Techniques and Procedures

Question 1

What is the method for weighting a solid?

Answer 1

1. Zero / tare the balance ( if a weighing boat or vessel is needed then place it on the scale before taring it )
2. Slowly start to add the solid until the mass is the required amount

If you cannot tare the balance, subtract the mass of the weighting vessel from the total mass to get the mass of the solid

Question 2

How can you use a pipette to measure an amount of liquid?

Answer 2

1. Ensure the pipette is clean by rinsing with distilled water
2. Dip the pipette into the solution and draw the solution into the pipette so the bottom of the meniscus is at the measurement line
3. Run the liquid out and into a piece of glassware.
4. Touch the pipette onto the side of the container, this will ensure all the liquid has been dispensed

Pipettes come in standard volumes, 1cm^3 50cm^3 25cm^3

Question 3

How do you use a burette to dispense the correct amount of liquid?

Answer 3

1. Clean the burette by rinsing it with distilled water
2. Ensure the burette tap is closed
3. Fill the burette with the liquid above the 0 line
4. Clamp the burette steady and dispense enough liquid so that the bottom of the meniscus is at the 0 line
5. Dispense the liquid into a container and read the burette to the nearest 0.05cm^3 and then work out the change in volume.

Question 4

What are the methods to determine the volumes of gas measured? (Two methods)

Answer 4

Using a gas syringe
or
Using an upturned cylinder

Question 5

What is the method of using a gas syringe?

Answer 5

A gas syringe is connected to a bung placed in a conical flask. The syringe starts being fully in and as gas is produced it moves out and the change is measured off measurements on the side of the syringe

Question 6

What is the method of using an upturned cylinder to measure the gas evolved?

Answer 6

1. A measuring cylinder is filled with water and is placed upturned in a water bath
2. place a delivery tube in a bung over a conical flask into the water bath and under the measuring cylinder
3. As gas is evolved in the conical flask it will flow through the delivery tube and into the upturned flask
4. Measure the change in the level of the water in the flask

Question 7

What is a conical flask?

Answer 7

It is flask that has a wide base and is triangular shape with a small opening at the top

Question 8

What is a delivery tube?

Answer 8

It is a tube that is shaped like a square root used to transfer gasses / liquids

Question 9

What is the method of heating under reflux?

Answer 9

1. Put the reactants in a pear shaped flask
2. Add a few anti-bumping granules
3. Attach a condenser directly above the flask and connect it to a supply of fresh cold water e.g. a tap and allow the water to flow through the condenser
4. Heat the pear shaped flask with a bunsen burner so that it boils gently
   When refluxing any vapours should be condensed and return to the reactant mixture

Question 10

How can water soluble inorganic salts be made?

Answer 10

Reacting an acid and an insoluble base together

Question 11

Method for purifying an organic liquid product using a separating funnel?

Answer 11

1. Mix an organic liquid with an immiscible liquid in a separating funnel. The more dense liquid sinks to the bottom
2. Allow the two liquids to separate in the funnel
3. Open the tap and allow one of the liquids ( the one on the bottom ) to flow out

If acidic impurities are present:
- Add sodium hydrogen carbonate solution and shake well to remove them.

If the organic product is alkaline:
- Add dilute acid until the mixture is neutral

4. Dry the organic product and separate via distillation

Question 12

What is a separating funnel?

Answer 12

It is a funnel with a tap on the bottom so that liquid can be allowed to leave

Question 13

How can you dry an organic product?

Answer 13

Add anhydrous sodium sulphate (or any other anhydrous salt) to remove any water

Question 14

What is the method of producing a salt via a titration (Soluble Base)?

Answer 14

1. Transfer 25cm^3 of an alkaline solution to a conical flask using a pipette
2. Use a burette to add the correct amount of acid to neutralise the solution
   DO NOT ADD ANY INDICATOR
3. Transfer the neutralised solution to a clean evaporating basin over heat from a bunsen burner to evaporate the water that is produced. Do not heat too strongly
4. Once salt crystals form stop heating an allow the mixture to cool
5. Filter the mixture
6. Wash the solid with COLD distilled water
7. Dry in an oven below the melting temperature of the salt
8. Measure the mass and dry more until there is no longer a mass change

Question 15

What is the method of producing a salt with an insoluble base?

Answer 15

1. In a beaker warm the insoluble base in the dilute acid
2. Use universal indicator to find out when the solution becomes neutral.
3. Leave to cool
4. Filter off the excess solid unreacted base using filter paper and transfer to an evaporating basin
5. Heat the evaporating basin and neutral solution until salt crystals form
6. Cool the basin and contents
7. Filter off the salt crystals using filter paper and a funnel
8. Wash the solid salt with COLD distilled water
9. Heat in an oven below the melting temperature of the salt
10. Check to see if the mass of the evaporating basin and contents change. When there is no longer a change, stop heating

Question 16

What is the method of making insoluble salts?

Answer 16

It is made from two soluble salts in solution

1. Add equal volumes of the desired salt solutions until a precipitate of the insoluble salt is formed.
2. The precipitate is filtered
3. Wash the precipitate with COLD deionised water
4. Filter off the water and transfer to a watch glass
5. Place in an oven set to a temperature below the melting point of the salt
6. Measure the mass change at intervals. If it doesnt change then stop heating

Question 17

What is distillation?

Answer 17

It is a method of separating two miscible liquids each with unique boiling points. The liquid with the lowest boiling point will evaporate first when boiled so if the temperature is kept at the right point only one will evaporate. The evaporated liquid can then be condensed using a condenser and this can then be collected

Question 18

What does miscible mean and what is its opposite?

Answer 18

it means that it is soluble / mix together.

The opposite is immiscible

Question 19

What is the method for distillation?

Answer 19

1. Put the mixture in a pear-shaped flask and add a few antibumping granules
2. Set up the distillatioin aparatus (See a diagram) and place a thermometer above the pear shaped flask and connect a condenser
3. Heat the mixture until it boils gently using a bunsen burner
4. When the temperature is 2*C below the boiling point, add a conical flask for collecting and collect until the temperature is above the boiling point of the liquid.
5. Then stop heating

Question 20

What do antibumping granules do?

Answer 20

They burst the bubbles in the boiling mixture and stop it from boiling over

Question 21

How does thin layer of paper chromatography work?

Answer 21

It works by different organic compounds having different affinities for a particular solvent and so will be carried through the chromatography medium at different rates

Question 22

What is the method for thin layer chromatography?

Answer 22

1. Draw a pencil line 1cm from the bottom of the chromatography paper or lilica plate
2. Place a spot of the test mixture on the line and a spot of a pure reference sample.
3. Suspend the plate in a beaker containing a solvent and cover the beaker with a watch glass to stop the solvent from evaporating
4. Remote the plate when the solvent is near the top
5. Mark how far the solvent has moved
6. Locate any spots with iodine, ninhydrin or under a UV light
7. Match the heights reached or rf values with those of known compounds using the same solvents

Question 23

What is recrystallisation used for?

Answer 23

It is used to purify solid crude ORGANIC products with small amounts of impurities
The products and impurities are dissolved in hot solvent and then the organic product will recrystalised as the solvent cools so it can be separated

Question 24

What is the method for recrystallisation?

Answer 24

1. Select a solvent in which the desired substance is very soluble at higher temperatures and insoluble at lower temperatures
2. Dissolve the crude product in the minimum quantity of solvent (the smaller the amount the better the yield of the product)
3. Filter out any insoluble impurities and retain the filtrate. It is best to preheat the filter funnel and conical flask to prevent any solid recrystallisation at this stage
4. Leave the filtrate to cool until crystals form
5. Collect the crystals using vacuum filtration
6. Dry the crystals in an oven

Question 25

What is the method for vacuum filtration?

Answer 25

1. Connect a conical flask to a vacuum pump via the side arm
2. Dampen a piece of filter paper and place it flat in a Buchner funnel
3. Switch on the vacuum pump and then pour in the mixture to be filtered.
   (The pump pulls the filtrate through quickly)
4. Disconnect the flask from the vacuum pump before turing the pump off to avoid suck back

Question 26

What is a standard solution?

Answer 26

It is a solution where the concentration is accurately known and it can be used to determine the concentration of another solution or the purity of a solid. It is made by accurately diluting a solid

Question 27

What is the method for making a standard solution from a solid?

Answer 27

1. Calculate the mass of the solute required and weigh out this amount accurately
2. Measure out 100cm^3 of deionised water and pour into a 250cm^3 beaker and add the solute
3. Stir the mixture so that the solute completely disolves
4. Transfer the solution to a new 250cm^3 volumetric flask and rinse the beaker with deionised water and pour into the volumetric flask
5. Keep on adding deionised water until it is within 1cm of the 250 mark on the volumetric flask
6. Use a dropping pipette to add deionised water so that the bottom of the meniscus is level with the 250 mark. Make sure that you look at it at eye level
7. Place a stopper in the end of the flask and shake to ensure full mixing

Question 28

What is the method of making a standard solution by dilution?

Answer 28

For this method a stock solution with a known concentration is required

1. Fill a 25cm^3 pipette with the stock solution
2. Run this into a 250cm^3 volumetric flask
3. Add deionised water to the volumetric flask until the bottom of the meniscus is at the 250 mark
4. Place a stopper in the end of the flask and shake it so that it mixes together

Question 29

What is the equation that could be used to work out how much a solution needs to be diluted?

Answer 29

Conc of diluted solution x volume of diluted solution = conc of stock solution x volume of stock solution

Question 30

Why would an acid-base titration be conducted?

Answer 30

To determine the concentration of an acid or alkali accurately

Question 31

What is the method for an acid-base titration to find out the concentration of an acid?

Answer 31

1. Rinse a burette with the acid and then fill the burette with the acid and run a little of the acid through the burette.
2. Record the initial burette reading to the nearest 0.05cm^3
3. Fill a 25cm^3 burette with the alkaline solution (of known concentration) and run into a 250cm^3 conical flask
4. Add a few drops of a suitable indicator and swirl to mix
5. Run the acid from the burette into the alkali in the 250cm^3 conical flask until solution changes colour.
6. Repeat steps 1 to 5 until there are 3 concordant results within 0.1 cm^3 of each other

Question 32

What are iodine - thiosulphate titrations used for? What is the overall process?

Answer 32

They are used to determine the concentration of a strong oxidising agent.
Iodine is displaced and liberated by an oxidising agent. This can then be titrated to find the concentration

Question 33

What is the method for displacing the iodine for a titration reaction?

Answer 33

1. Rinse a 25 cm^3 volumetric pipette with water and the with the oxidising solution
2. Transfer 25cm^3 of of the oxidising solution to a conical flask. This is called an aliquo
3. Add excess iodine ions using a measuring cylinder. The iodine ions can come in the form of a salt like potassium iodide
4. The iodine will then be displaced

Question 34

What is the method for a thiosulfate titration?

Answer 34

1. Wash the burette with water and then a standard solution of sodium thiosulfate
2. Fill the burette with sodium thiosulfate and then allow it to flow so that the jet is full
3. Put a white tile below the burette (this makes it clearer to see any indicator) and place the conical flask filled with the mixture of oxidising solution and potassium iodide on top
4. Read the initial burette reading to the nearest 0.05
5. Add a few drops of a starch indicator to the solution
6. Titrate until the solution turns a colourless. It will first go straw first
7. Read the final burette reading and work out how much was used by subtracting one from the other.
8. Wash out the conical flask with distilled water and repeat the titration (from step 4)
9. Stop testing when the titres are concordant of each other

Question 35

What is a colorometer?

Answer 35

This is a tool used to determine the concentration of a solution by measuring the colour of the solution

Question 36

What is the method for using a colorometer?

Answer 36

1. Select a complementary filter (this is the opposite to the colour of the solution)
2. Make a range of standard solutions above and below the concentration of the test solution to compare with the test solution
3. Zero the colorometer with a solvent (the same that the solution is based off)
4. Measure the abundance of the standard solutions and then create a calibration curve off the results.
5. Measure the abundance of the unknown solution and compare with the graph to estimate the concentration

Question 37

What is the difference between a colorometer and a visible spectrometer?

Answer 37

Both pass light through a solution to work out the concentration
Visible spectrometers compare all spectrums of light where as a colorometer only detects one because it uses a filter

Question 38

What is the method for measuring the energy transferred when a fuel burns?

Answer 38

1. Use a measuring cylinder to pour a known quantity of water into a copper calorimeter and measure its temperature
2. Weigh a spirit burner filled with fuel and leave the cap on it to stop the fuel evaporating
3. Support the calorimeter over a spirit burner and surround it with a draft excluder
4. Remove the cap and light the spirit burner
5. Use the thermometer to stir the water and extinguish the burner when it has risen about 15-20ºC and put the cap back on
6. Measure the temperature and weigh the burner again
7. Use the equation below

Q = mc∆t and the Q / moles of fuel = energy per mole