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Chemistry > topic 4 - chemical changes > Flashcards

topic 4 - chemical changes Flashcards

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1
Q

what are all substances made of?

A

atoms

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2
Q

what is an atom?

A

the smallest part of an element that can exist

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3
Q

what do atoms of each element represent?

A

atom of each element are represented by a chemical symbol
- eg. O represents an atom of oxygen

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4
Q

how many elements are there?

A

about 100 different elements

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5
Q

what are compounds formed from?

A

compounds are formed from elements by chemical reactions

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6
Q

what are chemical reactions?

A

chemical reactions always involve the formation of one or more new substances, and often involve a delectable energy change

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7
Q

what do compounds contain?

A

compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed

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8
Q

how can compounds be separated?

A

compounds can only be separated into elements by chemical reactions

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9
Q

what is a mixture?

A
  • a mixture consists of two or more elements or compounds not chemically combined together
  • the chemical properties of each substance in the mixture are unchanged
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10
Q

what can mixtures be separated by?

A
  • physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
  • these physical processes do not involve chemical reactions and no new substances are made
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11
Q

what were atoms thought to be a long time ago?

A
  • before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
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12
Q

how was the plum pudding model founded?

A
  • the discovery of the electron led to the plum pudding model of the atom.
  • the plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it
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13
Q

what did the alpha particle scattering experiment lead to?

A
  • the results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre and that the nucleus was charged
  • this nuclear model replaced the plum pudding model
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14
Q

who adapted the nuclear model?

A
  • Niels Bohr adopted the nuclear model by suggesting that electrons orbit the nucleus at specific distances
  • the theoretical calculations of Bohr agreed with experimental observations
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15
Q

how were protons invented?

A
  • later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge.
  • the name proton was given to these particles
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16
Q

how were neutrons discovered?

A
  • the experimental work of James Chadwick provided evidence to show the existence of neutrons within the nucleus
  • this was about 20 years after the nucleus became an accepted scientific idea
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17
Q

what is the number of electrons equal to in an atom?

A
  • in an atom, the number of electrons is equal to the numbr of protons in the nucleus
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18
Q

what charge to atoms have?

A
  • atoms have no overall electric charge
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19
Q

what is the atomic number?

A

the number of protons in an atom of an element

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20
Q

do all atoms of a particular element have a different number of protons?

A

no, all atoms of a particular element have the same number of protons

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21
Q

how small are atoms?

A
  • atoms are very small, having a radius of about 0.1nm (1 x 10 ^-10 m)
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22
Q

what is the radius of a nucleus?

A
  • the radius of a nucleus is less than 1/10 000 of that of the atom (about 1 x 10 ^-14)
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23
Q

where is all the mass of an atom concentrated?

A

in the nucleus

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24
Q

what is the mass number?

A

the sum of the protons and neutrons in an atom

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25
Q

what are isotopes?

A

atoms of the same element that can have different numbers of neutrons

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26
Q

what do elements in the same group in the periodic table have in common?

A
  • elements in the same group inthe periodic table have the same number of electrons in their outer shell and this gives them similar chemical properties
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27
Q

what are elements that react to form positive ions?

A

metals

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28
Q

what are elements that do not form positive ions?

A

non-metals

29
Q

what are elements in group called?

A

noble gases

30
Q

what are the features of elements in group 0?

A
  • they are unreactive and do not easily form molecules because their atom have stable arrangements of electrons
  • the noble gases have eight electrons in their outer shell, except for helium , which has only two electrons
  • the boiling points of the noble gases increase with increasing relative atom mass
31
Q

what are elements in group 1 of the periodic table known as?

A

the alkali metals

32
Q

what are the features of group 1 elements?

A
  • they have a single electron in their outer shell
  • in group 1, the reactivity of the elements increases going down the group
33
Q

what are observations that show there is a reaction between zinc and copper sulfate?

A
  • blue solution turns colourless
  • brown deposit on zinc
34
Q

why would sodium not be used in an investigation?

A
  • would not be safe
  • too reactive
35
Q

which metal is found in the Earth as the metal itself?

A

Gold

36
Q

what is an element used to reduce iron oxide?

A

carbon

37
Q

A universal indicator turned blue when added to a sample of a product. What is the pH value of the solution?

A

9

38
Q

what is one advantage of using nanoparticles in suncreams?

A
  • more protection from suns UV rays
39
Q

what is one disadvantage of using nanoparticles in sun creams?

A

potential cell damage to the body

40
Q

what are two reasons why copper should not be disposed of in landfill sites?

A
  • copper compounds are toxic
  • copper can be recycled
41
Q

the alloy stainless steel is used instead of pure iron for the ball of the pen. Give two reasons why

A
  • stainless steel is hard/strong
  • stainless steel is resistant to corrosion
42
Q

new 5p and 10p coins in the UK are now made from nickel-plated steel and not from cupro-nickel. Explain why.

A
  • copper is very expensive
  • because copper ores are ‘low grade’ and are running out
43
Q

why are different steels needed?

A
  • to give steels with different properties particular uses
44
Q

suggest how the oxygen removes most of the carbon from the molten iron

A
  • carbon dioxide is produced
  • which escapes as a gas
45
Q

what is the type of reaction that produces a metal from its metal oxide?

A
  • reduction
46
Q

what is the meaning of ore?

A
  • contains enough metal to make it economical to extract
47
Q

suggest why scientists in 1800 could not extract aluminium from alumina.

A
  • no knowledge on how
  • high melting point
  • potassium was not discovered
48
Q

suggest how Wohler was able to prove he had made a new metal

A
  • when tested it had the properties of a metal
  • the properties were different
49
Q

what is one environmental impact of recycling aluminium cans?

A
  • less landfill space used
50
Q

what is one social impact of recycling aluminium cans?

A
  • creates local employment
51
Q

the purification of aluminium oxide is usually done near the bauxite quarries. why?

A
  • save energy for transporting the ore
  • quarries nearby for waste
52
Q

what are two differences you would see between the reactions of potassium and lithium with water?

A
  • fizzes faster
  • produces a lilac flame
53
Q

what is used in phytomining to remove copper compounds from the land?

A

plants

54
Q

what is one reason why the extraction of pure copper is expensive?

A
  • large amounts of fuels/ energy used
55
Q

suggest one reason why it is difficult to dispose of the waste rock.

A
  • waste rock takes up a lot of space
56
Q

what is a word equation for the overall reaction that takes place in a hydrogen fuel cell?

A

hydrogen + oxygen = water

57
Q

what is the word equation for the decomposition of calcium carbonate?

A

carbon carbonate -> carbon oxide + carbon dioxide

58
Q

why can aluminium not be extracted by heating the aluminium oxide with carbon?

A

aluminium is more reactive than carbon

59
Q

why can aluminium form at the negative electrode during electrolysis?

A
  • aluminium ions are positively charged
  • so they move to the cathode which is negatively charged
  • where they gain electrons
60
Q

how can carbon dioxide form at the positive electrodes during electrolysis?

A
  • because anodes are made of carbon
  • oxygen is produced
  • which reacts with the anode
61
Q

why does a metal need to be separated?

A
  • the ore contains impurities
  • rock need to be removed
62
Q

state one property that makes aluminium more suitable than copper for overhead cables

A

aluminium has a low density

63
Q

how can you tell that copper is a transition metal and aluminium is not a transition metal from the position of each metal in the periodic table?

A
  • copper is in the central block of the periodic table
  • whereas aluminium is in group 3
64
Q

describe how ethene forms poly(ethene)

A
  • many ethene
  • join to form a long chain
65
Q

what property does a shape memory polymer have?

A
  • can be deformed but return to their original shape
66
Q

why does titanium cost more than steel?

A
  • titanium takes longer to make than steel
  • low abundance of ore
  • more energy used per tonne is titanium
67
Q

why is argon used in a light bulb?

A
  • it is very unreactive
  • full outer shell
  • does not share electrons
68
Q

explain why gold is found mainly as the metal itself in the Earth

A

unreactive

69
Q

why was sodium not extracted until 1807?

A
  • very reactive
  • cannot use displacement methods

Chemistry (10 decks)

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