C7.5
- Created by: amy_mair
- Created on: 21-06-16 07:46
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- C7.5
- Analytical Procedures
- Qualitative
- 1. Qualitative analyis tells you which substances are present in a sample
- 2. It does not tell you how much of each substance there is
- Quantitative
- 1. Quantitative analysis tells you how much of a substance there is
- 2. It can be used to work out the molecular formula of the sample.
- Chemical Analysis
- 1. Usually you analyse just a sample of the material under the test there are some reasons for this...
- 2. It might be very difficult to test all of the material if you have got an awful lot it
- 3. Taking a sample also means taht if something goes wrong with the test, you can go back for another simple and try again
- 4. A sample mist represent the bulk of the material being tested
- 1. Usually you analyse just a sample of the material under the test there are some reasons for this...
- Analysis
- They are analysed in a solution
- Samples are usually tested in solution
- A solution is made by dissolving the sample in a solvent
- There are 2 types of solution-aqeous and non aqueous
- An aqueous solution means the solvent is water
- An non aqueous solution means the solvent is anything other than water for example ethanol
- Standerd Procedures
- Everything is done the same way
- 1. Standard procedures are agreed methods of working
- 2. Standard procedures can be agreed within a company
- 3. They are useful because wherever and whenever a test is done
- 4. There are standard procedures for the collection and storage of a sample
- Qualitative
- Analysis- Chromatography
- Phases
- Chromatography is an analytical method used to separate the substance in a mixture.
- You can then use it to identify a substance
- There are a lot of different types of chromatography
- A mobile phase: Where the molecules can move
- A stationary phase: Where the molecules can not move
- 1. The components in the mixture separate out as the mobile phase moves across the stationary phase
- 2. How quickly a chemical moves depends on how it distributes itself between the 2 phases
- 3.The molecules of each chemical constantly move between the 2 phases
- 4. They are said to reach a dynamic equalibrium
- Method
- 1. The solvent moves up the paper
- 2. The chemicals in the sample dissolve in the solvent and move between it and the paper
- 3. When they are in the mobile phase the chemicals move up the paper with the solvent
- 4. Before the solvent reaches the top the paper is removed from the beaker
- 5. The different chemicals in the sample form separate spots on the paper
- Phases
- Analysis Chromatography
- You can calculate the Rf for each chemical
- 1. The result of chromatograpy analyis is called a chromatogram
- 2. Some of the spots on the chromatgram might by colourless. If they are you need to use a locating agent to show where they are
- 3 You need to know how to work out the Rf values for spots on a chromatogram
- Rf = distance travelled by solute / distance travelled by solvent
- 4. Chromatography is often carried out to see if a certain substance is present in a mixure
- 5. Chemists use substances called standard referance materials to check the identities of substances
- Gas Chromatography
- Gas Chromatography is used to analyse unknown substances
- The mobile phase is an unreactive gas such as nitrogen
- The stationary phase is a viscous liquid
- 1. The unknown mixture is injected into a long tube coated on the inside with the sationary phase
- 2. The mixture moves along the tube with the mobile phase untill it comes out the other end.
- 3. The time it takes a chemical to travel through the tube it is called the retention time
- 4. The retention time is different for each chemical
- The distance along the x axis is the retention time
- The peak height shows you how much of that chemical was in the sample
- You can calculate the Rf for each chemical
- Analysis- Solution concentrations
- Concentration= mass/volume
- A standard solution is any solution hat you know the concentration of. Making a standard solution needs careful measuring
- 1. First work out how many grams of solute you need by using the formula
- 2. Carefully weigh out this mass of solute
- 3. Add a small amount of ditilled water to the beaker and stir until all the solute has disolved
- 4. Tip the solution into a volumetric flask
- 5. Rince the beaker and stirring rod with distilled water and add to the fask
- 6. Top flask up to correct volume
- 7. Stopper the bottle and turn it upside down
- 8. Check the meniscus again and add a drop or two of water
- Analysis- Titration
- How to get consistent readings
- 1. Sometimes you get an outlier. This might be caused by faulty equipment or human error
- 2. If your values are very similar you can be confident your results are reliable
- 3. If they are more spread out, you can not be so certain of what the true value is
- Then you need to repeat the results carefully
- Interpreting
- You can use titrations wo work out the identity of an unknown element in a compound
- Step 1: First find out the mass of acid and the mass of alkali that react
- Step 2: Find the relative formula mass of the known solute
- Step 3: Find the relative formula mass of the unknown solute using the balanced equation
- Step 4: Identify the metal hydroxide
- How to get consistent readings
- Analytical Procedures
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