Chemistry 12, chemical analysis

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How do you test the purity of a substance
Measure its melting or boiling point and compare to the database
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How would you test for pure water?
You would measure its boiling point. If it was 100*c it would be pure water but if it was higher then the substance would have a higher boiling point
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How does an impurity affect a substances melting and boiling point
An impurity raises boiling points and lowers melting points, the size of the difference depends on the number of impurities
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What is a formulation?
A mixture that has been designed as a useful product. It is an impure substance that is important in the pharmaceutical industry
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How do you test for chlorine?
Hold a piece of damp litmus paper over the mouth of the test tube. If the litmus paper bleaches white, chlorine is present
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How do you test for carbon dioxide?
Bubble the gas through limewater. If it turns cloudy then carbon dioxide is present
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What are cations and anions?
Cations are positive ions and anions are negative ions
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How do you carry out a flame test?
1) A nichrome wire is dipped in conc. HCl and heated to clean it, this should be repeated after each metal 2) Dip the wire loop in the metal compound 3)Hold the loop in the blue flame of a bunsen 4) Use the colour of the flame to identify the metal
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What are the limitations of a flame test?
-Colours can be similar -If multiple metals are in the compound the flame may be masked
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What colours do the metals lithium, sodium, calcium, potassium and copper go in a flame test?
~Lithium=Crimson ~Sodium=Yellow ~Calcium=Orange-red ~Potassium=Lilac ~Copper=green
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Which metal ions form a white precipitate when NaOH is added and how do you distinguish them?
Al (3+), Mg(2+) and Ca(2+). Aluminium dissolves in excess NaOH, precipitate disappears. Calcium and Magnesium can be identified in a flame test
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Which metal ions form a coloured precipitate when NaOH is added and what colour are they?
Cu(2+), Fe(3+), Fe(2+). Copper forms a light blue precipitate. Iron (II) forms a light green precipitate which becomes dark green. Iron (III) forms a reddish-brown precipitate
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What is the carbonate test?
-Add dilute HCl to the unknown compound -If fizzing occurs then a carbonate is present -A salt, water and carbon dioxide will form -Carbon dioxide can be tested using limewater
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What is the halide test?
-Add dilute nitric acid to check for carbonates and dissolve the compound -Add silver nitrate solution -A coloured precipitate will form ~Chloride ions- White ~Bromide-Cream ~Iodide-Yellow (the colour darkens down the group)
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What is the sulfate test?
-Add HCl, to check for carbonate ions -Add Barium Chloride solution -If a white precipitate forms, sulfate ions are present
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What are the benefits of instrumental analysis over chemical tests?
-Rapid -Highly accurate and sensitive -Allow very small samples to be analysed -Removes human error
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What is the method for flame emission spectroscopy?
-Used to analyse metal ions -Sample is heated in a flame -The energy provided excites the electrons causing them to jump to a higher energy shell -As the electrons lose energy, they fall back down to their original shell, releasing energy as light
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What is the analysis for flame emission spectroscopy?
-A spectrometer analyses the wavelengths of the light and produces a line spectrum -The wavelength emitted depends on charge and electron arrangement so no ions have the same spectrum -It can be compared to a database to identify the ion(s)
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What is the intensity of lines on a line spectrum from flame emission spectroscopy indicate?
The concentration of the ion, a stronger line means that more of the ion is present
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Other cards in this set

Card 2

Front

How would you test for pure water?

Back

You would measure its boiling point. If it was 100*c it would be pure water but if it was higher then the substance would have a higher boiling point

Card 3

Front

How does an impurity affect a substances melting and boiling point

Back

Preview of the front of card 3

Card 4

Front

What is a formulation?

Back

Preview of the front of card 4

Card 5

Front

How do you test for chlorine?

Back

Preview of the front of card 5
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