Paper 2 C8 - Chemical Analysis Flashcards
Define pure substance
A single element or compound (not mixed in with any other substance)
Name two things that can be used to distinguish between pure and impure substances
- Melting point
- Boiling point
Explain how melting and boiling points can be used to distinguish between pure and impure substances
- Pure substances have a specific boiling and melting point
- Impure substances melt/boil over a range of temperatures
Impure substances normally melt at a _________ temperature than pure substances.
Lower
Define formulation
Mixture made for a specific purpose
State how formulations are made
Mixing specific amounts of chemicals to get certain properties
Give five examples of formulations
Any five from:
- Alloys
- Paint
- Medicine
- Fuels
- Fertilisers
- Cleaning agents
- Foods
Outline the purpose of chromatography
Separate mixtures into their components and identify them
Name the two phases in chromatography
- Stationary phase
- Mobile phase
Identify the stationary phase in chromatography
The chromatography paper
Identify the mobile phase in chromatography
The solvent
Describe the relationship between the solubility of a substance and how far it moves up the paper in chromatography
The more soluble the substance, the further up the paper it moves (and vice versa)
Name the value that is used to identify substances in chromatography
Rf value
Give the equation used to calculate the Rf value of a substance
distance travelled by substance/distance travelled by solvent
Outline the difference between the appearance of a mixture and a pure substance on chromatography paper
- Mixture will produce multiple spots
- Pure substance will only produce one spot
Write a method for chromatography
- Draw pencil start line on chromatography paper
- Place spot of [mixture] on start line
- Place [solvent] in a beaker
- Place chromatography paper in solvent
–> [solvent] should be below start line - Use a lid
- Wait for solvent to travel up chromatography paper
- Mark solvent front
- Dry the chromatography paper
Write a method to test for hydrogen, including the positive result
Place a burning splint at the open end of a test tube of the gas
—> Will burn with a squeaky pop
Write a method to test for oxygen, including the positive result
Place a glowing splint inside a test tube of the gas
—> Splint will relight
Write a method to test for carbon dioxide, including the positive result
Bubble through limewater
—> Limewater will turn cloudy
Write a method to test for chlorine, including the positive result
Place damp litmus paper into a test tube of the gas
—> Litmus will be bleached white
Name the two methods used to identify metal ions
- Flame test
- Metal hydroxide test
Write a method for a flame test
- Clean wire (using HCl)
- Dip wire into unknown compound
- Place in roaring (blue) flame
- Observe the colour
Name the 5 metal compounds that can be detected through flame tests
- Lithium
- Sodium
- Potassium
- Calcium
- Copper
(LSPCC)
Name the colour produced from a positive lithium flame test
Crimson
Name the colour produced from a positive sodium flame test
Yellow
Name the colour produced from a positive potassium flame test
Lilac
Name the colour produced from a positive calcium flame test
Orange-red
Name the colour produced from a positive copper flame test
Green
State why mixtures of ions are difficult to detect using flame tests
Some colours can be masked by others
Define precipitate
Insoluble product/solid formed from a reaction
State what determines the ion in a metal hydroxide test
Colour of precipitate
Write a method for a metal hydroxide test
- Put unknown solution in test tube
- Add sodium hydroxide
Give the positive result for copper (II) from a metal hydroxide test
Blue precipitate
Give the positive result for Iron (II) in a metal hydroxide test
Green precipitate
Describe a positive result for Iron (III) in a metal hydroxide test
Brown precipitate
Name the three metals that form a white precipitate in a metal hydroxide test
- Aluminium
- Calcium
- Magnesium
Name the metal precipitate that dissolves when excess sodium hydroxide is added
Aluminium
Write the word equation for reaction between carbonate ions and acids
carbonate ions + acid –> carbon dioxide + water
Write a method to test for carbonate ions, including the positive result
- Put carbonate into a test tube
- Add dilute hydrochloric acid
- Bubble through limewater
—> Limewater turns cloudy
Give the positive result for a carbonate ion test
Limewater turns cloudy
Name the chemical used to test for sulfate ions
Barium chloride
Write method to test for sulfate ions, including the positive result
- Add sulfate to test tube
- Add dilute hydrochloric acid
- Add barium chloride
—> White precipitate will form
Name the white precipate formed in a positive sulfate ion test
Barium sulfate
Write the word equation for the reaction of magnesium sulfate with barium chloride
magnesium sulfate + barium chloride –> barium sulfate + magnesium chloride
Write a method to test for halide ions
- Add halide to test tube
- Add nitric acid
- Add silver nitrate solution
Give the result for a positive chloride test
White precipitate
Give the result for a positive bromide test
Cream precipitate
Give the result for a positive iodide test
Yellow precipitate
Name the three precipitates that can form from a positive halide ion test
- Silver chloride
- Silver bromide
- Silver iodide
Give three qualities of instrumental methods (carried out using a machine) that make them better than chemical tests
- Rapid
- Sensitive
- Accurate
Give an example of an instrumental method used to detect/identify elements and compounds
Flame emission spectroscopy
Expain how flame emission spectroscopy works
- Sample is placed into a flame
- Light given off is passed through a spectroscope
- Spectroscope splits light up into different wavelengths
- Each ion produces a different line spectrum
State one thing that flame emission spectroscopy can do that flame tests cannot
Detect mixtures of metal ions and their concentrations
