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Chemistry A level > Practicals > Flashcards

Practicals Flashcards

1
Q

How do you weigh a solid? (3)

A
  1. Place Container on balance
  2. Tare
  3. Weigh the mass of solid
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2
Q

2 Ways to accurately dispense a volume of liquid

A

> Pipette

> Burette

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3
Q

How do you pipette a liquid? (3)

A
  1. Clean the pipette
  2. Draw enough liquid into the pipette with a pipette filler (bottom of the meniscus at the line on the stem)
  3. Run the liquid out
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4
Q

How do you titrate a liquid? (8)

A
  1. Clean the burette
  2. Close the burette tap
  3. Fill the burette with liquid
  4. Open tap to allow water to fill the jet
  5. Measure the volume of liquid (from the bottom of the meniscus)
  6. Titrate the liquid
  7. Measure the new volume of liquid
  8. The change in the volume is the volume of liquid dispensed
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5
Q

2 Ways to measure the volume of a gas

A

> Upturned cylinder

> Gas syringe

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6
Q

How do you use a gas syringe? (3)

A
  1. Press the gas syringe all the way down
  2. Connect it up
  3. Allow gas to flow in and measure the new volume of gas collected
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7
Q

How do you use an upturned cylinder? (5)

A
  1. Fill the cylinder with water
  2. Upturn it in a water bath
  3. Place a delivery tube under the cylinder in the water bath
  4. Allow gas to flow into the upturned cylinder
  5. Measure the change in the level of water in the cylinder
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8
Q

How do you heat under reflux? (4)

A
  1. Put reactants in a pear shaped flask
  2. Add anti-bumping granules
  3. Attach a condenser over the pear shaped flask and run cold water through it
  4. Heat the pear shaped flask so that it boils gently using a bunsen burner
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9
Q

5 Methods of purification

A 
> Separating funnel
> Distillation
> Thin layer chromatography
> Recrystallisation
> Vacuum Filtration
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10
Q

How is a separating funnel used? (3)

A
  1. Mix the organic product with another immiscible liquid
  2. Allow the two liquids to separate and form layers
  3. Open the tap and allow the aqueous layer to run out
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11
Q

How is an organic liquid purified? (5)

A
  1. Separate the organic product using the separating funnel
  2. Add sodium hydrogen carbonate solution and shake well to remove any acids
  3. If the organic product is alkaline (and needs to be neutralised) then add dilute acid until neutral
  4. Dry the crude product by adding anhydrous sodium sulfate and swirling the mixture
  5. The pure product can then be distilled
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12
Q

How is a water-soluble salt made?

A

Reacting a soluble acid with a (soluble or insoluble) base

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13
Q

How can an acid be reacted with a soluble base? (9)

A
  1. Carry out an acid base titration to calculate how much acid is needed to neutralise 25cm^3 of an alkaline solution
  2. Transfer 25cm^3 to a conical flask
  3. Using a burette add the correct amount of acid (as predetermined)
  4. Transfer the neutral solution to an evaporating basin and heat over a bunsen flame
  5. When salt crystals form, stop heating and leave to cool
  6. Filter the mixture
  7. Wash the solid with distilled water
  8. Heat in an oven
  9. Regularly measure the mass until there is no longer a mass change
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14
Q

How can an acid be reacted with an insoluble base? (9)

A
  1. Warm excess insoluble base with dilute acid
  2. Warm the solution until it is neutral
  3. Filter off excess base using a funnel and collecting the liquid
  4. Heat the liquid with a bunsen burner
  5. When salt crystals form, stop heating and leave to cool
  6. Filter the mixture
  7. Wash the solid with distilled water
  8. Heat in an oven
  9. Regularly measure the mass until there is no longer a mass change
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15
Q

How can an insoluble salt be made?

A

Be reacting two soluble salts in solution

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16
Q

How can two soluble salts be reacted to make an insoluble salt? (5)

A
  1. Add equal volumes of the soluble salts in a beaker until an insoluble salt precipitate forms
  2. Filter the precipitate
  3. Wash the precipitate with deionised water
  4. Heat in an oven
  5. Regularly measure the mass until there is no longer a mass change
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17
Q

What is the purpose of distillation?

A

This is used to separate two miscible liquids with unique boiling points

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18
Q

How do you set up the apparatus for distillation? (4)

A
  1. Put the mixture in a pear shaped flask
  2. Add anti-bumping granules
  3. Place a thermometer above the pear shaped flask
  4. Add a condenser to the side of the pear shaped flask with one end flowing into a conical flask to collect the condensed liquid
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19
Q

How do you conduct distillation? (4)

A
  1. Set up the distillation apparatus with the mixture and anti-bumping granules
  2. Heat the mixture until it boils using a bunsen burner
  3. When the vapour temperature is 2*C below the boiling point of the liquid we want to collect, put the conical flask in place to collect the distilled liquid
  4. Remove the conical flask when the vapour temperature is above the boiling point of the liquid we want to collect
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20
Q

What is thin layer chromatography?

A

This is a method used to separate small quantities of organic compounds depending on their affinity to the stationary of mobile phase

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21
Q

How do you do thin layer chromatography (without the analysis part)? (5)

A
  1. Draw a pencil line 1cm from the bottom of the paper
  2. Place a spot of the test mixture and the reference sample on the line
  3. Suspend the paper in a beaker with a suitable solvent below the pencil line
  4. Remove the plate when the solvent front is near the top of the paper.
  5. Mark where the solvent from has reached with a pencil
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22
Q

How do you analyse thin layer chromatography? (3)

A
  1. Locate the position of the spots with iodine, ninhydrin or using a UV light
  2. Calculate RF values by dividing the distance the sports have travelled by the distance the solvent front has travelled from the pencil line 1cm from the bottom of the paper
    RF = Spot distance / solvent distance
  3. Or you can compare the spots to the reference sample, if they are similar then it is pure
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23
Q

What is recrystallisation?

A

This is used to purify the solid crude organic solvent with small amounts of impurities

24
Q

How do you recrystallise? (6)

A
  1. Select a suitable solvent in which the desired substance is very soluble only at higher temperatures and insoluble at lower temperatures
  2. Dissolve the mixture in the minimum quantity of hot solvent
  3. Filter the solution to remove any insoluble impurities and retain the filtrate
  4. Cool the filtrate until crystals form
  5. Collect the crystals via vacuum filtration
  6. Dry the crystals in an oven
25
Q

How do you conduct vacuum filtration? (4)

A
  1. Connect a conical flask to a pump via the side arm
  2. Dampen a piece of filter paper and place it in a buchner funnel placed in the conical flask
  3. Switch on the vacuum and pour in the mixture
  4. Disconnect the flask before turning off the vacuum to avoid suck back
26
Q

How can you analyse the purity of a substance? (2)

A

> Melting point determination

> Thin layer chromatography

27
Q

How do you determine the melting point of a substance? (5)

A
  1. Seal the end of a glass melting point tube by melting it in a bunsen burner
  2. Tap the open end of the tube into a substance so that it falls into the bottom of the tube
  3. Fix the tube in the melting point apparatus and heat the surrounding liquid whilst mixing it
  4. Note down the temperatures at which the substance starts and finishes melting at by observing it
  5. If it is pure then it will melt within ±0.5*C
28
Q

What is a standard solution?

A

This is a solution which the concentration is accurately known

29
Q

How is a standard solution made from a solid? (8)

A
  1. Calculate and weigh out the correct amount of solid
  2. Pour 100cm^3 of deionised water in a 250cm^3 beaker and transfer the solid to the water
  3. Stir the mixture and if necessary heat it
  4. Transfer the solution to a 250cm^3 volumetric flask
  5. Rinse the beaker and add the washings to the volumetric flask
  6. Add deionised water to the volumetric flask until it is 1cm from the marker
  7. Then pipette the rest of the water until the bottom of the meniscus is at the line
  8. Insert the stopper in the flask and invert it so that it is well mixed
30
Q

How is a standard solution made using dilution? (5)

A

To dilute by a factor of 10

  1. Half fill a volumetric flask with deionised water
  2. Use a volumetric pipette to pipette 25cm^3 of the undiluted solution into the volumetric flask
  3. Add deionised water until it is 1cm from the 250cm^3 line on the volumetric flask
  4. Pipette the rest of the deionised water until the bottom of the meniscus is at the 250 line
  5. Put a top in the volumetric flask and invert it to mix it
31
Q

How is an acid-base titration conducted? (6)

A
  1. Rinse the burette with acid and then fill it
  2. Run some acid through to fill the jet and read and record the volume from the bottom of the meniscus
  3. Fill a volumetric pipette with the alkaline solution and run into a conical flask
  4. Add a few drops of of a suitable indicator and swirl to mix
  5. Run the acid from the burette into the flask and swirl the flask. Read and record the new volume and calculate the change in the readings to know how much acid was titrated
  6. Repeat until 3 concordant titration results are produced
32
Q

What is the purpose of an iodine thiosulfate titration?

A

To calculate the concentration of an oxidising agent that is strong enough to oxidise ioding

33
Q

What are the 2 steps of an iodine-thiosulfate titration?

A

Step 1: Reacting the iodine with the oxidising agent

Step 2: Titrating the product of the reaction

34
Q

How do you conduct the first step of an iodine-thiosulfate titration (using chlorate as the oxidising agent)? (5 + reaction equation)

A
  1. Pour the ClO- into a beaker
  2. Using a volumetric pipette, Pipette 25cm^3 of the ClO- into a conical flask
  3. Add excess IODIDE ions using a measuring cylinder (15cm^3 @ 0.5moldm^-3 of KI should do)
  4. Add excess H+ ions by adding sulfuric acid (20cm^3 @ 1moldm^-3)
  5. The mixture should now be brown in colcour
    Reaction: ClO- + 2I- + 2H+ ==> I2 + Cl- + H2O
35
Q

How do you conduct the second step of an iodine-thiosulfate titration (using chlorate as the oxidising agent)? (6 + reaction equation)

A
  1. Fill a burette with sodium thiosulfate solution and run until the jet is full. Measure the volume from the bottom of the meniscus
  2. Put the conical flask with the mixture below on a white tile below the burette
  3. Conduct a rough titration. You know the end point is near when the solution becomes a straw colour
  4. Add a starch indicator and continue titrating until the solution becomes colourless
  5. Read the burette and measure the change to calculate the volume of thiosulfate titrated
  6. Repeat with more accurate titrations until repeat titres are concordent
    I2 + 2S2O3[2-] ==> 2I- + S4O6[2-]
36
Q

What makes a result concordent?

A

When the titres are within 0.1cm^3

37
Q

How do you conduct a colorimetry test to determine the concentration of an unknown solution? (5)

A
  1. Select a filter with the complimentary colour to the solution being tested
  2. Make up a range of standard solutions above and below the estimated concentrations of the unknown solution
  3. Zero the colorimeter using a cuvette filled with just solvent
  4. Measure the absorbance of each standard solution of known concentration and produce a graph of concentration against absorbance. Draw a line of best fit.
  5. Measure the absorbance of the unknown solution and use the graph to estimate its concentration
38
Q

How can you preform an experiment to measure the energy transferred when a fuel burns? (6)

A
  1. Pour a known volume of water into a copper calorimeter and measure the initial temperature
  2. Weigh the spirit burner with the cap on to measure the initial mass
  3. Support the calorimeter using a clamp stand over the spirit burner and surround it with a draft excluder
  4. Remove the cap off the spirit burner and light the flame
  5. Use the thermometer to stir the water and when the temperature has increased by 15C to 20C extinguish the flame and measure the highest temperature reached
  6. Weigh the burner again
39
Q

How can you calculate the energy transferred when a fuel burns and how do you calculate enthalpy of combustion?

A 
Energy transferred: 
E = MC∆T
Number of moles of fuel burnt: 
Mass change / Mr = No. Moles
Enthalpy change of combustion: 
Energy transferred / No. Moles = ∆H
40
Q

How can you conduct an experiment to calculate the enthalpy change of neutralisation using changes in temperature? (6)

A
  1. Using a measuring cylinder, add a known volume of a known concentration acid to an insulated vessel
  2. Take the temperature of the acid
  3. Using a measuring cylinder, add a known volume of a known concentration Alkali to the insulated vessel and start a stop watch
  4. Place a lid on the vessel and put a thermometer through a hole in the lid into the solution and measure the temperature every 30 seconds
  5. Plot a graph of temperature (y-axis) against time (x-axis) and add a line of best fit through the straight part of the graph and extrapolate back to the point when you added the alkali to the acid
  6. ∆T can be calculated from this temperature and the initial reading
41
Q

How can the enthalpy change be calculated by using changes in temperature?

A
  1. By measuring the initial temperature before the chemicals were mixed
  2. Then by measuring the temperature change over time
  3. Extrapolating back to the time when the two solutions were mixed
  4. Extrapolated temperature - Initial temperature = Temperature change
  5. The used E = MC∆T
42
Q

How can you conduct and experiment to calculate the enthalpy change of solids and solutions using changes in temperature?

A
  1. Using a measuring cylinder add a known volume of a known concentration of the reactant solution to an insulated vessel
  2. Take the temperature of this solution
  3. Add a known mass of solid reactant (This should be in excess)
  4. Place a top on the vessel with a lid with a hole in
  5. Put a thermometer through the hole and measure the temperature change
  6. ∆T can be calculated from this temperature and the initial reading
43
Q

What is electrolysis?

A

This is when electricity is passed through a solution to produce products at both of the electrodes

44
Q

How are gasses collected in a electrolysis reaction?

A

The electrodes are placed in the solution and inverted test tubes filled with the electrolysis solution are placed over the electrodes. As gas is produced at the electrodes, it fills the test tubes and then this can be used to collect the gas.

45
Q

How are metals purified with electrolysis?

A

> The anode will be made of the impure metal and is placed in a solution
the cathode should be made of the pure metal
The electrolyte must contain ions of the collected metal
The electricity is turned on and the pure metal will be plated onto the cathode

46
Q

How is a standard hydrogen half cell made?

A

> A beaker containing a solution of 1moldm^-3 H+
A platinum electrode is placed into the solution
A supply of H2 is put into the solution around the electrode at standard pressures (10^5 Pa)

47
Q

How can an experiment be conducted to find the electrode potential of a half cell? (5)

A
  1. Set up a standard hydrogen half cell
  2. Set up a standard half cell (that is being tested)
  3. Join the two with a salt bridge and the electrodes with a voltmeter
  4. Turn on the hydrogen supply for the hydrogen half cell
  5. Read the potential difference from the voltmeter
48
Q

What are the standard conditions for a half cell?

A

> 1moldm^-3 solution
Atmospheric temperatures
Atmospheric pressures

49
Q

How is a pH electrode calibrated?

A

> Place the electrode in a neutral (pH 7) buffered solution adjust the electrode if necessary
Place the electrode in an acidic (pH4) buffered solution and adjust the electrode if necessary
Place the electrode in an alkali (pH10) buffered solution and adjust the electrode if necessary

50
Q

What is the apparatus for cracking a hydrocarbon over a catalyst?

A

> A boiling tube held in a clamp stand almost horizontally above a bunsen burner
The boiling tube has a mineral wool soaked in the hydrocarbon at the end and with porcelain chips (catalyst) half way down the tube
A bung is placed in the end of the boiling tube with a delivery tube going into a water bath with an upturned cylinder to collect the cracked hydrocarbon gas

51
Q

How do you conduct and experiment to crack hydrocarbon vapour over a catalyst? (7)

A
  1. Set up the apparatus to conduct the experiment
  2. Place several upturned cylinders in the water to collect the gas
  3. Heat the catalyst strongly with the bunsen burner
  4. Heat the hydrocarbon collecting any gas that passes through the delivery tube
  5. Discard the first test tube and continue collecting gas
  6. Remove the delivery tube BEFORE you stop heating the catalyst
  7. Leave to cool
52
Q

What is the main safety concern when cracking a hydrocarbon in the lab?

A

Suck back of water into the test tube.

This can then move to the hot part of the test tube and cause it to crack and explode

53
Q

What tests can be preformed on the collected gas and liquid product in the test tube left over from hydrocarbon cracking?

A

> The liquid in the test tube, when mixed with bromine should remain yellow / brown
The collected gas is shaken with bromine.
When the two have reacted, the bromine should decolourise the bromine
The liquid is an alkane and the gas is an alkene

54
Q

What are the two steps to determine Ksp?

A

Step 1: Making a saturated solution of the salt being tested

Step 2: Testing the concentration of the saturated solution

55
Q

Experimentally, how is Ksp determined [Step 1]? (4)

A
  1. Distilled water is warmed
  2. Add the salt until no more is able to dissolve. This is clear because some will stay solid in the saturated solution
  3. Leave the mixture to cool to room temperature
    [There will still be some solid at the bottom]
  4. Filter the mixture through filter paper and collect the filtrate. This is the saturated soltion
56
Q

Experimentally, how is Ksp determined [Step 2]?

A

> Take the temperature of the saturated solution because Ksp is dependent on temperature
Dependent on the salt, different tests will need to be conducted. These could include:
- Titration
- Colorimetry
- Indicators

57
Q

How can an equilibrium constant be determined?

A
  1. Mix reactants together of a known concentrations
  2. Allow the reactants and products to reach equilibrium
  3. Use quantitive analysis to determine the concentration of one of the reactants or products at equilibrium
  4. Use a RICE table to determine the concentration of other reactants
  5. Plug these into the equation to find Kc

Chemistry A level (13 decks)

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