All Science core practicals

Cheat Sheet Changelog - Last recorded content update to this one: 15/05/2022 21:46

Note this only shows the ones explicitly defined in advance information.

Note this is the higher paper only, we don’t care about foundations lmao

Chemistry

Paper 1

Advance Info avec Bitesize Links

3.6: Change in pH on adding powdered calcium hydroxide or calcium oxide to hydrochloric acid

Specification summary:
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This practical focuses on recording the pH at intervals when calcium hydroxide or calcium oxide reacts with dilute hydrochloric acid. An initial mass of the solid must be added to a fixed volume of the acid, and the pH recorded each time more of the solid is added to the acid. The pH can be recorded using a pH meter, or universal indicator paper with a glass rod used to take a pH measurement at each interval.

How to perform

  1. Firstly, use a measuring cylinder to add a known volume of HCl to a conical flask.
  2. Then, use a glass rod to transfer a drop of liquid onto an universal indicator paper, or pH meter. Wait a minute and record the pH according to the colour, or the reading
  3. Add a spatula with a known amount, e.g 2cm³, of calcium hydroxide powder, using a mass balance.
  4. Stir thoroughly for 10 seconds, and use the method earlier to transfer a drop and record the PH.
  5. Record the results to the experiment in a table, amount
  6. Repeat this until the pH no longer changes, which will be when unreacted calcium powder is sat on the bottom of the flask.

Analysing results

Use the table’s results above to plot a graph. Amount of base added would be on the x-axis, and pH on the y-axis.
enter image description here
^^ What the graph would look like

A more accurate result can be achieved by using a balance to measure sodium hydroxide amounts, or using a pH meter instead of universal indicator, as it is difficult to read an exact value from it.

3.31: Electrolysis of copper sulfate

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Part 1 - using inert electrodes

  1. Pour an amount of copper sulfate solution into a beaker, around 50ml.
  2. Place 2 graphite rods (these are inert - carbon) and attach these electrodes to a DC power pack
  3. Turn on the power supply. Ensure the rods don’t touch.
  4. Test any gas produced at the electrodes. This would be hydrogen or oxygen. Hydrogen - lit splint makes a squeaky pop sound. Oxygen - relights a glowing splint.
  5. Record the results and observations of the test.

Optional: place a test tube filled with CuSO4 over the anode to test for oxygen.

Results:
Copper will form at the cathode, and oxygen at the anode. This is because copper is less reactive than hydrogen so it will be discharged on to its surface, being shiny red. Oxygen will form at the cathode as a halide is not present.

Cu²⁺ + 2e⁻ -> Cu(s)
4OH⁻ -> O2 + 2H₂O + 4e⁻

The gas is produced in small quantities, so may be difficult to take an accurate measurement of it and test it at all.

Part 2 - using copper electrodes

  1. Pour an amount of copper sulfate solution into a beaker, around 50ml.
  2. Record the masses on a balance of two copper electrodes
  3. Attach one to the negative terminal of the DC power pack, acting as the the cathode. Do the opposite for the other electrode.
  4. Turn on the power pack and change the current (ammeter - amps in SERIES) to a constant value
  5. Observe what happens!
  6. Turn off the power pack after a few minutes, let’s say 10 mins
  7. Remove one electrode. Gently wash it with distilled water, and let all the liquid to evaporate. Don’t wipe them with anything!. Measure and record the mass of it, and repeat with the other.
  8. Record and repeat the experiment with more electrodes at different currents.

5.9C: Acid-alkali titration with burette, pipette and indicator

Paper 2

7.1 Investigate the effects of changing the conditions of a reaction on the rates of chemical reaction

9.28C: Investigate the temperature rise produced by the combustion of alcohols

Biology

Paper 1

1.6: Investigating biological specimens

Method

  1. Set up your microscope.
  2. Place the slide onto the stage, with clips to secure the coverslip in place. Make sure it is above the glass where light passes through.
  3. Choose the lowest power objective lens and focus it. It should be almost touching the slide. (Don’t look through the eyepiece while doing this)
  4. Look through the eyepiece. Turn the coarse focus dial to roughly focus by moving the space between the objective lens and the stage. The cells should be in focus
  5. Draw the image - to show general arrangement of cells in a region of tissue.
  6. Use the fine focusing dial to make the cells even more in focus

Multiply the eyepiece lens (10x) by the objective lens (4x) to calculate total magnification (total 40x)

  1. Choose a higher power objective lens and repeat. The dials will need to be refocused to produce a clear image.
  2. Redraw the image, showing individual cells.

Usually, the cytoplasm, nucleus, cell membrane and mitochondria are visible in animal cells, and usually the cytoplasm, nucleus, cell wall and maybe the permanent vacuole and chloroplasts in plants.

Risks include eye damage through high brightness and broken glass when handling slides and the cover slip.

Measuring cell size

The cell size can be measured using a calibrated graticule and a stage micrometer. Alternatively, a ruler can be clipped onto a slide, and counting the amount of cells that fit across the length (1mm for a ruler). Divide 1000 μm by the number of cells to get the length, in micrometres, of a single cell.

1.10: Investigate the effect of pH on enzyme activity

Recap: Enzymes are biological catalysts, meaning they speed up reactions. Only one substrate type can fit into their active site, by the lock and key model. They denature, meaning their active sites change shape, under high temperature or in pH extremes.

Method

  1. Set up a Bunsen burner on a heatproof mat. Place a tripod above it and a gauze to put things on.
  2. Get a beaker of water and place it on the gauze.
  3. Turn on the gas and the Bunsen and heat the water up to around 37°C to simulate internal body temperature. Keep it this temperature.
  4. Get a spotting tile (the white one with loads of dipples in) and place a drop of iodine solution in each ‘spot’ (still prefer dipple) to test for starch
  5. Get 2cm³ of amylase enzyme solution and place this into a test tube.
  6. Get 2cm³ of starch solution and place this in the same test tube.
  7. Get 2cm³ of pH buffer solution (around pH 5) to keep the pH constant.
  8. Place this test tube into the heated Bunsen water and mix with a stirring rod.
  9. Every 30 seconds, use the stirring rod to transfer a drop of solution to the dipple containing the iodine.
  10. Repeat until the iodine stops turning blue-black.
  11. When it stops turning blue-black (remaining orange) the reaction has completed as starch is no longer present. Record the time for this.
  12. Repeat the experiment several times, with different pH buffers at pH 6, 7 and 8.

Risks & problems

Other useful things
The independent variable is the pH level.
The dependant variable is the time it takes until there is no colour change (meaning that the starch has fully broken down)

5.18B: Investigate the effects of antiseptics, antibiotics or plant extracts on microbial cultures

Specification content
Specification content

Resources: Pearson Edexcel Example Video

Method (A)

  1. Sterilise the Petri dish and agar gel in an autoclave to kill any bacteria.
  2. Turn the petri dish upside down to draw quarters in pen, labelling:
    • 2 antibiotics (the name of them)
    • a control (paper circle)
    • plant extract (e.g rosemary oil)
  3. Light a Bunsen burner a safe distance from ethanol.
  4. Get a nutrient agar bottle and pass the neck through the Bunsen flame.
  5. Pour the agar carefully into the Petri dish, about halfway up, cover with the lid, and allow to fully set. Take care not to lift the Petri dish lid too much - this will allow microorganisms inside. (Alternatively use a pre-made agar plate)
  6. Get a bottle of microorganism, and pass the neck over the Bunsen flame.
  7. Use a pipette to draw a small amount of microorganism. Pass the bacteria bottle over flame again.
  8. Add a few drops of microorganism into the agar. Use a sterilised spreader to spread the bacteria across the whole plate. Then sterilise it.
  9. Add a paper disk with sterilised (in ethanol, then through Bunsen to ignite) forceps and place the paper in the ‘Control’ quarter.
  10. Re-sterilise the forceps and place the antibiotic discs to test into the other 2 agar plate quarters.
  11. Flip the Petri dish to stop any unwanted airborne bacteria into the dish. (This stops anaerobic bacteria growing which may be harmful while also giving the bacteria oxygen to grow).
  12. Leave at between 20-25 degrees in schools for 2-3 days (this again reduces the risks of harmful bacteria - hospitals would grow at body temperature)

Measuring

  1. Use 𝝅r² to work out the ‘Zone of Inhibition’ around each zone where there is no growth.
  2. The most effective antiseptic will have the largest zone of inhibition.

This was how Alexander Fleming found penicillin in 1928!

Paper 2

Investigate the rate of respiration in living organisms

THE MAGGOTS PRACTICAL!!

Boiling tube containing soda lime, cotton wool plug, capillary tube and bung.

Firstly heat the boiling tubes at different temperatures from 30 to 40 degrees at regular intervals, maximum 40. Cotton wool is used to protect organisms and the person, soda lime is corrosive and absorbs the carbon dioxide produced by respiration.

Place the maggots inside the tube, on top of the wool which is above the soda lime, and bung it. Copy this with a control tube without maggots. Move this into a water bath for 5 minutes to adjust to the temperature.

Then add coloured liquid to a beaker, and bring this to the end of the capillary tube so the liquid begins being sucked up by the maggots. Mark the position on the tube and wait 5 minutes. After this mark the value and measure the distance.

Repeat at regular temperature intervals

Investigate the relationship between organisms and their environment using fieldwork techniques including quadrats and belt transects

Using this is a systematic sampling method along an area. Measuring tape from one area to another, place a quadrat on the value 0m. Count the population of a species and record in a table. Progress further at regular intervals and repeat. Draw a bar chart to show the data obtained.

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