactivity Series

A
  • lists metals in order of reactivity to other substances
  • determined by how easily they lose electrons, forming positive ions
  • reacts more easily with water and acid if it is higher in the reactivity series
  • carbon and hydrogen are often included, as it gives information about extraction
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25
Q

Reactivity series order

A 
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
*Carbon*
Zinc
Iron
Tin 
Lead
*Hydrogen*
Copper
Silver
Gold
26
Q

Acid + metal =>

A

Salt + Hydrogen

27
Q

Metal + water =>

A

Metal hydroxide + hydrogen

28
Q

Separating metals from ores

A
  • most metals found in compounds, not as pure form
  • common metals (e.g. iron, aluminium) form oxides, which are found in the ground
  • reduction reactions separate metals from oxides
29
Q

Oxidation and Reduction

A
  • oxidation is the gain of oxygen
  • reduction is the loss of oxygen
    BUT…
  • oxidation is loss of electrons
  • reduction is gain of electrons
  • OILRIG
30
Q

Extracting Metals by reduction with carbon

A
  • chemically extracted with carbon
  • ore is reduced (loses oxygen) and carbon is oxidised (gains oxygen)
  • only metals lower than carbon in reactivity series; higher than carbon must be extracted using electrolysis
31
Q

Redox reactions

A
  • loss of electrons is oxidation
  • gain of electrons is reduction
  • redox reactions are where oxidation and reduction are happening at the same time
  • e.g. metals reacting with acids
32
Q

What is electrolysis?

A
  • ‘splitting up with electricity’
  • electric current passed through electrolyte (molten/dissolved ionic compound)
  • ions move towards electrodes, where they react and the compound decomposes
  • positive ions towards cathode where they are reduced
  • negative ions towards anode where they are oxidised
  • flow of charge through electrolyte as ions travel towards electrodes
33
Q

Why might we use electrolysis to extract metals from ores?

A
  • more reactive than carbon

- would react with carbon

34
Q

Electrolysis of Aluminium ore

A
  • aluminium extracted from bauxite, which contains Al2O3
  • Al2O3 had a very high MP, so it is mixed with cryolite to lower MP
  • molten mixture contains free ions - it will conduct electricity
  • positive Al3+ ions move to negative electrode, where they pick up three electrons and turn into Aluminium atoms (sink to bottom of tank)
  • negative O2- ions to positive electrode, where they lose two electrons each and combine to form O2 molecules
35
Q

What happens at the cathode during electrolysis of aqueous solutions?

A
  • H+ and metal ions are present
  • hydrogen gas formed if metal is more reactive than hydrogen
  • solid metal layer produced if less reactive than hydrogen
36
Q

What happens at the anode during electrolysis of aqueous solutions?

A
  • OH- and halide ions present
  • molecules of chlorine, bromine or iodine formed
  • no halide ions; OH- ions discharged and oxygen gas (and water) will be formed
37
Q

Test for chlorine

A

Bleaches litmus paper, turning it white

38
Q

Test for Hydrogen

A

Makes a “squeaky pop” with a lighted spliny

39
Q

Test for Oxygen

A

Will relight a glowing splint

40
Q

General word equation for reaction between acid and a base

A

Acid + base => salt + water

41
Q

What colour does universal indicator turn in a neutral solution?

A

Green

42
Q

Why do we do a rough titration first?

A

To find the approximate end-point

43
Q

State three indicators you could use for a titration and the colours they turn in acidic and alkaline conditions

A

Phenolphthalein (colourless - pink)
Litmus (red - blue)
Methyl orange (red - yellow)

44
Q

What is a strong acid?

A

The acid particles in a strong acid fully ionise in water (dissociate into H+ ions)

45
Q

By what factor does the H+ concentration increase for a decrease of 1 on the pH scale?

A

10

46
Q

Write a word equation for the reaction between hydrochloric acid and sodium carbonate

A

Hydrochloric acid + sodium carbonate => sodium chloride + water + carbon dioxide

47
Q

Write a word equation for the reaction between sulphuric acid and calcium hydroxide

A

Sulphuric acid + calcium hydroxide => calcium sulphate + water

48
Q

Write a word equation for the reaction between nitric acid and magnesium oxide

A

Nitric acid + magnesium oxide => magnesium nitrate + water

49
Q

Is zinc more or less reactive than iron?

A

More reactive

50
Q

General word equation for a metal and an acid

A

Acid + metal => salt + hydrogen

51
Q

Calcium + water =>

A

Calcium Hydroxide + Hydrogen

52
Q

Will copper react with water?

A

No

53
Q

If a metal is above carbon in the reactivity series, can it be extracted by reduction with carbon?

A

No

54
Q

Why is gold found as a pure metal in the earth

A

Gold is extremely unreactive, so it found in its unreacted form

55
Q

In terms of electrons, define oxidation

A

Oxidation is the loss of electrons

56
Q

In electrolysis, which electrode are the positive ions attracted to?

A

Cathode (negative electrode)

57
Q

Why can’t ionic solids undergo electrolysis?

A

The ions are held in place and aren’t free to move carrying electrical charge

58
Q

Do ions get oxidised or reduced at the anode in electrolysis?

A

The ions get oxidised, as they lose electrons

59
Q

Which electrode is aluminium formed at in electrolysis?

A

Aluminium is formed at the cathode

60
Q

Why would hydrogen gas be produced at the anode in electrolysis

A

If the metal ions present are more reactive than hydrogen

61
Q

If halide ions are present during electrolysis of an aqueous solution, will oxygen be produced at the anode?

A

No

Chemistry (10 decks)

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