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Chemistry Paper 1 > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

What are acids

A

Substances that form hydrogen (H+) ions when they dissolve in aqueous solutions

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2
Q

What are alkalis

A

Substances that form hydroxide (OH-) ions when they dissolve in aqueous solutions

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3
Q

What is oxidation

A

Involves gaining oxygen but losing electrons

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4
Q

What is reduction

A

Involves losing oxygen but gaining electrons

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5
Q

What are examples of the most reactive metals

A

Potassium,Sodium, lithium, calcium,magnesium,aluminium and carbon

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6
Q

What are examples of the least reactive metals

A

Zinc, iron, hydrogen, copper, silver, gold and platinum

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7
Q

When can a metal displace another metal

A

It can only displace another metal from a compound if it’s located above the reactivity series

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8
Q

What is an example of a displacement reaction

A

Magnesium+iron oxide——> magnesium oxide+ iron
Since magnesium is higher in the reactivity series magnesium atoms have oxidised and the iron atoms have been reduced

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9
Q

How does potassium react against water

A

Ignites instantly and the metal sets alight

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10
Q

How does sodium react against water

A

Fizzes rapidly and melts to form a ball that moves around on the water surface

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11
Q

How does lithium react against water

A

Fizzes steadily and floats

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12
Q

What metals can be extracted from their oxides

A

Metals that are less reactive than carbon

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13
Q

Why is carbon mainly used for extracting

A

It’s cheap and abundant

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14
Q

What is the equation of a reaction of a metal with acids

A

Metal+acid——>salt+hydrogen

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15
Q

What are examples of a reaction of metals with acids

A

Iron+sulfuric acid—>iron Sulfate+hydrogen
Magnesium+hydrochloric acid—>magnesium chloride+hydrogen

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16
Q

What does a redox reaction involve

A

Involves a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons

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17
Q

What is an example of an ionic equation

A

Magnesium-» Mg2+ + 2e-
Magnesium atom has been oxidised as it has lost electrons

S+2e- —». S2-
The sulfuric atom has been reduced as it has gained electrons

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18
Q

What are acid neutralised by

A

Acids are neutralised by alkalis and bases to produce salts and water
Acid+ alkali—> salt + water
Acid + bases—> salt + water
Also neutralised by metal carbonates to produce salts, water and carbon dioxide
Acid+ metal carbonate—> salt + water + carbon dioxide
For example
Hydrochloric acid+ copper carbonate makes copper chloride+ water+ carbon dioxide

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19
Q

What do salts contain as a product from the reaction

A

Contain a positive ion which comes from the base or alkali
Contains a negative ion which comes from the acid
Hydrochloric acid——-» _____ chloride
Sulfuric acid——-» ______ sulfates
Nitric acid ——-»> ______ nitrates

20
Q

What is the required practical to create blue copper Sulfate crystals

A

1) start with a fixed volume of dilute sulfuric acid. This is our limiting reactant
2) gently heat the acid with a Bunsen burner until almost boiling
3)Using a spatula add small amounts of copper oxide to the acid
4)stir with a glass rod until the reaction stops (some powder will remain)

21
Q

Required practical to create blue copper sulphate crystals (2)

A

5)use filtration to remove the excess insoluble solid
6)Place the solution in an evaporating basin to heat above a beaker of water
7)leave the solution for 24 hours in a cool place for crystallisation to occur
8) scrape the crystals onto a paper towel and gently pat them dry

22
Q

How can you measure pH

A

Universal indicator-the indicator changes to a particular colour depending on colour
pH probe-the probe returns a numerical value for a pH of a substance

23
Q

What happens by every increase of 1 in pH

A

pH 1 has a 10 x greater concentration of H+ ions than pH 2 so it is in one order of magnitude
pH 1 has an 100x greater concentration of H+ ions that pH 3 so it is in two orders of magnitude

24
Q

What happens with weak acids

A

Only partially ionise in aqueous solutions meaning that not all of the acid molecules break up to form H+ ions
You can tell that weak acids are weak from the reversible reaction sign shoeing that some of the molecules ionise but not all
Carbonic acid
Ethanoic acid
Citric acid

25
Q

What happens with strong acids

A

Fully ionise in aqueous solutions meaning that all of the acid molecules break up to form a greater concentration of H+ ions
Hydrochloric, sulfuric and nitric acid are strong

26
Q

What is electrolysis

A

A process that splits ionic compounds into their different elements

27
Q

What happens when a voltage is applied on an electrolyte

A

The charged ions are attracted to the electrode with the opposite charge to the ion
Positive charged ions move to negative electrode (cathode)
Negative charged ions move to the positive electrode (anode)
Ions are discharged at the electrodes producing elements

28
Q

What is the process of electrolysis in molton compounds

A

When simple ionic compounds the is electrolysed in the molton state using inert electrodes the metal is produced at the cathode and the non metal is produced at the anode
This is because the metal is the positive ion and the non metal is the negative ion

29
Q

Why is carbon normally used for extracting metals with electrolysis

A

It’s a good conductor and it’s cheap

30
Q

What are the disadvantages to suing electrolysis to extract metal

A

Lots of energy is needed to melt the solid ionic compounds to allow the ions to flow and produce the current
Energy costs a lot of money

31
Q

What happens at the anode with electrolysis of aqueous solutions

A

It depends if halide ions are present. If they are present the halogen forms (bromine fluorine chlorine)!
If halide ions are absent oxygen will form

32
Q

What happens with the cathode with electrolysis of aqueous solutions

A

At the cathode it depends on the reactivity of the metal
If the metals more reactive than hydrogen, hydrogen is produced
If the metals less reactive than hydrogen the metal is produces

33
Q

How do you write half equations

A

Negative electrode: X+ —> X so ionic equation must be X+ + e- —> X electrons gained so positive ions are reduced

Positive electrode: X- —> X so ionic equation must be X- —> e- + X electrons are lost so negative ions are oxidised

For example 2Br- —> Br2 + 2e-

34
Q

What is the required practical for electrolysis

A

1) add about 50cm2 of copper chloride solution to a beaker
2)add the lid and insert electrodes Theo if I the holes making sure the electrodes don’t touch
3)attach crocodile leads to the electrode and connect the rods to the DC terminals of a low voltage power supply
4)Set the power supply ti 4V and switch the power supply on

35
Q

Required practical for electrolysis

A

5)using the forceps hold the litmus paper near the positive electrode
6)after a few minutes turn the power supply off and observe the negative electrode
7)record observations at the electrodes

36
Q

What safety precautions do you need to take

A

Safety goggles need to be worn
Room should be well ventilated because large quantities of chlorine gas is toxic

37
Q

What are metal oxides

A

Metals + oxygen—> metal oxides
This is known as oxidation reactions because the metals gain oxygen
Reduction=loss of oxygen and oxidation =gain of oxygen

38
Q

In calcium+coppe oxide—> calcium oxide+ copper what has been oxidised and reduced?

A

Calcium has been oxidised as it has gained oxygen and copper has been reduced as it has lost oxygen

39
Q

What happens when you react a metal with water

A

Metal+water-»> metals hydroxide + hydrogen

40
Q

What can happen when some metals react

A

They can lose electrons and form a positive ion
The reactivity of a metal depends on ur ability to lose electrons and form a positive ion
The more reactive an element is the higher the ability it has to form a positive ion

41
Q

How do you write ionic equation

A

If sodium is oxidised it has lost an electron leaving it with a +1 charge
So Na—» Na+ + e-
If à sodium +1 ion is reduced it has gained an electron leaving it with a charge of 0 so it’ll be
Na+ + e- —> Na

42
Q

What are examples of redox reactions

A

2HCl + Mg —> MgCl2 + H2

Mg—> Mg2+ + 2e-
This is oxidation reaction as it loses electrons
2H+ + 2e- —> H2
This is a reduction reaction as it gains electrons

43
Q

What are the rate of reactions with dilute acids

A

Magnesium- very rapid reaction so it easily forms Mg2+
Zinc- quite rapid reaction so it quite easily forms Zn2+
Iron- slow reaction so it less easily forms Fe 2+

44
Q

What is the ionic equation for any neutralisation reaction

A

H+ + OH- —-> H2O (l)

45
Q

How does the concentration of acids affect the pH

A

The concentration of an acid tells us the amount of acid molecules in a given volume of solution
A dilute acid will have fewer acid molecules in a given volume than a concentration acid even if the strength of the acid is the same

46
Q

How do you extract metals using electrolysis

A

Metals that are more reactive than Carbon (like aluminium) are too reactive to be extracted by reduction with carbon so they are extracted by electrolysis of molton compounds
Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current

47
Q

How is aluminium extracted

A

Manufactured by the electrolysis of molton mixture of aluminium oxide and cryolite using carbon as the anode
Aluminium oxide has a high melting point so it would be too expensive to melt it which is why it’s mixed with cryolite
The positive electrodes need to be continually replaced because oxygen is formed which reacts with the carbon of positive electrode forming carbon dioxide and they gradually burn away

Chemistry Paper 1 (5 decks)

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