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Science Required Practicals (Biology (Effect of antiseptics on growth of…
Science Required Practicals
Biology
Light Microscope
Prepare the onion skin, by peeling off a layer (epidermal tissue), and placing it on the slide
Use iodine solution to dye the cells, and place a cover slip, taking care to mop up extra liquid with (filter) paper
Use the coarse and then fine adjustment knobs to focus on the cells
Effect of antiseptics on growth of bacteria
Aseptic techniques used
-Keeping equipment below the bunsen flame
-Flaming the neck of the culture bottle
-Burning ethanol off the spreader
-Securing the lid with tape (but NOT creating anaerobic conditions)
Split the agar dish into 3 (on the bottom of the dish, labelling the culture and antiseptic), and spread the bacteria culture (after having flamed).
Place 1 filter paper disc in each section, having dipped them in different antiseptics
Secure the lid, and incubate at 25* (to prevent the growth of dangerous bacteria etc)
Measure the diameters (90* to one another to obtain a mean diameter)
Effect of different conc. salt solutions on plant tissue
Collect 5 potato chips, and measure their masses, having trimmed them to the same length
Put each chip in a test tube with a different concentration solution, and leave for at least 20mins
Remove, and place on a paper towel to remove excess liquid
Remeasure mass, and calculate the change in mass
Shows the effect of osmosis; a lower concentration will lead to a more swollen chip (more movement of water into the chip)
Effect of pH on rate of reaction of amylase enzyme
Set up multiple test tubes, and regulate the pH using given buffer solutions (1cm3) in each, in a waterbath
Put two separate labelled boiling tubes of starch (10cm3) and amylase (10cm3), in a waterbath
Once they reach 30*. mix starch (2cm3) and amylase (2cm3) in one of the buffer test tubes, start the test tube, and place 1 drop in a depression each 15ish seconds
Set up a spotting tray with 1 drop of iodine solution in each spot
This test shows the effect of pH on the amylase enzymes; their optimal performance should be at around 7 pH. The first drops will be blue-black, as the starch will still be present. Furthermore, performance should begin to degrade at more extreme pH, as they will denature
Food tests
Benedict's test
Tests for sugars
Used to test for reducing sugars (NOT FRUCTOSE, nor starch)
Method
Prepare a food sample and transfer a set amount (5cm^3) to a test tube
Prepare a water bath and set to 75 degress
Add around 10 drops of Benedict's solution using a pipette
Place the test tube in the water bath and leave it there for 5 minutes.
If the food sample contains a reducing sugar, the solution in the test tube will change from normal blue to green, yellow or brick red - it depends on the amount of sugar that is in the food
Iodine solution
Test for starch
Foods like pasta, rice and potatoes contain a lot of starch
Method
Make a food sample and transfer a set amount of the sample to a test tube
Add a few drops of iodine solution and gently shake the test tube to mix the contents
If the sample contains starch, the colour of the solution will change from browny-orange to black or bluey-black
Biuret test
Tests for proteins
Meat and cheese are protein rich and good foods to use in this test
Method
Prepare a sample of good and transfer a set amount of the sample to a test tube (2cm^3)
Add a set amount (2cm^3) of biuret solution to the sample and mix the contents of the tube by gently shaking it.
If the food sample contains protein, the solution will change from blue to pink, or purple
Sudan III test
Tests for lipids
Found in foods such as olive oil, margarine and milk.
Method
Prepare a sample of the food and transfer a set amount (5cm^3) into a test tube
Use a pipette to add 3 drops of Sudan III solution to the test tube and gently shake the tube.
Sudan III stain solution contains stain lipids. If the sample contains lipids, the mixture will separate out into 2 layers. The top layer will be bright late. If no lipids are present, no separate layer will form.
The effect of light intensity on the rate of photosynthesis
Set up a test tube (rack) with a boiling tube, containing a piece of pond weed, and sodium hydrogen carbonate to ensure the amount of carbon dioxide is not limited
Start at 10cm away from the light source, and start a stop watch, to count the amount of bubbles produced in a minute. Repeat, ideally 3x, then move 10cm further away
Useful equations
Rate = dependent variable (bubbles) / time
Light intensity = 1/distance^2
Effect of caffeine on human reaction times
Student-planned
Either measure measure reaction times with/out caffeine, or with varying levels (i.e. more cola drunken). The student/subject must catch a ruler dropped by a friend
Convert length dropped, and repeat to obtain a mean - non-caffeinated cola done first, to insure results remain unaffected
Effect of tropisms on germinating seeds
Three petri dishes of mustard seeds and moist cotton wool are placed in differing locations; total, partial and no darkness
This will vary the effect of phototropism, and allow gravi/geotropism to be demonstrated (i.e. in absence of light)
However, once germinated (having regularly topped up the water), excess seedlings should be removed to equal the other dishes
Measure the mean height of the seedlings in each dish, and plot against time
Should illustrate how phototropism grows towards the light, and may thus stunt growth (height-wise), where as geotropism will cause them to keep growing upwards (against gravity), and therefore grow more (upwards, as they may become spindly due to a lack of light).
These both control the distribution of auxin
Measuring population size
Transect line v Quadrat
Quadrats are used to measure the average distribution of an organism in a habitat (and usually compare to another)
Transect line is used to measure the distribution of an organism over a distance - e.g. from under a tree outwards (increasing light intensity)
The two can be used together to gain a more accurate mean
Place a tape measure across a well-trampled area, and align a quadrat with the line (at 0m) to count how many of the population are present at that point
Repeat, moving along the line/away from the school, e.g. in intervals of 5m
Calculate the mean for a quadrat in that area
Repeat in an un-trampled area, and use the mean to calculate the amount of the population in a m2
The effect of temperature on the decay of fresh milk
The lipids in the milk are broken down into fatty acids, lowering the pH of the solution. This is detected by phenolphthalein
Prepare two boiling tubes, one with lipase, the other with milk - add 5cm3 of sodium carbonate, and 10 drops of phenolphthalein to the milk, and 2.5cm3 of lipase to the other. Add both to a water bath, and stir till they reach 20*C
Add the two solutions, start the stopwatch, and stir until it loses the pink colour - it's gone acidic
Repeat at increasing intervals of temperature (e.g. 10*C)
The lipase enzymes should be most effective at around 40*C (body temp), and thus the milk should then decay the quickest
Link to all the official methods
Physics
Thermal insulation - effectiveness of different materials
Boil water (80ml) in a kettle, and pour into a small beaker
Place into a larger beaker, and cover it with a cardboard lid - insert the thermometer through this, and measure every 5 mins
Can also be done using rubber bands to secure the material
Repeat, but with selected insulating materials placed inbetween the two beakers
For accuracy - ideally, repeat for each beaker to obtain a mean, and use the same volume of water at the same temp.
Ray Diagrams (light)
Set up a raybox, and a block of material on a piece of paper
Mark the normal, and in a darkened room, begin to change the ray's angle of incidence until you can see BOTH a reflected and refracted ray
Mark both of these, either with crosses (two ideally), or trace the line
Now connect the lines/crosses across the drawn block, and repeat with another block of differing density/material
Measure the angles of incidence and reflection for both blocks using your drawn lines
Angle of incidence should equal angle of reflection, but angle of refraction depends on the density of the object
Making and calibrating a newtonmeter
Attach two clamps to a clamp stand - the upper one being higher out. Place it on the edge of a bench, and place a heavy counter-balance
Hang the spring from the top, and ruler from the other, aligning 0 on the now vertical ruler with the top of the spring
Attach a splint to the bottom of the spring to help you obtain a more accurate reading off the reader (acts as a pointer)
Take a reading of this spring, then begin to add weights to the weight stack, taking a measurement each time- use this to calculate extension. Repeat this to plot a graph
Can now be used to weigh objects, by hanging them, and using the extension to determine its weight
Should be directly proportional (extension v weight/force), Hooke's law, up to the limit of proportionality
Waves in a ripple tank
Dipper (wooden rod connected to a motor) set up so that it just touches the surface of the water of the ripple tank
Pour depth of about 5mm of water into ripple tank
Lamp shines over ripple tank and white card placed under ripple tank for shadows of waves to be viewed
Measure wavelength of the waves with a metre rule on the card. Measure across many waves then divide that value by the number of waves to give average wavelength
Count number of waves passing a point in a given time (eg. 10 seconds) and divide by number of seconds to give the average frequency
Multiply wavelength and frequency to calculate the wave speed
Waves on a string
Set up elastic string attached to vibration generator and pulley which is on the edge of a table, connected to weights, with a wooden bridge supporting the string
Switch on vibration generator (connected to a power supply of variable frequency) and adjust tension in string (move wooden bridge or adjust length of string with weights on pulley) until a clear wave pattern can be seen. The waves will look like they are stationary
Wavelength pattern will look like this - made up of "half-waves" which look like loops
Use a metre rule to measure across many half wavelengths. Divide measurement by number of half-waves then multiply by two to give the full wavelength
The frequency is the frequency of the power supply, therefore multiply frequency by wavelength to calculate the wave speed
Acceleration
Uses an air track to minimise the effect of friction
Attach the air track to a vacuum cleaner, and set to blow - place the glider, and adjust the track until the glider doesn't touch the edge or slide one way.
Cut out a piece of card, and attach to the glider, to trigger the light gates (which you should attach). Connect the light gates to the computer.
Attach the glider via string to a weight pulley/stack, and attach weights to this incrementally, and let it fall - accelerating the glider through the gates. Repeat at least twice, and obtain a mean, for each weight
Leslie's Cube (IR radiation)
Place the cube on a heat-proof mat, and fill with hot/boiling water. Replace the lid, and use a detector to take a reading from each side of the cube
Each side of the cube is a different material - thus affecting the amount of IR radiation. Ensure the detector's distance remains constant
Measuring the effect of length on resistance
Connect a circuit, with an ammeter, battery/cell, and voltmeter, connected in parallel with the wire (which is in turn connected to a ruler, ideally wooden)
Connect two crocodile clips to the wire, one at the 0 end of the ruler., and the other at 20cm (depends on the gauge of the wire) Take a measurement from the ammeter and voltmeter, and disconnect the lead.
Increase the length of the wire/between the leads incrementally, and take another measurement.
You can calculate the resistance using V = I*R (So R = V/I). Be careful that the wire doesn't get too hot, by avoiding contact, and disconnecting it when not taking measurements
Chemistry
Paper Chromatography
Used to separate different dyes and inks
Method
Draw a line near the bottom of the paper using pencil (pencil is insoluble)
Add spots of ink to the line and place the bottom of the sheet in a beaker of solvent - for example water
Make sure the ink doesn't touch the solvent
The solvent will seep up the paper, carrying the ink with it. Each dye will move up the paper at a different rate so the dyes will separate
Each dye will form a spot, unless it is insoluble - then it won't be carried up the paper by the solvent
One the solvent is nearly at the top of the paper, remove the paper from the beaker and leave it to dry
Rf value = distance travelled by solute / distance of solvent
Mobile phase
Where the molecules can move - always a liquid or gas
Stationary phase
Where the molecules can't move - solid or thick liquid
Filtration
Used if the product is an insoluble solid that needs to be separated from a liquid reaciton mixture
Used in purification as well - eg. to remove solid impurities
Separating soluble solids from solutions
Evaporation
Pour the solution into an evaporating dish
Slowly heat the solution - the solvent will evaporate and the solution will become more concentrated - eventually crystals will start to form
Keep heating the evaporating dish until all that is left are the dry crystals
Crystallisation
Pour the solution into an evaporating dish and gently heat the solution
Some of the solvent will evaporate and the solution will become more concentrated
Once solvent evaporated or when crystals start to form remove the dish from the heat and leave the solution to cool.
The salt should start to form crystals as it becomes insoluble in the cold concentrated solution
Filter the crystals out of the solution and leave them in a warm place to dry
Separating rock salts
Mixture of salt and sand - both compounds but salt dissolves and sand doesn't.
Grind the mixture to make sure the salt crystals are small - so dissolve easily
Put the mixture into water and stir - the salt will dissolve
Filter the mixture to remove the sand, but the mixture will still contain the salt
Evaporate the water from the salt so it forms dry crystals
Distillation
Used to separate out a liquid from a solution
Heat the solution so the part of the solution with the lowest boiling point evaporates first
Cool the vapour so it condenses, then collect it
Can use distillation to get pure water from sea water - leaves the salt behind
Problem with distillation is that it can only be used to separate out compounds or elements with different boiling points
If the temp goes higher than the boiling points of the other substances they will mix again
Titrations
Allow you to find out exactly how much acid is needed to neutralise a known quantity of alkali
Can then use this data to work out the concentration of the acid or alkali
Method
Using a pipette and a pipette filler - add a set volume of the alkali to the conical flask as well as 2-3 drops of indicator (use a single indicator eg. phenolphthalein.
Use a funnel to fill a burette with an acid of known concentration and record the initial volume of acid.
Using the burette, add the acid to the alkali a bit at a time, regularly swirling the conical flask - slow down near the end point
The indicator will change colour when all the alkali has been neutralised - phenolphthalein is pink in alkaline conditions and colourless in acidic conditions
Record the final volume of acid in the burette, then work how much acid was needed.
Do this several times where the first titration is a rough titration then the next ones are to find the exact volume of alkali needed.
Calculate the mean of the results, ignoring any anomalous results.
Concentration = moles/volume
Measuring energy transfer
Measure energy released by a chemical reaction, where the temp of the reactants is measured, mix them into a polystyrene cup and measure the temperature of the solution at the end of the reaction
Biggest problem is the energy lost th the surroundings
Can reduce this energy loss by surrounding the cup in cotton wool in a beaker, and putting a lid on the beaker
Works for neutralisation reactions, reactions between acids and metals, and for reactions between acids and carbonates.
Can also investigate the effects of different variables on the amount of energy transferred eg. effect of mass
Method: (for HCI and NaOH neutralisation reaction)
Put 25cm^3 of 25 mol/dm^3 HCI and NaOH in separate beakers
Place the beakers in a water bath set to the same temperature (25 degrees)
Add HCI followed by the NaOH into a polystyrene cup with a lid
Take the temperature of the mixture every 30 seconds and record the highest temperature
Repeat above steps using 0.5 mol/dm^3 and then 1 mol/dm^3 of HCI
Measuring rates of reaction
Rate of reaction: amount of reactant used or amount of product formed/time
Three ways to measure rate of reaction
Precipitation and colour change
You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution
Observe a mark through the solution and measure the time it takes to disappear
If the reactants are coloured and the products are colourless then you can time how long it takes for the solution to lose its colour
The results are subjective - different people might not agree exactly when the mark disappears or when the solution changes colour
Change in mass (usually gas given off)
Measuring the speed of a reaction that produces a gas can be done using a mass balance
As a gas is released the amount of released gas is measured on the balance (difference from start to finish)
The quicker the mass drops the faster the rate of reaction
If you take measurements at regular intervals you can plot a rate of reaction graph and find the rate of reaction easily
Disadvantage is that it releases the gas straight into the room
The volume of gas given off
Involves a gas syringe to measure the volume of gas given off
The more gas given off during a certain time period, the faster the rate of reaction
Gas syringes usually give volumes accurate to the nearest cm^3.
If you take measurements at regular intervals you can also plot a rate of reaction graph
Effect on concentration of rates of reaction
Mg and HCI react to produce hydrogen
Add a set volume of dilute HCI to a conical flask, then place on a mass balance
Add some magnesium ribbon to the acid and plug the top with cotton wool
Start a stopwatch and take readings of the mass at regular intervals
Plot the results in a table and then work out the mass lost, then plot a graph of lost mass against time
Repeat the experiment with more concentrated solutions but only change the concentration of the acid
Conclusion should be - a higher concentration givers a faster rate of reaction
Sodium Thiosulfate and HCI produce a cloud precipitate
Both chemicals are clear solutions
They react to form a yellow precipitate of sulphur
Add dilute sodium thiosulfate to a conical flask
Place the flask on a piece of paper with a cross drawn on it, then add dilute HCI and start the stopwatch
Time how long it takes for the cross to disappear from sight completely
Repeat the reaction with either of the solutions of different concentrations
The higher the concentration the faster the rate of reaction
Hard to get a set of results where you can draw a graph for this experiment (qualitiative)
Analytical Chemistry
Tests for gases and anions
Test for chlorine
Chlorine bleaches damp litmus paper turning it white
Test for oxygen
If you put a glowing splint inside a test tube containing oxygen, it will relight the glowing splint
Test for carbon dioxide
Bubbling carbon dioxide through limewater will cause the solution to turn cloudy
Test for hydrogen
If you hold a lit splint at the open end of a test tube containing hydrogen, there will be a 'squeaky pop'
Test for carbonates
Put a sample of mystery solution in a test tube and add a few drops of dilute acid
Connect the test tube to a tube with lime water, and bubble the gas released through the lime water
If carbonate ions are present the lime water will turn cloudy due to the carbon dioxide released when the acid reacts with the carbonate
Test for Sulfates
Add a few drops of dilute HCI followed by some barium chloride solution to a test tube containing the mystery soluition
If sulfate ions are present a white precipitate of barium sulfate will form
Test for Halides
Add a couple drops of dilute nitric acid followed by a few drops of silver nitrate solution
Chloride gives a white precipitate of silver chloride
Bromide gives a cream precipitate of silver bromide
Iodide gives a yellow precipitate of silver iodide
Test for cations
Flame Test
Dip the loop into the sample and see what colour it burns
Only works for samples which contain a single ion
Clean a platinum wire loop by dipping it in dilute HCI then hold in in the bunsen until it burns without a colour
Calcium
Copper
Lithium
Sodium
Potassium
NaOH
Add a few drops of sodium hydroxide to the compound
Many metal hydroxides are insoluble and precipitate out of solution when formed - some of these have a characteristic colour
Aluminium (Dissolves in excess NaOH)/Calcium/Magnesium (White)
Copper
Iron (II)
Iron(III)
Chromatography
Formed out of two phases
Mobile phase - where the solute molecules can move, normally a liquid or gas - e.g., the solvent
Stationary phase - where the solute molcules cannot move, this is a solid or thick liquid - the material on which the test takes place (e.g. paper)
Normally done on paper - paper is the stationary phase, and water/ethanol the mobile phase
How long molecules spend in the phases (i.e. move up the paper) depends on its solubility and attraction to the paper
Pure substances form one spot, so mixtures will form multiple spots
This can be used with the Rf value to see if a certain substance is present in a mixture - it'll form one spot for which the Rf value can also be calculated and compared to a pure sample
Rf value is used to calculate how far a given substance moves in a given solvent (in ratio form)
Rf = distance of substance/distance of solvent
As it is affected by the solvent, the reference (pure) compound must be tested in multiple solvents, as otherwise it may not be the same
