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OCR Gateway A GCSE Chemistry > C2 - Elements, Compounds and Mixtures > Flashcards

C2 - Elements, Compounds and Mixtures Flashcards

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1
Q

what is the relative atomic mass ,Ar

A
  • the mean mass of an atom of an element compared to 1/12th the mass of a carbon-12 atom
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2
Q

what does a chemical formula tell you

A
  • how many atoms of each element there are in a unit of a substance
    > e.g. H2O tells you that for each molecule of water there are 2 hydrogen atoms and 1 oxygen atom joined together
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3
Q

what is the relative formula mass, Mr

A
  • the mean mass of a unit of a substance compared to 1/12th the mass of carbon 12 atom
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4
Q

how do you work out Mr

A
  • adding up the Ar values for all atoms in the formula for the substance
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5
Q

what does an empirical formula show

A
  • the simplest whole number ratio of the atoms of each element in a compound
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6
Q

what is meant by pure substance in scientific terms

A
  • a pure substance consists of just one element or compound
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7
Q

what is meant by impure substance in scientific terms

A
  • they are mixtures which contain more than one element or compound
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8
Q

how can you use melting points to determine purity

A
  • the melting point of pure substances have fixed melting and boiling points
  • impure substances have no fixed melting and boiling points
    > they melt + boil at a range of temps
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9
Q

what can adding impurities to a pure substance do

A
  • vary the melting + boiling points of pure substance
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10
Q

how can you determine melting point

A
  • by heating the substance:
    > slowly to ensure the whole sample’s temp increases
  • by mixing the substance as it melts
    > ensures the entire sample is at the same temp
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11
Q

what apparatus is used to measure temperature + which is more precise

A
  • thermometer or temperature probe
    > temp probe is most precise as it can record temp to 2 dp
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12
Q

what is an alloy

A
  • a mixture of two or more metals
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13
Q

what are some properties of alloys

A
  • stronger than pure metals
  • atoms have diff sizes
  • layers can’t slide easily
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14
Q

what is a soluble

A
  • a solid which can dissolve in a solvent
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15
Q

what is an insoluble

A
  • a solid which can’t dissolve in a solvent
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16
Q

what is a solvent

A
  • the liquid for the soluble to dissolve in
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17
Q

what is a solute

A
  • a solid that dissolves in a solvent
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18
Q

what is a solution

A
  • a mixture of dissolved solute and solvent
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19
Q

what process is sued to separate an insoluble salt from a solution

A
  • filtration
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20
Q

what does filtration do + how

A
  • separates an insoluble salt from a solution
  • when you filter the substance through a filter paper, the smaller molecules like the liquid can pass through but the larger grains of insoluble sand can’t
    > the sand stays behind on the filter paper as residue while the water passes through as filtrate
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21
Q

what process is used to separate a soluble salt from a solution

A
  • crystallisation
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22
Q

how does crystallisation work

A
  • gently heat the solution in an evaporating basin to increase concentration of the solution
  • remove from heat + allow solution to cool
  • slowly salt crystals will form as rest of water evaporates
    > when you heat a solution, the solvent evaporates leaving the solute behind
    > if you heat the solution too strongly, you get a powder
    > if you allow the solvent to evaporate slowly, you get regularly shaped crystals
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23
Q

why does crystallisation take a long time

A
  • because you need to gently heat the solution until it becomes a saturated solution
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24
Q

what is a saturated solution

A
  • a solution which can no longer dissolve anymore solute at that temperature
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25
Q

in crystallisation, what happens as the solution cools

A
  • the solubility of the solute decreases, so more crystals form
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26
Q

how do you obtain the crystals when crystallisation is done

A
  • by separating them from the remaining solution by filtration + letting them dry in the air of a warm oven
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27
Q

what is distillation

A
  • a process that separates a pure liquid from a mixture of liquids
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28
Q

when can distillation only work

A
  • when the liquids have different boiling points
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29
Q

what are the 2 different types of distillation

A
  • simple
  • fractional
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30
Q

what is simple distillation used fro

A
  • to separate a solvent from a solution
    > separates 2 liquids essentially
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31
Q

describe the process of separating ethanol from a mixture of ethanol + water using simple distillation

A
  • place the mixture in a round bottomed flask + connect to a condenser with a beaker at the end
    > cold water should enter condenser at bottom + leave at top
  • heat flask using Bunsen burner
  • ethanol has lower boiling point than water so will evaporate + enter condenser first
  • vapour cools in the condenser and drips into the beaker as a liquid
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32
Q

what is fractional distillation used for

A
  • to separate a mixture of liquids
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33
Q

what equipment is used in fractional distillation

A
  • fractionating column
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34
Q

what is fractional distillation usually used to separate + why

A
  • crude oil
    > fractional distillation can separate several substances of diff boiling points
    > useful for crude oil as it allows the separation of the hydrocarbons it contains
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35
Q

how does the process of fractional distillation work

A
  • solution is heated
  • vapour enters the fractionating column and if the temperature is at it’s boiling point then the vapour will go ahead through the condenser and condense
    > any other vapour which hasn’t reached its boiling point yet will condense because of the cool temp at top of fractionating column and will trickle back into the flask
    > repeat this with the boiling points for all the liquids present untill all are separated
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36
Q

what are the properties of a fractionating column

A
  • cooler at top
  • has many glass rods inside to increase surface area which allows the vapour to continually condense
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37
Q

what two chemical phases does chromatography rely on

A
  • stationary phase - does not move
  • mobile phase - does move
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38
Q

what are the two phases in paper chromatography

A
  • stationary phase = paper
  • mobile phase = solvent in liquid state
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39
Q

what is paper chromatography used to separate

A
  • to separate coloured substances in ink or sweets
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40
Q

what is chromatography

A
  • a process used to separate a mixture of soluble substances
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41
Q

what are the 2 phases in thin-layer chromatography

A
  • stationary phase = thin layer of inert substance e.g. silica or alumina powder spread on a plate of glass or plastic
  • mobile phase = solvent
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42
Q

describe how to carry out thin layer chromatography

A
  • pencil line is drawn 2cm up from base of stationary phase
  • dot of mixture being tested is placed on this line
  • stationary phase is placed in a chromatography tank with the solvent
  • solvent travels up stationary phase + mixture is dissolved into mobile phase
    > the substances separate depending on how soluble they are in the solvent
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43
Q

why must the solvent line be below the pencil line in paper + thin layer chromatography

A
  • to prevent the solvent submerging the substance being tests + washing it away
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44
Q

why is pencil used to draw the baseline in paper chromatography

A
  • pencil = insoluble
    > won’t affect results of experiment as it can’t travel through solvent
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45
Q

what does it mean if a substance travels higher up the stationary phase

A
  • it has a stronger attraction to the mobile phase
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46
Q

what is an Rf value

A
  • retention factor
  • the Rf value is a ratio between the distance travelled by dissolved substance (solute) and distance travelled by the solvent
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47
Q

how do you calculate Rf value from a chromatogram

A

Rf = distance travelled by substance / distance travelled by solvent

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48
Q

what is gas chromatography used for

A
  • to separate mixtures of volatile liquids
    > can determine what chemicals there are + amount
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49
Q

what are the 2 phases in gas chromatography

A
  • stationary phase = thin layer of inert substance on inert solid support e.g. silica or alumina powder packed into a metal column
  • mobile phase = inert carrier gas
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50
Q

how does gas chromatography separate a mixture of compounds

A
  • liquid sample is injected which turns into a gas because of the oven
  • the carrier gas pushes the sample through the column
    > the diff components have different affinity for the stationary phase so travel through the column at diff times
    > compounds favoring the mobile phase (usually volatile - easily convert from liquid to gas) emerge first
    > a detector monitors each component coming out and a recorder produces a chromatogram in which each component is a peak plotted against retention time
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51
Q

what is retention time

A
  • the time in a column
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52
Q

how can chromatography be used to distinguish between pure + impure substances

A
  • pure = one spot on chromatogram (paper/TLC) or one peak on gas chromatogram
  • impure = multiple spots / peaks
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53
Q

what are some general properties of metals

A
  • shiny
  • high melting + boiling points
  • solid at room temp
  • malleable
  • ductile
  • good conductors
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54
Q

what are some general properties of non-metals

A
  • dull
  • low melting + boiling points
  • solid/gas at room temp
  • brittle
  • non-ductile
  • poor conductors (insulators)
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55
Q

how are positive + negative ions formed

A
  • positive ions are formed when a metal loses an electron
  • negative ions are formed when a non-metal gains an electron
56
Q

metals + non-metals react with oxygen to produce

A
  • oxides
57
Q

do metals react with each other

A
  • no
    > instead they mix to form alloys
58
Q

when non-metals react with each other what do they produce

A
  • compounds that consist of molecules
59
Q

metal oxide + water =

A
  • alkaline solutions
60
Q

non-metal oxide + water =

A
  • acidic solutions
61
Q

what is a period in periodic table

A
  • the horizontal row
62
Q

what is a group in periodic table

A
  • the vertical column
63
Q

why do elements in a group have similar chemical properties

A
  • because they have the same number of electrons on their outer shell
64
Q

what does the electronic structure of an element show

A
  • how the electrons are arranged in its atoms
65
Q

how are elements arranged in the periodic table

A
  • in order of increasing atomic number so that elements in the same group have similar properties
66
Q

what does the period number tell you about the elements in that row

A
  • the number of shells of electrons
    > e.g. all elements in period 4 have 4 electron shells
67
Q

what does the group number tell you about all the elements in that group

A
  • they all have the same number of outer shell electrons
    > e.g. all elements in group 2 have 2 electrons in their outer shell
68
Q

what is an ion

A
  • an electrically charged particle formed when an atom (or group of atoms) lose/gain electrons
69
Q

what are electron diagrams

A
  • they represent the electronic structure of an atom or ion
70
Q

how are ionic compounds formed

A
  • when a metal reacts with a non-metal, the electrons are transferred from metal atoms to non-metal atoms so both achieve more stable electronic structures
  • the metal atoms become positive ions and non-metal atoms become negative ions
  • the ionic compounds are held together by strong electrostatic forces of attraction between the oppositely charged ions
71
Q

describe the structure and bonding in ionic compounds

A
  • ionic compounds have giant ionic lattice structures (regular arrangement)
  • the ions are held by ionic bonds which are strong electrostatic forces of attraction between oppositely charged ions
72
Q

what does giant ionic lattice mean

A
  • giant = arrangement is repeated many times
  • ionic = structure contains ions
  • lattice = arrangement is regular and not random
73
Q

what are limitations of ball and stick models used to model giant ionic lattices

A
  • ions are close together unlike the model shows
  • bonds are forces and not physical objects made from matter
74
Q

why do ionic compounds have high melting + boiling points

A
  • because the strong electrostatic forces of attraction between oppositely charged ions require a lot of energy to overcome
75
Q

when do ionic compounds conduct electricity

A
  • when molten or aqueous
    > because the ions are free to move and carry charges
76
Q

what is a covalent bond

A
  • a shared pair of electrons
77
Q

when do covalent bonds form

A
  • when 2 non-metals share electrons in their outer shell to complete their outer shells
78
Q

what can covalent bonds be modeled using

A
  • dot and cross diagrams
79
Q

what is a molecule

A
  • a particle in which non-metal atoms are joined together by covalent bonds
80
Q

what is a simple molecule

A
  • a molecule that only contains a few atoms
81
Q

what is structure + bonding in simple molecules like

A
  • have electrostatic forces of attraction
  • strong covalent bonds between atoms
  • weak intermolecular forces between molecules
82
Q

what are giant covalent structures

A
  • a giant lattice consisting of many non-metal atoms joined by covalent bonds
    > has many strong covalent bonds
    > also called giant covalent lattices
83
Q

why do simple molecules have low boiling points despite containing strong covalent bonds

A
  • to change state, simple molecules need to overcome intermolecular forces
  • simple molecules are held together by weak intermolecular forces which require little energy to overcome
84
Q

why are simple molecules unable to conduct electricity

A
  • they have no overall charge
85
Q

how + why do boiling points of simple molecules change as the size of the molecule increases

A
  • as size of molecules increase, so does the strength of intermolecular forces
  • larger simple molecules have higher boiling points as more energy is required to overcome the intermolecular forces
86
Q

why do giant covalent structures have very high melting points

A
  • because all of the atoms in the structure are covalently bonded to other atoms
    > these strong covalent bonds need to be broken to melt the substance which requires a lot of energy meaning the melting point is very high
87
Q

what are polymers made from

A
  • many smaller molecules called monomers
88
Q

what are monomers

A
  • simple molecules
    > consist of few non-metal atoms joined to each other by covalent bonds
89
Q

what are chain links

A
  • chains joined together by strong covalent bonds in polymers
90
Q

what are thermosoftening polymers

A
  • chains held by weak intermolecular forces so can easily slide + bend and be stretched easily
    > low melting point
91
Q

what are thermosetting polymers

A
  • chains held by strong covalent bonds (cross linking) so chains can’t move or be stretched
    > higher melting point
92
Q

what state are metals in at room temp

A
  • solid
    > apart from mercury
93
Q

what is the structure of metals like

A
  • atoms are packed together in regular way, forming a giant metallic lattice
94
Q

what is the bonding in metals

A
  • metals lose their outer shell electrons forming a ‘sea’ of delocalised electrons around the positively charged metal ions
    > the electrons are free to move and carry charge
95
Q

what are metallic bonds

A
  • metallic bonds are the strong electrostatic forces of attraction between delocalised electrons and closely packed positively charged ions
95
Q

what did Mendeleev produce

A
  • the first Periodic Table
95
Q

why are metals typically very malleable

A
  • the atoms are arranged in uniform rows which can easily slide over each other
    > this allows metals to be bent + shaped
95
Q

why do metals have relatively high melting points

A
  • they have very strong metallic bonds
    > a lot of energy is required to overcome the electrostatic attraction between positive metal ions + negative electrons
95
Q

how is the modern table ordered

A
  • the elements are now ordered by increasing atomic number (proton number) rather than increasing atomic mass
95
Q

how did Mendeleev arrange his elements in the periodic table

A
  • in order of increasing atomic weight
  • he grouped together elements with similar chemical properties
  • he also left spaces for elements he thought would exist but weren’t discovered yet + predicted their properties from nearby elements
96
Q

what is electronic structure determined by

A
  • the number of electrons
97
Q

what is the atomic number

A
  • the number of protons in an element (+electrons)
98
Q

what is the atomic mass

A
  • the number of protons + neutrons in an element
99
Q

how many covalent bonds can carbon form + why

A
  • 4
  • because it’s in group 4 and so has electrons in its outer shell and can form covalent bonds with all 4
100
Q

when a carbon atom joins with another carbon atom what are formed

A
  • chains and rings
  • covalent bonds
101
Q

why is there such an array of natural and synthetic organic compounds

A
  • because carbon can form families of similar compounds, chains + rings
102
Q

what are allotropes

A
  • different forms of an element in the same state but different atomic arrangement
103
Q

what are some allotropes of carbon

A
  • diamond
  • graphite + graphene
  • fullerenes
104
Q

describe the structure of diamond

A
  • each carbon atom is covalently bonded to 4 other carbon atoms
  • no charged particles
105
Q

describe the properties of diamond

A
  • very hard + high melting points due to strong covalent bonds
  • doesn’t conduct electricity because there are no charged particles (or delocalised electrons)
106
Q

describe the properties of graphite

A
  • high melting point because of strong covalent bonds in the layers
  • slippery/soft because the weak intermolecular forces allow the layers to slide over each other easily
  • electrical conductor because it contains delocalised electrons which are free to carry charge
106
Q

describe the structure of graphite

A
  • each carbon atom is covalently bonded to 3 carbon atoms
  • one delocalised electron per carbon atom
  • layers of hexagonal rings of carbon atoms
107
Q

what is graphene

A
  • a carbon allotrope which resembles a single layer of graphite
107
Q

why is graphene useful in electronics

A
  • extremely strong
  • has free electrons so can conduct electricity
  • only one atom thick
107
Q

what are fullerenes

A
  • large molecules made up of carbon atoms shaped like a closed tube or hollow ball
108
Q

name a fullerene

A

C60 = buckminsterfullerene

109
Q

what are the properties + uses of fullerenes

A
  • large surface area so useful for trapping catalysts onto their surfaces
  • hollow structure makes them useful for capturing substances by forming around target molecule
    > used for targeted drug delivery systems
  • conducts electricity
110
Q

what happens when substances change state

A
  • forces of attraction between particles are overcome
111
Q

when do bonds form in changes of state

A
  • condenses
  • freezes
112
Q

when chemical bonds form, where is energy transferred

A
  • to the surroundings
113
Q

when do bonds break in changes of state

A
  • evaporating
  • melting
114
Q

when chemical bonds break, where is energy transferred

A
  • to the substance
115
Q

what substances are usually solid at room temp

A
  • metals
  • ionic compounds
  • giant covalent structures
116
Q

which substances aren’t solid at room temp

A
  • simple molecules are liquid/gas at room temp
    > or solid but easily melted
117
Q

do individual atoms have the same physical properties of the substance that contains them + explain

A
  • no
  • physical properties of a substance depend on the bonds it contains + the strength + arrangement of these bonds
118
Q

why are metals malleable despite having strong metallic bonds

A
  • metal ions are held in lattice
  • if a large enough force is applied, layers of metal ions slide over one another
    > as delocalised electrons are free to move, overall no bonds are broken
119
Q

what compounds are brittle

A
  • giant covalent structures
  • ionic compounds
    > they both have strong bonds which break at once when a large enough force is applied
120
Q

why are simple molecules + polymer molecules brittle

A
  • the molecules are attracted to each other by weak intermolecular forces which are easily broken when large enough forces are applied
121
Q

how big is a nanoparticle

A
  • between 1nm and 100nm across
  • 1 x 10-9nm
122
Q

what is a nanoparticulate

A
  • a material made from nanoparticles
123
Q

what are nanoparticles used for

A
  • sports
  • cosmetics
  • medicine
124
Q

what is the surface area : volume ratio of particles + nano particle

A
  • nanoparticles have a much larger surface area to volume ratio
125
Q

why are nanoparticles useful catalysts

A
  • they have a very high surface area to volume ratio so provide more reaction side
126
Q

why might nanotubes be suitable for making electrical circuits for computers

A
  • they are electrical conductors
  • very small so take up little space in computer
  • lightweight
127
Q

why might nanoparticles be used in sunscreen

A
  • they block UV light without leaving visible white marks on the skin
128
Q

what are some possible risks of nanoparticles

A
  • little research has been conducted so there are many unknown factors
  • may be harmful to health as they could enter the bloodstream and are not easily disposed of by the body
    > small so can easily be breathed in, absorbed by skins, or pass into cells
  • easily released into the environment

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