Chemical analysis Flashcards
What is purity in chemistry?
Something that only contains one element or compound
How can the boiling/melting point of a substance tell you how pure it is?
All pure substances melt or boil at a specific temperature so the closer the value measured is to the boiling/melting point it is purer.
What will impurities do to your substance?
It will lower the melting point and increase the boiling point whilst also increasing the range of temperatures.
What is a formulation?
A formulation is a mixture made in a specific way for a specific purpose and recipe.
What can formulations be used for?
In the pharmaceutical industry for pills, paint, fuels, cleaning products.
What is paper chromatography
It is an analytical method to separate the substances in a mixture.
What is the mobile phase?
Where the molecules can move - this is a liquid or a gas.
What is the stationary phase?
Where the molecules cannot move- this is a solid or a thick liquid.
What do substances do between the phases and how does this affect how long a molecule moves?
Substances move between the two phases and an equilibrium is formed. How far a molecule moves depends on how long it spends in the mobile phase.
Why do some molecules spend in longer in a certain phase?
How soluble they are in the solvent and how attracted they are to the paper. If they have a high solubility and are less attracted to the paper they will be in the mobile phase for longer.
How can we analyze what is in a mixture in paper chromatography?
The different spots of chemicals will separate and we will see them distributed out.
What is the Rf value?
It is the ratio between the dissolved substance and the distance travelled by the solvent front.
How do you calculate the Rf value?
distance travelled by substance/ distance travelled by solvent.
How do you test for chlorine?
Chlorine bleaches litmus paper but it may turn red for a second.
How do you test for oxygen?
Place a glowing splint into a test tube and it will relight if oxygen is present.
How do you test for hydrogen?
Place lit splint and there will be a squeaky pop if hydrogen is present.
How do you test for carbon dioxide?
Bubble carbon dioxide through limewater and if it is present it will turn cloudy.
How do you test for carbonates?
Add a couple of drops of dilute acid and then connect it to a tube of limewater. If carbonates are present it will turn cloudy.
How do you test for sulfates?
Add a few drops of dilute hydrochloric acid and barium chloride to the test tube. If there are sulfate ions present a white precipitate will form.
How do you carry out flame tests?
Clean a platinum loop with HCL and hold it to a blue bunsen burner until it burns without color. Next, dip the loop into the sample and record the colour of the flame
What color flame will lithium ions produce?
Crimson
What color flame will sodium ions produce?
Yellow
What color flame will potassium ions produce?
Lilac
What color flame will calcium ions produce?
Orange-red
What color flame will copper ions produce?
Green
How do you test for metals?
Metal hydroxides are insoluble and precipitate out of solution. These have certain colors. So add drops of sodium hydroxide solution to the metal.
What is the color of the precipitate for calcium?
White
What is the color of the precipitate for copper?
Blue
What is the color of the precipitate for iron (II)?
Green
What is the color of the precipitate for iron (III)
Brown
What is the color of the precipitate for aluminium?
White at first but redissolves in excess NaOH to form a colorless solution.
What is the color of the precipitate for magnesium?
White
How do you test for halides?
Add some dilute drops of dilute nitric acid and some silver nitrate solution.
What does chloride give as a precipitate?
A white precipitate and silver chloride.
What does bromide give as a precipitate?
A cream precipitate and silver bromide
What does iodide give as a precipitate?
A yellow precipitate and silver iodide.
What is flame emission spectroscopy?
A sample is placed in a flame. As the ions heat up the electrons get excited and drop back to their original energy levels and at this point, they transfer energy through light. The light goes through a spectroscope which detects different wavelengths of light to produce a line spectrum,
Why is there a different combination of wavelengths?
This depends on the charge and electron arrangement so they will emit different wavelengths of light.
What does the intensity of the light indicate?
The concentration of the ion.
Why is flame emission spectroscopy better than flame tests?
They can be used for mixtures, not just a single ion.
What are the advantages of flame emission spectroscopy?
Accurate, fast, and sensitive.
