Chapter 3: Amount of substance Flashcards
(128 cards)
1
Q
what does the atom consist of?
A
- nucleus with protons + neutrons
- electrons in shells
2
Q
masses in atom
A
protons 1
neutrons 1
electrons 1/1836 of proton
3
Q
charge in atom:
A
proton +1
neutron 0
electron -1
4
Q
charges balancing:
A
charge of proton and electron are equal and opposite
- cancel each other out
5
Q
charge of atom:
A
zero
6
Q
how does a nucleus get larger?
A
more neutrons
7
Q
what identifies an element?
A
number of protons
8
Q
isotope definition:
A
atoms of the same element which have the same amount of protons but different neutrons
9
Q
what are most elements made up of?
A
a mixture of isotopes
10
Q
A=
A
mass number
11
Q
Z=
A
number of protons
12
Q
what do chemical reactions involve?
A
electrons surrounding the nucleus
13
Q
why do isotopes of the same element react the same?
A
number of neutrons has no effect on reactions
but may have different melting/boiling points and densities
14
Q
what is heavy water used in?
A
nuclear reactors
15
Q
what is heavy water made up of?
A
2/1 H isotope and not 1/1 H isotope like in normal water
16
Q
name of 2/1 H isotope:
A
deuterium (D)
17
Q
formula for heavy water:
A
D2O
18
Q
chemical properties of heavy and normal water:
A
melting point- normal: 0.00° heavy: 3.80°
boiling point- normal: 100° heavy: 101.40°
density- normal: 1.00° heavy: 1.11°
19
Q
where does D2O get its name from?
A
heavy density. if all water were heavy you would see ice more often as it would freeze at a higher temperature
20
Q
what is an ion?
A
a charged atom. the number of electrons is different from the number of protons
21
Q
what are cations?
A
positive ions with fewer electrons than protons
- give an overall positive charge
22
Q
what are anions?
A
negative ions. more electrons than protons
- anions have an overall negative charge
23
Q
what are ions always shown with?
A
their overall relative charge
24
Q
why does the strong nuclear force holding protons and neutrons cause?
A
mass defect
25
how do chemists calculate the mass of atoms?
compare it to carbon-12
26
carbon 12 isotope definition:
12 atomic mass unites (12u)
27
what is the standard mass for atomic mass?
1u, the mass of 1/12th of an atom of carbon 12
28
what is 1u equal to?
the mass of a proton/neutron
29
relative isotopic mass definition:
the mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
30
units for relative isotopic mass:
none as it is a ratio of two masses
31
Relative atomic mass (Ar) definition
the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon 12
32
what does the weight mean mass take account of?
- percentage abundance of each isotope
- relative isotopic mass of each isotope
33
how are percentage abundances of isotopes in a sample of an element found?
mass spectrometer
34
process of mass spectrometer:
1. sample is place in mass spectrometer
2. vaporised and ionised to form positive ions
3. ions are accelerated, heavier ions move slower and more difficult to deflect than lighter ions. so they are separated
4. ions are detected as mass to charge ratio. each ions reaching detector adds to the signal so greater abundance gives larger signal
35
mass to charge ratio formula:
mass to charge ratio = relative mass of ion / relative charge on ion
36
ratio in an ion with positive charge:
ratio = relative isotopic mass
- recorded on the x axis of mass spectrum
37
what can the mass spectrometer also record?
accurate m/z ratio for each isotope so accurate values of relative isotopic mass can be measured
38
why do atoms lose/ gain electrons?
to achieve full outer shell (group 0)
39
where are metals on the periodic table?
left. lose electrons to form cations
40
where are non-metals on the periodic table?
right. gain electrons to form anions (negative ions)
41
what ions does copper form?
copper (I) Cu+
copper (II) Cu2+
42
what ions does Iron form?
iron (II) Fe2+
iron (III) Fe3+
43
what is a binary compound?
containers two elements only
44
naming a binary compound:
- use name of first element but change ending to -ide
- for ionic compounds metal ion always comes first
45
what are polyatomic ions?
when an ions contains atoms of more than one element bonded together
46
1+ ion name:
ammonium (NH4+)
47
1- ion names:
hydroxide (OH-)
nitrate (NO3-)
48
2- ion names:
carbonate (CO3 2-)
sulfate (SO4 2-)
49
what does an ionic compound contain?
cation and anion. the formula can be worked out from the charge if each ion
50
correct formula for ions:
- the overall charge is zero so ionic charges balance
- sum of positive charges = sum of negative
51
writing the formula for ions:
- the number of ions present is shown as a subscript after the ion
- the ionic charges are omitted in the completed formula
- brackets used if there is more than one poly atomic ion
e.g aluminium sultate contains 2Al 3+ and 3SO4 2- ions so formula is Al2(SO4)3
52
diatomic molecules:
H2, N2, O2, F2, Cl2, Br2, I2
53
other small molecules:
P4, S8
54
what do covalent compounds NOT contain?
ions
- most covalent compounds exist as molecules with a smaller number of atoms bonded together e.g CO2, H2O
55
what is the formula unit?
the formula worked out from the ionic charges used in equations for ionic compounds
56
state symbols:
gas (g)
liquid (l)
solid (s)
aqueous (aq) (dissolved in water)
57
balancing equations:
- must not change any chemical formula
- balancing numbers of in front of chemical formulae and not subscripted
- equation is balanced with same number of each element on each side of the equation
58
what are chemicals measured by?
mass or volume
59
why do chemists need to convert a measured mass or volume?
reactions take place on an atomic scale
60
what is amount of substance (n)?
used to count the number of particles in a substance
- measured in mol
61
what is one mole equal to?
6.02 x 10^23 mol-1
- same as the number of particles in each mole of carbon 12
62
what does 12g of carbon 12 contain?
6.02 x 10^23 atoms
63
mass of one mole of H:
1g
64
mass of one mole of Mg:
24.3g
65
mass of one mole of Fe iron:
55.8g
66
what does amount of substance refer to?
not just atoms, an refer to anything
67
atoms definition:
the smallest particle of a chemical element that can exist.
68
molecules definition:
a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction
- e.g 1 mol of H2 = 1 mol of hydrogen molecules
69
molar mass definition:
the mass per mole of a substance
units = gmol^-1
70
formula linking m, M, n
amount n = mass/ molar mass M
71
molecules definition:
two or more atoms held together by covalent bonds
72
molecular formula definition:
the number of atoms of each element in a molecule
73
what can compounds exist as?
compounds can exist as molecules where molecular formula used in equation e.g H2
74
empirical formula definition:
simplest whole number ratio of atoms of each element in a compound
- important for substance that do not exist as molecules e.g metals + some non metals (sodium chloride NaCl)
75
what do substances that don’t exist as molecules where molecules form?
giant crystalline structure of atoms or ions
76
what do compound exist as?
- simple molecules e.g H2O, CO2
- giant crystalline structures e.g all ionic compounds
77
relative molecular mass definition:
compared the mass of a molecule with the mass of an atom of carbon 12
- Mr calculated by added relative atomic masses
78
relative formula mass definition:
compared the mass of a formula unit with the mass of an atom of carbon 12
- calculated by adding relative atomic masses in empirical formula
79
what are hydrated crystals:
water molecules are part of their crystalline structures
- water is known as water of crystallisation
80
what happens when blue crystals or hydrated copper (II) sulfate are heated?
bonds holding water within crystal are broken down + water is driven off leaving white anhydrous copper (II) sulfate
81
equation for change when water is removed:
CuSO4.5H2O (s) (hydrated) → CuSO4 (s) (anhydrous) + 5H2O (l)
82
crystalline structure without water:
structure is lost and white linder remains
- it is difficult to remove last traces of water shown by pale blue colour
83
experiment for water of crystallisation
1. weigh empty crucible
2. add hydrated salt into weighed crucible + weigh crucible and hydrated salt
3. use pipe clay triangle, support crucible containing hydrated salt on a tripod
4. heat gently for 1 min, strongly for 3 mins
4. leave to cool, weigh crucible + anhydrous salt
84
how accurate is water of crystallisation experiment?
real experiments may not always work out well
85
assumption of water lost in water of crystallisation:
if hydrated + anhydrous forms have different colours, water has been removed
- however you can only see surface so water might remain inside
86
how to make sure all water has been removed in water of crystallisation:
reheat repeatedly until the mass of the residue no longer changes (all water has been removed)
87
assumption on no further in water of crystallisation:
- many salts decompose further when heated strongly e.g copper (II) sulfate decomposes to black copper oxide
- difficult to judge if no colour change
88
1cm3 to ml
1ml
89
1dm3 to cm3
1dm3 = 1000cm
90
1000cm3 to ml:
1000cm3 = 1000ml = 1l
91
concentration definition:
the amount of solute in moles, dissolved in each 1dm3 of solution
92
what does 1moldm-3 of solution contain?
1 mol of solute dissolved in each 1dm3 of solution
93
formula linking n v c
n = v x c
- volume in dm3 so divide by 1000
94
standard solution definition:
a solution of a known concentration
- prepared by dissolving an exact mass of the solute in a solvent and making up of the solution the same volume
95
conditions for equal volumes of different gases having the same number of molecules:
same temperature, pressure
96
molar gas volume definition:
the volume per mole of gas molecules at a stated temperature and pressure
97
what does the volume of a gas depend on?
pressure and temperature
98
RTP values:
20°C and 101kPa
at RTP 1 mole of gas molecules has volume of 24dm3 = 24000cm3
- at RTP molar gas volume = 24dm3mol-1
99
assumptions for molecules making up ideal gas:
- random motion
- elastic collision
- negligible size
- no intermolecular forces
100
formula for ideal gas equation:
pV =nRT
101
units for ideal gas equation:
pressure = Pa
volume = m3
ideal gas constant = 8.314
amount of gas molecules (n) = mol
temperature = K
102
cm3 to m3
x 10^ -6
103
dm3 to m3:
x 10^-3
104
C° to K:
+ 273
105
kPa to Pa:
x 10^3
106
standard room temp:
25°C
101kPa = 24.5dm3 mol-1
107
assumptions of real gas equations:
- forces between molecules are negligible
- gas molecules have negligible size compared to their container
108
volume of molecules compared to container when gas molecules are close together:
volume of molecules compared with rye volume of the container is higher
109
real gas equation:
nRT = (p + n^2a / V2) (V - nb) = nRT
110
stoichiometry definition:
balancing numbers into ratio of amount in moles of each substance
111
why do chemists use balanced equations?
- the quantities of reactants required to prepare a required quantity of a product
- quantities of products that should be formed from certain quantities of reactants
112
steps for identifying an unknown metal:
1. set up apparatus with gas syringe, dilute HCl, unknown metal
2. weigh sample of metal + add to flask
- use measuring cylinder add 25cm3, HCl 1.0 moldm-3 (an excess) to flash and quickly replace bung
- measure maximum volume of gas in syringe
113
theoretical yield definition:
the maximum possible amount of product
114
why is the theoretical yield hard to achieve?
- reaction may be incomplete
- other reactions may have taken place alongside
- purification of product may result in loss of product
115
is the actual or theoretical yield higher?
theoretical
116
formula for percentage yield:
percentage yield = actual yield / theoretical yield x 100
117
what happens to reactants in theoretical yield?
two reactants with one in excess
118
limiting reagent definition:
the reactant that is not in excess and is completely used up first to stop the reaction
119
what do you do if you do not know which reactant is in excess?
work out moles of each reactant and compare with equation
- calculations must be based on limiting reagent
120
atom economy definition:
a measure of how well atoms have been utilised
121
what do atoms with high atom economies produce?
- large proportion of desired products + few unwanted waste products
-
122
why are high atom economies important?
important for sustainability as they make the best use of natural resources
123
formula for atom economy:
atom economy = sum of molar masses of desired products / sum of molar masses of all products x 100
124
why has atom economy been developed?
- awareness of finite resources + environmental concerns of processing + disposing harmful waste
- improving atom economy makes industrial processes more efficient
125
what is the most useful percentage of atom economy?
100%
126
why is CO2 an undesired product?
it is one of the gases that cause global warming
127
what happens when using reactants that are readily available?
e.g carbon from coal and steam from water where energy will be needed to produce steam but costs for obtaining starting materials are low
128
what does efficiency of percentage yield depend on?
- atom economy and percentage yield
