1- Make chromatograms for all the unknown substances you want to identify
2- Make chromatograms of known substances for references (e.g. substances that you think might be in the ink)
3- Now compare the chromatograms to work out what dyes are in your unknown substance - spots on the unknown substance will match spots on the reference materials should the dyes be the same.
Showing posts with label atoms. Show all posts
Showing posts with label atoms. Show all posts
Tuesday, 15 March 2016
1.7 Describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallisation and paper chromatography
Simple distillation
This is used to separate out a liquid from a solution.
Method
1- The solution is heated until the part of the solution that has the lowest boiling point evaporates
2- The vapour is cooled, condensed and collected
3- The rest of the solution is just left in the flask.
You can use simple distillation to get pure water from seawater, for example.
Problems: you can only use it to separate out solutions that have very different boiling points, if you have a mixture with similar boiling points, you need to use fractional distillation to separate them.
Fractional distillation
This is used to separate out a mixture of liquids.
Method
1- Put the mixture in a flask and put a fractionating column on top.
2- Heat the flask
3- The different liquids will all have different boiling points, so they will all evaporate at different temperatures. The liquid with the lowest boiling point will evaporate first, when the temperature on the thermometer (attached to the fractionating column) reaches the boiling point of this liquid, the liquid will evaporate and reach the top of the column.
4- This liquid will condense down the tube and run into an empty test tube waiting at the bottom.
5- Once the first liquid has been collected, raise the temperature until the next one reaches the top.
Problems: Liquids with higher boiling points high may also start to evaporate. However, the fractionating column is cooler towards the top, so these will only get part way up before condensing and running back down into the flask.
Filtration
Filtration is used to separate an insoluble solid and a liquid.
Crystallisation
This can be used to separate a soluble solid from a solution.
1- Pour the solution into an evaporating dish (also known as a crucible)
2- Heat the solution, this will cause the solution to start to evaporate, stop heating when crystals start to form
3- Remove the dish from the heat and leave it in a warm place for the rest of the solvent to evaporate - this will result in big crystals
4- Dry the product using a drying oven or a desiccator.
Paper chromatography
Method
1- Draw a line near to the bottom of a sheet of filter paper (use a pencil as they are insoluble and won't react with the solvent)
2- Add dots of different dyes to the line at regular intervals.
3- loosely roll the sheet up and put it in a beaker of solvent. The solvent used will depend on what is being separated - some compounds dissolve well in water while others dissolve well in ethanol. Make sure the dyes are not touching the solvent (you dont want them to dissolve)
4- Place a lid on the container to stop the solvent evaporating - NOTE: this step is kind of optional, if your only doing chromatography for a few minutes rather that hours or days, it can be skipped out.
5- Should all go well, the solvent will seep up the paper, carrying the dyes with it. Each dye should move up the paper at a different rate, forming sport at different places on the paper.
The end result is a pattern of spots, this is known as a chromatogram.
This is used to separate out a liquid from a solution.
Method
1- The solution is heated until the part of the solution that has the lowest boiling point evaporates
2- The vapour is cooled, condensed and collected
3- The rest of the solution is just left in the flask.
You can use simple distillation to get pure water from seawater, for example.
Problems: you can only use it to separate out solutions that have very different boiling points, if you have a mixture with similar boiling points, you need to use fractional distillation to separate them.
Fractional distillation
This is used to separate out a mixture of liquids.
Method
1- Put the mixture in a flask and put a fractionating column on top.
2- Heat the flask
3- The different liquids will all have different boiling points, so they will all evaporate at different temperatures. The liquid with the lowest boiling point will evaporate first, when the temperature on the thermometer (attached to the fractionating column) reaches the boiling point of this liquid, the liquid will evaporate and reach the top of the column.
4- This liquid will condense down the tube and run into an empty test tube waiting at the bottom.
5- Once the first liquid has been collected, raise the temperature until the next one reaches the top.
Problems: Liquids with higher boiling points high may also start to evaporate. However, the fractionating column is cooler towards the top, so these will only get part way up before condensing and running back down into the flask.
Filtration
Filtration is used to separate an insoluble solid and a liquid.
This can be used to separate a soluble solid from a solution.
1- Pour the solution into an evaporating dish (also known as a crucible)
2- Heat the solution, this will cause the solution to start to evaporate, stop heating when crystals start to form
3- Remove the dish from the heat and leave it in a warm place for the rest of the solvent to evaporate - this will result in big crystals
4- Dry the product using a drying oven or a desiccator.
Paper chromatography
Method
1- Draw a line near to the bottom of a sheet of filter paper (use a pencil as they are insoluble and won't react with the solvent)
2- Add dots of different dyes to the line at regular intervals.
3- loosely roll the sheet up and put it in a beaker of solvent. The solvent used will depend on what is being separated - some compounds dissolve well in water while others dissolve well in ethanol. Make sure the dyes are not touching the solvent (you dont want them to dissolve)
4- Place a lid on the container to stop the solvent evaporating - NOTE: this step is kind of optional, if your only doing chromatography for a few minutes rather that hours or days, it can be skipped out.
5- Should all go well, the solvent will seep up the paper, carrying the dyes with it. Each dye should move up the paper at a different rate, forming sport at different places on the paper.
The end result is a pattern of spots, this is known as a chromatogram.
1.6 Understand the differences between elements, compounds and mixtures
Elements
Elements consist of one type of atom only. Examples include Aluminium, Copper, Iron, Oxygen and Nitrogen.
Compounds
- A compound is a substance that is made of two or more different elements which are bonded together.
- For example, carbon dioxide is a compound formed from the chemical reaction of carbon and oxygen. One carbon atom reacts with two oxygen atoms to form a molecule of CO2, we know its one carbon and two oxygens because the formula is CO2.
- once formed, it is very difficult to separate molecules (as they have been chemically bonded with each other)
- The properties of a compound are often not the properties of the original elements. For example, hydrogen and oxygen are both gases, but when chemically bonded they form a liquid - H2O (water) - at room temperature.
Mixtures
Mixtures are a group of elements and compounds mixed together. They can be easily separated as they are not bonded together, the parts can be separated out by physical methods such as distillation. An example of a mixture is air, it contains nitrogen, oxygen, carbon dioxide and argon - they are not bonded together, which makes them a mixture not a compound.
The properties of a mixture are just the properties of the separate parts. For example, a mixture of iron and sulfur will show the properties of iron and sulfur, it will also look the same - it will contain grey magnetic bits of iron and bright yellow bits of sulfur.
Elements consist of one type of atom only. Examples include Aluminium, Copper, Iron, Oxygen and Nitrogen.
Compounds
- A compound is a substance that is made of two or more different elements which are bonded together.
- For example, carbon dioxide is a compound formed from the chemical reaction of carbon and oxygen. One carbon atom reacts with two oxygen atoms to form a molecule of CO2, we know its one carbon and two oxygens because the formula is CO2.
- once formed, it is very difficult to separate molecules (as they have been chemically bonded with each other)
- The properties of a compound are often not the properties of the original elements. For example, hydrogen and oxygen are both gases, but when chemically bonded they form a liquid - H2O (water) - at room temperature.
Mixtures
Mixtures are a group of elements and compounds mixed together. They can be easily separated as they are not bonded together, the parts can be separated out by physical methods such as distillation. An example of a mixture is air, it contains nitrogen, oxygen, carbon dioxide and argon - they are not bonded together, which makes them a mixture not a compound.
The properties of a mixture are just the properties of the separate parts. For example, a mixture of iron and sulfur will show the properties of iron and sulfur, it will also look the same - it will contain grey magnetic bits of iron and bright yellow bits of sulfur.
1.5 Understand the terms atom and molecule
Atoms
All substances are made up of atoms, they are the smallest thing that can exist. They contain...
- A nucleus (made up of protons and neutrons)
- Electrons
This is a model of an atom (known as the 'nuclear model')...
Molecule
Molecules are two or more atoms bonded together
All substances are made up of atoms, they are the smallest thing that can exist. They contain...
- A nucleus (made up of protons and neutrons)
- Electrons
Nucleus...
- situated in the middle of an atom
- It contains protons and neutrons
- It has a positive charge (because of the protons)
The electrons...
- They move around the nucleus in energy levels called shells
- They are negatively charged
Masses and charges...
- Protons have a relative mass of 1 and a relative change of +1
- Neutrons have a relative mass of 1 and a relative charge of 0
- Electrons have a relative charge of 1/1800 and a relative charge of -1
Molecule
Molecules are two or more atoms bonded together
1.4 describe and explain experiments to investigate the small size of particles and their movement including: i dilution of coloured solutions ii diffusion experiments
Potassium manganate (VII) and water can be used for both of these experiments.
Diffusion experiments
Potassium manganate (VII) works very well for diffusion experiments as its bright purple.
Take a beaker of water and add some potassium manganate (VII) to the bottom. OBSERVATION: the purple colour will slowly spread out to fill the beaker.
This is the particles of potassium manganate (VII) diffusing out among the particles of water. It's the random motion of particles in a liquid that cause the potassium manganate (VII) to eventually be evenly spread out throughout the water.
Dilution of coloured substances
Diffusion experiments
Potassium manganate (VII) works very well for diffusion experiments as its bright purple.
Take a beaker of water and add some potassium manganate (VII) to the bottom. OBSERVATION: the purple colour will slowly spread out to fill the beaker.
This is the particles of potassium manganate (VII) diffusing out among the particles of water. It's the random motion of particles in a liquid that cause the potassium manganate (VII) to eventually be evenly spread out throughout the water.
Dilution of coloured substances
If you were to add even more water to the final purple solution, the potassium manganate (VII) particles would spread out even further and the solution would be less purple.
Subscribe to:
Posts (Atom)