Monday, 10 November 2014

Investigating how the concentration of Calcium ions present in samples of water affect the volume of water softener needed to soften the water.

Equipment List

250 cm3 Conical Flask & Bung
Measuring cylinder, 100cm3, 25cm3 & 10cm3.
1% Soap Solution
Hard Water
Distilled Water
Sodium Carbonate Solution (0.40 mol/dm3)
Stop Watch

Method

1.     Measure 20cm3 of hard water (containing the calcium ions) and pour it into the conical flask.
2.     Measure out 80cm3 of distilled water and add it to the conical flask.
3.     Add 5cm3 soap solution to the water.
4.     Add 1cm3 of sodium carbonate solution (water softener), put on the bung and shake vigorously for 10 seconds.
5.     Leave the flask for 20 seconds and if there is still a lather then record the volume of sodium carbonate solution added. If not add another 1cm3 of sodium carbonate solution, shake for 10 seconds and leave for another 20 seconds. Repeat this process until you have a lather and record the volume of sodium carbonate added.
6.     Rinse out the flask thoroughly.
7.     Now measure out 40cm3 of hard water, add it to the conical flask and add 60cm3 of water to dilute it up to 100cm3 and repeat the experiment.
8.     Do this for 60cm3, 80cm3 and 100cm3 of hard water ensuring that enough distilled water is added to keep the total volume at 100cm3.


Volume of hard water (cm3)
Volume of distilled water (cm3)
Volume of sodium carbonate solution added (cm3)
20
80
 
40
60
 
60
40
 
80
20
 
100
0
 










Risk assessment
The soap solution is flammable to keep it away from naked flames.
The soapy water is very slippery so you must mop up any spills as soon as possible to avoid someone slipping over on it.

Monday, 3 November 2014

Measuring yeast activity vs temperature

Equipment

Yeast
Sugar (glucose for preference)
Balance
Water
Water bath
Conical flask
bung and delivery tube
water trough
Measuring cylinders
Stopclock

Method

Make up a solution of water and yeast, enough for five experiments (1.5 litre should be sufficient)
Swirl the solution and then measure 200ml into a conical flask.
Add 20g of sugar to the solution in the conical flask and swirl so it dissolves.
Place the conical flask into the water bath set to initial temperature of 20 degrees.
Place in the bung and delivery tube and run the delivery tube into the water trough.
Fill and upend the measuring cylinder over the end of the tube and start the stopclock.
Time how long it takes for 20ml of gas to be produced by the yeast.

Repeat the experiment at a temperature range of 20 degrees to 50 degrees in 5 degree intervals.

Hazards
Water may be spilled so care should be taken and spills mopped up straight away. Any glass breakages should also be cleared up straight away using a dustpan and brush. At the upper end of the temperature range care should be taken when removing the conical flask from the waterbath to make sure it is not too hot to touch and move safely.

Wednesday, 4 June 2014

Centre of mass & stability

Equipment

2 litre straight sided plastic drinks bottle with lid
Ruler
Protractor
Water
Wooden board with wooden lolly stick glued on

Method

Place the empty bottle on the wooden board so that the edge of the base buts up against the lolly stick so it does not slide.
Align the centre of the protractor with the edge of the board and slowly raise the opposite side so that the bottle starts to lean.
When the bottle falls read off the angle on the protractor. Repeat this at least twice more.
Add 5cm depth of water to the bottle using the ruler to measure.
Screw the lid on again tightly and repeat the tipping and recording of the topple angle.
Continue to add 5cm dept of water and repeat the tipping until the bottle is full.

Plot a graph of water height vs toppling angle. Why does it have this shape?

Risk assessment

Ensure lid is screwed on tightly when carrying out this experiment. Any spills should be mopped up straight away. As the bottle fills it will become heavier and could hurt feet if it rolls off the table, to reduce the chance of this happening carry out the experiment in the middle of the table and have a second person ready to catch the bottle as it falls.

Plant growth and crop density

Equipment

Sunflower seeds
Plot of soil 10m long and 50cm wide
Metre stick

Method

Mark out 5 points in the centre of the width of the planting bed that are 2 m apart.
Around each point mark a 10 square centimetre box.
In the first box plant one sunflower seed, two in the second etc until there are five seeds in the last box.
Water in all the seeds and continue to water every couple days.
Ensure when choosing the planting direction that the plants in one box will not cast a shadow on the plants in another box as they grow.
Allow the plants to grow for one month and then record the height of each plant.
Where there is more than one plant in a box work out the average plant height.

Risk assessment

Ensure hands are washed after working with soil.

Monday, 2 June 2014

Polymer strength testing

Equipment

Clamp and stand
Slotted masses (100g) and hanger
Strips of plastic bag of different widths (1 to 5cm in 1cm intervals)
Sticky tape
Ruler

Method

Take a strip of plastic bag and use the tape to secure the end into a loop.
Hang the loop with the taped end over the clamp and secure the loop using some more tape. Use the ruler to measure the unstretched length of the bag.
Add the masses 100g at a time until the loop breaks or until you reach 1kg and record the mass. If you reach 1kg without the loop breaking measure the length to which the loop has now stretched.
Repeat this three times for each width of loop.

Risk assessment

The bag can break suddenly so care should be taken to stand clear when adding masses so that they do not fall onto the floor and land on the feet of the experimenter. The experiment should be set up in the middle of a table so that it does not risk tipping over . The Bag loop should be suspended over the base of the stand to ensure the experiment remains stable.


Thursday, 29 May 2014

Centripetal force vs speed of rotation

Equipment

Glass tube 15cm length with ends flamed so that they are smooth.
1.5m length of string
Hooked mass hanger for 100g slotted masses
Large rubber bung with home through centre
Marker pen
Stopclock

Method

Tie the bung to one end of the string. then measure 60cm from the centre of the bung along the string and make a mark with the pen.
Run the string through the tube and tie a loop at the end to hang the masses from.
Hang the mass hanger and spin the bung at the correct speed to keep the pen mark at the top of the tube.
Start the stopclock and time how long it takes for 10 swings of the bung. Take two more readings of the time for 10 swings to calculate an average and check for anomalies.
Add a mass to the hanger and repeat the swinging and timing being careful to ensure that the pen mark stays at the top of the tube. It is important that the radius of the swing does not change as this is another factor that affects the centripetal force needed and so will affect the speed you measure.
Continue adding masses and timing 10 swings until you have 500g on the hanger.

Calculate the centripetal force applied by multiplying the mass used by the gravitational field strength.
Calculate the average speed by taking the circumference of the circle the bung travels in and dividing by the average time for one swing.

Plot a graph of centripetal force vs speed of motion.

Risk assessment

Ensure you are working in a clear area before starting to swing. After each repeat check the string to make sure it is not beginning to fray. There is still a risk of the string breaking and the bung flying free. As such only rubber bungs should be used. Do not attach a metal mass to the swinging end. Goggles should be work to protect eyes from any possible flying bungs. As you are using a glass tube care should be taken not to grip it too tightly as this increases the chance of the tube breaking. The tube should also be well supported at the rotating string end to prevent any extra stress on the tube increasing the risk of it breaking.

Friday, 23 May 2014

Factors affecting circular motion & centripetal force

This is a series of three short experiments which examine how a different factors affect the size of the centripetal force needed to maintain motion.

The three factors you will investigate are; Mass of object, Radius of circle, Speed of object.

Equipment

Plastic ballpoint pen tube sanded to smooth off the ends
1.5 m length of string marked every 10 cm
Slotted masses on a hanger 100g/division and 10g/division
Large and small rubber bung with a hole through the centre
Stopclock

Diagram



Method 1 - Effect of mass.

Set up the equipment as shown using the small bung with a 50cm length between tube and bung centre. Maintain this distance throughout
Add 100g mass to the end of the string and swing the bung so that the 50cm mark stays in position.
Time 10 swings and record the time. Stop and start again and record the time for 10 swings. Repeat this once more and take an average of the three readings.
Replace the small bung with a large one.
Start to swing the bung at the same rate as before (same time for 10 swings).
If the bung moves outwards and will not maintain the 50cm radius when swung at this rate add more masses to the hanger. If it slides towards the ballpoint tube remove masses from the hanger.
Keep adding/subtracting masses until the larger bung will swing at the same distance and at the same rate as the smaller bung. Note down the new mass needed and check three times as before that it is swinging at the same rate as for the small bung.

Does a larger bung need a larger or smaller centripetal force to make it swing at the same rate and distance?

Method 2 - Effect of radius

Using the small bung start with 100g mass and a 10cm radius. Sing the bung to maintain the 10cm radius and time 10 swings. Repeat as above twice more and calculate the average time at this radius.
Increase the radius by 10cm.
Start to swing the bung at the same rate as before (same time for 10 swings).
If the bung moves outwards and will not maintain the 20cm radius when swung at this rate add more masses to the hanger. If it slides towards the ballpoint tube remove masses from the hanger.Keep adding/subtracting masses until the  bung will swing at the correct distance and at the same rate as for 10cm. Note down the new mass needed and check three times as before that it is swinging at the same rate as for 10cm.
Repeat the process at 10cm intervals up to 50cm radius.

How does the radius of the swing affect the centripetal force required to make it swing at the same rate for the same mass object?

Method 3 - Effect of speed

Using the small bung start with 100g mass and a 50cm radius. Sing the bung to maintain the 50cm radius and time 10 swings. Repeat as in method 1 twice more and calculate the average time at this radius.
Add a new mass to the hanger and repeat the above, timing 10 swings.
Repeat for one more addition of mass.

How does the speed affect the centripetal force required to keep a fixed mass moving at a constant radius?

In each experiment it is important you only change one variable and control the others so that you can see the effect it has on the centripetal force. Do not for example change the bung, the radius and the speed of swing all at once as you will not be able to tell which factor is affecting the mass required to provide teh centripetal force.

Risk assessment.

Ensure you are working in a clear area before starting to swing. After each repeat check the string to make sure it is not beginning to fray. There is still a risk of the string breaking and the bung flying free. As such only rubber bungs should be used. Do not attach a metal mass to the swinging end. Goggles should be work to protect eyes from any possible flying bungs.



Wednesday, 14 May 2014

Thermistor resistance dependent on temperature

Two methods of measurement are presented here depending on the equipment you have available.

Equipment

NTC Thermistor
Hot water
Jug of cold water
Beaker
Thermometer
Digital Multimeter (option 1)
Ammeter and Voltmeter (digital or analogue - option 2)
12V d.c. Power supply (option 2)
Connecting leads

Method - Option 1

Connect the thermistor to the multimeter and set to read Ohms.
Immerse the thermistor in hot water in the beaker. Use the thermometer to measure the temperature and record this and the resistance.
Add a small amount of cold water to change the temperature by at least 5 degrees C and repeat the readings.
If you have time repeat the experiment twice more.
See image below for setup.

Method - Option 2

Connect the thermistor and ammeter in series to the power supply (set to 10V). Connect the voltmeter in parallel to the thermistor.
Immerse the thermistor in hot water in the beaker. Use the thermometer to measure the temperature and record this, the current and the voltage..
Add a small amount of cold water to change the temperature by at least 5 degrees C and repeat the readings.
Divide the voltage by the current to find the resistance.
If you have time repeat the experiment twice more.
See image below for setup.

Safety

Care should be taken with the hot water and a stack of paper towels should be kept handy to mop spills up straight away. You should also be aware that hot water can cause scalds so should work standing up to allow you move away quickly if there is a spill. leads should be prevented from wrapping around the beaker causing extra chance of a snag and spill occurring. If performing option 2 extra care should be taken to ensure that the water and power supply are kept as far away from each other as possible.

Option 1 Setup

Option 2 setup

Tuesday, 13 May 2014

Diffusion, surface area and volume.

This experiment will allow you to find how surface area/volume ratio affects the rate of diffusion.

Equipment

Hydrochloric Acid solution (1 molar)
Beaker
Stopclock
Agar cubes of different sizes (three each with sides of 0.5 to 3 cm in 0.5cm intervals) made using alkali and Phenolphthalein indicator
Tweezers
White paper
Deionised water
Goggles


Method

Using the tweezers add one of the smallest cubes to the beaker. Place the beaker on the white paper so as to me able to monitor the colour change easily.
Pour the enough acid into the beaker to just cover the cube and start the stopclock. Stop the stopclock when the cube has become clear. Record the time taken.
Empty the beaker and rinse out using the deionised water.
Repeat with the remaining two 0.5cm side cubes.
Repeat the entire process using the remaining cubes.

Calculate the surface area and volume of each cube. Divide the surface area by the volume and plot a graph of this value against the time taken for the diffusion to complete.


Safety

Goggles must be worn when working with acids. Tweezers should be used when moving the cubes as the indicator used acts as a laxative. Care should also be taken to wash hands after completing the experiment.



Resistance of a Thermistor

This experiment gives a way to find the resistance of a thermistor at a fixed temperature.

Equipment

Water bath held at 20 degrees C
Jug of cold water
Thermometer
Thermistor
12V d.c. power supply
Variable resistor
Connecting leads
Ammeter
Voltmeter

Method

Place the thermistor in the water bath with the thermometer to allow you to monitor the temperature throughout.

Connect the power supply, thermistor and variable resistor and ammeter in series. Then connect the voltmeter in parallel across the thermistor.

Adjust the variable resistor so it is allowing the least current to flow through the circuit and note the current. Then adjust the variable resistor to find the maximum value for the current flow. This is the range of your independent variable. Use these values to decide on a suitable interval for your current values to ensure that you get at least 5 different values of the current

Starting at the lowest current value record the current and voltage. Increase the current using the variable resistor and again record the current and voltage. Repeat this increase and measurement until you reach the maximum current.

Monitor the temperature of the water to ensure that the thermistor is not heating the water during operation.

Take another two sets of readings for the same values of current you used on the first run though. Then calculate an average of these values.

Safety

Be careful that the water from the water bath does not splash onto any of the electrical equipment being used. Also be aware that they thermistor may be warm after use - the temperature should be 20 degrees however if you are not carefully maintaining this the thermistor may get warm.

Analysis

Plot a graph of current on the x axis and voltage on the y axis. The gradient of this graph will be the resistance of the thermistor

Tuesday, 22 April 2014

Testing plastic bag (polymer) strength

This experiment will let you compare the strength of carrier bags provided by different retailers.

Equipment

Plastic bags from different supermarkets
Masses
Two tables
Four G clamps
Four wooden battens
Ruler
Scissors

Method

Cut a 30cm square from the plastic bag.
Place one edge between two wooden battens and clamp to the edge of one table firmly with two of the clamps.
Repeat with the opposite edge and clamp to the other table.
Measure how far the tables are apart and make sure this is the same for each test.
Add masses 100g at a time to the centre of the plastic sheet until it breaks and record the mass used.
Repeat for each plastic bag from the different supermarkets.

Risks

Be careful to stand well back when adding masses as the plastic may break unexpectedly and the masses could fall on your feet. Also make sure you are using heavy enough tables that will not be pulled over by the mass in between them.

Wednesday, 19 March 2014

Diffusion in egg white

This experiment will allow you to investigate how the rate of diffusion into egg white is affected by the concentration of the solution they are suspended in.

Equipment

Food colouring (red or black will work best)
Pipette
6 egg whites
Ice cube tray
Steamer or hot water bath
Ruler
Knife
Measuring cylinder
Water
6 beakers
Stopclock
Paper towels

Method

Distribute the egg white into the ice cube tray so that the wells are filled.
Either in a steamer or water bath (taking care not to let the water get into the wells) heat the egg white until it solidifies. Do not use a microwave as the heating is too vigorous and will result in air bubbles forming in the egg white.
Gently remove the egg white from the trays and use the ruler and knife to cut the egg white into uniform 1cm cubes - you should aim for at least 12 cubes.
Make 6 different concentrations of food colouring solution using 100ml of water and 1, 2, 3, 4, 5 and 6 ml of food colouring.
Place each solution in a different beaker and add at least two cubes of egg white.
Leave in the solution for 3 hours then remove the egg white cubes and dry the outside using the paper towels.
Carefully slice the cube in two and use the ruler to record how far the colour has penetrated into the cubes in each solution.

Risks

Steam or hot water used to solidify the egg white could cause a scald so take care to let the ice cube tray cool before handling.
Any spills should be cleared up as quickly as possible. Any breakages should also be carefully cleared up using a dustpan and brush.
Care should be taken when using the knife to make sure you do not cut yourself.


Ball bounce height vs surface material

Equipment

Squash ball
Metre stick
Clamp and stand
Different materials (e.g. carpet, lino, cork, wood, rubber)

NOTE: ideally materials should all be the same thickness.

Method

Place one material on the floor and use the clamp and stand to support the metre stick next to it.
Next drop the ball from the top of the metre stick onto the surface and record the maximum height to which the ball bounces.
Repeat this experiment at least another two times.
Change the material and carry out another three tests.

Risk Assessment

Ensure the ball does not roll away into an area where it could get underfoot and cause a fall.
When setting up the metre stick make sure it is clamped securely so it won't fall onto people carrying out the experiment.

Squash Ball bounce height vs temperature

In this experiment you can investigate how the height at which a squash ball bounces is affected by the termpaerture of the ball.

Equipment

5 squash balls of the same type
Water bath with temperature control
Thermometer
Paper towels
Tongs
Digital video camera (high speed if possible)
Metre stick with clear markings
Clamps & stands

Method

Place the squash balls into the water bath set to 20 degrees Celcius and ensure they are completely submerged.
Leave the balls in the water for at least 5 minutes to ensure the temperature of the rubber has stabilised.
Set up the metre stick so one end is on the floor using the clamp and stand to support it.
Set up the video camera so there is room to drop the balls between it and the metre stick and so that it has a clear view of the metre stick scale.
Use the tongs to remove one rubber ball and quickly blot off any excess water using a paper towel.
Start the video camera and drop the ball from level with the top of the metre stick.
Repeat with each of the remaining 4 balls.
Stop the camera and note the recording time.
Increase the temperature of the water bath by 10 degrees and replace the balls in it, again for at least 5 minutes.
Repeat a new recording of the balls being dropped.
Continue increasing the water bath temperature and recording the balls being dropped at 10 degree intervals until you reach at least 60 degrees.
Finally review the tape to record the maximum height each ball reached on its first bounce.

Risk assessment

Slips and falls may occur if the floor gets wet, this should be prevented by drying the balls carefully and by mopping up any wet areas quickly.
At higher tempertures there is a risk of scalding from the water. Tongs should always be used to remove the balls from the water bath to prevent contact with the skin. Additionally the experiment should not be run at a water bath temperature higher than 60 degrees Celcius