Chemistry 1 - The Development of Practical Skills in Chemistry Flashcards
(166 cards)
1
Q
Describe how to set up the apparatus to measure the volume of gas produced in a reaction.
A
A gas syringe or an upside-down water-filled measuring cylinder in a trough of water may be used to collect the gas.
2
Q
What are the formulae relating the volume of a gas and the number of moles present?
A
At room temperature and pressure (RTP), use the equation n=V/24 Where: n=Number of moles V=Volume (dm³) If not at RTP, use the ideal gas equation PV=nRT Where: P=Pressure (Pa) V=Volume (m³) n=Number of moles R=Ideal gas constant (8.314) T=Temperature (K)
3
Q
What is used to accurately measure mass?
A
A digital balance that records mass to 2 decimal places.
4
Q
Why is it important to rapidly put the bung into the conical flask after starting a reaction that releases a gas?
A
The reaction can start as soon as the reactants mix, and gas will start being released. So to reduce the amount of gas that escapes, the bung should be put in place as quickly as possible.
5
Q
Give three possible sources of error when investigating the volume of a gas produced in a reaction.
A
Some gas could have escaped before the bung us put in the conical flask.
The reaction may be incomplete.
Some gas may dissolve in water meaning a smaller volume would be collected than was released.
6
Q
What is the purpose of safety goggles?
A
To protect the eyes from chemicals and small impacts to prevent damage.
7
Q
What safety procedures should be followed when working with potentially irritant chemicals?
A
Safety glasses must be worn.
Skin contact to chemicals should be avoided.
Food mustn’t be eaten near the workspace, and not until hands have been thoroughly washed.
Avoid bringing chemicals close to face.
8
Q
What apparatus is used in a titration to accurately measure volumes?
A
A burette is used to measure the volume of solution added.
A pipette filler is used to measure a specific volume of solution into the conical flask.
9
Q
Describe the ‘weighting-by-difference’ method.
A
Add roughly the desired mass of a substance to a weighing bottle and weigh
Transfer the substance to a beaker/conical flask
Reweigh the weighing bottle
The difference between the masses is the mass of solid
10
Q
Describe how to carry out an acid-base titration.
A
Use a pipette to add 25cm³ of acid to a conical flask. Add a few drops of indicator.
Pour alkali into the burette. Record the initial burette volume.
Complete a trial titre. The conical flask should be swirled constantly above a white tile. Stop adding the alkali as soon as the end point is reached. Record the final burette volume.
Repeat the titration until two concordant results are obtained. Add alkali drop by drop near the end point.
(25cm³ of alkali may initially be put into the conical flask if the burette is filled with acid.
11
Q
When transferring a solution from one beaker to another, how can you ensure as much of the dissolved substance has been transferred as possible?
A
Use distilled water to wash any leftover solution from the old apparatus into the new beaker.
12
Q
How do you accurately fill a volumetric flask to the graduated mark?
A
Fill so that the bottom of the meniscus rests on the graduated mark.
13
Q
What is the meniscus?
A
The curve on the surface of a liquid.
14
Q
What is a standard solution?
A
A solution of a known concentration,
15
Q
Describe how to make a standard solution of NaHCO₃.
A
Weigh out a specified amount of NaHCO₃.
Add a small volume of distilled water to the beaker containing the NaHCO₃ to dissolve it.
Use a funnel to add the solution to a 250cm³ volumetric flask.
Rinse the beaker with distilled water and add the washings to the flask.
Make the flask up to the graduation mark with distilled water.
Stopper and shake the flask.
16
Q
Suggest 2 indicators that could be used in an acid-base titration.
A
Phenolphthalein and methyl orange
17
Q
What are concordant results in a titration?
A
Titres that are within 0.1cm³ of each other.
18
Q
What degree of precision should burette readings be recorded to?
A
To the nearest 0.05 cm³.
19
Q
Which results are used when calculating a mean titre?
A
Two concordant results (within 0.1cm³ of each other).
20
Q
When completing a titration, what piece of apparatus is used to make the colour change easier to observe?
A
A white tile, placed underneath the conical flask.
21
Q
What three things are required to take an accurate burette reading?
A
Read from the bottom of the meniscus.
Allow any liquid on the walls of the burette to settle before taking a reading.
Ensure that there are no air bubbles.
22
Q
What is the end point of a titration?
A
The first point at which the indicator changes colour permanently.
23
Q
Why is the conical flask swirled continuously during a titration?
A
To ensure that all the reactants are combined so that the reaction is complete.
24
Q
Why is it better to have a titre volume of 25cm³ than 10cm³?
A
The larger the titre volume, the smaller the percentage error.
25
What equation links the number of moles and concentration?
```
n=CV
Where:
n=Number of moles
C=Concentration
V=Volume
```
26
If you know the volume of acid required to neutralise an alkali, how could you calculate the concentration of the acid given the alkali concentration and volume?
Calculate the number of moles of the alkali using the known volume and concentration.
Use the chemical equation to work out the ratio of acid and alkali that react and hence work out how many moles of acid have reacted.
Divide the moles of acid by the volume used in neutralisation.
27
What is calorimetry?
A process used to find the amount of energy released or taken in during a chemical reaction.
28
What is an exothermic reaction?
A reaction which releases energy to its surroundings.
29
What is an endothermic reaction?
A reaction which takes in energy from its surroundings.
30
What is a neutralisation reaction?
A reaction between an acid and a base, forming a salt and water.
31
What is meant by the term standard enthalpy change of combustion?
The enthalpy change that accompanies the formation of one mole of water from a neutralisation reaction under standard conditions.
32
Give the word and chemical equations for the neutralisation reaction between sodium hydroxide and hydrochloric acid.
sodium hydroxide +
hydrochloric acid → sodium chloride + water
NaOH+HCl→NaCl+H₂O
33
The enthalpy change of neutralisation is being investigated. Why might the neutralisation reaction be carried out in a Styrofoam cup?
A Styrofoam cup is a better thermal insulator than a glass cup, so less heat energy will be lost to the surroundings, meaning that the calculated temperature is more accurate.
34
What equation is used to calculate the energy absorbed by a solution in calorimetry?
```
Q=mcΔT
Where:
Q=Heat energy (J)
m=Mass of the solution (g)
c=Specific heat capacity of the solution (often the value for water is used)
ΔT=Temperature change (°C or K)
```
35
How is enthalpy change of neutralisation calculated from the thermal energy absorbed by the solution?
Q/n
Where:
Q=Heat energy (J)
n=Number of moles =Volume×Concentration of specified substance/species used
36
How can you find the maximum temperature reached during a neutralisation reaction?
Plot a graph of temperature (y-axis) against time (x-axis) and extrapolating to the time that the reactants were combined.
37
Suggest three possible sources of error when investigating the enthalpy change of neutralisation. How could these errors be reduced?
Heat transfer to and from the surroundings, mitigated through insulating the reaction.
Incomplete combustion if using fuel, a bomb calorimeter could be used to combat these two errors.
Inaccuracy in temperature measurement, mitigated by using an electronic thermometer.
38
Describe and experiment to investigate the enthalpy change of neutralisation of a reaction between hydrochloric acid and sodium hydroxide.
Add 25cm³ HCl(aq) to a polystyrene cup. Place the cup in a glass beaker. Measure 25cm³ NaOH(aq).
Start the timer. Record the initial temperature of the HCl at minute intervals for 3 minutes.
At minute 4, add the sodium hydroxide, do not record the temperature.
Continue recording the temperature at minute intervals for 5 to 10 minutes. Stir the solution when measuring the temperature.
39
Describe the chemical test for halide ions.
Add dilute nitric acid to react with carbonate ions, so no Ag₂CO₃ forms (a white solid)
Add silver nitrate; a precipitate forms:
-White: AgCl (soluble in dilute and concentrated ammonia)
-Cream: AgBr (soluble in concentrated ammonia)
-Yellow: AgI (Insoluble in ammonia)
40
How can SO₄²⁻ ions be identified?
Add aqueous barium nitrate. A white precipitate (BaSO₄) will form if sulfate ions are present, This precipitate is insoluble in excess dilute strong acids.
41
Describe the chemical test used to detect CO₃²⁻ and HCO₃⁻ ions.
Add aqueous acid.
If either ion is present bubbles of CO₂ will be released.
Test the gas by bubbling it through limewater via a delivery tube. If it is CO₂, the limewater will turn cloudy.
42
What are the solubilities of the first 3 group 2 metals (Mg, Sr, Ba) in sulfate solution?
Mg - soluble
Sr - insoluble
Ba - insoluble
43
What are the solubilities of the first 3 group 2 metals (Mg, Sr, Ba) in chromate solution?
Mg - soluble
Sr - soluble
Ba - insoluble
44
What type of reaction occurs when a haloalkane is formed from an alcohol?
Nucleophilic substitution.
45
Write the word and chemical equations for the formation of 2-chloro-2-methylpropane from 2-methylpropan-2-ol.
2-methylpropan-2-ol + hydrochloric acid → 2-chloro-2-methylpropane + water
CH₃C(CH₃)₂OH+HCl → CH₃C(CH₃)₂Cl+H₂O
46
What are the 3 main stages in the synthesis of a haloalkane from an alcohol?
Preparation
Separation
Distillation
47
Why do 2 layers form in the separation funnel when synthesising a haloalkane from an alcohol?
The aqueous and organic layers have different densities and they are immiscible.
48
What is the purpose of anti-bumping granules?
To prevent the formation of large gas bubbles that cause violent boiling.
During distillation, anti-bumping granules prevents the mixture boiling over into the condenser, meaning impurities won't contaminate the product.
49
When producing a haloalkane from an alcohol, why is sodium hydrogen carbonate added to the organic layer after it has been separated from the aqueous layer?
To react with any leftover hydrochloric acid.
50
Why is it important to open the stopper of the separating funnel regularly?
To release the build up of pressure and reduce the risk of the apparatus breaking.
51
When producing a haloalkane from an alcohol, why is anhydrous sodium sulfate added to the organic mixture after separation?
To remove water (small amounts only)- it acts as a drying agent.
52
Why is distillation used when synthesising a haloalkane from an alcohol?
To separate and purify the organic product.
53
Describe the key features of the apparatus set-up for distillation.
Tilt the condenser down so any liquids flow into the beaker.
The water must enter at the bottom of the condenser and leave at the top for efficient cooling.
The collection flask should not be sealed to the condenser- it should not be airtight as the hot air in the system could cause the apparatus to crack.
Use a thermometer to identify when the desired product has evaporated from the reaction mixture.
54
Why might a water bath or electric heater be used instead of a Bunsen burner to heat a reaction mixture?
If the reactants are flammable as using a Bunsen burner would be a safety risk.
55
What safety precaution should be taken when carrying out the formation of a haloalkane from an alcohol practical?
2-methylpropan-2-ol is highly flammable and harmful if inhaled- to mitigate this risk, keep it away from naked flames and keep the lab well ventilated.
Concentrated sulfuric acid causes severe skin burns and eye damage. Use a fume cupboard and wear safety goggles and gloves.
Take care when heating apparatus. Move hot apparatus with tongs to avoid burns.
56
What two reactants are used to synthesize methyl 3-nitrobenzene?
Methyl benzoate
| Nitric acid
57
What is the purpose of concentrated sulfuric acid in the synthesis of methyl 3-nitrobenzoate?
it acts as a catalyst, speeding up the rate of reaction.
58
In the preparation stage of the synthesis of methyl 3-nitrobenzoate, what should the temperature be kept below? Why?
Below 10°C, this is to maximise yield.
59
Describe the process of filtration under reduced pressure.
Place a piece of filter paper in a Büchner flask. Connect the side arm of the flask to a water pump.
Connect the water pump to a tap and turn the tap on to create the vacuum. Pour the solution into the funnel.
Once the solution has drained through, rinse the solid on the filter paper with a small volume of solvent.
60
Describe the process of recrystallisation.
Dissolve the solid in the minimum volume of hot solvent.
Filter to remove insoluble impurities.
Cool the filtrate.
Filter to remove soluble impurities (the product remains on the filter paper).
61
Why is ethanol used for the recrystallisation of methyl 3-nitrobenzoate?
Methyl 3-Nitrobenzoate is soluble in ethanol but not in water, it is also a cheap and relatively safe organic solvent.
62
During recrystallisation, why is the product dissolved in a minimum amount of solvent?
If there is a large is a large volume of solvent when the mixture is cooled (and solubility is decreased), some of the product may remain in solution.
63
How does recrystallisation improve the purity of a product?
The desired product is dissolved in an appropriate solvent that the impurities are insoluble in. Subsequent filtration leaves the insoluble impurities on the filter paper while the solution flows through.
64
Why is the solution cooled in ice immediately after recrystallisation?
To decrease the solubility of the product so that it crystallises. Lower temperatures increase the size of crystals formed.
65
Why must the crystals be completely dry before measuring their mass to calculate the percentage yield?
Excess solvent on the crystals could falsely increase the yield.
66
How can percentage yield be calculated?
(%Yield)=((Max theoretical yield)/(Actual yield))×100
67
Give 3 reasons why the yield may be lower than 100%
Product may be lost when filtering/transferring between apparatus.
Some product may stay in solution after recrystallisation.
Other side reactions may occur,
68
What technique could be used to investigate the purity of the product before and after recrystallisation?
Thin layer chromatography- comparison of Rf values from the product before and after recrystallisation to a pure lab sample.
69
What piece of apparatus is used to transfer a small amount of each liquid onto the chromatography plate?
A capillary tube.
70
During chromatography, why should the beaker containing the solvent and the TLC plate be covered with a clear watch glass?
To prevent the evaporation of the solvent.
| The watch glass should be clear to allow the plate to be monitored.
71
In chromatography, what is the solvent front?
The furthest distance travelled by the solvent up the TLC plate.
72
Why should the baseline be drawn in pencil on a TLC plate?
The graphite of a pencil is insoluble in solvent so it won't travel up the plate and obscure the results.
73
When using chromatography to asses the purity of a sample of methyl 3-nitrobenzoate, what is used to make the spots visible?
Iodine crystals.
74
How do you calculate an Rf value?
Rf=(distance travlelled by the substance)/(distance travelled by the solvent)
75
What does Rf stand for?
Retention factor.
76
Without using chromatography, how can the purity of a sample be assessed?
Use melting point apparatus.
Pure substances have a specific melting point whereas impure substances will melt over a larger range of temperatures. The smaller the range, the purer the sample.
77
What safety precautions should be taken during the synthesis of methyl 3-nitrobenzoate?
Methyl 3-nitrobenzoate is an irritant so wear safety goggles and avoid contact with skin.
Iodine crystals are harmful if in contact with skin or when inhaled so avoid contact with skin and keep away from your face,
Methyl benzoate is an irritant so wear safety goggles and avoid contact with skin.
Ethanol is highly flammable so keep away from naked flames.
78
What reagent is used to test for the presence of an alkene?
Bromine water.
79
What is observed when bromide water is added to an alkene?
The solution will change from orange to colourless.
80
What is observed when bromine water is added to a saturated hydrocarbon?
The solution remains orange.
81
Briefly describe how to test for haloalkanes.
Heat the sample with a solution of sodium hydroxide under reflux to release any halide ions.
Add some dilute nitric acid.
Add silver nitrate solution and observe the colour of any precipitate formed.
82
What colour precipitate forms when silver nitrate solution reacts with chloride ions?
White.
83
What colour precipitate forms when silver nitrate solution reacts with bromide ions?
Cream.
84
What colour precipitate forms when silver nitrate solution reacts with iodide ions?
Yellow.
85
Describe the solubilities of the silver halide precipitates in dilute and concentrated ammonia.
AgCl - soluble in dilute and concentrated ammonia.
AgBr - soluble in concentrated ammonia.
AgI - insoluble in ammonia.
86
Briefly describe how to test for carboxylic acids.
Add some sodium carbonate solution to the sample. If a carboxylic acid is present, there will be effervescence and CO₂ will be produced.
To test a produced gas, bubble it through limewater- CO₂ causes the limewater to turn cloudy.
87
What reagent can be used to test for the presence of an alcohol?
Acidified potassium dichromate solution.
88
What is observed when a primary or secondary alcohol is heated under reflux with acidified potassium dichromate solution?
There is a colour change from orange to green.
89
What is observed when a tertiary alcohol is heated under reflux with acidified potassium dichromate solution?
No colour change- the solution remains orange.
90
What two reagents can be used to distinguish between an aldehyde and a ketone?
Fehling's solution and Tollens' solution.
91
What is observed when Fehling's reagent is heated with;
An aldehyde?
A ketone?
When heated with an aldehyde, a brick red precipitate forms.
| When heated with a ketone, no precipitate forms and the solution remains a deep blue colour.
92
What is observed when Tollens' solution is heated with;
An aldehyde?
A ketone?
When heated with an aldehyde, a silver mirror forms on the surface of the test tube.
When heated with a ketone, no change is observed.
93
What is Brady's reagent used to identify? Describe the positive result for this test.
It is used to identify carbonyls (aldehydes and ketones). In a positive result, a yellow-orange precipitate forms in the presence of a carbonyl.
94
Briefly describe the test for phenol and the positive result for this test.
Add bromine water. If a phenol is present, the solution will change from orange to colourless and a white precipitate will form.
95
When would a water bath or electric heater be used instead of a Bunsen burner to heat a sample?
When either the temperature needs to be controlled more or when the chemicals being heated are highly flammable.
96
What must a half cell contain?
An element in two oxidation states.
97
Define the terms oxidation and reduction.
Oxidation is the loss of electrons, reduction is the gain of electrons. This can be remembered easily using the mnemonic; OILRIG.
98
Why must metal electrodes be cleaned with sandpaper before creating an electrochemical cell?
To remove any metal oxide that has formed on the surface and improve electrical conductivity.
99
Describe the movement of electrons in an electrochemical cell.
Electrons flow through the wire from the positive electrode to the negative electrode.
100
In a standard Zn/Zn²⁺ cell, what is the role of potassium nitrate solution?
Potassium nitrate is used to saturate a piece of filter paper so that it can be used as a salt bridge.
101
Why is a salt bridge used in an electrochemical cell?
To maintain the charge balance and complete the circuit. This is because negative electrons are moving from one half cell to another. Without the salt bridge, positive charge would build up in the half cell containing the anode and negative charge would build up in the half cell containing the cathode. This would cause the reaction to stop.
102
Why must an inert salt be used in the salt bridge?
So that the salt doesn't react with the solutions and alter their concentrations. If a reactive salt was used, the cell potential would change.
103
What moves across the salt bridge?
Ions.
104
In an electrochemical cell, each metal electrode is placed in a solution containing what?
Its ions.
105
Standard conditions are often used when investigating electrochemical cells. What are the standard conditions?
1 moldm⁻³ for solutions
1 atm for gasses
298 K temperature
106
After setting up a electrochemical cell, the reading on the voltmeter is negative. What should be done?
Switch the connection of the wires so the electrodes are the right way round.
107
What is the formula for the electromotive force (EMF)?
EMF=Eᵣ-Eₗ
Where:
Eᵣ=The right hand cell's potential, where the reduction occurs.
Eₗ=The left hand cell's potential, where the oxidation occurs.
108
For a reaction of an electrochemical cell to be thermodynamically feasible, what must the value of the EMF be?
Positive.
109
What is the role of manganese dioxide in the decomposition of hydrogen peroxide?
Catalyst.
110
What is the purpose of catalysts?
Provide an alternative reaction route with a lower activation energy, which increases the rate of reaction.
111
Write the word and chemical equations for the reaction involving manganese(IV) oxide and hydrogen peroxide.
hydrogen peroxide→water + oxygen
2H₂O₂→2H₂O+O₂
(MnO₂ isn't included as it is a catalyst)
112
Describe how to set up the apparatus to measure the volume of gas produced during a reaction.
A gas syringe or an upside-down water-filled measuring cylinder in a trough of water may be used to collect the gas.
113
What is meant by the term "half-life" for a reaction?
The time taken for the reactant concentration to half.
114
Briefly describe how to find the half-life of the decomposition of hydrogen peroxide.
Set up apparatus to collect any gas produced during the reaction.
Record the volume of O₂ collected at regular intervals and calculate [H₂O₂}.
Plot a graph of [H₂O₂] against time and use it to find 2 values for the half-life.
115
What formula can be used to calculate [H₂O₂] from the volume of oxygen collected from its decomposition?
[H₂O₂] (in moldm⁻³)=(40-V(O₂))/240
116
Why is it important to rapidly put the bung in the conical flask after H₂O₂ and the catalyst have been combined?
The reaction will have started so O₂ will be produced. If the bung is not in place, oxygen will escape (this won't be included in the volume measurement).
117
Why might the volume of gas be measured in a burette rather than a measuring cylinder?
To obtain more precise measurements.
118
What is a "clock reaction"?
A reaction in which the concentration of a reagent quickly changes after a certain time period, causing a colour change.
119
Briefly describe a method that could be followed to find the order of reaction with respect to iodide ions in the iodine clock reaction.
Mix potassium iodide, sodium thiosulfate and starch solutions in a conical flask.
Add potassium peroxodisulphate and start the timer.
Record the time taken for the solution to turn blue-black.
Repeat steps 1-3 with varying concentrations of KI.
120
How can the order of a reactant be deduced from the rate of reaction?
The rate of reaction is proportional to 1/time. Use changes in the rate of reaction and concentrations to deduce the order with respect to each reagent.
121
Write the word and chemical equations for the reaction between potassium iodide and potassium peroxodisulphate (K₂S₂O₈).
potassium peroxodisulphate + potassium iodide → potassium sulphate + iodine
K₂S₂O₈+2KI→2K₂SO₄+I₂
122
What equation links moles, volume and concentration?
```
n=V×C
Where:
n=Number of moles
V=Volume
C=Concentration
```
123
How can the initial rate be calculated for an iodine clock reaction?
initial rate=moles of iodine (mol)/time taken for colour change (s)
124
Give 2 possible sources of error in an iodine clock experiment.
Inaccurate timing of the appearance of blue colour; a way to minimise this is to have multiple people timing the experiment and calculate an average value.
Adding starch increases the volume which affects the concentrations of the reactants and thus the amount they change over time.
125
Suggest some control variables for this experiment.
Total volume of reactants
Volume of starch and thiosulfate used
The concentrations of all the reagents (except potassium iodine solution)
Temperature (as this can also affect the rate of reaction)
126
Write the rate equation for the reaction between iodide ions and peroxodisulphate ions.
Rate=k[I⁻][S₂O₈²⁻]
127
What is the overall order of the reaction between iodide ions and peroxodisulphate ions?
2
128
Give three ways you could identify whether a solution was acidic or basic.
Litmus paper
Indicator (such as universal indicator) and comparison to a colour scale
pH meter
129
How can litmus paper be used to identify an alkali?
Red litmus paper will turn blue.
| Blue litmus paper will remain blue.
130
How can litmus paper be used to identify an acid?
Red litmus paper will remain red.
| Blue litmus paper will turn red.
131
Why might a pH meter be used rather than universal indicator to measure pH?
Gives a numerical value for pH
| It is more accurate (typically read to 2 decimal places)
132
What is meant by the term "accuracy"?
How close the measurement is to the true value.
133
What equations link pH and hydrogen ion concentration?
pH=-log[H⁺]
| [H]⁺=10⁻ᵖᴴ
134
Briefly outline how to carry out a titration?
Use a pipette to measure the first solution into a conical flask.
Add a few drops of a suitable indicator.
Add the other solution into a burette and record the initial volume.
Slowly add the solution in the burette into the conical flask.
Swirl the mixture continuously until the end point is reached.
Repeat until concordant results are obtained.
135
What colour is methyl orange in;
Acid?
Alkali?
Neutral solution?
Methyl orange is;
red in acid
yellow in alkali
and orange in neutral solutions.
136
What colour of phenolphthalein in:
Acid?
Alkali?
Phenolphthalein is:
colourless in acid
and pink in alkali.
137
What is a Brønsted-Lowry acid?
A substance that donates protons (H⁺ ions).
138
What is a Brønsted-Lowry base?
A substance that accepts protons (H⁺ ions).
139
What is the difference between a strong and weak acid?
A strong acid completely dissociates in solution (readily releases H⁺ ions) whereas a weak acid only partially dissociates.
140
A solution has a pH of 1.00 when measured using a pH meter. Suggest the characteristics of this solution.
It is acidic and likely to contain a strong acid.
141
What is a prediction using scientific knowledge called?
Hypothesis.
142
What are variables?
Factors that can affect the outcome of the experiment.
143
What is an independent variable?
A factor that is changed during the experiment to see the effect it has on another factor.
144
What is a dependent variable?
A factor that is measured or observed in the experiment.
145
What is a control variable?
A factor that is kept constant throughout the experiment.
146
What is oxidation?
The loss of electrons or increase in oxidation state.
147
What is reduction?
The gain of electrons or decrease in oxidation state.
148
What is a redox reaction?
A reaction in which some atoms are oxidised and others are reduced.
149
How can the percentage of iron in iron tablets be found?
Prepare a standard solution of iron(II) using the tablets and sulfuric acid.
Titrate a set volume of this iron(II) solution against a solution of KMnO₄.
Repeat until you obtain concordant results and calculate a mean titre.
Calculate the number of moles of KMnO₄ that reacted.
Use the ratio in the chemical equation to calculate the number of moles of iron that reacted.
Calculate the percentage mass of iron using the mass present in the standard solution.
150
Describe how to make a standard solution of acidified iron(II) sulfate.
Grind up some iron tablets. Measure the total mass of the iron tablets in a weighing boat.
Add the powdered tablets to a conical flask and reweigh the weighing boat. The difference between the masses is the mass of iron tablets in the solution.
Add a 50cm³ of sulfuric acid to the conical flask to dissolve the iron. Stopper the flask and shake well. Leave the flask for the residue to settle.
Filter the solution into a volumetric flask without disturbing the residue. Rinse the filter paper with a small volume of distilled water.
Fill the volumetric flask up to the graduation mark with sulfuric acid, then stopper and invert the flask to mix.
151
Write an equation for the redox reaction between iron(II) ions and manganate(VII) ions.
5Fe²⁺+MnO₄⁻+8H⁺→5Fe³⁺+Mn²⁺+4H₂O
152
When making a standard solution, what method should be used to find the mass of solute?
The weighing-by-difference method.
153
Why is an indicator not required in the titration between Fe²⁺ and MnO₄⁻?
KMnO₄ It is self-indicating; the end point is when you get the first permanent pale pink colour.
154
In a titration, what are concordant results?
Titres that are within 0.1cm³ of each other.
155
Give three possible sources of error in the titration of iron(II) ions and manganate(VII) ions experiment.
The iron may not completely dissolve- warming may help.
Some iron may not be transferred between containers- take washings.
The end point may be hard to see- place a white tile underneath the conical flask to make the colour change easier to observe.
156
What equation links mass, molecular mass and the number of moles?
```
m=M×n
Where:
m=Mass (g)
M=Molecular mass
n=Number of moles
```
157
What is primary research?
A new set of data that has been collected. Conclusions are drawn from this new data.
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Give two examples of primary research.
Surveys and experiments.
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What is secondary research?
Data from other studies that are used to draw conclusions.
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What is the difference between qualitative and quantitative data
Qualitative data are descriptions of observation, such as colours.
Quantitative data is numerical data.
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Online and offline resources can be used for what?
Research.
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Describe the Vancouver referencing system.
Full references are numbered at the end of a document (with numbers linked to the appropriate reference in the order they appear in the text).
Often times this is in the form (Number).Author (Year of publication), title
Other information such as page number, volume/issue number, web address or date of access (online only) may also need to be recorded.
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Describe the Parenthetical (Harvard) referencing system.
The author's name and the date of the work are put in brackets at an appropriate point in the text.
The references are listed at the end of the document in alphabetical order without numbers. If there are more than 3 authors, write the first name followed by 'et al.'.
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What is the general reference format for books?
Author (year), Title, Edition (if relevant), publisher's location, publisher
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What is the general reference format for journal articles?
Author (year), 'Article title', Journal title, volume number, issue number, pp. xxx-xxx
(Where pp. xxx-xxx is the range of pages)
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What is the general reference format for websites?
Author (year), Title. [online] last accessed date: URL
| If the author is not listed on the webpage, name the organisation.
