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Chemistry > C4 Chemical Changes > Flashcards

C4 Chemical Changes Flashcards

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1
Q

describe oxidation and reduction

A

Oxidation Is Loss, Reduction Is Gain
* oxidation - gaining oxygen or losing hydrogen - loss of electrons
* reduction - losing oxygen or gaining hydrogen - gain of electrons

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2
Q

describe displacement

A

the reaction that occurs when a more reactive metal takes a metal’s place in a compound

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3
Q

describe a redox reaction

A
  • one substance is reduced (displaced) - forms ions
  • other substance is oxidised - forms atoms - regains electrons given to non-metal
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4
Q

state the equation for when a metal (oxide) is extracted from an ore using carbon reduction

A

metal oxide + carbon -> metal + carbon dioxide
(used when the metal is less reactive than carbon)
zinc, iron, tin, lead
metal oxide is heated with carbon, CO2 escapes into surroundings

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5
Q

define native metals

A
  • unreactive so are found as pure elements
  • do not need to be extracted by electrolysis/ carbon reduction
  • copper, silver, mainly gold+platinum
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6
Q

construct 2 half equations for the equation:
Mg(s) + 2H+(aq) -> Mg2+(aq) + H₂(g)

A

Mg(s) -> Mg2+(aq) + 2e-
2H+(aq) + 2e- -> H₂(g)

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7
Q

reconstruct the equation without spectator ions:
Mg(s) + 2H+(aq) + 2HNO₃(aq) -> Mg2+(aq) + 2HNO₃aq) + H₂(g)

A

Mg(s) + 2H+(aq) -> Mg2+(aq) + H₂(g)
(remove 2HNO₃ as it is unchanged by the reaction)

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8
Q

what is required to split up ionic substances into ions

A

the substance must be dissolved in water/aqueous

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9
Q

state the equation for neutralisation

A

H+(aq) + OH-(aq) -> H₂O(l)
acid + alkali -> water + SALT

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10
Q

describe acids when dissolved in a solution (water)

A
  • produce hydrogen ions
  • as pH number decreases, H+ concentration increases
  • strong acids will fully ionise (1-3)
  • weak acids will partially ionise (4-6)
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11
Q

describe the difference between strong+ weak acids

A
  • strong acid are completely ionised in an aqueous solution, high concentration of hydrogen ions (H+)
    -> hydrochloric acid (HCl), sulfuric (H2SO4), nitric (HNO3)
  • weak acids are partially ionised in an aqueous solution, less reactive, lower concentration of hydrogen ions
    -> ethanoic, citric, carbonic acids
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12
Q

describe the difference between concentrated+dilute acids

A
  • concentrated acid contains a high proportion of acid molecules compared to water molecules in a solution
  • dilute acid contains a lower proportion of acid molecules compared to water molecules
  • adding water to a strong acid dilutes it
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13
Q

describe alkalis when dissolved in a solution (water)

A
  • produce hydroxide ions
  • as pH number dincreases, OH- concentration increases
  • strong alkalis will fully ionise (pH 11-14)
  • weak acids will partially ionise (8-10)
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14
Q

describe indicators used to test acids+alkalis

A
  • universal indicator
  • red litmus paper: stays red for acidic, stays red for neutral, turns blue for alkaline
  • blue litmus paper: turns red for acidic, stays blue for neutral, stays blue for alkaline
  • universal indicator: solution turns red/ green/ blue
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15
Q

describe the scale used for pH levels

A
  • increase 10-fold
  • pH1 is 10x more acidic than pH2
  • pH13 is 10x less alkaline than pH14
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16
Q

state 4 equations that form salts

A

acid + metal -> salt + hydrogen
acid + alkali -> salt + water (neutralisation)
acid + metal oxide -> salt + water
acid + metal hydroxide -> salt + water

17
Q

describe the process of electrolysis

A
  • metals more reactive than carbon are extracted from compounds
  • positive metal ions travel to the cathode - they gain electrons to form a neutral atom/element (reduction)
  • negative non-metal ions travel to the anode - they lose electrons to become a neutral atom/element (oxidation)
  • ions are discharged at the electrodes to form atoms
18
Q

describe the pros+cons of apparatus used for electrolysis

A
  • electrodes are made of carbon (graphite)- delocalised electrons so conduct electricity
  • electrodes are inert so don’t form ions during electrolysis
  • requires a lot of energy to melt the compounds+ produce electric current - expensive
  • substances with a high melting point (bauxite) are dissolved in molten cryolite to lower the substance’s melting point
  • when oxygen is formed at the anode it reacts with the carbon electrodes to form CO2 - anodes have to be frequently replaced
19
Q

why is molten cryolite used in the electrolysis of bauxite (aluminium oxide/ ore)

A
  • bauxite is insoluble in water so must be molten to act as an electrolyte
  • bauxite has a high melting point - a lot of energy is required to break its strong ionic bonds - expensive
  • to reduce costs it is dissolved in molten cryolite - ionic compound melts at a lower temp than bauxite
20
Q

describe how electrolysis splits apart molten ionic compounds

A
  • substance is melted so ions are free to move
  • positive metal ions travel to the cathode - they gain electrons to become a neutral element
  • negative non-metal ions travel to the anode - they lose electrons to become a neutral element
  • Positive Anode, Negative Is Cathode
21
Q

describe how electrolysis splits apart aqueous ionic solutions

A
  • hydrogen is produced at the cathode if the metal is more reactive than hydrogen, otherwise the metal is produced
  • oxygen is produced at the anode unless the non-metal is a halogen, otherwise the halogen gas is produced
22
Q

describe the method for RP: making salts/neutralisation

A
  • measure a vol. of dilute (sulphuric) acid using a measuring cylinder and pour into a beaker
  • set up a bunsen burner/tripod/gauze then heat beaker over a gentle flame until acid is almost boiling
  • remove from heat and add base (copper oxide) until it is in excess, stir with glass rod
  • filter mixture into conical flask using filter paper/funnel
  • pour solution into evaporating basin and warm over a water bath, then leave to cool until crystals form
23
Q

describe precautions for RP: making salts/neutralisation

A
  • hot apparatus - don’t touch when hot
  • bunsen burner - tie hair/tuck loose clothing to prevent catching fire
  • sulphuric acid - concentrated acid is corrosive and damages skin/clothes - use dilute acid, use copper oxide in excess so no acid remains on the salt
24
Q

what is seen when alkali metals react with water

A

forms metal hydroxide (s) + hydrogen (g)
* bubbles/ fizzes
* moves on surface of water
* metal disappears/ melts
* hydrogen may ignite with orange flame (sodium) or explosion (potassium)
* faster reaction down the group

25
Q

what is seen when alkali metals react with chlorine

A

forms metal chloride
* forms a white powder
* faster reaction down the group

26
Q

what is seen when alkali metals react with oxygen

A

forms metal oxide
* forms a white powder
* burns with a flame
-> lithium: red
-> sodium: yellow
-> potassium: lilac
* faster reaction down the group

27
Q

state the reactivity series inc. carbon+ hydrogen

A

potassium (easiest to lose electrons+ form pos ions)
sodium
lithium
calcium
magnesium
aluminium
-> carbon
zinc
iron
tin
lead
-> hydrogen
copper
silver
gold/ platinum

28
Q

state the equation for when a metal reacts with an acid

A

metal + acid -> salt + hydrogen

29
Q

describe the reaction between metals and dilute acids

A

alkalis: (potassium, sodium, lithium): react vigorously, form salt solution+ hydrogen
(calcium, magnesium, zinc, iron): react more slowly, form salt solution+ hydrogen
(copper): no reaction, no products

30
Q

state the equation for when a metal reacts with water

A

metal + water -> metal hydroxide + hydrogen

31
Q

describe the reaction between metals and water

A

(potassium, sodium, lithium, calcium): react quickly, form metal hydroxide+ hydrogen
(magnesium, zinc, iron): react slowly or not at all with cold water, form hydrogen+ metal oxide (with steam)
(copper): no reaction, no products

32
Q

state the equation for when a metal carbonate reacts with an acid

A

acid + metal carbonate -> salt + water + carbon dioxide
(neutralisation)- metal carbonates are bases

Chemistry (5 decks)

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