C7.5 Chemical Analysis

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  • Created by: Lili
  • Created on: 19-06-13 17:50
What do Chemists Use Qualitative Analysis For?
To identify chemicals in a sample.
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What do Chemists Use Quantitative Analysis For?
To find out amounts of chemicals.
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Why is it Important That Samples for Analysis are Collected Properly?
The sample must represent the bulk of the material.
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Why is it Important That Samples for Analysis are Stored Properly?
The sample must not 'go off' or be contaminated.
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Why is it Important That Samples for Analysis are Prepared Properly?
The sample is often dissolved in solution.
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In Chromatography What does a Mobile Phase Move Through?
The mobile phase moves through the stationary phase. A chemist adds a sample of mixture to the stationary phase. The mobile phase flows along this makes the chemicals in the sample move through the stationary phase.
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Each Chemical Moves at a Different Speed, So the Chemicals Separate. Why is This?
It is because there molecules distribute themselves between the mobile and stationary phases. For each chemical there is a dynamic equilibrium between the 2 phases.
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What Does the Position Of Equilibrium Determine?
It determines how quickly a chemical moves. If the Equilibrium lies towards the mobile phase, the chemical moves quickly.
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What is the Stationary Phase in Paper Chromatography?
It is the chromatography paper.
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What is the Stationary Phase in Thin-Layer Chromatography (TLC)?
It is an absorbent solid supported on glass or plastic.
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What is the Mobile Phase in Both TLC and Paper What is the Stationary Phase in Paper Chromatography?
It may be an aqueous solvent (water) or a non-aqeuos solvent (one with no water in it).
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To Analyse a Sample by Paper Chromatography or TLC You...1
Prepare the paper or slide - draw a pencil line and add a drop of the sample. Put spots or reference material solutions on the line, These are substances you might suspect in the unknown mixture.
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To Analyse a Sample by Paper Chromatography or TLC You...2
Run the Chromatogram - Set up the apparatus. When the solvent gets near the top, take out the paper or plate. Mark the solvent front.
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To Analyse a Sample by Paper Chromatography or TLC You...3
Locate the Separated Chemicals - Use pencil to draw around coloured dots. Use locating agent to find colourless spots.
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To Analyse a Sample by Paper Chromatography or TLC You...4
Interpret the Chromatogram - Identify spots by comparing them with reference material spots. OR Calculate a chemicals retardation factor.
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How do you Calculate a Chemical's Retardation Factor (Rf)?
Rf= Distance Moved by Chemical/Distance Moved by Solvent
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How Does Gas Chromatography (GC) Work?
It separates and detects chemicals. Chemists use it qualitatively and quantitatively.
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What is the Stationary Phase and Mobile Phase in GC?
SP= A thin film of liquid on the surface of a powder. MP= a carrier gas (helium)
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To analyse a sample by GC You...1,2
Use the oven to keep the column at the correct temperature; Turn on the carrier gas and adjust its flow;
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To analyse a sample by GC You...3
Inject the sample where the column enters the oven. The chemicals in the sample become gases and mix with the carrier gas. The mixture moves through the column to the detector;
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To analyse a sample by GC You...4
Interpret the chromatogram, each peak represents one compound. The position of a peak shows it retention (time for it to pass through the column), Peak heights show relative amounts of substance.
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Why do Chemists Use Titrations?
To check purity and to find out the amount of chemicals that react together.
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To Use an Acid-Base Titration to Find the Concentration of a Sodium Hydroxide Solution You...1
Make up a standard solution of acid and pour it into a burette, read the burette scale.
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To Use an Acid-Base Titration to Find the Concentration of a Sodium Hydroxide Solution You...2,3
Use a pipette to measure accurately a fixed volume of sodium hydroxide solution. Put it in a conical flask; Add a few drops of indicator.
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To Use an Acid-Base Titration to Find the Concentration of a Sodium Hydroxide Solution You...4
Add acid from the burette. Stop when the indicator changes colour. Read the burette scale. Calculate the amount of acid added. This rough titration gives an idea of how much acid you need to neutralise the sodium hydroxide, or reach the end point.
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To Use an Acid-Base Titration to Find the Concentration of a Sodium Hydroxide Solution You...5,6
Repeat the procedure, but add the acid one drop at a time when you near the end point. Continue until you have 3 consistent values for the volume of acid; Calculate the mean and range for your results.
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How Do You Prepare a Solution of Sodium Carbonate with an Accurately Known Concentration?..1,2,3
1. Accurately weigh the sodium carbonate. 2. Dissolve the solute in a small amount of solvent, warming it if necessary. 3.Transfer the sodium carbonate solution to a graduated flask.
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How Do You Prepare a Solution of Sodium Carbonate with an Accurately Known Concentration?..4,5,6
4.Rinse all the solution into the flask with more solvent. 5. Add solvent drop by drop to make up the volume to the mark on the flask. 6. Stopper and shake flask.
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What is the Titration Triangle?
Concentration= Mass of Solute/Volume of Solute
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Card 2

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What do Chemists Use Quantitative Analysis For?

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To find out amounts of chemicals.

Card 3

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Why is it Important That Samples for Analysis are Collected Properly?

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Card 4

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Why is it Important That Samples for Analysis are Stored Properly?

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Card 5

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Why is it Important That Samples for Analysis are Prepared Properly?

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