C12 - Chemical Analysis Flashcards
What is a pure substance
one that is made up of just one substance. That substance can be either an element or a compound
what is an impure substance
a mixture of two or more different elements or compounds
What is different between the boiling and melting points of pure and impure substances
Pure substances melt and boil at specific temperatures (fixed points) and impure substances don’t have a sharp melting or boiling point and change state over a range of temperatures
What are formulations
Useful mixtures made up in definite proportions, designed to give a product the best properties possible to carry out its function and
What is a mobile and stationary phase
The mobile phase moves through the stationary phase, carrying the components of the mixture being investigated with it
What happens if a substance has stronger forces of attraction between itself and the mobile phase than for the stationary phase
The substance will be carried a greater distance in a given time. The further through the stationary and user a substance moves, the larger the Rf value
What is the mobile and stationary phase in paper chromatography
The mobile phase is the solvent chosen and the stationary phase is the paper
Instructions on how to carry out paper chromatography
- Draw a base line in pencil (so it doesn’t dissolve in the solvent) near the bottom of the paper and draw crosses at equal distances
- Place drops of different dyes at equal distances on the base line using a capillary tube
- Place paper in a beaker with the solvent with the solvent below the base line
- Then dry the paper and calculate the distance moved by the solvent and the Rf value of each substance
What is the Rf value and how is it calculated
The Rf (Retention Factor) value is the ratio between the distance travelled by the dissolved substance (solute) and the distance travelled by the solvent
Rf = distance travelled by substance/ distance travelled by solvent
How to tell if a certain substance is present in the mixture
Run a pure sample of that substance (a reference) alongside the unknown mixture and repeat with different solvents. If the Rf values match in all substances, the substance is present
How to test for chlorine
Chlorine bleached damp blue litmus was paper and turns it white
How to test for Oxygen
if you put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint
How to test for carbon dioxide
Bubble the gas through an aqueous solution of calcium hydroxide (limewater) and it will turn cloudy if the gas is carbon dioxide
How to test for hydrogen
If you hold a burning splint at the open end of a test tube containing hydrogen, you’ll get a ‘squeaky pop’. This noise comes from the hydrogen burning quickly in the oxygen in the air to form water
How to test for CO3^2- (carbonate) ions in carbonates
- Add a few drops of a dilute acid to a test tube containing the mystery substance
- Then connect the test tube to a test tube contains limewater
- If carbonate ions are present, the solution will effervesce and the reaction will release carbon dioxide which will turn the limewater cloudy
How to test for sulfate ions (SO4^2-)
- Use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution (BaCl2)
- If sulfate ions are present, a white precipitate of barium sulfate will form
Ba^2+ + SO4^2- —> BaSO4
How to test for halide ions and determine which halide is present
Add a couple of drops of dilute nitric acid followed by a couple of drops in f silver nitrate solution to your mystery solution
•A chloride will give a white precipitate of silver chloride Ag+ + Cl- —> -AgCl
•A bromide will give a cream precipitate of silver bromide Ag+ + Br- —> AgBr
•An iodide will give a yellow precipitate of silver iodide Ag+ + I- —> AgI
How to test for metal ions using the flame test and what ions it tests for
- First dip a nichrome wire loop in concentrated hydrochloric acid and heat it to clean it until the flame remains blue
- Then dip the wire loop into the acid again before dipping it into the metal compound being tested
- Hold the loop in the blue flame of the bunsen burner and record the colour of the flame
The flame test tests for Lithium, Sodium, Potassium, Calcium and Copper ions
How to determine which metal ion is present from the colour of the flame
- Lithium Ions (Li+) produce a Crimson flame
- Sodium ions (Na+) produce a Yellow flame
- Potassium ions (K+) produce a Lilac flame
- Calcium ions (Ca^2+) produce a Orange-Red flame
- Copper ions (Cu^2+) produce a Green flame
How to test for metal ions with sodium hydroxide and what ions it tests for
Many metal hydroxides are insoluble and precipitate our of solutions when formed and some of these hydroxides have a characteristic colour
In this test, add a few drops of sodium hydroxide solution to a solution of your mystery compound
This tests for Calcium, Copper (II), Iron (II), Iron (III), Aluminium and Magnesium ions
How to identify which metal ion is present from adding sodium hydroxide
- Calcium (Ca^2+) - white precipitate
- Copper (II) - Blue precipitate
- Iron (II) - Green precipitate
- Iron (III) - Brown precipitate
- Aluminium (Al^3+) - white precipitate at first but redissolves in excess NaOH to become colourless
- Magnesium (Mg^2+) - white precipitate
Why is light released during flame emission spectroscopy?
A sample is placed in a flame and as the ions heat up, their electrons become excited (they move up to a higher energy level). When the electrons drop back to their original energy levels, they release energy as light.
How does flame emission spectroscopy work
A sample is placed in a flame and releases energy as light. The light passes through a spectroscope which can detect different wavelengths of light to produce a line spectrum
How to determine the substance and concentration from a line spectrum
- The combination of wavelengths emitted by an ion depend on its charge and electron arrangement. This means that no two ions will produce the same wavelengths and so will have different line different line spectrums
- The intensity of the spectrum indicates the concentration of the ion in the solution
What are the pros of instrumental methods
- Small sampler sizes can be analysed as the methods are very sensitive
- Very fast and tests can be automated
- Very accurate
Cons of Instrumental methods
- Require training to use
- Results often need to be compared to known substances
- Expensive
