Unit 1.3 - Chemical Calculations Flashcards
1
Q
Relative atomic mass symbol
A
Ar
2
Q
Why can atoms not be weighed?
A
They’re too small
3
Q
What do we do as atoms are too small to be weighed?
A
Compare them to a standard - the C-12 isotope
4
Q
What is the standard we compare atoms to?
A
The Carbon 12 isotope
5
Q
What’s the mass of C-12 isotopes?
A
12 units
6
Q
What can atoms of the same element have due to the existence of isotopes?
A
Different masses
7
Q
What do we have to do to define relative atomic masses due to the existence of isotopes?
A
Take an “average” mass of the atoms
8
Q
Does relative atomic mass (Ar) have units? Why?
A
No, as they’re ratios of units
9
Q
What do all of the “relative….mass” definitions have reference to?
A
The C-12 isotope
10
Q
Relative atomic mass (Ar)
A
The ratio of the average mass of an atom of the natural nuclidic composition of the element to 1/12 of the mass of an atom of the C-12 isotope
11
Q
Relative isotopic mass
A
The ratio of the average mass of an atom of the element to 1/12 of the mass of an atom of the C-12 isotope
12
Q
Relative molecular mass symbol
A
Mr
13
Q
Relative molecular mass (Mr)
A
The ratio of the mass of a molecule of a chemical compound to 1/12 of the mass of an atom of the C-12 isotope
14
Q
How do you calculate the relative molecular mass (Mr)?
A
Add up all of the relative atomic masses (top numbers), multiplying only by the small numbers and ignoring big ones, using the molecular formula
15
Q
How are relative formula mass and relative molecular mass the same?
A
-Same definition
-Same symbol (Mr)
-Same calculation
16
Q
How is relative formula mass different to relative molecular mass?
A
Relative molecular mass = Molecular formula
Relative formula mass = Empirical formula
17
Q
What do we measure the amount of a substance in?
A
Moles
18
Q
Mole
A
One mole is the amount of a substance which contains the same number of particles as there are atoms in 12g of the C-12 isotope
19
Q
What is Avogadro’s Constant?
A
The number of atoms in one mole of an element
20
Q
Avogadro’s constant symbol
A
NA
21
Q
What is the number of atoms in one mole of an element?
A
Avogadro’s constant
22
Q
How do we calculate the mass of 1 mole of an element in grams
A
Ar in grams (super easy!)
23
Q
What’s the ratio of the average mass of an atom of the natural nuclidic composition of the element to 1/12 of the mass of an atom of the C-12 isotope?
A
Relative atomic mass (Ar)
24
Q
What’s the ratio of the average mass of an atom of an element to 1/12 of the mass of an atom of the C-12 isotope?
A
Relative isotopic mass
25
What’s the ratio of the mass of a molecule of a chemical compound to 1/12 of the mass of an atom of the C-12 isotope?
Relative formula mass (Mr)
26
What’s the amount of a substance which contains the same number of particles as there are atoms in 12g of the C-12 isotope?
A mole
27
What does the mass spectrometer do?
Accurately measures relative atomic masses
28
What do we obtain from a mass spectrometer?
A mass spectra, which has a wide variety of uses in labs
29
What’s the order of the processes that take place within the mass spectrometer?
-Vaporisation
-Ionisation
-Acceleration
-Deflection
-Detection
30
Where does the vaporised sample enter in order to be ionised in the mass spectrometer?
The ionisation chamber
31
Why must our sample into the mass spectrometer be vaporised?
You can only ionise vapour
32
How does the ionisation stage within the mass spectrometer work?
The electron gun gives out high energy electrons, which knock the electron out of an atom in the gaseous sample due to its speed, thus ionising them
33
Why is ionisation necessary in the mass spectrometer in order to accurately measure relative atomic masses?
-Only ions will create a current when hitting the detector
-We want ions, not molecules to interact with the magnetic field
34
What happens during the acceleration stage to ions within the mass spectrometer?
They’re sped up by a magnetic field until they’re all at the same speed into a finely focused beam
35
How are ions sped up in the mass spectrometer?
By a magnetic field
36
Until when are the ions sped up in a mass spectrometer?
Until they’re all travelling at the same speed into a finely focused beam
37
Draw and label the mass spectrometer
(Check notes)
38
What’s the purpose of the vacuum pump on the mass spectrometer?
To prevent the ions colliding with air molecules
39
What are ions deflected by in the mass spectrometer?
A magnetic field (an electromagnet)
40
What is at the detection stage of the mass spectrometer?
-Amplifier
-Chart recorder
41
Why is it the MASS that impacts how much the ions are deflected by the electric field of the electromagnet in a mass spectrometer?
As the ions are all equal charge so this doesn’t effect it
42
What are ions deflected according to in a mass spectrometer?
Their mass/charge ratio
43
If an ion is lighter, how does this effect how it’s deflected?
Deflected more
44
What type of ions reach the detector first in a mass spectrometer?
The lighter ones
45
Which ions have the lowest m/z value in a mass spectrometer?
The lightest ones
46
What happens to ions with different mass to charge ratios in the mass spectrometer?
They’re deflected and measured separately
47
What do we look at for an ions m/z number?
Its mass number
48
Mass to charge ratio symbol
m/z or m/e
49
List what happens at the detection stage on the mass spectrometer
-Beam of ions detected electrically
-Electric current = amplified + recorded
-More ions = more current
-Results analysed by a computer and displayed on the visual display unit of the computer
50
How does the amount of ions effect the current in a mass spectrometer?
More ions = higher current
51
How are the results from a mass spectrometer analysed on a computer?
Displayed on the visual display unit of the computer
52
What two things do we need to know in order to calculate the relative atomic masses of elements?
- The relative isotopic mass (top number)
-The relative abundance of the isotopes
53
Relative abundance
The fraction of that isotope found in the natural nuclidic composition of the element
54
What’s the fraction of an isotope found in the natural nuclidic composition of an element?
Its relative abundance
55
What’s the formula for calculating the relative atomic mass of an element?
(%abundance X isotopic mass of element - top number) + (next one) + (next one) …
———————————————————————————————————————
100
56
How can we confirm if the relative atomic mass that we’ve calculated is correct?
Is says it on the periodic table (the top number)
57
What do we need to do if the abundance given to us for a relative atomic mass formula is in decimals?
We do NOT have to divide it by 100
58
What do we do if relative abundance isn’t given in decimals or percentages and simply as a number?
Add them together and divide by this total
59
What’s the highest possible relative abundance?
100%
60
What’s relative abundance (simply)?
How much of that isotope is in that element
61
What’s goes along the x and y axis on a graph for calculating relative atomic mass?
X - mass/charge (m/z)
Y - relative abundance
62
What’s really important to show on the isotopes we’re using for relative atomic mass calculations?
Their charges
63
What do we do if peak height is given instead of relative abundance to calculate the relative atomic mass?
Relative abundance = peak height
——————
Total height
64
Equation for the ionisation of Cl-35 in the mass spectrometer
Cl2 (g) + e- ——> Cl2+ (g) +2e-
65
Equation for the ionisation of Chlorine
Cl2 (g) + e- ——> Cl2+ (g) + 2e-
66
What can molecular ions do in the mass spectrometer?
Undergo fragmentation to give us monatomic chlorine ions
67
What does the fragmentation of chlorine molecular ions give us?
Monatomic chlorine ions
68
Why does fragmentation happen to molecular chlorine ions in the mass spectrometer?
Due to the instability of Cl2+ ions
69
What ions does Chlorine come out as out of the ionisation chamber and what’s wrong with this?
Cl2+ are unstable = undergo fragmentation
70
Fragmentation
the dissociation of energetically unstable molecular ions formed from passing the molecules in the ionization chamber of a mass spectrometer
71
Chlorine Cl2+ ions fragmentation equation
Cl2+ (g) ——> Cl+ (g) + Cl (g)
72
How many isotopes does chlorine have and what are they?
Two
35Cl
37Cl
73
What is the abundance of the Cl35 Chlorine isotope in its natural nuclidic composition?
75%
74
What is the abundance of the Cl37 Chlorine isotope in its natural nuclidic composition?
25%
75
What is the ratio in the atomic ion region of chlorine?
3:1
76
What gives us the molecular ion region on chlorines graph?
The fact that chlorine exists as a diatomic molecule - it consists of molecules, not individual atoms (think of the possible combinations of Cl35 and Cl37)
77
What type of molecule does chlorine exist as and what does this give us?
Diatomic, giving us the molecular ion region on the graph
78
What are the two ion regions we have o chlorine’s mass spectrum?
-atomic ion region
-molecular ion region
79
What do we call the graph with relative abundance and m/z?
The mass spectrum
80
What does chlorine’s atomic ion region peak in?
3:1 ratio
81
What does chlorine’s molecular ion region peak in?
9:6:1 ratio
82
Which molecular ions do we have for chlorine?
M/z = m70, m72 and m74
83
What’s the possibility of an atom being 35Cl?
3/4
84
What’s the possibility of an atom being 37Cl?
1/4
85
How do we get the fractions for figuring out the ratio of the molecular ion region on chlorine’s mass spectrum?
Multiply the possibility of getting each isomer
E.g - 35Cl-35Cl
3/4 x 3/4
= 9/16
(The 9 in the ratio)
86
What’s it important to do with all of the fractions when working out the ratio of a molecular ion region?
Keep them relative (same bottom number) so as to get the correct ratio - the calculator might simplify!
87
What do we do if we’re asked to work out the percentage of an isotope in a molecule, or the mass number?
Use algebra - the same method as before with the relative atomic mass but with an ‘x’ where relevant - remember you can find the relative atomic mass for the start of the equation on the periodic table
88
How do you work out the ratio of the molecular ion region of an element?
Multiply the possibilities of getting each isotope (abundance) with it’s possible pair - make sure all fractions have the same bottom number
(Check notes for chlorine example, it’ll look confusing here)
89
What isotopes does Bromine have?
79Br and 81Br
90
What is the ratio of 79Br and 81Br isotopes in a Bromine molecule?
50:50
91
How many peaks does a diatomic molecule have on its mass spectrum? How do we know this?
5
Think - we have 2 isotopes, which is 2 peaks in the atomic ion region
Then, we have 3 different possibilities of combinations of these isotopes for the molecular ion region = 3 more peaks
92
How many peaks does Bromine’s mass spectrum have?
5
93
Which diatomic molecules do we need to remember their mass spectrums and why they look like this (know the ratios, abundances, isotopes e.t.c.)?
Mostly Chlorine, an idea of Bromine too
94
Empirical formula
The simplest ratio of atoms in the molecule
95
Molecular formula
The actual number of each atom present in the molecule
96
How do we calculate the relative molecular mass?
Sum of Ar’s in the molecule (multiply only by the little numbers, ignoring the big ones)
97
Relative molecular mass symbol
Mr
98
Molecular formula of glucose molecules
C6H1206
99
Molar mass unit
gmol-1
100
Molar mass of glucose molecules
180gmol-1
101
Empirical formula of glucose molecules (how is this worked out?)
CH20
(Molecular formula divided by 6)
102
What do we do if working out the empirical formula from a diagram?
Ignore ions
103
Are ions part of empirical formulas?
No
104
What do we have to know in order to calculate empirical formulas?
The % composition by mass of each element in the molecule in order to divide it by their relative atomic masses
105
Steps in working out Empirical formulas
1. Write symbols of elements
2. Write masses/percentages from the question
3. Divide each mass/percentage by the mass number of that element (Ar)
4. Divide each answer with the smallest answer to find the ratio
106
Do we ever round up or down when working out empirical formulas?
No, instead we multiply them up if the ratios are in decimals (individual elements)
107
What would you multiply a 0.2 decimal in a ratio for an empirical formula by?
5
108
What would you multiply a 0.3 decimal in a ratio for an empirical formula by?
3
109
What would you multiply a 0.5 decimal in a ratio for an empirical formula by?
2
110
What do we have to know in order to work out the molecular formula of a molecule?
The relative molecular mass
111
How do we calculate the molecular formula of a molecule?
1. Determine the relative mass of empirical formula
(Add up the Ar numbers, multiplying only by the small numbers and ignoring the big ones)
2. Divide the Mr (given in question) by mass of empirical formula (our last answer) to get a multiple
3. Multiply empirical formula by the multiple
112
How do we determine the relative mass of an empirical formula?
Add up all of the Ar numbers (relative atomic masses of the atoms), multiplying only by the small numbers and ignoring the big ones
113
What’s the most likely mass of a chlorine molecule?
70
114
Define the mole
The standard unit (an SI unit) for the amount of a substance, which is Avogadro’s constant (NA)
115
Avogadro’s constant symbol
NA
116
Simple way of defining the mole in terms of particles
One mole has (Avogadro constant) amount of atoms
117
What type of quantity is molar mass and what does this mean for it?
A physical quantity, therefore it has units
118
Molar mass units (Mr)
gmol-1
119
Define the molar mass of an element
The mass of one mole of the element in grams
120
What is molar mass equal to?
Mr
121
Triangle showing the relationship between molar mass, mass and amount of moles
m
—
n I M
122
What does M stand for?
Molar mass
123
What does m stand for?
Mass
124
What does n stand for?
Amount in moles
125
Amount in moles unit
Mol
126
What do we use as our molar mass in equations and when?
If we get no information on the moles or mass, make the molar mass equal to the Mr
127
Number of particles/atoms formula
Number of moles x NA
(Remember - this can be rearranged!)
128
Number of particles unit
It doesn’t have one
129
What is necessary in calculations such as ones discovering the number of particles?
Combining both the molar mass, mass, moles triangle equation and the number of particles, moles and NA one
130
What do the same conditions of temperature and pressure cause any gas to do?
Occupy the same volume
131
What conditions are require to be kept the same for one mole of any gas to occupy the same volume?
Temperature
Pressure
132
When does one mole of any gas occupy the same volume?
Under the same conditions of temperature and pressure
133
How much of any gas will occupy the same volume under the same conditions of temperature and pressure?
1 mole
134
What is the molar volume of a gas?
Under the same conditions of temperature and pressure, one mole of any gas will occupy the same volume
135
What’s the name for the fact that under the same conditions of temperature and pressure, one mole of any gas will occupy the same volume?
Molar volume
136
Stp
Standard temperature and pressure
137
What is the standard temperature and pressure?
273K
1 atm (1.01x10^5 Pa)
138
What is 1 atm?
1.01 x10^5 Pa
139
22.4dm^3 in litres
22.4 litres (the same)
140
What’s the difference between the two molar volumes given in the data sheet?
Different temperatures
141
What happens to a gas with increased temperature, providing that the pressure remains constant?
Gas occupies a bigger volume
142
When does a gas occupy a bigger volume?
With increased temperature, providing that the pressure remains constant
143
What do we need to check before answering any of the questions surrounding molar volume?
The temperature, to get our molar volume based off of information on the data sheet
144
Volume unit
dm^3
145
Moles unit
Mol
146
Triangle for the equations on molar volume
V
—
n I Vm
147
Amount in moles symbol
n
148
Volume symbol
V
149
Molar volume symbol
Vm
150
How do we transfer between cm^3 and dm^3?
cm^3 ———> dm^3
÷1000
151
What does the volume always have to be in molar volume questions?
dm^3
152
How do we figure out how much one mole of an element is?
Ar in grams (super easy)
153
What do we do if a molar volume question gives us the temperature in degrees Celsius?
Add 273 to the number and it’ll be in Kelvin
(It says this on the front of the data sheet though)
154
How do we know whether to combine the molar volume equations with the molar mass equations?
Just think of the information that we have - for example, if it’s asking us to calculate the mass with data on the moles, use the molar mass equations, but if we’re given the volume, we need to use the molar volume equation for the amount of moles and then use the molar mass equations to go back to the mass - I’ve made it sound really confusing. Just think what equations you know and what information you have and what makes sense together - you’ll get it.
155
What do you call the solution that moles are in?
Concentration
156
Concentration
How much of a dissolved substance is present per unit volume of a solution (number of moles in 1dm^3)
157
How many dm^3 and cm^3 is one litre?
1 dm^3
1000cm^3
158
How many litres and dm^3 is 1000cm^3?
1 litre
1 dm^3
159
How many cm^3 and litres is 1 dm^3?
1000cm^3
1 litre
160
What is the main solvent used in chemistry?
Water
161
What is concentration measured in?
gdm^-3 OR moldm^-3
162
How do we convert between gdm^3 and moldm^3?
gdm^-3
——-————
moldm^-3 I Mr
163
Moles in solution equations
n
—
c I V
164
Shorthand of moldm^-3
M
165
What is “M” the shorthand of?
Concentration (moldm^-3)
166
What is the mass to charge ratio (m/z) equal to and when?
When the ions generated by a mass spectrometer have a 1+ charge (like chlorine!), it’s equal to the atomic mass of the element
167
Concentration in parts per million (ppm) equation
Mass solute
—————— x1,000,000
Mass Solution
168
When do we take into account the big numbers of a molecule and when don’t we?
Molecular = ignore big numbers
Formula = use big numbers
(Mr)
169
What are the masses of the molecular ion region in the mass spectrum of chlorine?
70, 72 and 74
170
What are the masses in the molecular ion region on the mass spectrum of Bromine?
158, 160, 162
171
Show algebraically the relationship between the amount of moles o A, B, C and D involved in a reaction
nA nB. nC nD
— = — = — = —
a. b. c. d.
172
What does the algebratic equation between nA, nB, nC and nD show?
The amount in moles of A, B, C and D respectively involved in the reaction
173
What’s the reaction between sodium hydroxide and hydrogen chloride?
NaOH + NCl ———> NaCl + H20
174
How can we see if different elements have the same number of moles as each other or not?
Look at the big numbers - the same = same number of moles
175
What do we need to be given to calculate the mass of the products formed?
-Mass of reactants
-A balanced chemical equation
176
What happens in a chemical reaction?
Reactants are changing into products
177
Ratio between amount of moles of reactants and products
Stoichiometric ratios (mole ratios)
178
Stoichiometric ratios
Ratio between the amount of moles of reactants and products (mole ratios)
179
Do we multiply with the big numbers for molar mass (Mr)?
NO
180
What do we need to avoid doing in reacting masses calculations?
Over-round a figure too early on in the calculation (accuracy marks!!)
181
What do we do if asked to work out the identity of an element after we’ve figured out its mass?
Just match it with that relative atomic mass off of the periodic table
182
1 tonne in kilograms
1000kg
183
1000kg in tonnes
1 tonne
184
What do we do if we have an unknown mass and don’t have the moles or molar mass to work it out?
Total mass of reagents = total mass of products
e.g -
0.800g of M(OH)2 ——> 0.553g of MO + ?g of H20
0.800-0.553 = 0.247g
185
What is one of the main aims in green chemistry?
To reduce pollution created in a chemical reaction
186
What happens when a large proportion of a reagent ends up as waste? (3 things)
-Pollution contribution
-Ineffective use of resources
-Raise in production costs
187
What contributes to pollution, ineffective use of resources and a raise in production costs?
Large proportions of reagents ending up a waste
188
Atom economy
A measure of the amount of starting materials that become useful products
189
What is a measure of the amount of starting materials that become useful products?
Atom economy
190
Atom economy equation
Atom economy (%) = mass of useful product from equation
——————————————————— x100
Mass of reagents from equation
191
What do insufficient, wasteful processed have?
A low atom economy
192
What have low atom economies?
Insufficient, wasteful processes
193
What do efficient processes have?
High atom economies
194
What have high atom economies?
Efficient processes
195
What are efficient, high atom economy processes important for?
Sustainable development - fewer resources, less waste
196
What is the ideal atom economy and what would this actually mean?
100% - no waste products, everything is useful products
197
Do we take into account the big numbers for Mr when working out atom economies?
(Sigh) - yes.
198
In what equations do we take into account the big numbers for Mr?
Atom economy equations
199
Why is hydrogen a useful product?
Hydrogen fuel cells make electricity, with the only product being water
200
Name 2 non-renewable sources
Coal
Methane
201
What type of sources are coal and methane?
Non-renewable
202
% yield equation
% yield = actual mass of product obtained
————————————————
Theoretical yield
203
How does percentage yield working out start?
Very similar to to reacting masses sums - underline what’s important, work out the masses through comparing molar ratios etc, but use the formula at the end
204
Do we take into account the big numbers for Mr with percentage yields?
No
205
Give 2 reasons why a % yield wouldn’t be at 100%
-Some reactants not fully reacting
-Formation of side products (especially oxygen, which often reacts with reagents)
206
Which element often reacts with reagents?
Oxygen
207
Do you use the big numbers (molar ratios) in atom economy and percentage yields?
Atom economy - yes
Percentage yields - no
208
Is it possible for atom economy to be above 100%?
No
209
What do we do if a question states that something is ‘burning in air’?
Put it down as reacting with oxygen to create an oxide
210
What is the ratio of in empirical and molecular formulas?
Moles - in a more complex question, remember that’s what we’re trying to get the ratio of! Use the formula!
211
What do we do with the multiples we receive when figuring out the relative formula of a compound?
Don’t round them up - only round up the final molecular formula
212
How do you calculate the number of molecules in a sample?
Moles (n = m x Na (Avogadro’s number)
—
M)
213
How do you calculate the number of atoms in a sample?
Number of molecules x number of individual elements (e.g - SOCL2 has 4)
214
What do we need to remember with empirical formula?
Divide down to the SIMPLEST ratio of atoms in the molecule
215
Boyle’s law
PV=constant
Product of pressure and volume is a constant
-At a constant temperature, the volume of a fixed gas is inversely proportional to its pressure
216
Which law is PV = constant?
Boyle’s law
217
Charles’ law
V
— = constant
T
The volume of gas is constant as long as the pressure remains constant
218
Which law is V
— = constant?
T
Charles’ law
219
Gay-Lussac’s law
P
— = constant
T
The pressure is proportional to the temperature as long as the volume remains constant
220
Which law is P
— = constant
T
Gay-Lussac’s law
221
What has to remain constant for Boyle’s law?
Temperature
222
What has to remain constant for Charles’ law?
Pressure
223
What has to remain constant for Gay-Lussac’s law?
Volume
224
How did we get the gas constant and what is its symbol?
Combining Boyle’s, Charles’ and Gay-Lussac’s laws gives…
PV
— = constant for a fixed mass of gas (R)
T
So, PV=RT (for 1 mole of gas)
225
What is the ideal gas equation?
PV = nRT
226
Does every gas obey the ideal gas equation?
No gas obeys it entirely
227
Under what conditions does the ideal gas equation hold quite well?
Room temperature and pressure
228
Under room temperature and pressure, what holds quite well?
The ideal gas equation
229
2 features of an ideal gas
-All collisions between atoms or molecules are perfectly elastic
-No intermolecular attraction forces
230
What would having all collisions between atoms or molecules perfectly elastic and no intermolecular attraction forces give us?
An ideal gas
231
Perfectly elastic collisions between atoms or molecules
All energy is transferred - no loss of energy
232
If there’s no loss of energy and all is transferred during a collision between atoms or molecules, describe the collision
Perfectly elastic
233
SI units used with the ideal gas equation
Pressure - Pa
Volume - m^3
Temperature - K
234
What’s the first thing we do before anything else when dealing with the ideal gas equation questions?
Convert into the SI units
235
Standard pressure
1.10x10^5
(Data booklet)
236
atm ——> Pa
x1.10x10^5
(data booklet)
237
kPa ——> Pa
x1000
238
dm^3 to m^3
divided by 1000
239
cm^3 to m^3
Divided by 1,000,000
240
Degrees Celsius to kelvin
Celsius + 273
(on data booklet)
241
Standard temperature
273K
(data booklet)
242
What can 273K be described as?
Standard temperature
243
What can 1.01x10^5 be described as?
Standard pressure
244
What’s an alternative use for the ideal gas equation?
Calculating the volume a gas would occupy at temperatures and volumes other than those it was originally measured at
245
Equation for calculating the volume a gas would occupy at temperatures and pressures other than those it was originally measured at
P1V1 P2V2
—— = ——
T1 T2
246
What is the following equation used for?
P1V1 P2V2
—— = ——
T1 T2
Calculating the volume a gas would occupy at temperatures and pressures other than those it was actually measured at
247
Evolved
Created
248
What is titration an example of?
Quantitative analysis
249
Quantitative analysis
Uses statistics
250
What type of analysis uses statistics?
Quantitative analysis
251
When are titrations used?
When two solutions can be reacted and we want to determine the concentration of an identified solution
252
What type of apparatus do we have to use for titrations?
Accurately calibrated
253
Summarise the process of a titration
Take a fixed volume of a solution with a known concentration
React it with a solution with an unknown concentration
With an accurately measured volume needed to react, we can determine the solution’s concentration
254
What are the apparatus required for titrations?
Electronic balance
Gravitated/volumetric flask
Pipette
Burette
255
Two names for the type of flask used during titrations
Graduated/volumetric
256
What can an electronic balance weigh to within?
+-0.001g
257
What type of facility do most electronic balances have?
“Tare” facilities
258
What do we do with an electronic balance with a “tare” facility?
-Place beaker on the balance (tared)
-Required amount is placed into the beaker
-Amount weighed should be inside a specified range
259
What should the amount of a substance weighed on an electronic balance be?
Within a specified range
260
What’s the name of the balance on an electronic balance?
Tared
261
Tared
The balance on an electronic balance
262
What happens within the graduated/volumetric flask?
Make a solution of known concentration (a standard solution)
263
Standard solution
Solution of known concentration
264
Solution of known concentration
Standard solution
265
How is a solution of known concentration generated within the volumetric flask?
-Exact quantity of solid is weighed and dissolved in water
-Solution is placed in the graduated flask using a funnel
-Beaker is rinsed at least twice (add the water from the rinsing into the flask too)
-Add water to the flask until it reaches the mark
-Invert the flask a number of times to ensure complete mixing
266
How do we ensure complete mixing within the graduated/volumetric flask?
Invert a few times
267
How is solution placed into a graduated flask?
Using a funnel
268
What’s a pipette used for during titrations?
To get samples from the graduated flask - measures an exact volume of liquid
269
What must we use when filling up a pipette?
A pipette filler (take care when fitting it - see the instructions sheet)
270
What should always be forbidden in terms of pipettes?
Mouth pipetting
271
How much should the pipette be filled with liquid?
A little past the 25cm3 mark (the level drops slightly when removed which could give an inaccurate volume)
272
Important things to do when using a pipette
-Slowly and carefully to avoid bubbles
-Use a pipette filler
273
Why must the pipette be filled slightly past the 25cm3 mark?
The level drops slightly when removed from the liquid - inaccurate volume
274
What’s a burette used for during titrations?
Measuring liquid volumes accurately
275
What does a burette usually measure and why?
The volume of acid that reacts with alkali, as a base (alkali is a soluble base) can clog it up if left in for too long
276
What are the steps for using a burette during a titration?
Initially rinsed with the solution to be placed in it
Solution is placed in burette + initial reading is noted
The titration is carried out
When the reaction is complete, the burette reading is noted again
277
Tolerance of a burette
+-0.05cm3
278
How do you read the measurements on a burette?
-From the top down
-From the bottom of the miniscus
279
What do we do with titration calculations?
Use the same method as reacting masses (molar ratios etc)
280
What’s it really important not to do too early on with moles?
Over-round
281
What’s the name for the volume used during the titration?
Titre
282
Volume used during a titration
Titre
283
What is the first titre?
A rough titration
284
How do we calculate the volume used during a titration (titre)?
2nd - 1st burette reading
285
What can we do for the next titres after carrying out our rough titration and why?
Add the acid drop by drop, as we now have an idea of the titre
286
Concordent
Closeness of values
287
Closeness of values
Concordant
288
What do the volumes used/titres need to be within of each other in order to be concordant?
0.2cm3
289
To how many decimal places do we measure…
i) Volume used (titre)
ii) Mean reading
i) 2 d.p
ii) 3 d.p
290
How do we keep the burette level?
Clamp it
291
Why do we clamp the burette?
To keep it level
292
What’s in the conical flask underneath the burette?
Stuff (usually bases) measured by the pipette (exactly 25cm3) + indicator
293
What’s underneath the conical flask during a titration and why?
A white tile to easily see the colour change of the indicator
294
What does the indicator in the conical flask during a titration indicate?
The end of a titration
(The same number of acids and bases reacting)
295
What’s happened at the end of a titration?
The same number of acids and bases are reacting
296
How much indicator should we add to the stuff in the conical flask (usually bases) and why?
Only a few drops as it’s a weak acid and so it could give us inaccurate results
297
What could the fact that an indicator is a weak acid lead to?
Inaccurate results
298
What is usually the stuff in the conical flask and why?
Base, as this would clog up the burette if it were switched with the acid and left there too long
299
What do we have to ensure before taking a reading from a burette?
Ensure that the jet below the tap has solution in it
300
Where on the meniscus do we take a reading on the burette?
The bottom
301
What do we never start at using a burette?
Zero
302
What 2 things do we do with the burette after finishing?
Rinse with water
Leave the tap open when replacing the burette in the stand so that any liquid can drain
303
What’s the main error caused by using a burette?
Overshooting the end point
304
What is overshooting the end point an error with using?
A burette during titrations
305
Reaction between sodium hydroxide and hydrochloric acid
NaOH + HCl ——> NaCl + H20
306
Reaction between sodium carbonate and hydrochloric acid
Na2CO3 + 2HCL ——> 2NaCl + H20 + C02
307
Alkali
Soluble bases (usually hydroxide)
308
Soluble bases (usually hydroxide)
Alkali
309
Bases
All alkali is base (usually oxide)
310
All are base (usually hydroxide)
Alkali
311
Products of reacting an acid with an alkali
Salt and water
312
Products of reacting acid with a base
Salt and water
313
Products of reacting acid and a metal
Salt and hydrogen
314
Products of reacting acids and a carbonate
Salt and water and carbon dioxide
315
Describe the reaction between acid and alkali/a base
-Exothermic
-Neutralisation
-No effervescence (fizzing)
316
Word for fizzing
Effervescence
317
Effervescence
Fizzing
318
Describe the reaction between acid and a metal
Effervescence (fizzing)
Exothermic
319
Describe the reaction between acid and a carbonate
Effervescence
neutralisation
320
Salt
Hydrogen with the atom replaced with metal or ammonium ion e.g -
Sulphuric acid - Sulphate salt
Hydrochloric acid - Chloride salt
Nitric acid - Nitrate salt
321
How are the ions accelerated within the mass spectrometer?
Negatively charged plates accelerate positive ions
322
What happens to the volume of a gas at lower temperatures and why?
Decreases as the sample changes from gas to a liquid, reducing the volume of gas
323
What is the volume of a gas proportional to?
Temperature and pressure
324
Define an ideal gas
All collisions between atoms or molecules are perfectly elastic and there’s no intermolecular attractions
325
How do you calculate the percentage by mass of an element in a compound?
Mr of element
———————. x100
Mr of compound
326
What mass is a chlorine molecule most likely to have?
70
327
Define the mole and Avogadro’s constant
One mole is the amount of any substance that contains the same number of particles as here are atoms in exactly 12g of carbon-12
This fixed number is called Avogadro’s constant
328
What’s the volume measured in with the ideal gas equation?
metres cubed
329
What’s the equation for general first ionisation?
x (g) —> x+ (g) + e-
330
What’s an important concept to remember about emission and absorption spectra?
You cannot get an emission spectrum without getting an absorption spectrum first
331
Transition metal
An element whose atom has a partially filled d-sub shell
332
An element whose atom has a partially filled d-sub shell
Transition metal
333
How do we get an empirical formula from a molecular formula?
Divide by the highest common factor
334
Percentage error equation
Error
———. x100
Quantity being measured
335
What’s the ‘error’ in the percentage error equation?
The precision of which the equipment measures to/tolerance
336
Tolerance
The precision of which equipment measures to
337
Word for the precision of which equipment measures to
Tolerance
338
What do you do with percentage error if you have more than one piece of equipment?
The total error is the sum of the % error for each piece of equipment
339
To how many significant figures do we give our percentage error answer for errors between 0.1% and 1%?
3 s.f.
340
Give two ways that percentage error can be reduced
Make use of more accurate pieces of equipment
Arrange things so that the measurement itself is bigger
341
Tolerance of a pipette
0.05cm^3
342
Tolerance of a burette
0.05cm^3
343
What’s the exception for multiplying with big numbers for Mr?
a hydrate, for example CuSO4.5H20, where you’d work out the Mr of CuSO4, then the Mr of water and multiply water’s one by 5 and add these together
344
Why would a lid be left on whilst heating during an experiment?
Avoid spitting and thus loss of liquid
345
Why would a lid be left on whilst cooling during an experiment?
To avoid water being absorbed from the atmosphere
346
What can we do to avoid the problem of not all water being lost in a reaction?
Heat to constant mass
347
How many decimetres in a litre?
1
348
How many litres in a decimetre?
1
349
How do you calculate the number of particles in a sample?
Moles x Avogadro’s constant
350
How do we work out the value of X in front of a hydrated compound such as BaCl2.XH2O?
Mr of each
Mass of each
Compare moles as ratio
351
How do we know if enough of a reactant has been added to react with ALL of the other reactant by the end of the reaction process?
Allow it to settle
Add another few drops to see if precipitate still forms
352
If we get 0.6 in empirical and molecular formulae questions, what do we multiply it with to get a whole number?
5
353
What’s an alternative method for calculating concentrations?
1. Work out the amount of moles in 1dm^3 of the solution
2. Multiply this by the mor ratio value
For example…
As203 + 3H20 —> 2H3As03
n = m. 0.0104 moles in 100cm^3 of As203
—
M
So, in 1dm^3 —> 0.0104 x 10 = 0.104mol
Concentration of H3As03 —> 0.104 x 2 = 0.208moldm^3
354
Why doesn’t it matter if some solid remains in a weighing bottle?
We’re weighing by difference
355
Do you use mass or moles to calculate percentage yield?
Either is fine
356
How do we calculate the mass of a certain element present in a sample?
Total mass x Mr element
——————
Mr total
357
What is the error in a mass when weighing by difference?
+-0.0005g
358
Which impurities are removed from a sample when washed?
Soluble impurities
359
How do we know what our error is to use when calculating percentage error?
Half the unit of the last decimal place
360
What’s the uncertainty of our measurement when using a 2 d.p balance?
+-0.005
361
If you get 2 different mole values you could use in a % yield question, which one do we use? Why?
Figure out which one is lowest - this is the limiting factor
Use this for the theoretical yield
362
What type of ions does the mass spectrometer produce?
Positive ones
363
Under what condition is the whole system of a mass spectrometer?
Under vacuum
364
What’s a different way in which a percentage yield question could be asked?
Percentage purity
365
Why is the entire inside of a mass spectrometer under vacuum?
So that air molecules don’t interfere with the movement of the ions
366
How many dm^3 in a litre?
1
367
How do we go from gdm^-3 to moldm^-3?
Divide by Mr
368
Error in a 2 decimal place balance
+-0.005g
369
Relationship between cm^3 and grams?
(Under the correct conditions…)
1cm^3 = 1g
370
Do we use molar ratio (big numbers) in percentage by mass questions?
No
371
What do we input as our “error” with percentage errors?
Half the tolerance of the equipment
