unit one: principles of chemistry Flashcards
1
Q
what are the three states of matter
A
solid, liquid and gas
2
Q
describe the structure and arrangement of molecules in a solid
A
the molecules are tightly packed
held in fixed positions by strong forces
the molecules can vibrate around their fixed positions
as the solid gets hotter the vibrations get bigger.
3
Q
describe the structure and arrangement of molecules in a liquid
A
the molecules are closely packed do not have a regular structure the forces between the molecules are strong molecules move randomly molecules are close together
4
Q
describe the structure and arrangement of molecules in a gas
A
molecules are widely spaced
in a continuous state of random motion.
the forces between molecules are small except during collisions
5
Q
solid to liquid is
A
melting
6
Q
liquid to gas is
A
boiling
7
Q
gas to liquid is
A
condensing
8
Q
liquid to solid is
A
freezing
9
Q
solid to gas is
A
subliming
10
Q
the substance that dissolves is called the
A
solute
11
Q
the liquid a solute dissolves in is called the
A
solvent
12
Q
a solute and a solvent forms a
A
solution
13
Q
solubility is
A
the mass of solute which must dissolve in 100g of solvent at that temperature
14
Q
what is a saturated solution
A
a solution that contains as much dissolved solid as possible at a paticular temperature
15
Q
what do you plot against what to get a solubility curve
A
solubility against temperature
16
Q
what are atoms made up of
A
sub atomic particles : neutrons, protons and electrons
17
Q
what are molecules made up of
A
usually, two or more atoms covalently bonded together. however the noble gases exist as atoms at room temperature and pressure, and are called monatomic molecules
18
Q
describe the melting and boiling point of a pure substance
A
they will be fixed temperatures (it will not melt and boil over a range)
19
Q
describe the melting and boiling point of a mixture
A
mixtures usually melt or boil over a range of temperatures.
20
Q
the narrower a range a substance melts and boils over…
A
the purer the subtance is
21
Q
filtration
A
to separate an (undissolved) solid from a mixture of the solid and a liquid/solution
22
Q
evaporation
A
to separate a dissolved solid from a solution, when the solid has similar solubilities in both cold and hot solvent
23
Q
crystallisation
A
to separate a solute from a solution
24
Q
simple distillation
A
to separate a liquid from a solution
25
fractional distillation
to separate two or more liquids that are miscible with one another (separate a mixture of liquids)
26
paper chromatograpy
to separate substances that have different solubilities in a given solvent.
27
Rf =
distance travelled by solute / distance travelled by solvent
28
what is thermal decomposition
when the elements in a compound that are chemically joined together are heated, and the compound decomposes into the elements.
29
where are the protons and neutrons in an atom
the nucleus
30
what is the relative charge of a neutron
0
31
what is the relative charge of a proton
+1
32
what is the realtive charge of a electron
-1
33
what is the relative mass of a proton
1
34
what is the relative mass of a neutron
1
35
what is the relative mass of an electron
virtually nothing 1/1836
36
what is the atomic number
number of protons in the nucleus of an atom of an element
37
what is the mass number
number of protons + number of neutrons in the nucleus of an atom of an element
38
what are isotopes
atoms (of the same element) which have the same atomic number but different mass numbers. they have the same number of protons but different numbers of neutrons
39
what is the relative atomic mass calculated from
from the masses and relative abundances of all the isotopes of a paticular element.
40
what is the symbol for relative atomic mass
Ar
41
where are electrons in an atom
around the nucleus in different energy levels called electron shells
42
what is electronic configuration
the way electrons are arranged
43
how many electrons can the first shell take
maximum of 2
44
how many electrons can the second shell take
maximum of 8
45
how many electrons can the third shell take
18
46
what are periods in the periodic table
the horizontal rows
47
what are groups in the periodic table
the vertical columns
48
what is a pattern within groups
elements with the same number of electrons in their outermost shell are in the same group
49
when do elements have similar chemical properties
when theyre in the same group
50
group 1 is called
the alkali metals because they all react with water to form alkaline solutions
51
group 7 is called
the halogens 'salt - maker' because they from salts when they react with metals.
52
group 8 is called
the noble gases because they are chemically unreactive as they have a full outer shell and so none gain or lose electrons easily
53
hydrogen's ion
H+
54
lithiums ion
Li+
55
sodiums ion
Na+
56
potassiums ion
K+
57
rubidiums ion
Rb+
58
Caesiums ion
Cs+
59
beryilliums ion
Be2+
60
magnesiums ion
Mg2+
61
calciums ion
Ca2+
62
strontiums ion
Sr2+
63
bariums ion
Ba2+
64
borons ion
B3+
65
aluminiums ion
Al3+
66
galliums ion
Ga3+
67
silvers ion
Ag+
68
coppers ion
Cu2+
69
iron II ion
Fe(II)2+
70
iron III ion
Fe(III)3+
71
leads ion
Pb2+
72
zincs ion
Zn2+
73
ammoniums ion
NH4
74
nitrides ion
N3-
75
phosphides ion
P3-
76
asenides ion
As3-
77
oxides ion
O 2-
78
sulfides ion
S 2-
79
selenides ion
Se2-
80
tellurides ion
Te2-
81
fluroides ion
F-
82
chlorides ion
Cl-
83
bromides ion
Br-
84
iodides ion
I-
85
hydroxides ion
OH-
86
carbonates ion
CO3 2-
87
nitrates ion
NO3 -
88
sulfates ion
SO4 2-
89
what are the four different state symbols
s - solid
l - liquid
g - gas
aq - aqueous
90
what is the symbol for relative formula mass
Mr
91
how do you calculate Mr
add up the relative atomic masses of all the atoms present in the formula
92
what is a mole
a measure of the amount of substance. one mole is the amount of substance that contains 6.022 x 10 to the power of 23 particles.
93
what is the mass of one mole of atoms
the relative atomic mass expressed in grams
94
amount in moles =
mass of substance in grams / Mr
95
what is the empirical formula
the simplest whole number ratio of atoms of each element in the compound
96
what is the molecular formula
the exact numbers of atoms of each element present in the formula of the compound
97
what is the molar volume of a gas
one mole or any gas has a volume of 24dm cubed (24,000 cm cubed) at room temperature and pressure (r.t.p.)
98
how do you calculate volume of gas from amount of gas
volume of gas (in dm cubed) = amount x 24
99
1dm cubed =
1000 cm cubed
100
how do you calculate amount of gas from volume of gas
amount of gas (in moles) = volume of gas / 24
101
amount of dissolved substance =
(volume of solution x concentration of solution mol/dm )
____________________________
1000
102
what is an ion
an electrically charged atom or group of atoms formed by the loss or gain of electrons
103
when is an ionic lattice formed
when an ionic compound forms, the positively charged ions attract the negatively charged ions and arrange themselves in to a three - dimensional structure called an ionic lattice.
104
what is an ionic bond
the electrostatic force of attraction between the oppositely charged ions within an ionic lattice.
105
why do ionic compounds have high melting and boiling points
the electrostatic forces are strong and there are many of them to break apart, so it requires a large amount of energy to overcome the forces.
106
when a non - metal and a metal combine what do they form
an ionic bond
107
when a non - metal and a non - metal combine what do they form
a covalent bond
108
when a covalent bond is formed why is the new substance described as a simple molecular compound
because it consists of indiviual molecules
109
what does diatomic mean
the molecule contains two atoms
110
what is a displayed formula
use an unbroken line to represent a shared pair of electrons / single covalent bond instead of dots and crosses
111
do simple molecular substances have low or high melting and boiling points?
low because the forces of attraction between the molecules are typically weak compared to the eletrostatic forces of attraction between oppositely charged ions and very little energy is needed to overcome them.
112
what is a giant covalent structure
millions of atoms covalently bonded together like diamond, graphite and silicon dioxide
113
what are properties of diamond
very high melting point as many strong covalent bonds have to be broken, hard and abrasive and does not conduct electricity.
114
properties of graphite
very high melting point, soft and slippery and conducts electricty.
115
forces in diamond
strong covalent bonds
116
forces in graphite
strong covalent bonds and weak forces of attraction
117
how is diamond bonded
each carbon atom forms four single covalent bonds and a 3D structure is formed.
118
how is graphite bonded
each carbon atom forms three single bonds to other carbon atoms and a layered structure is formed.
119
uses for diamond
cutting tools
| jewellery
120
uses for graphite
lubricant
| electrodes for electrolysis
121
what is C60 fullerene
an allotrope of carbon
122
what is an allotrope
different forms of the same element
123
does C60 have low or high melting and boiling points
only the weaker intermolecular forces of attraction need to be broken so low.
124
does C60 conduct electricity
no as each carbon atom only forms 3 bonds there are delocalised electrons in C60 but these electrons are only free to move within molecules and not between them
125
how are metals arranged
in a giant, three - dimensional lattice structure in which postive ions are arranged in a regular pattern in a 'sea of electrons'.
126
what is the metallic bond in metals
the attraction between the delocalised electrons (detached from their atoms) and the positive ions.
127
why do metals have high melting and boiling points
metallic bonds are strong and there are many of them in a giant structure, hence a lot of heat energy is required.
128
why are metals good conductors of electricity
the delocalised electrons are free to move when voltage is applied across the metalk
129
why are metals malleable and ductile
the layers of positive ions can easily slide over one another and take up different positions. the delocalised electrons move with them so the metallic bonds are not broken.
130
do ionic compounds conduct electricity as a solid
no because the ions are not free to move.
131
do ionic compounds conduct electricity when molten or when dissolved
yes because electrolysis takes place.
132
what is electrolysis
the decomposition (chemical breakdown) of an ionic substance by passing an electric current through it.
133
the substance being electrolysed is called the
electrolyte
134
the electical connections between the electrolyte and the external electrical circuit are called
electrodes.
135
the positive electrode is called an...
anode
136
the negative electrode is called a...
cathode
137
when electrolysing a molten binary compound, where is the metal formed?
at the negative electrode (cathode)
138
when electrolysing a molten binary compound, where is the non-metal formed?
at the postive electrode (anode)
139
explain the reaction at the cathode
positive metal atoms are attracted to the negative electrode. when they get to the electrode, they gain electrons and are reconverted back into their atoms.
140
explain the reaction at the anode
negative non-metal ions are attracted to the positive electrode. when they get to the electrode, they lose electrons to form atoms. the atoms then then pair up to form molecules.
141
in electrolysis of aquous solutions, the product at the negative electrode is either...
hydrogen or a metal
142
in electrolysis of aqueous solutions, the product at the positive electode is either...
oxygen or another non-metal
143
in electrolysis of aqueous solutions, what happens if the metal in the salt is above hydrogen in the reactivity series?
hydrogen is evolved at the cathode.
144
in electrolysis of aqueous solutions, what happens if the metal in the salt is below hydrogen in the reactivity series
the metal is deposited on the cathode
145
describe C60 fullerene's structure
it is a molecular covalent structure with weak intermolecular forces between each sphere.
146
what is an electrolyte
liquid or solution that undergoes electrolysis
147
what substances are often used as electrodes
carbon (inert), platinum, and other metals
148
give an example of a molten substance that can be used an electrolyte
lead bromide
149
if something loses electron(s) then it has been...
oxidised
150
if something gains electron(s) then it has been...
reduced
151
how would you show diffusion
fill the lower gas jar with bromine gas, and the top one with air. remove the gas lids, and the brown colour of the bromine will diffuse upwards, whilst the air diffuses downwards until it is all a uniform brown .
152
how would you show that particles of different gases travel at different speeds
soak a piece of cotton wool in ammonia, and another piece in hydrochloric acid. place these at either end of a long glass tube with rubber bungs to stop the poisonous gas from escaping. the particles will diffuse along the tube, forming a white ring considerably closer to the end containing hydrochloric acid. this is because ammonia particles are lighter and so move faster.
153
how would you show diffusion through a liquid
fill a gas jar with water, then add a small jar of strongly coloured solution, such as potassium manganate. this will diffuse upwards and colour the whole solution purple.
154
what is solubility measured in
g per 100g of water
155
when is a compound formed
when two or more elements chemically combine.
156
when is a mixture formed
when various substances are mixed together and no chemical reation occurs
157
do properties of elements change in a mixture
no, the elements keep the same properties
158
do properties of compounds change in a mixture
yes
159
mass number is
protons + neutrons
160
atomic number is
protons = electrons
161
how do you work out number of neutrons from the periodic table
mass number - atomic number
162
what is relative atomic mass
average mass of an atom, taking into account the amount of each isotope present in a naturally occuring sample of the element.
163
as the shells of an electron get further away, and the distance increases, what happens to the energy
it increases
164
elements in the same group contain
elements with similar properties.
165
do metals or non-metals conduct electricity
metals
166
what do metals generally form
basic oxides
167
what is a basic oxide
one which reacts with acids to form salts
168
what do non-metals generally form
acidic oxides
169
what is an acidic oxide
acidic oxides react with bases/alkalis to form salts.
170
properties of metals:
```
high melting and boiling points
shiny
malleable
ductile
good conductors
form ionic compounds
form positive ions in their compounds (give away their electrons)
```
171
properties of non-metals
tend to have low melting and boiling points
brittle when solid
not as shiny
not conductors (except carbon in the form of graphite for electricity, and diamond for heat)
form both ionic and covalent compounds
tend to form negative ions in ionic compounds
172
what does the state symbol (s) mean
solid
173
what does the state symbol (l) mean
liquid
174
what does the state symbol (aq) mean
an aqueous solution
175
what does the state symbol (g)
gas
176
what is Ar
the atomic mass of an element
177
what is the relative atomic mass of an element
the weighted average mass of the isotopes of an element. it is measured on a scale on which a carbon-12 atom has a mass of exactly 12.
178
what is Mr
relative formula mass
179
what is relative formula mass sometimes called
relative molecular mass
180
how do you find Mr
add up all the Ar's of the formula.
181
how do you find Ar
it's the mass number
182
how do you find percentage by mass of a Ar of a compound
calculate the Ar's, then divide the Ar you want to find the percentage mass of, by the total Mr of the compound. then multiply this by 100.
183
how would you find the formula of magnesium oxide by combustion in a practical
weigh a crucible with a lid.
place a piece of magnesium ribbon about 10cm long in the crucible.
reweigh it and its contents.
set up the apparatus with the crucible above a bunsen burner on a tripod held in place by a pipeclay triangle.
heat strongly, lifting the lid every few seconds.
when the reaction is finished, allow everything to cool.
weigh everything again.
184
why does the mass of magnesium increase when you heat it strongly
it combines with the oxygen in the air. the mass of magnesium oxide is greater than the mass of just magnesium.
185
how would you find the formula of a metal oxide by reduction in a practical
weigh a ceramic dish.
put about 3g of copper oxide in the dish and reweigh.
place in a tube.
pass hydrogen gas over the copper oxide.
ignite the excess hydrogen, which comes out of the small hole in the boiling tube.
heat the copper oxide strongly until the reaction is finished. the copper will turn pink-brown.
186
why does the mass of the copper oxide decrease when you heat it strongly
the oxygen leaves the copper and combines with the hydrogen to form water.
187
how would you find the formula of water in a practical
use the practical to find the formula of metal oxide by combustion but put a U tube in beaker filled with ice and water connecting a pump and the release of hydrogen gas. this means the water vapour produced will condense.
188
how do you calculate empirical formula
work out the number of moles in each element in the compound, then divide by the smallest result.
189
how do you calculate percentage yield
actual yield
--------------------------- x 100
theoretical yield
190
what do you need to do when calculating the substance inexcess
use the molar ratio
191
what is avogadros law
equal volumes of gases at the same temperature an pressure contain equal numbers of molecules
192
what happens when an ionic compound is formed
electron(s) are transferreed from a metal atom to a non-metal atom to form positive and negative ions
193
what is ionic bonding (def)
the strong electrostatic attraction between positive and negative ions
194
when an atom loses an electron it becomes...
positively charged
195
when an atom gains an electron it becomes..
positively charged
196
what is a positive ion called
a cation
197
what is a negative ion called
an anion
198
what do elements in groups 1,2,6 and 7 always form
ions that are isoelectronic with the nearest noble gas atom
199
how do you work out the charge on an ion
look at what group its in
200
what do all metals form
positive ions
201
what do names like lead(II) chloride mean
that it contains a Pb 2+ ion
202
ion for zinc
Zn 2+
203
ion for silver
Ag +
204
ion for hydrogen
H +
205
ion for ammonium
NH4 +
206
ion for nitrate
NO 3-
207
ion for hydroxide
OH -
208
ion for carbonate
CO 3 2-
209
what happens if you have an 'ate' ending not an 'ide' ending
it means the compound contains oxygen and possibly other things
210
what is a lattice
a regular array of particles
211
what do all ionic compounds form crystals that consist of
lattices of positive and negative ion spacked together in a regular way
212
what is the lattice held together by
strong electrostatic attractions between the positively and negatively charged ions
213
why do we call it a giant ionic latticw
to describe a structure where there are no indiviual molecules
214
charactersititcs of ionic substances
they tend to be soluble in water
| they tend to be insoluble in organic solvents
215
why dont ionic compunds conduct electricity when theyre solid
the ions are fixed in posistion and are not free to move around.
216
why do ionic compounds conduct electricity when theyre molten or dissolved in water
the ions become free to move aroumd.
217
why do ionic compunds have high melting and boilingpoints
because of the strong electrostatic forces of attraction holding the lattice together. a lot of enegy has to be supplied to break the strong electrostatic forces of attraction between oppostielt charged ions in the giant lattice structure.
218
what is a covalnet bond
a pair of electrons is shared between two atoms.
219
what holds the atoms together in a covalent bond
the strong electrostatic attraction between the nuclei (positively charged) of the atoms that make up the bond and the shared pair of electrons (negatively charged)
220
why are hydrogen molecules said to be diatomic
they contain two atoms
221
what defines an element
how many protons it has
222
the more bonds are formed..
the more energy is released and the more stable the system becomes.
223
what is a double (covalent) bond
when two pairs of electrons are shared betweeen atoms.
224
what is a triple (covalent) bond
when three pairs of electrons are shared between atoms
225
what does intermolecular mean
between molecules
226
describe the forces in watrer
strong covalent bonds between the H and O atoms,
| intermolecular molecules, (between molecules) to keep it in liquid state
227
when we boil water which forces are broken
the intermolecular ones, NOT the strong covalent bonds
228
between what does ionic bonding ususally occur
a metal and a non metal
229
between what does covalent bonding usuallly occur
a non metal and a non metal
230
when do we say a substance has a simple molecular structure
when a substance consists of molecules with intermolecular forces of attraction between them
231
why do substances with simple molecular structures tend to be gases or liquid with low melting and boiling points
not much energy is required to break the weak intemolecuakr bonds
232
what do halogens all have
a simple molecular structure consisting of diatomic molecules with intermolecular forces between them.
233
as relative molecular mass increases...
the intermolecular forces of attraction become stronger, so more energy must be put in to break the intermolecular forces.
234
do covalent molecular compounds conduct electricity
no because they dont have nay overlal electrical charge
235
are covalent molecular substances soluble
no they tend not to be in water, but often in organic solvents
236
does diamond have high or low boiling points
very high
237
why does diamond ahev very high melting and boiling points
because of the very strng carbon-carbon covalent bonds which extend throughout the entire crystal in three dimensions. a lot of enrgy has to be supplied to break these.
238
does diamond haev intermolecular forces
no, it has a giant structure, there are no molecules.
239
what is diamond a form of
pure carbon
240
other characteristics of diamond
```
very hard (los of energy to break the covalent bonds)
doesnt conduct electricity (no electrons can move around)
```
241
difference between graphite and diamond
in graphite, it has a layer structure, each layer is strong, but they are easily separated from another layer.
242
is graphite hard or soft
soft, the forces holdinga toms together in each layer are strong,but he attactions between layers are much weaker and not much energy is needed to overcome them. layers slide over eachother and can easily be flaked off.
243
other characteristiics of graphite
high melting and boiling points because you have to break up the whole structure.
it conducts electricity because each carbon atom is joined to only three others, meaning one is free to mvo around throughout the whole of the layer. this is called a delocalised electron
244
what are diamon and carbon
allotropes of carbon
245
what strucutes do diamond and carbon have
giant
246
what structure doe C60 have
simple molecular
247
in solid or liquid C60, there are...
C60 molecules with weak intermoleular forces between them. (60 carbon atoms joined by covalent bonds)
248
charicterstics of C60 or fullerene
lower melting and boiling points, when it's melted, only the relatively weak intermolecular forces of attraction must be broken. this does not require as much energy as breaking all the strong covalent bond when diamond and graphite are melted
not as hard as diamond (doesnt take as much energy to break the intermolecular forces of attraction)
does not conduct electricity because the fouth electron on each carbon atom cannot jump from molecule to molecule
249
describe the bonding in a giant ionic lattice structure
positive and negative ions in a regular arrangement. the oppositely charged ions will be attracted to eachother by electrostatic forces
250
where would non-metal oxides be on the pH scael
4 because theyre (usually) acidic
251
group of noble gases
0
252
C60 is
a simple molecular substance that contains delocalised electrons
253
explain how the pattern of spots produced in a paper chromatography experiment can be used to distinguish a pure substance from an impure substance
a pure substanace leaves a single spot, and impure substance leaves multiple spots
254
why are the noble gases not very reactive
they don't easily lose or gain electrons
255
describe the bonding in a giant ionic lattice structure like sodium chloride
oppositely charged ions are attracted to eachother by electrostatic forces
256
solubility def
maximum mass of solute that dissolves in 100g of solvent at a particular temperature.
257
saturated solution def
a solution which contains as much dissolved solid as possible at a particular temperature. there must be some undissolved solute present.
258
what can you use solubility curves for
to work out what mass of crystals you would get if you cooled a saturataed solution.
259
what is avogadros law
equal volumes of gases at the same temperature and pressure contain equal numbers of molecules
260
what are volumes of gases or liquids are measured in
cubic centimetres
cubic decimetres
litres
261
link between litres, cubic decimetres and cubic centimetres
1 litre = 1dmcubed = 1000cmcubed
262
convert 1dmcubed to 1000cmcubed
multiply by 1000
263
convert 1000cm cubed to 1dmcubed
divide by 1000
264
1 mole of any gas contains the
same number of molecules and so occupies the same volume as 1 mole of any other gas at the same temperature and pressure
265
at room temp and pressure, what is the volume occupied by 1 mole of any gas?
24dmcubed or 24,000cmcubed
266
volume of a gas =
number of moles x molar volume (24dmcubed)
267
what are concentrations measured in
g/dmcubed
| mol/dmcubed
268
number of moles =
concentration (mol/dmcubed) x volume of solution (dmcubed)
269
what is a titration
the technique to find out how uch of one solution reacts with a certain volume of another solution of known concentration.
270
wahat is measured into a conical flask in a titration using what
a solution of an alkali using a pippette.
271
where is the acid run from in a titration
a burette.
272
as the acid in a titration is run into the conical flask of an alkali, what must you do
swirl it constantly.
273
what happens near the end of a titration
the acid is run in a drop at a time until the indicaotr just changes colour.
274
if you know the concentration of the acid or alkali in a titration what can you do
use the results of the concentration to calculate the concentration of the other solution you reacted it with.
275
what is a metallic structure
a lattice of positive ions in a sea of delocalised electrons
276
what happens when metal atoms bond together
they form the solid metal, meaning the outer electron on each sodium atom becomes free to move throughout the whole structure. these electrons are said to be delocalised.
277
what are delocalised electrons
electrons that are no longer attatched to particular atoms or pairs of atoms, instead they 'flow through the whole metal'.
278
what is metallic bonding
the electrostatic forces of attraction between each positive ion and the delocalised electrons. this holds the structure together.
279
what type of structure do metals have
giant structures.
280
are there any indiviual molecules in metal giant structures
no all the positive ions in the lattice attract all the delocalised electrons
281
what does the ion formed by the metal depend on (in metallic bonding)
then number of electrons the original atoms has in its outer shell.
282
describe the melting points of metals
high due to the strong electrostativ forces of attraction betwen the positive ions and the delocalised electrons in a giant metallic strucutre
283
describe the electrostatic forces of attraction between the positive ions and the delocalised electrons in a giant metallic structure
strong (leading to the metal's high melting point)
284
why do metals conduct electricity
the delocalised electrons are free to move throughout the structure.
285
what happens when force is applied to a piece of metal
the layers of positive ions slide over eachother. this does not affect bonding, the positive ions are still attracted to the delocalised electrons. this means metals are malleable.
286
why dont ionic compounds conduct electricity when they are solid
the ions are held tightly in position in the lattice and they are not free to move around.
287
why do ionic compounds conduct electricity when molton or dissolved in water
the ions are now free to move around
288
do covalent molecular compounds conduct electricity
no never, they consist of indiviual molecules without any overall electrical charge, so there are no charged particles to move around. the electrons are also all held tightly in the atoms or in covalent bonds and so they are not able to move from molecule to molecule.
289
what is electrolysiss
a chemical change caused by passing an electric current through a compound which is either molten or in solution.
290
what is an electrolyte
a liquid or solution that undergoes electrolysis. they all contain ions. the movement of the ions is responsible for both the conduction of electricity and the chemical changes that take place.
291
what are electrodes
the way electricity is passed into and out of the electrolyte
292
what material is commonly used for electrodes
carboin because it conducts electricity and is chemically fairly inert, so it doesnt react with things. platinum can be usedinstead.
293
when you connect a power source in electrolysis, what happens
it pumps mobile electrons away from one electrode to the next one. as there are more electrons there, it has a negative charge (the cathode). the other electrode has had electrons removed from it so is positively charged. (the anode). then the cations are attracted to the cathode (and gain electrons to form neutral charges) and the negative ions (anions) are attracted to the anode (and lose electrons to form neutral charges)
294
what does discharging an ion mean
that it loses its charge.
295
how does discharging an ion happen
by giving up eletrons to the electrode or receiving electrons from it
296
what is oxidation
when something loses electrons
297
what is reduction
when something gains electrons
298
what happens if you electrolyse a molten ionic compound only containing two elements,
you will get the metal at the cathode (because metals form positive ions) and the non-metal at the anode (because non-metals form negative ions
299
where does reduction always occur at in electrolysis of molten substances
reduction always occurs at the cathode and oxidation always occurs at the anode.
300
cations are attraced to
the cathode
301
anions are attracted to
the anode
302
why would it be easier to add an ion to a less reactive metal than a reactive on
the reactive one will just lose it again, so it would be better to add it to the unreactive one
303
what is water called
a weak electrolyte.
304
what does water ionise to give
hydrogen and hydroxide ions.
305
why do ions have to be present for electrolysis to work
the current in the external circuit can only flow if there are ions which can move and be discharged. if you tried to electrolyse a covalent compound (either molten or in solution (there wouldn't be a current flow because there aren't any ions)
