TOPIC 5 Formulae, Equations And Amounts Of Substance Flashcards
(154 cards)
1
Q
What is a molecule?
A
Group of 2 or more atoms joined together by covalent bonds
2
Q
Summarise how you would obtain copper from an oxide of copper.
A
Place a known mass of copper oxide in the tube
Heat it in a stream of hydrogen gas
The hydrogen atoms in the gas react with the oxygen atoms in the copper oxide and form steam
The solid gradually changed from black to orange-brown
The excess gas is burned off at the end of the tube
After cooling , remove and weigh the solid copper
Heat again to a constant mass
3
Q
How do you calculate the empirical formula using combustion analysis?
A
Calculate the mass of carbon:
Mass of CO2 formed x 12/44
Calculate the mass of hydrogen:
Mass of H2O formed x 2/18
Calculate the mass of oxygen:
Mass of organic product - mass of hydrogen - mass of carbon
Calculate the empirical formula
4
Q
The mass of copper oxide before burning was 4.28g. After burning, the mass of be remaining copper was 3.43g. Calculate the empirical formula of the original copper oxide.
A
CuO
5
Q
A comping has the percentage composition by mass:
C = 38.4%
H = 4.8%
Cl = 56.8%
What is the empirical formula?
A
C2H3Cl
6
Q
A compound has the percentage composition by mass of:
Na = 29.1%
S = 40.5%
With the remainder being oxygen
What is it’s empirical formula?
A
Na2S2O3
7
Q
A 1.87g sample of an organic compound was completely burned, forming 2.65g or carbon dioxide and 1.63g of water. What is it’s empirical formula?
A
CH3O
8
Q
A compound has the percentage composition by mass:
Ca = 24.4%
N = 17.1%
O = 58.5%
What is it’s empirical formula?
A
CaN2O6
9
Q
Combustion analysis of 2.16g of an organic compound produced 4.33g of carbon dioxide and 1.77g of water. What is it’s empirical formula?
A
C2H4O
10
Q
How do you calculate the molecular formula of a compound from it’s empirical formula?
A
Compare the actual relative molecular mass to the relative molecular mass of the empirical formula and then deduce the molecular formula of the compound
11
Q
When can the term relative molecule mass be used?
A
When talking about molecules only
12
Q
When can the term relative formula mass be used?
A
When talking about both ionic and molecular compounds
13
Q
How do you calculate the amount of substance using the molar mass?
A
Amount (mole) = mass of substance (g) / molar mass (g mol-1)
n= m / M
14
Q
What are the SI units for the ideal gas equation?
A
Pressure = pascals (Pa) Volume = cubic meters (m3) Temperature = kelvins (K) Amount of substance = moles (mol) Gas constant = 8.31 J mol-1 K-1
15
Q
How do you convert:
kPa —> Pa
cm3 —> m3
dm3 —> m3
degrees C —> K?
A
Multiply by 10^3
Divide by 10^6 or multiply by 10^-6
Divide by 10^3 or multiply by 10^-3
Add 273
16
Q
A 2.82g sample of a gas has a volume of 1.26 dm3 , measured at a pressure of 103 kPa and a temperature of 55 C. Calculate the molar mass of the gas.
A
Amount of substance = 0.04768 mol
Molar mass = 59.2 g mol-1
17
Q
A compound has the percentage composition by mass C=40.0% , H=6.7% , O=53.3%. A sample containing 0.146g of the compound had a volume of 69.5 cm3 when measured at 98 kPa and 63 C. What is the molecular formula of this compound?
A
Empirical formula = CH2O
Amount of substance = 0.00243933
Molar mass = 59.85 g mol-1
Molecular formula = C2H4O2
18
Q
A compound has the empirical formula CH and a relative molecular mass of 104. What is it’s molecular formula?
A
C8H8
19
Q
A compound contains the percentage composition by mass Na = 34.3 %
C = 17.9 %
O = 47.8 %
What is it’s empirical formula?
The compound has a molar mass if 134 g mol-1
What is it’s molecular formula?
A
Empirical formula = NaCO2
Molecular formula = Na2C2O4
20
Q
A 0.280 g sample of a gas gas a volume of 58.5 cm3 , measured at a pressure of 120kPa and a temperature of 70 C. Calculate the molar mass of the gas.
A
Amount of substance = 0.00246
Molar mass = 114 g mol-1
21
Q
A compound has the percentage composition by mass
C=52.2%
H=13.0%
O=34.8%.
A sample containing 0.173g of the compound had a volume of 95.0 cm3 when measured at 105 kPa and 45 C.
What is the molecular formula of this compound?
A
Empirical formula = C2H6O
Amount of substance = 0.00377 mol
Molar mass = 45.9 g mol-1
Molecular formula = C2H6O
22
Q
When can the term relative formula mass be used?
A
When talking about both ionic and molecular compounds
23
Q
A 0.280 g sample of a gas gas a volume of 58.5 cm3 , measured at a pressure of 120kPa and a temperature of 70 C. Calculate the molar mass of the gas.
A
Amount of substance = 0.00246
Molar mass = 114 g mol-1
24
Q
A compound has the percentage composition by mass
C=52.2%
H=13.0%
O=34.8%.
A sample containing 0.173g of the compound had a volume of 95.0 cm3 when measured at 105 kPa and 45 C.
What is the molecular formula of this compound?
A
Empirical formula = C2H6O
Amount of substance = 0.00377 mol
Molar mass = 45.9 g mol-1
Molecular formula = C2H6O
25
A compound contains the percentage composition by mass Na = 34.3 %
C = 17.9 %
O = 47.8 %
What is it’s empirical formula?
The compound has a molar mass if 134 g mol-1
What is it’s molecular formula?
Empirical formula = NaCO2
Molecular formula = Na2C2O4
26
A compound has the empirical formula CH and a relative molecular mass of 104. What is it’s molecular formula?
C8H8
27
A compound has the percentage composition by mass C=40.0% , H=6.7% , O=53.3%. A sample containing 0.146g of the compound had a volume of 69.5 cm3 when measured at 98 kPa and 63 C. What is the molecular formula of this compound?
Empirical formula = CH2O
Amount of substance = 0.00243933
Molar mass = 59.85 g mol-1
Molecular formula = C2H4O2
28
A 2.82g sample of a gas has a volume of 1.26 dm3 , measured at a pressure of 103 kPa and a temperature of 55 C. Calculate the molar mass of the gas.
Amount of substance = 0.04768 mol
Molar mass = 59.2 g mol-1
29
How do you convert:
kPa —> Pa
cm3 —> m3
dm3 —> m3
degrees C —> K?
Multiply by 10^3
Divide by 10^6 or multiply by 10^-6
Divide by 10^3 or multiply by 10^-3
Add 273
30
What are the SI units for the ideal gas equation?
```
Pressure = pascals (Pa)
Volume = cubic meters (m3)
Temperature = kelvins (K)
Amount of substance = moles (mol)
Gas constant = 8.31 J mol-1 K-1
```
31
How do you calculate the amount of substance using the molar mass?
Amount (mole) = mass of substance (g) / molar mass (g mol-1)
n= m / M
32
When can the term relative molecule mass be used?
When talking about molecules only
33
How do you calculate the empirical formula of a compound from it’s empirical formula?
Compare the actual relative molecular mass to the relative molecular mass of the empirical formula and then deduce the molecular formula of the compound
34
How do you calculate the empirical formula of a compound from it’s empirical formula?
Compare the actual relative molecular mass to the relative molecular mass of the empirical formula and then deduce the molecular formula of the compound
35
When can the term relative molecule mass be used?
When talking about molecules only
36
When can the term relative formula mass be used?
When talking about both ionic and molecular compounds
37
How do you calculate the amount of substance using the molar mass?
Amount (mole) = mass of substance (g) / molar mass (g mol-1)
n= m / M
38
What are the SI units for the ideal gas equation?
```
Pressure = pascals (Pa)
Volume = cubic meters (m3)
Temperature = kelvins (K)
Amount of substance = moles (mol)
Gas constant = 8.31 J mol-1 K-1
```
39
How do you convert:
kPa —> Pa
cm3 —> m3
dm3 —> m3
degrees C —> K?
Multiply by 10^3
Divide by 10^6 or multiply by 10^-6
Divide by 10^3 or multiply by 10^-3
Add 273
40
A 2.82g sample of a gas has a volume of 1.26 dm3 , measured at a pressure of 103 kPa and a temperature of 55 C. Calculate the molar mass of the gas.
Amount of substance = 0.04768 mol
Molar mass = 59.2 g mol-1
41
A compound has the percentage composition by mass C=40.0% , H=6.7% , O=53.3%. A sample containing 0.146g of the compound had a volume of 69.5 cm3 when measured at 98 kPa and 63 C. What is the molecular formula of this compound?
Empirical formula = CH2O
Amount of substance = 0.00243933
Molar mass = 59.85 g mol-1
Molecular formula = C2H4O2
42
A compound has the empirical formula CH and a relative molecular mass of 104. What is it’s molecular formula?
C8H8
43
What is the value of Avogadro’s constant?
6.02 x 10^23 mol-1
44
What is the amount of substance in each of the following?
(a) 8.0g of sulphur , S
(b) 8.0g of sulphur dioxide , SO2
(c) 8.0g of sulphate ions , SO4 2-
(a) 0.249 mol
(b) 0.125 mol
(c) 0.0832 mol
45
How many particles are there in the specified substance?
(a) atoms in 2.0g of sulphur , S
(b) molecules in 4.0g of sulphur dioxide , SO2
(c) ions in 8.0g of sulphate ions , SO4 2-
(a) 3.75 x 10^22
(b) 3.76 x 10^22
(c) 5.01 x 10^22
46
What is the amount of substance in 6.51 g of sodium chloride?
0.111 mol
47
What is the mass of 0.263 mol of hydrogen iodide?
33.6 g
48
A sample of 0.284 mol of a substance has a mass of 17.8 g. What is the molar mass of the substance?
62.7 g mol-1
49
How many H2O molecules are there in 1.25g of water?
Amount of substance = 0.0694 mol
Number of molecules = 4.18 x 10^22
50
What is the mass of 100 million atoms of gold?
Amount of substance = 1.66 x 10^-16 mol
Mass = 3.27 x 10^-14 g
51
A compound contains the percentage composition by mass Na = 34.3 %
C = 17.9 %
O = 47.8 %
What is it’s empirical formula?
The compound has a molar mass if 134 g mol-1
What is it’s molecular formula?
Empirical formula = NaCO2
Molecular formula = Na2C2O4
52
A 0.280 g sample of a gas gas a volume of 58.5 cm3 , measured at a pressure of 120kPa and a temperature of 70 C. Calculate the molar mass of the gas.
Amount of substance = 0.00246
Molar mass = 114 g mol-1
53
A compound has the percentage composition by mass
C=52.2%
H=13.0%
O=34.8%.
A sample containing 0.173g of the compound had a volume of 95.0 cm3 when measured at 105 kPa and 45 C.
What is the molecular formula of this compound?
Empirical formula = C2H6O
Amount of substance = 0.00377 mol
Molar mass = 45.9 g mol-1
Molecular formula = C2H6O
54
Coefficients
Numbers written in front of species when balancing an equation
55
Spectator ions
The ions in an ionic compound that do not take part in a reaction
56
```
What is the correct formula for:
Nitrogen
Sodium hydroxide
Nitric acid
Iron (II) sulphate
Iron (III) oxide
Calcium carbonate
```
```
N2
NaOH
HNO3
FeSO4
Fe2O3
Fe2O3
CaCO3
```
57
What is an ionic equation?
Show any atoms and molecules involved but only the ions that react together and no the spectator ions
58
How do you write an ionic equation?
Start with the full equation
Replace the formulae of ionic compounds by their separate ions
Delete any ions that appear identically on both sides
59
Sodium thiosulphate (Na2S2O3) solution reacts with dilute hydrochloric acid to form a precipitate of sulphur, gaseous sulphur dioxide and a solution of sodium chloride. Write an equation, including state symbols , for this reaction.
Na2S2O3 (aq) + 2HCl (aq) —> S (s) + SO2 (g) + 2NaCl (aq) + H2O (l)
60
Solutions of ammonium sulphate and sodium hydroxide are warmed together to form sodium sulphate solution , water and ammonia gas. Write the simplest ionic equation for this reaction.
Full equation:
(NH4)2SO4 + 2NaOH —> NaSO4 + 2H2O + 2NH3
Replacing the formulae of ionic compounds:
2NH4+ + SO4- + 2Na+ + 2OH- —> 2Na+ + SO42- + 2H2O + 2NH3
Deleting spectator ions:
2NH4+ + 2OH- —> 2H2O + 2NH3
Simplified ionic equation:
NH4+ + OH- —> H2O + NH3
61
When carbon dioxide reacts with calcium hydroxide, calcium carbonate and water are formed. Write the balanced equation for this reaction.
CO2 + Ca(OH)2 —> CaCO3 + H2O
62
Hydrogen peroxide (H2O2) decomposes to water and oxygen. Write the balanced equation for this reaction.
2H2O2 —> 2H2O + O2
63
What is the simplest ionic equation for the neutralisation of sodium hydroxide solution by dilute nitric acid?
Full equation:
NaOH (aq) + HNO3 (aq) —> NaNO3 (aq) + H2O (l)
Replacing the formulae of ionic compounds:
Na+ + OH- + H+ + NO3- —> Na+ + NO3- + H2O
Ionic equation:
H+ + OH- —> H2O
64
What is the simplest ionic equation for the reaction that occurs when solutions of lead (II) nitrate and sodium sulphate react together to form a precipitate of lead (II) sulphate and a solution of sodium nitrate?
Full equation:
Pb(NO3)2 (aq) + Na2SO4 (aq)—> PbSO4 (s) + 2NaNO3 (aq)
Replacing the formulae of ionic compounds:
Pb2+ + 2NO3- + 2Na+ + SO42- —> PbSO4 + 2Na+ + 2NO32-
Ionic equation:
Pb2+ + SO42- —> PbSO4
65
What is the simplest ionic equation that occurs when carbon dioxide reacts with calcium hydroxide solution to form water and a precipitate of calcium carbonate?
Full equation:
CO2 (g) + Ca(OH)2 (aq)—> CaCO3 (s) + H2O (l)
Ionic equation:
CO2 + Ca2+ + 2OH- —> Ca2+ + CO32- + H2O
66
The equation for a reaction is:
SO3 + H2O —> H2SO4
What mass of sulphur trioxide is needed to form 75.0g of sulphuric acid?
Amount of sulphuric acid = 0.765 mol
Mass = 61.2 g
67
The equation for a reaction is:
2NH3 + H2SO4 —> (NH4)2SO4
What mass of ammonia is needed to form 100g of ammonium sulphate?
Amount of ammonium sulphate = 0.757 mol
Mass = 25.7g
68
A 16.7g sample of a hydrate of sodium carbonate (Na2CO3•10H2O) is heated at a constant temperature for a specified time until a reaction is complete. A mass of 3.15g of water is obtained. What is the equation for the reaction occurring?
Amount of reactant = 0.0584 mol
Amount of water = 0.175 mol
Equation:
Na2CO3•10H2O —> Na2CO3•7H20 + 3H2O
69
An oxide of copper is heated in a stream of hydrogen to constant mass. The masses of copper and water formed are Cu = 17.6g and H2O = 2.56g. What is the equation for the reaction occurring?
Amount of copper = 0.277 mol
Amount of water = 0.142 mol
Equation:
Cu2O + H2 —> 2Cu + H20
70
A fertiliser manufacturer makes a batch of 20kg of ammonium nitrate. What mass of ammonia does he need?
Amount of ammonium nitrate = 250 mol
Mass = 4.25 kg
71
What is Avogadro’s law?
States that equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules
72
Hydrogen and chlorine react to form hydrogen chloride according to this equation:
H2 (g) + Cl2 (g) —> 2HCl (g)
100cm3 of hydrogen is mixed with 100cm3 of chlorine and reacted. What volume of hydrogen chloride is formed?
200cm3
73
Carbon dioxide and carbon react react to form carbon monoxide according to this equation:
CO2 (g) + C (s) —> 2CO (g)
1.00dm3 of carbon dioxide is reacted with an excess of carbon to form carbon monoxide. What volume of carbon monoxide is formed?
2.00dm3
Ignore the carbon as it is a solid
74
Nitrogen monoxide and oxygen react to form nitrogen dioxide according to this equation:
2NO (g) + O2 (g) —> 2NO2 (g)
50cm3 of nitrogen monoxide are mixed with 25cm3 of oxygen and reacted. What volume of nitrogen dioxide is formed?
50cm3
75
Sulphur dioxide and oxygen react to form sulphur trioxide according to this equation:
2SO2 (g) + O2 (g) —> 2SO3
200cm3 of sulphur dioxide are mixed with 200cm3 of oxygen and reacted. What volume of sulphur trioxide is formed?
200cm3
The volumes given are equal and so do not match the ratio
All of the sulphur dioxide will react but only with only half the volume of oxygen
100cm3 of unreacted oxygen gas is left
76
Methane and oxygen react to form carbon dioxide and water according to this equation:
CH4 (g) + 2O2 —> CO2 (g) + 2H2O (g)
100cm3 of methane is mixed with 100cm3 of oxygen and reacted. What volume of gas is formed?
150cm3
Volume given are equal and so do not match the ratio
There are 2 gases so the total needs to be calculated
77
Hydrogen sulfide and oxygen react to form sulphur dioxide and water according to this equation:
2H2S (g) + 3O2 (g) —> 2SO2 (g) + 2H2O (l)
250cm3 of hydrogen sulfide is mixed with 600cm3 of oxygen and reacted. What is the volume of the resulting gaseous mixture?
475cm3
Water is a liquid so is not included
All of the hydrogen sulfide will react but with only 375cm3 of the oxygen. This will form 250cm3 of sulphur dioxide
The answer include any gaseous reactants that are not completely used up
78
Hydrogen sulfide and sulphur dioxide react at room temperature to form sulphur and water as shown in this equation:
2H2S (g) + SO2 (g) —> 2H2O (l) + 3S (s)
1dm3 of hydrogen sulfide and 1dm3 of sulphur dioxide are mixed together and the reaction occurs until complete. What is the final volume of the gas?
0.5dm3
79
A mixture of 50cm3 of propane and 150cm3 of oxygen is ignited to form carbon dioxide and water. The equation for this reaction is:
C3H8 (g) + 5O2 (g) —> 3CO2 (g) + 4H2O (l)
What is the volume of the final reaction mixture?
110cm3
80
Molar volume
The volume occupied by 1 mol of any gas
81
What is molar volume?
The volume of gas that contains one mole of that gas
82
What are the conditions for RTP?
```
Temperature = 298K / 25 C
Pressure = 101325 kPa / 1 atm
```
83
What is the Vm value?
24.0dm3 / 24000cm3
84
What is the equation for calculating Vm?
Vm = 24.0 = volume in dm3 / amount in mol
OR
Vm = 24000 = volume in cm3 / amount in mol
85
What is the amount in moles , of CO in 3.80dm3 of carbon monoxide?
0.158 mol
86
What is the amount, in moles , of CO2 in 500cm3 of carbon dioxide?
0.0208 mol
87
What is the volume of 0.256 mol of hydrogen?
8.54dm3 OR 8540cm3
88
A piece of magnesium with a mass of 1.0g is added to an excess of dilute hydrochloric acid. What volume of hydrogen gas is formed?
My (s) + 2HCl (aq) —> MgCl2 (aq) + H2 (g)
n(Mg) = 0.0412 mol
998cm3
89
Calcium carbonate reacts with nitric acid to form calcium nitrate, water and carbon dioxide:
CaCO3 (s) + 2HNO3 (aq) —> Ca(NO3)2 (aq) + H2O (l) + CO2 (g)
In a reaction, 100cm3 of carbon dioxide is formed. What is the mass of calcium carbonate is needed for this?
n(CO2) = 0.00417 mol
0.417g
90
Ammonium sulphate reacts with sodium hydroxide solution to form sodium sulphate, water and ammonia:
(NH4)2SO4 (s) + 2NaOH (aq) —> Na2SO4 (aq) + 2H2O (l) + 2NH3 (g)
What volume of ammonia is formed by reacting 2.16g of ammonium sulphate with excess sodium hydroxide solution?
n((NH4)2SO4) = 0.01635 mol
785cm3
91
A flask contains 2dm3 of butane. What is the amount of moles of gas in the flask?
0.0833 mol
92
10.0g of copper (II) oxide is heated with hydrogen according to this equation:
CuO(s) + H2 (g) —> Cu (s) + H2O (l)
What volume of hydrogen gas is needed to react with the copper (II) oxide and what mass of copper is formed?
3019cm3
7.99g
93
What is the equation for calculations using mass concentration? Include units.
Mass concentration (g dm-3) = mass of solute (g) / volume of solution (dm3)
94
What is the equation for calculations using molar concentration? Include units.
Molar concentration (mol dm-3) = amount (mol) / volume (dm3)
95
200cm3 of a solution contains 5.68g of sodium bromide. What is it’s mass concentration?
28.4 g dm-3
96
The concentration of a solution is 15.7 g dm-3. What mass of solute is there in 750 cm3 of solution?
11.8 g
97
A chemist uses 280g of a solute to make a solution of concentration 28.4 g dm-3. What volume of solution do they make?
9.86 dm3
98
A chemist makes 500 cm3 of a solution of nitric acid of concentration 0.800 mol dm-3. What mass of HNO3 do they need?
n(HNO3) = 0.400 mol
m(HNO3) = 25.2g
99
A student has 50.0 g of sodium chloride. What volume of a 0.450 mol dm-3 solution can they make?
n(NaCl) = 0.855 mol
V(NaCl) = 1.90 dm3
100
An excess of magnesium is added to 100cm3 of 1.50 mol dm-3 dilute hydrochloric acid:
Mg + 2HCl —> MgCl2 + H2
What mass of hydrogen is formed?
n(HCl) = 0.150 mol
n(H2) = 0.0750 mol
m(H2) = 0.150 g
101
A mass of 47.8 g of magnesium carbonate reacts with 2.50 mol dm-3 hydrochloric acid:
MgCO3 + 2HCl —> MgCl2 + H2O + CO2
What volume of acid is needed?
n(MgCO3) = 0.567 mol
n(HCl) = 1.134 mol
V(HCl) = 0.454 dm3
102
50.0 g of sodium hydroxide is dissolved in water to make 1.50 dm3 of solution. What is the molar concentration of the solution?
n(NaOH) = 1.25 mol
C(NaOH) = 0.833 mol dm-3
103
150 cm3 of 0.125 mol dm-3 lead (II) nitrate solution is mixed with an excess of potassium iodide solution:
Pb(NO3)2 (aq) + 2KI —> PbI2 (s) + 2KNO3 (aq)
What mass of lead (II) iodide is formed?
```
n(Pb(NO3)2) = 0.01875
n(PbI2) = 0.01875
```
m(PbI2) = 8.64g
104
What should a primary standard ideally be? (6)
Solids with high molar masses
Available in a high degree of purity
Chemically stable
Should not absorb water from the atmosphere
Soluble in water
React rapidly and completely with other substances in titrations
105
What is sulfamic acid?
A readily available primary standard for use in acid base titrations
106
What are the typical values for concentration and volume when making a standard solution?
```
Concentration = 0.1 mol dm-3
Volume = 250cm3
```
107
What is the approximate mass of sulfamic acid (NH2SO3H) needed to create a standard solution with the typical values for concentration and volume?
n(Sulfamic acid) = 0.025 mol
m(Sulfamic acid) = 2.4 g
108
Explain the method of how you would prepare a standard solution of sulfamic acid.
1) add between 2.3 g and 2.5 g of sulfamic acid to the weighing bottle and weigh accurately
2) transfer as much of the acid as possible to a clean beaker and rewrite the weighing bottle
3) add about 100cm3 of deionised water to the beaker and stir until all of the sulfamic acid has dissolved
4) remove the stirring rod, washing traces of the solution from the rod into the beaker using the wash bottle
5) place the funnel in the neck of the volumetric flask and pour the solution from the beaker into the flask
6) rinse the beaker several times using the wash bottle and transfer the rinsings to the flask
7) add deionised water to the flask and make up exactly to the graduation mark
8) stopped the the flask and invert several times to make a uniform solution
109
What is the purpose of doing a titration?
Aims to measure the volumes of 2 solutions that react together as using the results to calculate the concentration of one of the solutions
110
What is the method for carrying out a titration for the reaction between sulfamic acid and sodium hydroxide , when sulfamic acid is in the burette?
1) rinse the conical flask with deionised water and place on a white tile
2) using a pipette filler , rinse the pipette with deionised water and some of the sodium hydroxide solution
3) use the pipette to transfer 25.0cm3 of the sodium hydroxide solution to the conical flask
4) add about 3 drops of methyl orange indicator
5) rinse the burette with deionised water and then with some sulfamic acid solution
6) fill the burette with sulfamic acid solution and set it up in the stand above the conical flask
7) record the burette reading
8) add the sulfamic acid solution to the flask until the indicator changes colour and record the burette reading
9) empty and rinse the conical flask with deionised water and repeat the titration until concordant titres have been obtained
111
What colour is methyl orange in both acid and alkali and what is it’s acid base combination?
Acid- red
Alkali- yellow
Acid-base combination- strong acid - weak base & strong acid - strong acid
112
What colour is phenolphthalein in both acid and alkali and what is it’s acid base combination?
Acid- colourless
Alkali- pink
Acid-base combination- weak acid - strong base & strong base - strong base
113
Name 2 strong acids and 2 strong bases.
Strong acids:
Hydrochloric acid
Nitric acid
Strong base:
Sodium hydroxide
Potassium hydroxide
114
Name a weak acid and a weak base.
Weak acid:
Ethanoic acid
Weak base:
Ammonia
115
Volume of sodium hydroxide solution used = 25.0cm3
Volume of sulfamic acid solution used = 22.65cm3 (mean titre)
Concentration of sulfamic acid solution = 0.0985 mol dm-3
NaOH (aq) + NH2SO3 (aq) —> NH2SO3Na (aq) + H2O (l)
What is the concentration of sodium hydroxide used?
n(NH2SO3H) = 0.00223 mol
c(NaOH) = 0.0892 mol dm-3
116
A titration is done to calculate the concentration of a solution of nitric acid, using a standard solution of sodium carbonate. The equation for the reaction is:
Na2CO3 + 2HNO3 —> 2NaNO3 + H2O + CO2
The titration results are:
Volume of sodium carbonate solution used = 25.0 cm3
Volume of nitric acid solution used = 27.25 cm3
Concentration of sodium carbonate solution = 0.108 mol dm-3
What is the concentration of nitric acid used?
n(Na2CO3) = 0.00270 mol
c(HNO3) = 0.198 mol dm-3
117
A titration is done to calculate the concentration of a solution of hydrochloric acid, using sodium hydroxide solution. The equation of the reaction is:
Volume of sodium hydroxide solution used = 25.0 cm3
Volume of hydrochloric acid used = 22.68 cm3
Concentration of sodium hydroxide used = 0.0892 mol dm-3
0.0983 mol dm-3
118
What is the shorter method for titration calculations?
V1 x M1 / n1 = V2 x M2 / n2
```
V = volume
M = molar concentration
n = coefficient in the equation
```
119
A student does a titration using this reaction :
2KOH + H2SO4 —> K2SO4 + 2H2O
They recorded these results:
Volume of KOH solution = 25.0 cm3
Volume of H2SO4 = 19.83 cm3
Concentration of H2SO4 = 0.0618 mol dm-3
What is the concentration of the KOH solution in mol dm-3?
0.980 mol dm-3
120
How do you calculate percentage uncertainty?
Measurement uncertainty x number of times measurement taken x 100 / measurement obtained
121
How do you obtain the approximate total uncertainty when more than one piece of apparatus has been used?
Add together the individual percentage uncertainties
122
How do you minimise the percentage uncertainty?
Have more accurate equipment
| Use a higher value
123
Mass of marble chip = 3.57g
The measurement uncertainty in a 2 dp balance is 0.005 g.
What is the percentage uncertainty
0.28%
The measurement was taken twice
124
Mass of weighing bottle + solid = 20.354g
Mass of weighing bottle = 19.816g
Mass of solid = 0.538
Measurement uncertainty = 0.0005g
What is the percentage uncertainty?
0.37%
Twice for each measurement , 2 measurements
125
What are the reasons why maximum yield may not be achieved? (3)
The reaction is reversible and so may not be complete
There are side-reactions that lead to other unwanted products
The product may need to be purified which may result in loss of product
126
How is theoretical yield calculated?
Using the equation for the reaction
127
Copper (II) carbonate is decomposed to obtain copper (II) oxide:
CuCO3 —> CuO + CO2
What is the theoretical yield of copper (II) oxide obtainable from 5.78g of copper (II) carbonate?
n(CuCO3 & CuO) = 0.0468 mol
m(CuO) = 2.97g
128
Magnesium phosphate can be prepared from magnesium by reacting it with phosphoric acid:
3Mg + 2H3PO4 —> Mg3(PO4)2 + 3H2
What is the theoretical yield of magnesium phosphate obtainable from 5.62g of magnesium?
```
n(Mg) = 0.231 mol
n(Mg3(PO4)2) = 0.0770 mol
```
m(Mg3(PO4)2) = 20.2g
129
How is the actual yield found?
By weighing , not by calculation
130
How is percentage yield calculated?
100 x actual yield / theoretical yield
131
The theoretical yield in a reaction is 26.7 tonnes. The actual yield is 18.5 tonnes. What is the percentage yield?
69.3%
132
A manufacturer uses this reaction to obtain methanol from carbon monoxide and hydrogen:
CO + 2H2 —> CH3OH
He obtains 4.07 tonnes of methanol starting from 4.32 tonnes of carbon monoxide. What is the percentage yield?
Theoretical yield= 4.94 tonnes
Percentage yield= 82.4%
133
What are the conversions for:
g —> kg
g—> tonnes?
Divide by 1000
Divide by 1 000 000
134
A student prepares a sample of copper (II) sulphate crystals, CuSO4•5H2O, weighing 7.85g. She starts with 4.68g of copper (II) oxide. What is the percentage yield?
Ratio = 1:1
n(CuO) = 0.0589 = n(CuSO4•5H2O)
m(CuSO4•H2O) = 14.7g
135
What does atom economy calculate?
How many atoms from the reactants ended up in the desired product
136
How do you calculate atom economy?
Molar mass of the desired product / sum of the molar masses of all products x 100
137
What is the general atom economy for the following reactions:
Addition reactions
Elimination and substitution reactions
Multi-step reactions
Addition = 100%
Elimination and substitution reactions = lower
Multi-step reactions = lower
138
Sodium carbonate is an important industrial chemical manufactured by the Solvay process:
CaCO3 + 2NaCl —> Na2CO3 + 2NaCl
A manufacturer starts off with 75.0kg of calcium carbonate and obtains 76.5kg of sodium carbonate. Calculate the percentage yield and atom economy for this reaction.
Theoretical yield = 79.5kg
Percentage yield = 96.2%
Atom economy = 47.5%
139
Hydrazine (N2H4) can be used as a rocket fuel and is manufactured using this reaction:
2NH3 + NaOCL —> N2H4 + NaCl + H2O
What is the atom economy for this reaction?
29.5%
140
A manufacturer of ether wants to convert some of the ethene into 1,2-dichloroethane. He considers two possible reactions:
Reaction 1 H2C=CH2 + Cl2 —> ClCH2CH2Cl
Reaction 2 2H2C=CH2 + 4HCl + O2 —> 2ClCH2CH2Cl + 2H2O
Explain, without any calculation, which reaction would be a good choice on the basis of atom economy.
Reaction 1 because there is only one product which means all the atoms in the reactants end up in the desired product and the atom economy is 100%.
Reaction 2 has a lower atom economy because some of the atoms in the reactants form water which has no value as a product.
141
Ethanol can be manufactured by the hydration of ethene:
C2H4 + H2O —> C2H5OH
What is the atom economy of this process?
100%
142
Ethene can be manufactured by the dehydration of ethanol:
C2H5OH —> C2H4 + H2O
What is the atom economy of this process?
60.87%
143
Iron metal reacts with silver nitrate in a displacement reaction to form silver and iron (II) nitrate. Write the full equation and a simplified ionic equation for this reaction.
Fe (s) + 2AgNO3 (aq) —> 2Ag (s) + Fe(NO3)2 (aq)
Fe (s) + 2Ag+ (aq) —> 2Ag (s) + Fe2+ (aq)
144
A mixture of zinc metal and copper (II) oxide is ignited, causing an exothermic reaction to occur. Write a full equation and simplified ionic equation for this reaction.
Zn (s) + CuO (s) —> Cu (s) + ZnO (s)
Zn (l) + Cu2+ (l) —> Cu (l) + Zn2+ (l)
145
Write down the equation for the test for carbon dioxide.
Ca(OH)2 (aq) + CO2 (g) —> CaCO3 (s) + H2O (l)
146
Write down the equation and ionic equation for the test for sulphates.
Na2SO4 (aq) + BaCl2 (aq) —> BaSO4 (s) + 2NaCl (aq)
SO4^2- (aq) + Ba2+ (aq) —> Ba^2+ SO4^2- (s)
147
Write the equation and ionic equation for the test for halides.
NaCl (aq) + AgNO3 (aq) —> AgCl (s) + NaNO3 (aq)
| Cl- (aq) + Ag+ (aq) —> Ag+Cl- (s)
148
What is the general reaction for acids with metals?
Acid + metal —> salt + hydrogen
149
What is the general reaction for acids with metal oxides?
Metal oxide + acid —> salt + water
150
What is the general reaction for acids with metal hydroxides / alkalis?
Metal hydroxide + acid —> salt + water
151
What is the general equation for acids with carbonates?
Metal carbonate + acid —> salt + water + carbon dioxide
152
What are hydrogencarbonates?
Compounds containing the HCO3 - ion
153
What is the general equation for acids with hydrogencarbonates?
Metal hydrogencarbonate + acid —> salt + water + carbon dioxide
154
What is a test for carbonates and hydrogencarbonates?
Add an aqueous acid and test the gas given off with limewater
