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CHEMISTRY > Chemical Changes.5 > Flashcards

Chemical Changes.5 Flashcards

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1
Q

Properties of acids

A

pH of aqueous solutions is less than 7

Source of hydrogen ions
H+ (aq) in solution

Hydrochloride acid releases H+ ions:
HCL (aq) -> H+ (aq). + Cl- (aq)

Ethanoic

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2
Q

What is electrolysis used for

A

To decompose ionic compounds in the molten state or dissolved in water

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3
Q

Electrolyte

A

Ionic compound in the molten state (liquid) or dissolved in water

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4
Q

Electrolysis is

A

A process in which electrical energy from a direct current (dc) supply, decomposes an electrolyte

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5
Q

Anions are

A

Negatively charged ions that move to the positive electrode (anode)

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6
Q

Cations are

A

Positively charged ions that life to the negative electrode (cathode)

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7
Q

Moving charges

A

The ions in an electrolyte are charged particles. An electric current will pass through the electrolyte only if the ions are free to move from place to place

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8
Q

Remember that ions :

A

Can move about in liquids and solutions

Cannot move about in solids

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9
Q

Ions in a solution

A

Water is a covalent compound some of its molecules naturally form ions

H2O (l) reversible H+(aq) + OH-(aq)

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10
Q

Presence of these ions means that a solution of an ionic compound contains

A

Cations and anions from the dissolved ionic compound and

H+ and OH- ions from the water

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11
Q

Competing ions

A

During electrolysis of an aqueous solution all the ions in the electrolyte compete to be discharged and from products

1- hydrogen gas is produced if H+ ions are discharged: 2H+ (aq) + 2e- -> H2 (g)

2- oxygen gas is produced if OH- ions are discharged: 4OH- (aq) -> 2H2O (l) + O2 (g) + 4e -

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12
Q

What happens st the cathode

A

Negative electrode:
Hydrogen is produced unless the compound contains ions from a metal less reactive than hydrogen
In that case
The metal is produced instead

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13
Q

What happens at the anode

A

The positive electrode:

Oxygen is produced from OH- ions unless 
The compound contains halide ions (Cl-, Br- or I- )
In that case: 
Chloride produce chlorine, Cl2 
Bromides produce bromine, Br2 
Iodides produce iodine, I2
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14
Q

Metal + water ->

A

Metal hydroxide + hydrogen

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15
Q

Hydrogen is produced if a metal reacts with

A

Dilute acid

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16
Q

Metal + acid ->

A

Salt + hydrogen

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17
Q

Rates of reaction is greater in warm or cold acid?

A

WArm

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18
Q

In general the more reactive the metal the greater the rate of

A

Bubbling

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19
Q

Some reactive metals react unexpectedly slowly with water or acids

A

1 aluminium has a layer of aluminium oxide that stops water reaching the metal below

2 in the reaction of calcium with dilute sulfuric acid a layer of insoluble calcium surface forms slowing the reaction

3 in the reaction of magnesium with water a layer of sparingly soluble magnesium hydroxide forms slowing the reaction

20
Q

What does magnesium react vigorously with?

A

Steam

21
Q

What is the reactivity series

A 
Potassium
Sodium
Calcium
Magnesium
Aluminium
Sin
Iron
—— HYDROGEN——
Copper
Silver 
Gold
22
Q

A more reactive metal will ——— a less reactive metal from its salts in solution

A

Displace

23
Q

Magnesium is more reactive than copper thederfore what happens in a copper surface solution?

A

It can displace the copper

24
Q

Magnesium displacing copper from copper sulfate solution, in this reaction you observe:

A

1 the colour of the solution fading as blue copper sulfate is replaced by colourless magnesium sulfate

2 an orange-brown coating of copper forming on the surface of the magnesium

3 an increase in temperature because reaction is exothermic

25
Q

Method for deducing a reactivity series

A

You can work out a reactivity series for metals by observing what happens when you mix different combinations of metals and their salt solutions to do this:

Add a powdered metal to a test tube or beaker of a metal salt solution (as above right) or

Dip a small piece of metal into a metal salt solution on a sporting tile

Then look for evidence o a reaction such as a change in colour or temperature

26
Q

How are cations formed

A

Metal atoms lose electrons

27
Q

OIL RIG

A

Oxidation is loss

Reduction is gain

28
Q

Metal atoms form cations when metals react with

A

Water or dilute acids

29
Q

Metals react with water to form

A

Metal hydroxides

30
Q

Metals react with dilute acids to form

A

Salts

31
Q

Displacement reactions are known as

A

Redox reactions

32
Q

Shat happens in redox atoms

A

The atoms of the more reactive metal are oxidised - they lose electrons

The metal cations of the less reactive metals are reduced - they gain electrons

33
Q

Most metals are extracted by the

A

Reduction of ores found in the earths crust

34
Q

What’s an ore

A

Is a rock that contains enough of a metal to make its extraction economical

35
Q

Rocks may contain too little metal to make extraction worthwhile so over time metal prices may

A

Rude and these low-grade ores may become useful

36
Q

Unreactive metals

A

Such as gold are placed at the bottom of reactivity series

Found in earths crust

In their ‘native state’ unconvinced with other elements:
They are not found as compounds but
They may occur naturally as alloys (mixtures of metals)

37
Q

Oxidation is

A

The gain of oxygen by a substance eg magnesium is oxidised to magnesium oxide in air
2Mg + O2 -> 2MgO

The loss of electrons by a substance eg
Mg -> Mg2+ + 2e-

38
Q

Reduction is

A

The loss of oxygen by a substance eg zinc oxide is reduced to zinc when it is heated with carbon :

ZnO + C -> Zn + CO

the gain of electrons by a substance eg
Zn2+ + 2e- -> Zn

39
Q

Resistance to corrosion

A

Metals corrode when they react with substances around them such as air and water. How easily a metal corrodes depends on how reactive it is

40
Q

What metal does not corrod

A

Gold

41
Q

Easily corrodes is at the ——— of the reactivity series

A

Top

42
Q

The method used to extract a metal from its ore is related to

A

Cost of extraction process

Posting in reactivity series

In principle, all metals can be extracted from their compounds using electrolysis. But:
Electricity is needed, which is expensive
Reduction by heating with carbon can be used if a metal is less reactive than carbon
Chemical reactions may be needed to separate silver and gold from other metals

43
Q

Iron extraction

A

Iron is less reactive than carbon
So it’s produced by reducing iron oxide using carbon
This happens in industrial equipment called a blast furnace

44
Q

Iron extraction

At the high temperatures inside the blast furnace :

A

Iron oxide is reduced by carbon

Iron oxide + carbon -> iron + carbon monoxide

Also it’s reduced by carbon monoxide

Iron oxide + carbon monoxide -> iron + carbon dioxide

Molten iron is produced

45
Q

Aluminium extraction

A

Aluminium is more reactive than carbon it is produced by reducing aluminium oxide in and electrolytic cell

46
Q

Aluminium extraction steps

A

1 aluminium oxide is dissolved in molten cryolite. This reduces the temperature needed for electrolysis to happen when an electric current passes through the mixture
1 at the cathode aluminium ions gain electrons and are reduced to aluminium atoms:
Al3+ + 3e- -> Al
3 at anode oxide ions lose electrons and form oxygen gas:
2O2- -> O2 + 4e-
Oxygen reacts with the graphite anodes so these must be replaced every few weeks

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