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[GCSE] chemistry > C4: Chemical Changes > Flashcards

C4: Chemical Changes Flashcards

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1
Q

define oxidation and reduction

A

oxidation: when a substance gains oxygen / loses electrons
reduction: when a substance loses oxygen/ gains electrons

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2
Q

what is the reactivity series of metals?

A

A list of elements ordered by their reactivity

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3
Q

what are the trends in reactivities of metals in reactions with acids/water?

A
  • metals above hydrogen in reactivity series react with acid to produce hydrogen
  • The more reactive the metal is, the quicker and more violent reaction with acid occurs
  • metals below H2 dont react with acids
  • not all metals above H2 react with water
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4
Q

Write the reactivity series from
most reactive to least reactive

A

potassium
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
tin
lead
hydrogen
copper
silver
gold
platinum

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5
Q

what is a displacement reaction?

A
  • a reaction where a more reactive metal displaces a less reactive metal from a compound
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6
Q

how are unreactive metals found in Earth?

A

in their natural state

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7
Q

Explain why zinc can be
extracted from zinc oxide with
carbon but magnesium cannot
be extracted from magnesium
oxide with carbon

A

Magnesium is more reactive than carbon (1), Zinc is less reactive than carbon (1), Carbon can therefore remove oxygen from zinc oxide but not magnesium oxide (1

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8
Q

What process is used to extract
metals more reactive than
carbon

A

Electrolysis

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9
Q

how can metals less reactive then carbon be extracted?

A
  • reduction with carbon
  • Carbon displaces the metal in a metal oxide
  • Carbon gets oxidised to form carbon oxides .
  • Metal from the metal oxide gets reduced to the pure metal
  • eg Copper oxide + carbon → copper + carbon dioxide
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10
Q

what is the general equation for a reaction between metals and acids? what type of reaction is this?

A

metal + acid –> salt + hydrogen
redox reaction, also a displacement reaction

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11
Q

which metals in the reactivity series will react with acid?

A

those above hydrogen

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12
Q

what is the general equation for a neutralisation reaction?

A

Base + acid –> salt + water

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13
Q

what is the general equation for the reaction between metal carbonate and acid?

A
  • metal carbonate + acid—>salt + water + carbon dioxide
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14
Q

what is the general equation for the reaction between metal oxides and acids?

A

metal oxide + acid—> salt + water

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15
Q

what is a redox reaction?

A
  • a reaction where both oxidation and reduction occurs
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16
Q

explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid

A

magnesium has lost electrons and thus has been oxidised (Mg to MG2+)
- the hydrogen in HCL has gained electrons and thus has been reduced (H+ to H2)

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17
Q

how is a soluble salt formed?

A
  1. react the excess acid with some insoluble chemical (e.g. metal oxide)
  2. filter off the leftovers
  3. Crystallise the product
18
Q

what do acids and alkalis produce in aqueous solutions?

A
  • acids produce hydrogen ions, alkalis produce hydroxide ions
19
Q

define bases , acids and alkalis?

A
  • bases are compounds that neutralise acids
  • acids produce hydrogen ions in aqueous solutions
  • alkalis are soluble bases - produce hydroxide ions in aqueous solutions
20
Q

what is the pH scale and what does a pH of 7 show?

A
  • the measure of acidity/ alkalinity of a solution
  • a neutral solution
21
Q

state the general equation for a neutralisation reaction in a short, ionic form

A

H* + OH- –> h20

22
Q

what is a strong acid? what is a weak acid?

A
  • strong acid is completely ionised in aqueous solution
  • weak acid is only partially ionised in aqueous solution
23
Q

what happens to pH as concentration of H+ increases?

A
  • the pH decreases
24
Q

what is a concentrated acid and what is a dilute acid? is this the same as a strong and weak acid?

A
  • concentrated acid has more moles of acid per unt volume than dilute acids
  • it is not the same - strength refers to whether the acid is completely ionised in water
25
Q

As the pH is decreased by one unit , what change is seen in the hydrogen ion concentration

A

increases by a factor of 10

26
Q

name the following salts:
- LiNO3
- K2CO3
- MgBr2
- BaSO4

A
  • lithium nitrate
  • potassium carbonate
  • magnesium bromide
  • barium sulfate
27
Q

what is electrolysis?

A
  • the passing of an electric current through ionic substances that are molten to break them down into elements
  • ions are discharged (they lose/gain electrons) at electrodes to produce these
28
Q

what is an electrolyte?

A

the liquid/solution which conducts electricity

29
Q

what is a cathode and what is an anode?

A

cathode is the negative electrode
anode is the positive electrode

30
Q

what occurs at the cathode and what occurs at the anode during electrolysis?

A

reduction occurs at the cathode
oxidation occurs at the anode

31
Q

in aqueous electrolysis, which element is discharged at the cathode?

A
  • the less reactive element discharges at the cathode.
  • hydrogen is produced unless there is a less reactive metal
  • in which case the said metal is produced
32
Q

how is aluminium manufactured? why is it expensive?

A
  • aluminium is made through the electrolysis of aluminium oxide and cryolite
  • lots of energy is needed to produce the current in electrolysis which makes this process expensive
33
Q

what are the half equations in the extraction of aluminium?

A

cathode: Al3* + 3e- –> Al(cathode)
anode: 2O 2- → O 2 + 4e -( anode)
oxygen reacts with Carbon of the anode producing CO2-

34
Q

why is cryolite used in manufacturing of aluminium

A
  • it lowers the melting point of aluminium oxide, reducing energy costs
35
Q

what are the half equations in electrolysis of the aqueous Na2SO4?

A

2H* + 2E- –> H2 (cathode)
4OH- –> 2H20 + 02 + 4e- (anode)

36
Q

delete me

A

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37
Q

what are the half equations in electrolysis of the aqueous CuBr2

A

Cu2* + 2e- —> Cu (cathode)
2Br- –> Br2 + 2e-

38
Q

define an ore

A

material containing enough metal in it for it to be economically worthwhile to extract the metal.

39
Q

give the empirical formulae for
- hydrochloric acid
- sulfuric acid
- nitric acid

A
  • HCl
  • H₂SO₄
  • HNO₃
40
Q

describe what occurs at the anode in the electrolysis of aqueous solutions

A
  • negatively charged OH– ions and non-metal ions are attracted to the positive electrode
  • If halide ions (Cl-, Br-, I-) and OH- are present then the halide ion is discharged at the anode, loses electrons and forms a halogen (chlorine, bromine or iodine)
  • If no halide ions are present, then OH- is discharged at the anode, loses electrons and forms oxygen
41
Q

describe what occurs in the cathode in the electrolysis of aqueous solutions

A
  • Positively charged H+ and metal ions are attracted to the negative electrode
  • If the metal is above hydrogen in the reactivity series, then hydrogen will be produced and bubbling will be seen at the cathode

[GCSE] chemistry (12 decks)

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