C2 - Elements, Compounds and Mixtures Flashcards
(136 cards)
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
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
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
4
Q
how do you work out Mr
A
- adding up the Ar values for all atoms in the formula for the substance
5
Q
what does an empirical formula show
A
- the simplest whole number ratio of the atoms of each element in a compound
6
Q
what is meant by pure substance in scientific terms
A
- a pure substance consists of just one element or compound
7
Q
what is meant by impure substance in scientific terms
A
- they are mixtures which contain more than one element or compound
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
9
Q
what can adding impurities to a pure substance do
A
- vary the melting + boiling points of pure substance
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
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
12
Q
what is an alloy
A
- a mixture of two or more metals
13
Q
what are some properties of alloys
A
- stronger than pure metals
- atoms have diff sizes
- layers can’t slide easily
14
Q
what is a soluble
A
- a solid which can dissolve in a solvent
15
Q
what is an insoluble
A
- a solid which can’t dissolve in a solvent
16
Q
what is a solvent
A
- the liquid for the soluble to dissolve in
17
Q
what is a solute
A
- a solid that dissolves in a solvent
18
Q
what is a solution
A
- a mixture of dissolved solute and solvent
19
Q
what process is sued to separate an insoluble salt from a solution
A
- filtration
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
21
Q
what process is used to separate a soluble salt from a solution
A
- crystallisation
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
23
Q
why does crystallisation take a long time
A
- because you need to gently heat the solution until it becomes a saturated solution
24
Q
what is a saturated solution
A
- a solution which can no longer dissolve anymore solute at that temperature
25
in crystallisation, what happens as the solution cools
- the solubility of the solute decreases, so more crystals form
26
how do you obtain the crystals when crystallisation is done
- by separating them from the remaining solution by filtration + letting them dry in the air of a warm oven
27
what is distillation
- a process that separates a pure liquid from a mixture of liquids
28
when can distillation only work
- when the liquids have different boiling points
29
what are the 2 different types of distillation
- simple
- fractional
30
what is simple distillation used fro
- to separate a solvent from a solution
> separates 2 liquids essentially
31
describe the process of separating ethanol from a mixture of ethanol + water using simple distillation
- 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
32
what is fractional distillation used for
- to separate a mixture of liquids
33
what equipment is used in fractional distillation
- fractionating column
34
what is fractional distillation usually used to separate + why
- 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
35
how does the process of fractional distillation work
- 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
36
what are the properties of a fractionating column
- cooler at top
- has many glass rods inside to increase surface area which allows the vapour to continually condense
37
what two chemical phases does chromatography rely on
- stationary phase - does not move
- mobile phase - does move
38
what are the two phases in paper chromatography
- stationary phase = paper
- mobile phase = solvent in liquid state
39
what is paper chromatography used to separate
- to separate coloured substances in ink or sweets
40
what is chromatography
- a process used to separate a mixture of soluble substances
41
what are the 2 phases in thin-layer chromatography
- stationary phase = thin layer of inert substance e.g. silica or alumina powder spread on a plate of glass or plastic
- mobile phase = solvent
42
describe how to carry out thin layer chromatography
- 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
43
why must the solvent line be below the pencil line in paper + thin layer chromatography
- to prevent the solvent submerging the substance being tests + washing it away
44
why is pencil used to draw the baseline in paper chromatography
- pencil = insoluble
> won't affect results of experiment as it can't travel through solvent
45
what does it mean if a substance travels higher up the stationary phase
- it has a stronger attraction to the mobile phase
46
what is an Rf value
- retention factor
- the Rf value is a ratio between the distance travelled by dissolved substance (solute) and distance travelled by the solvent
47
how do you calculate Rf value from a chromatogram
Rf = distance travelled by substance / distance travelled by solvent
48
what is gas chromatography used for
- to separate mixtures of volatile liquids
> can determine what chemicals there are + amount
49
what are the 2 phases in gas chromatography
- 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
50
how does gas chromatography separate a mixture of compounds
- 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
51
what is retention time
- the time in a column
52
how can chromatography be used to distinguish between pure + impure substances
- pure = one spot on chromatogram (paper/TLC) or one peak on gas chromatogram
- impure = multiple spots / peaks
53
what are some general properties of metals
- shiny
- high melting + boiling points
- solid at room temp
- malleable
- ductile
- good conductors
54
what are some general properties of non-metals
- dull
- low melting + boiling points
- solid/gas at room temp
- brittle
- non-ductile
- poor conductors (insulators)
55
how are positive + negative ions formed
- positive ions are formed when a metal loses an electron
- negative ions are formed when a non-metal gains an electron
56
metals + non-metals react with oxygen to produce
- oxides
57
do metals react with each other
- no
> instead they mix to form alloys
58
when non-metals react with each other what do they produce
- compounds that consist of molecules
59
metal oxide + water =
- alkaline solutions
60
non-metal oxide + water =
- acidic solutions
61
what is a period in periodic table
- the horizontal row
62
what is a group in periodic table
- the vertical column
63
why do elements in a group have similar chemical properties
- because they have the same number of electrons on their outer shell
64
what does the electronic structure of an element show
- how the electrons are arranged in its atoms
65
how are elements arranged in the periodic table
- in order of increasing atomic number so that elements in the same group have similar properties
66
what does the period number tell you about the elements in that row
- the number of shells of electrons
> e.g. all elements in period 4 have 4 electron shells
67
what does the group number tell you about all the elements in that group
- 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
what is an ion
- an electrically charged particle formed when an atom (or group of atoms) lose/gain electrons
69
what are electron diagrams
- they represent the electronic structure of an atom or ion
70
how are ionic compounds formed
- 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
describe the structure and bonding in ionic compounds
- 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
what does giant ionic lattice mean
- giant = arrangement is repeated many times
- ionic = structure contains ions
- lattice = arrangement is regular and not random
73
what are limitations of ball and stick models used to model giant ionic lattices
- ions are close together unlike the model shows
- bonds are forces and not physical objects made from matter
74
why do ionic compounds have high melting + boiling points
- because the strong electrostatic forces of attraction between oppositely charged ions require a lot of energy to overcome
75
when do ionic compounds conduct electricity
- when molten or aqueous
> because the ions are free to move and carry charges
76
what is a covalent bond
- a shared pair of electrons
77
when do covalent bonds form
- when 2 non-metals share electrons in their outer shell to complete their outer shells
78
what can covalent bonds be modeled using
- dot and cross diagrams
79
what is a molecule
- a particle in which non-metal atoms are joined together by covalent bonds
80
what is a simple molecule
- a molecule that only contains a few atoms
81
what is structure + bonding in simple molecules like
- have electrostatic forces of attraction
- strong covalent bonds between atoms
- weak intermolecular forces between molecules
82
what are giant covalent structures
- a giant lattice consisting of many non-metal atoms joined by covalent bonds
> has many strong covalent bonds
> also called giant covalent lattices
83
why do simple molecules have low boiling points despite containing strong covalent bonds
- 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
why are simple molecules unable to conduct electricity
- they have no overall charge
85
how + why do boiling points of simple molecules change as the size of the molecule increases
- 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
why do giant covalent structures have very high melting points
- 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
what are polymers made from
- many smaller molecules called monomers
88
what are monomers
- simple molecules
> consist of few non-metal atoms joined to each other by covalent bonds
89
what are chain links
- chains joined together by strong covalent bonds in polymers
90
what are thermosoftening polymers
- chains held by weak intermolecular forces so can easily slide + bend and be stretched easily
> low melting point
91
what are thermosetting polymers
- chains held by strong covalent bonds (cross linking) so chains can't move or be stretched
> higher melting point
92
what state are metals in at room temp
- solid
> apart from mercury
93
what is the structure of metals like
- atoms are packed together in regular way, forming a giant metallic lattice
94
what is the bonding in metals
- 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
what are metallic bonds
- metallic bonds are the strong electrostatic forces of attraction between delocalised electrons and closely packed positively charged ions
95
what did Mendeleev produce
- the first Periodic Table
95
why are metals typically very malleable
- the atoms are arranged in uniform rows which can easily slide over each other
> this allows metals to be bent + shaped
95
why do metals have relatively high melting points
- they have very strong metallic bonds
> a lot of energy is required to overcome the electrostatic attraction between positive metal ions + negative electrons
95
how is the modern table ordered
- the elements are now ordered by increasing atomic number (proton number) rather than increasing atomic mass
95
how did Mendeleev arrange his elements in the periodic table
- 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
what is electronic structure determined by
- the number of electrons
97
what is the atomic number
- the number of protons in an element (+electrons)
98
what is the atomic mass
- the number of protons + neutrons in an element
99
how many covalent bonds can carbon form + why
- 4
- because it's in group 4 and so has electrons in its outer shell and can form covalent bonds with all 4
100
when a carbon atom joins with another carbon atom what are formed
- chains and rings
- covalent bonds
101
why is there such an array of natural and synthetic organic compounds
- because carbon can form families of similar compounds, chains + rings
102
what are allotropes
- different forms of an element in the same state but different atomic arrangement
103
what are some allotropes of carbon
- diamond
- graphite + graphene
- fullerenes
104
describe the structure of diamond
- each carbon atom is covalently bonded to 4 other carbon atoms
- no charged particles
105
describe the properties of diamond
- very hard + high melting points due to strong covalent bonds
- doesn't conduct electricity because there are no charged particles (or delocalised electrons)
106
describe the properties of graphite
- 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
describe the structure of graphite
- each carbon atom is covalently bonded to 3 carbon atoms
- one delocalised electron per carbon atom
- layers of hexagonal rings of carbon atoms
107
what is graphene
- a carbon allotrope which resembles a single layer of graphite
107
why is graphene useful in electronics
- extremely strong
- has free electrons so can conduct electricity
- only one atom thick
107
what are fullerenes
- large molecules made up of carbon atoms shaped like a closed tube or hollow ball
108
name a fullerene
C60 = buckminsterfullerene
109
what are the properties + uses of fullerenes
- 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
what happens when substances change state
- forces of attraction between particles are overcome
111
when do bonds form in changes of state
- condenses
- freezes
112
when chemical bonds form, where is energy transferred
- to the surroundings
113
when do bonds break in changes of state
- evaporating
- melting
114
when chemical bonds break, where is energy transferred
- to the substance
115
what substances are usually solid at room temp
- metals
- ionic compounds
- giant covalent structures
116
which substances aren't solid at room temp
- simple molecules are liquid/gas at room temp
> or solid but easily melted
117
do individual atoms have the same physical properties of the substance that contains them + explain
- no
- physical properties of a substance depend on the bonds it contains + the strength + arrangement of these bonds
118
why are metals malleable despite having strong metallic bonds
- 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
what compounds are brittle
- giant covalent structures
- ionic compounds
> they both have strong bonds which break at once when a large enough force is applied
120
why are simple molecules + polymer molecules brittle
- the molecules are attracted to each other by weak intermolecular forces which are easily broken when large enough forces are applied
121
how big is a nanoparticle
- between 1nm and 100nm across
- 1 x 10-9nm
122
what is a nanoparticulate
- a material made from nanoparticles
123
what are nanoparticles used for
- sports
- cosmetics
- medicine
124
what is the surface area : volume ratio of particles + nano particle
- nanoparticles have a much larger surface area to volume ratio
125
why are nanoparticles useful catalysts
- they have a very high surface area to volume ratio so provide more reaction side
126
why might nanotubes be suitable for making electrical circuits for computers
- they are electrical conductors
- very small so take up little space in computer
- lightweight
127
why might nanoparticles be used in sunscreen
- they block UV light without leaving visible white marks on the skin
128
what are some possible risks of nanoparticles
- 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
