Starch Amylase Experiment

I made up a starch solution  with 1/4 teaspoon  of starch dissolved in about 100ml of water I used soluble starch but corn starch will do or even the water from boiling potatoes.
I had a failure with the experiment the last time I did it with a student so I tried the same chemicals again to test to see if they worked. Into the first tube I added some starch and a few mls of a 1% Amylase solution. Into the next tube I put the same amount of starch and 2-3 mls of spit - I know this enzyme works.

After 20mins I took a sample of each of the tubes and added a squirt of Benedicts reagent and placed in a beaker of near boiling water for a few minutes. The left hand tube with the commercial Amylase powder enzyme turned the brown colour - confirming that the enzyme was working and converted some of the starch to maltose.

The middle tube went green showing that the Amylase in my mouth worked - slower - but some Maltose was made.

The tube on the right with just starch and no enzyme did not change showing that Starch does not react with Benedicts solution and there was no Maltose present in the starch.

So the Amylase enzyme does work and does convert starch to Maltose which is a reducing sugar (the Benedicts Test)
My spit works too albeit slower.
Now why did this not work for the student? I have no idea.

Kipps Apparatus

I bought a Kipps apparatus to generate Carbon Dioxide Gas or Hydrogen Gas. I don't need very much or make it that often so gas cylinders are a waste of time. It is a fascinating piece of equipment which is so simple to use.The Kipps generator was invented in 1844 by Petrus Jacobus Kipp and was used throughout the rest of the 19th and the entire 20th centuries for making gases.  Kipp generators are still being used in some places even now because of their ability to make a gas and then stop and then to be turned on again.
The Kipps apparatus is used to make a variety of gases such as Carbon Dioxide, Hydrogen and Hydrogen Sulphide. This is often why the Kipps apparatus was often left in a fume cupboard in the back of a classroom for all to see.
To make hydrogen gas some granulated zinc is put into the middle vessel by removing the  stopper.
Acid is then poured into the top vessel which is connected by a glass tube to the bottom vessel.
When the chemist requires the gas the valve in the middle chamber is opened and this allows the acid in the top chamber to force by air pressure the acid in the lower chamber into the middle chamber. The acid mixes with the zinc and there is a reaction. The zinc reacts with the acid and generates hydrogen gas. If the valve is open then the gas is collected often under water into a gas jar.
When enough gas has been collected the valve is turned off. The pressure in the middle chamber starts to increase and pushes the acid out of the middle chamber back into the bottom and also into the top chamber. When all the acid has been removed the reaction stops because there is no longer any acid to react with the zinc.
The Kipps apparatus is very simple to use, interesting to understand how it works and gives a good insight to how old fashioned ideas are still good to use today

Convection Currents in a beaker of water

 One of my A level students yesterday had never seen convection currents in water, so I set up this simple experiment for him. Into a large beaker I poured some cold water and at the bottom I placed a small coloured crystal.
I heated the water with a burner and watch as the water heated,  the water coloured by the crystal rose up in the beaker - not straight as the books suggest but in a more spiral direction until they reached the top when they spread out even more.

The water showed that it was less dense than the water around it because it was hotter and therefore it was lighter and rose to the surface - albeit not in a quite vertical direction.

There we are warm water rises and disperses the heat around the beaker from the bottom to the top.

New toys - old concepts - The Leslie Cube

A Leslie cube is a small hollow metal box with different painted sides. One is bare metal, the others are matt black, gloss black and gloss white.
The cube is filled with water and then heated until it boils.
Using an infrared thermometer we look at the temperatures  of the different surfaces. Each is a different temperature as seen in the pictures.

With a burner under the cube the water is heated until it is boiling. and the temperature of each surface is measured.
The bare metal surface came out as 49.3C

The Matt black surface came out as 97.9C

The smooth black surface as 95.9C

And the white surface as 97.0C

There is a difference. The bare metal was cooler by far. Now why might that be?

Maths GCSE Retake in Nov

Its time to start panicking. Do a set of exam papers ( calc and non-calc every week. Compare your answer to the marking scheme. The answer is not good enough all the working is required. Look at their working out in the marking scheme. How many marks would you get. Read the examiners report for each exam. It helps you know where others went wrong and perhaps how to avoid the pifallls.

Many schools don't use a Maths book. The revision guides are ok but a real Maths book with lots of questions are so much better. There are many to choose from amazon.


These books can help but any are good
Try to attempt one question from each section or exercise of the book each time you revise. It should take a little over two hours - almost the time of an exam paper.
Ideally you need to do this once or twice a week if you want a good grade.

The difference in a grade is about 2-3 hours of revision, so if you want the grade then you must do the learning. Maths is about practice as well as doing the learning how to do it.
Generally know how to do a sum is not the same as doing it.

Lego NXT Calculating force of gravity

I made a simple lego contraption to measure the force due to gravity.
The device consists of a lego retort stand with a switch at the top and a switch at the bottom.
We drop a lego tyre via a quick release mechanism. The tyre is connected from top to bottom by a piece of string that does nor impede the fall but guides the wheel down onto the switch at the bottom.
When we release the wheel at the top the timer starts and when the switch at the bottom is hit then the timer stops. Knowing the distance and the time then the NXT can calculate the force of gravity.

Lego NXT Science Bot as a Dynamics Trolly

When I was at school and when I taught in schools a few years ago dynamics trolleys with ticker tape timers were often used to teach the fundamentals of mechanics and newtons laws. My son at 18 and having just survived A level and GCSE physics had never seen such a trolley so with the help of Lego and an NXT brick here is an updated version. I have used this with my students to perform similar experiments without using the ticker tape timer. The NXT acts as a data logger and then uploads the information to the PC where the files are displayed as graphs in Excel.
Building Instructions for the Science Bot.
Program for the Science Bot

When the Science Bot is ready to go, the program removes the old data file and then records the number of 1/16 rotations (this corresponds to 1cm distance traveled. The distance and the time is recorded. This information is then sent to the PC as a comma separated file and then graphed in Excel.

The time is taken every 0.02 seconds which gives plenty of data per second.

As assembled the science bot has uses an acceleration sensor (not used in this program) and one of the old RCX mindstorms rotation Sensors.
The yellow box on the side is an old rpm sensor, which works independently of the mindstorms.