Monday, 25 February 2013

Carbonate content 2 - reaction with hydrochloric acid.

This method describes how to ascertain the relative proportion of carbonate in an ore sample based on the duration of a reaction with HCl.

Equipment

Conical flask
Balance with .01g resolution
Measuring trays
HCl 2mol/litre
Ore samples
Pestle and mortar
Spatula
Measuring cylinder
Stopclock

Method

Grind your first sample in the pestle and mortar until it is finely divided into a powder.
Measure out 20ml of acid and add to the measuring cylinder and pour into the conical flask.
Measure out 1g of the ground sample into a measuring tray.
Add the ground sample to the conical flask and start the stopclock, giving the flask a quick swirl to ensure the two mix.
Stop the stopclock when the reaction finishes and no more gas is evolved.

Record the time and move onto your next sample.

Goggles should be worn whenever working with acids.

Results

The longer the reaction continues for, the greater the proportion of carbonate in your sample. Depending on the proportions you may find the reaction completes too quickly to be able to time, or continues for too long. If this is the case you could either adjust the amount of sample used, or change the concentration of the acid.

Carbonate content 1 - Thermal measurement

This method will allow you to measure the amount of carbonate present in a sample of a material. It uses thermal decomposition to remove carbon dioxide from the carbonates and uses mass differences to assess the amount of carbonate in your sample.

This method assumes that carbonates will be the only gases evolved in the thermal decomposition and that you are working with carbonates of less reactive metals.

Equipment

Carbonate containing samples
Pestle and mortar
Crucible
Bunsen
Pipe clay triangle
Tripod
Tongs
Balance with .01g resolution

Method

Set up bunsen under a tripod with a pipe clay triangle on it.
Grind up some of your first sample (around 2-5 grams) in the pestle and mortar until it is finely divided.
Record the mass of your crucible.
Add your ground sample to the crucible and record the mass of both.
Strongly heat the sample for sufficient time to thermally decompose the carbonates. This can be a lengthy process with the end point associated with no further colour change of the material. You may need to agitate the crucible with the tongs to ensure that all the carbonates have been decomposed.
Record the mass of sample and crucible again and calculate the mass difference.
Repeat for each of your other samples.

Analysis

Divide the mass lost by each sample by the initial mass of each sample to find the a relative proportion of carbonates within each sample. This process could be calibrated against a known mass of a sample of calcium carbonate.

Reflection 2 - Mirrors and angles

This set of experiments demonstrates some of the properties of reflections in a pair of plane mirrors.

When we consider a reflection in a plane mirror we have an object and an image which is produced 'in' the mirror (as it is a virtual image).

Experiment 1 - number of images

If we begin to use two mirrors which we hinge together along one side and change the angle between them the path of the light and the number of images can be altered.

Equipment

Two plane mirrors
Sellotape to hinge them
A protractor
A small object such as a pencil sharpener

Method

Place the object on your page and draw a line a few centimetres away from it to place one of the mirrors along - this one will be fixed. Adjust the angle between the mirrors to 180 degrees (so flat) and note that including the object you can see two of whatever it is you have chosen.

Keeping the one mirror still slowly reduce the angle between the mirrors stopping when you have three versions of your object - i.e. the object and two reflections. Note the angle between the mirrors.

Repeat this for additional whole numbers of object + images, nothing the angle each time.

Results

You should see a clear pattern between the angles and the number of objects - if not then consider dividing the angle in a complete circle by the number of object & images you saw at each step.

Experiment 2 - the corner reflector

This experiment demonstrates how a combination of mirrors can be used to reflect light back parallel to its initial path - an arrangement which is used in the reflectors on bicycles.

Equipment

Two plane mirrors
Sellotape to hinge them
A protractor
A ruler
A single slit raybox and powerpack
A sharp pencil

Method

Fix the mirrors such that the angle between them is 90 degrees.
Place them on a page and shine a ray from the raybox so that it bounces of both mirrors.
Mark the path of the ray with dots and then remove the mirror so you can join them with the ruler. Add arrows to show the direction the ray travelled.

Try this for a different incident angle, and again mark the rays.

Results

You should notice the the reflection off the second mirror is parallel to the incident ray. Use the law of refelction to see if you can explain why this should be. (Hint - think about the angle the normal is to the mirror surface)















Reflection 1 - Plane Mirrors

This experiment seeks to demonstrate the law of reflection - the angle of incidence is equal to the angle of reflection when measured from the normal.

Equipment

Single slit raybox with power supply
Paper
Ruler
Protractor
Sharp Pencil
Plane mirror
Support for mirror (e.g. wooden block with a groove in, or plasticine)

Method

Draw a line on the paper. Place the mirror on the line and support it so it does not move.
Shine the beam from the raybox towards the mirror. Use the pencil to carefully mark two dots in the centre of the incident and reflected rays.
Move the mirror to one side and use the ruler to join the dots to show the complete path of the ray. Add arrows so you know which direction the ray travelled.
At the point where the ray reflects from the mirror add a line perpendicular to the mirrors surface - this is the normal line.
Use the protractor measure the angle between the normal and the incident ray, and the normal and the reflected ray.

Note these angles in a table and then repeat the experiment for at least three more different angles.

Care should be taken when moving the raybox as those which use an incandescent bulb can get hot to the touch.

Results

You should find that the results show that the incident angle and reflected angle are equal. Your results may be a little out, due to errors introduced with how carefully you marked the path, the normal and measured the angle.