1.2 Calculations Flashcards
1
Q
How many particles does one mole contain?
A
6.022 x10^23
2
Q
How to calculate the number of particles in a substance.
A
Number of particles =
Number of moles x Avagadro’s constant
3
Q
How to calculate the number of moles with a given mass.
A
Number of moles =
Mass of substance / Mr
4
Q
How to calculate the number of moles with a given volume/concentration of solution.
A
Number of moles =
Concentration (mol dm-3) x Volume (dm3)
5
Q
What is the ideal gas equation?
A
pV = nRT
Where: p = pressure (Pa) V = volume (m3) n = number of moles R = Gas constant - 8.31 JK-1mol-1 T = temperature (K)
6
Q
How many meters3 are in 1 cm3 and 1 dm3?
A
1cm3 = 1 x10-6 m3 1dm3 = 1 x10-3 m3
7
Q
Balance this equation:
C2H6 + O2 -> CO2 + H2O
A
(see page 16 in the revision guide)
8
Q
Write the ionic equation for the reaction of nitric acid with sodium hydroxide.
HNO3 + NaOH -> NaNO3 + H2O
A
(see page 16 in the revision guide)
9
Q
What do these state symbols mean?
s
l
g
aq
A
s = solid l = liquid g = gas aq = aqueous
10
Q
Calculate the mass of iron oxide produced if 27.9g of iron is burnt in air.
4Fe + 3O2 -> 2Fe2O3
A
39.9g
see page 17 in the revision guide
11
Q
What volume of gas, in dm3, is produced when 15.0g of sodium reacts with excess water at a temperature of 25.0 degrees C and a pressure of 100 kPa? Gas constant is 8.31 J K-1 mol-1
2Na (s) + 2H2O (l) -> 2NaOH (aq) + H2 (g)
A
8.07dm3
see page 17 in the revision guide
12
Q
Explain how you would make 250cm3 of a 2.00 mol dm-3 solution of sodium hydroxide.
A
(see page 18 in the revision guide)
13
Q
How do you carry out a titration?
A
(see page 18 and 19 in the revision guide)
14
Q
What colour does methyl orange change from and to in the presence of an acid and an alkali?
A
acid - red
alkali - yellow
15
Q
What colour does phenolphthalein change from and to in the presence of an acid and an alkali?
A
acid - colourless
alkali - pink
16
Q
In a titration experiment, 25.0 cm3 of 0.500 mol dm-3 HCl neautralised 35.0 cm3 of NaOH solution. Calculate a concentration of the sodium hydroxide solution is mol dm-3.
A
(see page 19 in the revision guide)
17
Q
20.4cm3 of a 0.500 mol dm-3 solution of sodium carbonate reacts with 1.50 mol dm-3 nitric acid. Calculate the volume of nitric acid required to neutralise the sodium carbonate.
A
(see page 20 in the revision guide)
18
Q
What is the empirical formula?
A
The empirical formula gives just the simplest whole number ratio of atoms of each element in a compound.
19
Q
What is the molecular formula?
A
The molecular formula gives the actual numbers of each atoms of each element in a compound.
20
Q
A molecule with Mr = 166.0 has the empirical formula C4H3O2. Find its molecular formula.
A
(see page 21 in the revision guide)
21
Q
A compound is found to have percentage composition of 56.5% potassium, 8.70% carbon and 34.8% oxygen by mass. Find its empirical formula.
A
(see page 21 in the revision guide)
22
Q
When a hydrocarbon is burnt in excess oxygen, 4.40g of carbon dioxide and 1.80g of water are made. What is the empirical formula of the hydrocarbon?
A
(see page 21 in the revision guide)
23
Q
How to calculate percentage yield?
A
Percentage Yield =
Actual Yield / Theoretical Yield x 100
(see page 22 in the revision guide for an example)
24
Q
0.475g of CH3Br reacts with excess NaOH in the following reaction:
CH3Br + NaOH -> CH3OH + NaBr
0.153g of CH3OH is produced. What is the percentage yield?
A
(see bottom of page 22 in the revision guide)
25
How to calculate atom economy.
% atom economy =
molecular mass of desired products /
sum of molecular masses of all reactants
x 100
26
Ethanol (C2H5OH can be produced by fermenting glucose (C6H12O6)
C6H12O6 -> 2C2H5OH + 2CO2
Calculate the atom economy of this reaction.
51.1%
| see page 23 in the revision guide
27
Why do companies in the chemical industry try to use processes with high atom economies?
- Better for the environment because they produce less waste.
- Make more efficient use of raw materials, more sustainable.
- Less expensive, the company will spend less on separating the desired product from the waste products. It is also cheaper to treat the waste as there is less of it.
28
Give the definition of the the mole.
The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.
29
Give the definition of relative atomic mass.
The relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.
30
Give the definition of relative molecular mass.
Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.
31
What is Avogadro's number?
There are 6.022x10^23 atoms in 12 grams of carbon-12
32
How do you turn any Celsius temperature into Kelvin?
add 273
33
How do you convert dm3 into cm3?
dm3 / 1000
34
How do you convert m3 into cm3?
m3 / 1000000
35
How do you convert m3 into dm3?
m3 / 1000
36
Answer example 1 on page 1 in the chemrevise revision guide.
correct?
37
Answer example 2 on page 1 in the chemrevise revision guide.
correct?
38
How do you convert g into mg?
g x 1000
39
How do you convert kg into g?
kg x 1000
40
How do you convert tonnes into kg?
tonnes x 1000
41
Answer example 3 on page 2 in the chemrevise revision guide.
correct?
42
Answer example 4 on page 2 in the chemrevise revision guide.
correct?
43
How do you calculate density?
| What unit is density in?
density (gcm-3) = mass/ volume
44
Answer example 5 on page 2 in the chemrevise revision guide.
correct?
45
Answer example 6 on page 2 in the chemrevise revision guide.
correct?
46
When can a density calculation be used?
Density calculations are usually used with pure liquids but to work out the mass from a measured volume. It can also be used with solids and gases.
47
What is the definition of an empirical formula?
An empirical formula is the simplest ratio of atoms of each element in the compound.
48
What is the general method to work out empirical formulae?
1. Divide each mass (or % mass) by the atomic mass of the element.
2. For each of the answers from step 1 divide by the smallest one of these numbers.
3. If the numbers aren't whole numbers, multiply them up to give whole numbers.
These whole numbers are the empirical formula.
49
Answer example 7 on page 3 in the chemrevise revision guide.
correct?
50
Give the definition of a molecular formula.
A molecular formula is the actual number of atoms of each element in the compound.
51
Answer example 8 on page 3 in the chemrevise revision guide.
correct?
52
How do you calculate the molecular formula from the empirical formula?
From the relative atomic mass (Mr) work out how many times the mass of the empirical formula fits into the Mr.
53
Answer example 9 on page 4 in the chemrevise revision guide.
correct?
54
When would you heat substances in a crucible?
This method would be used for measuring mass loss in various thermal decomposition reactions and also for mass gain when reacting magnesium in oxygen.
55
How would you heated hydrated calcium sulphate to obtain calcium sulphate crystals?
1. Weigh an empty, clean, dry crucible and lid.
2. Add 2g of hydrated calcium sulphate to the crucible and weigh again.
3. Heat strongly with a Bunsen burner for a couple of minutes.
4. Allow to cool.
5. Weigh the crucible and contents again.
6. Heat crucible again and reweigh until you reach a constant mass.
(to ensure the reaction is completed, the calcium sulphate has fully dehydrated)
56
Give the equation for dehydration of calcium sulphate by method of heating in a crucible.
CaSO4.xH2O(s) -> CaSO4(s) + xH2O(g)
57
Why should too large and too small amounts of hydrated calcium sulphate not be used in the experiment of heating this compound in a crucible?
Large amounts of hydrated calcium sulphate, such as 50g, should not be used in this experiment as the decomposition is likely to be incomplete.
Small amounts of the solid, such as 0.100g, should not be used in this experiment as the percentage uncertainties in weighing will be too high.
58
Why does the crucible need to be dry, in the experiment of heating hydrated copper sulphate in a crucible?
The crucible needs to be dry otherwise a wet crucible would give an inaccurate result. It would cause mass loss to be too large as the water would be lost when heating.
59
Why should you place a lid on the crucible in the experiment of heating hydrated copper sulphate in a crucible?
The lid improves the accuracy of the experiment as it prevents loss solid from the crucible but should be loose fitting to allow gas to escape.
60
Answer example 10 on page 4 in the chemrevise revision guide.
correct?
61
What is a solution?
A solution is a mixture formed when a solute dissolves in a solvent.
- We most commonly use water as the solvent, which forms aqueous solutions.
- Solute can be a solid, liquid or gas.
62
Give the equation for calculating concentration of a solution.
concentration = moles (of solute) / volume (of solution)
63
What is the unit for concentration and volume of a solution.
```
concentration = moldm-3
volume = dm3
```
64
Convert m3 into cm3.
m3 x 1000000
1m3= 100cm x 100cm x 100cm
65
Convert dm3 into cm3
dm3 x 1000
1dm3 = 10cm x 10cm x 10cm
66
Convert 1 cm3 into 1 ml
1cm x 1cm x1cm = 1ml
67
Answer example 11 on page 5 in the chemrevise revision guide.
correct?
68
Answer example 12 on page 5 in the chemrevise revision guide.
correct?
69
Give the equation for calculating mass concentration.
mass conc. = mass (of solute) / volume (of solution)
70
What is the unit of mass concentration of a solution?
mass concentration = gdm-3
71
How do you convert the conc. in moldm-3 to conc. in gdm-3?
conc. in gdm-3 = conc. in moldm-3 x Mr (of substance)
72
What happens to soluble ionic solids in water?
When soluble ionic solids dissolve in water they will dissociate into separate ions. This can lead to the concentration of ions differing from the concentration of the solute.
73
How do you make a solution of a sample substance?
1. Weigh the sample bottle containing the required mass of solid on a 2dp balance.
2. Transfer to beaker and reweigh sample bottle.
3. Record the difference in mass.
4. Add 100cm3 of distilled water to the beaker. Use a glass rod to stir to help dissolve the solid.
(Sometimes the substance may not dissolve well in cold water so the beaker and its contents could be heated gently until all the solid has dissolved.)
5. Pour the solution into a 250cm3 graduated flask via a funnel.
6. Rinse the beaker and funnel and add washings from the beaker and glass rod to the volumetric flask.
7. Make up to the mark with distilled water using a dropping pipette for the last few drops.
8. Invert the flask several times to ensure of a uniform solution.
74
How would you dilate a solution?
1. Pipette 25cm3 of original solution into a 250cm3 volumetric flask.
2. Make up to the mark with distilled water using a dropping pipette for the last few drops.
3. Invert the flask several times to ensure of a uniform solution.
75
Why is a volumetric pipette more accurate than a measuring cylinder?
Using a volumetric pipette is more accurate than a measuring cylinder because it has a smaller uncertainty.
76
Give the equation for calculating a new diluted concentration from the old concentration.
new diluted conc. = original conc. x (original volume / new diluted volume)
77
Answer example 15 on page 7 in the chemrevise revision guide.
correct?
78
Answer example 16 on page 7 in the chemrevise revision guide.
correct?
79
When does does the ideal gas equation apply?
The ideal gas equation applies to all gases and mixtures of gases. If a mixture of gases is used the value n will be the total moles of all gases in the mixture.
80
Answer example 17 on page 8 in the chemrevise revision guide.
correct?
81
Answer example 18 on page 8 in the chemrevise revision guide.
correct?
82
What are the potential errors of using a gas syringe in an experiment?
- Gas escapes before bung is inserted.
- Syringe sticks (doesn't move properly)
- Some gases are soluble in water, like CO2 or sulphur dioxide, so the true volume of gas is not measured.
83
Draw a diagram of how you would use a gas syringe attached to a conical flask in an experiment.
(see page 8 in the chemrevise revision guide)
84
Answer example 19 on page 9 in the chemrevise revision guide.
correct?
85
At room temperature 25 degrees and room pressure (1atm), what will the volume be of 1 mol of any gas?
24dm3
86
Answer example 20 on page 9 in the chemrevise revision guide.
correct?
87
Answer example 21 on page 9 in the chemrevise revision guide.
correct?
88
Answer example 22 on page 10 in the chemrevise revision guide.
correct?
89
Answer example 23 on page 10 in the chemrevise revision guide.
correct?
90
Answer example 24 on page 10 in the chemrevise revision guide.
correct?
91
Answer example 25 on page 10 in the chemrevise revision guide.
correct?
92
Answer example 26 on page 10 in the chemrevise revision guide.
correct?
93
Answer example 27 on page 10 in the chemrevise revision guide.
correct?
94
Answer example 28 on page 10 in the chemrevise revision guide.
correct?
95
How do you carry out a titration?
(see top of page 12 in the chemrevise revision guide)
96
What colours do phenolphthalein change to when indicating an acid and an alkali?
Acid - colourless
| Alkali - pink
97
When would you use phenolphthalein indicator?
If NaOH is used.
98
What colours do methyl orange change to when indicating an acid and an alkali?
Acid - red
| Alkali - Yellow
99
When would you use methyl orange indicator?
If HCl is used
100
What do concordant results mean?
Results within 0.1 of each other
101
What safety precautions should you ensure of when carrying out a titration?
WEAR EYE PROTECTION AND GLOVES
- Acids and alkalis are corrosive (at low concentrations acids are irritants)
If spilled immediately wash affected parts after spillage
If substances unknown treat it as potentially toxic and wear gloves
102
What will happen if the jet space is not filled properly prior to commencing the titration?
If the jet space is not filled properly prior to commencing the titration it will lead to errors if it then fills during the titration, leading to a larger than expected titre reading.
103
Why is a conical flask preferably used over a beaker in a titration?
A conical flask is used in preference to a beaker because it is easier to swirl the mixture in a conical flask without spilling the contents.
104
Why do you only add a couple of drops of indicator do the mixture in a titration?
Indicators are generally weak acids so only add a few drops of them. If too much is added it will affect the titration result.
105
Why is water sometimes added round the sides of the conical flask in a titration reaction?
Distilled water can be added to the conical flask during a titration to wash the sides of the flask so that all the acid on the side is washed into the reaction mixture to react with the alkali.
I does not affect the titration reading as water does not react with the reagents or change the number of moles of acid added.
106
When can you make an average of the titre results?
Only make an average of the concordant results.
107
What can we say about the experiment if the results are within 0.10cm3 of each other?
If 2 or 3 values are within 0.10cm3 and therefore concordant, we can say the results are accurate and repeatable and the titrations technique is good/consistent.
108
Write an equation for the reaction of CH3CO2H + NaOH
(see page 12 in the chemrevise revision guide)
109
Write an equation for the reaction of H2SO4 + NaOH
(see page 12 in the chemrevise revision guide)
110
Write an equation for the reaction of HCl + NaOH
(see page 12 in the chemrevise revision guide)
111
Write an equation for the reaction of NaHCO3 + HCl
(see page 12 in the chemrevise revision guide)
112
Write an equation for the reaction of Na2CO3 + 2HCl
(see page 12 in the chemrevise revision guide)
113
Answer example 29 on page 13 in the chemrevise revision guide.
correct?
114
Answer example 30 on page 13 in the chemrevise revision guide.
correct?
115
Answer example 31 on page 13 in the chemrevise revision guide.
correct?
116
Give the definition for readings (for an experiment)
The values found from a single judgement when using a piece of equipment.
117
Give the definition for measurements (for an experiment)
The values taken as the difference between the judgements of two values
(e.g. using a burette in a titration)
118
What is the uncertainty of a reading and a measurement?
The uncertainty of a reading (one judgement) is at least ±0.5 of the smallest scale reading.
The uncertainty of a measurement (two judgements) is at least ± 1 of the smallest scale reading.
119
How do you calculate the percentage uncertainty for each piece of equipment?
% uncertainty = (±uncertainty / measurement made on apparatus) x 100
120
How can you decrease apparatus uncertainties?
You can either decrease the sensitivity uncertainty by using apparatus with a greater resolution (finer scale divisions) or you can increase the size of the measurement made.
121
How do you reduce uncertainties in a titration?
- Replace measuring cyclinders with pipettes or burettes.
122
How do you reduce uncertainties in measuring mass?
Using a balance that measures to more decimal places or using a larger mass will reduce the % uncertainty in weighing a solid.
Weighing a sample before and after addition and then calculating difference will ensure a more accurate measurement of the mass added.
