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
Difference between pure and impure substances’ MP & BP
a pure substance melts and boils at specific temperature and these fixed points can be used to identify them. A mixture does not have a sharp melting or boiling point and it changes 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
Paint formulation contents
- A pigment to provide colour
- A binder to help the paint attach itself to objects and to form a protective layer when dry
- A Solvent to help the pigment and binder spread well during painting by thinning them out
Describe Chromatography in terms of phases
Chromatography involves a mobile and stationary phase. The mobile phase moves through the stationary phase, carrying the components of the mixture being investigated with it
Describe why some substances are carried a great distance in a given time
A substance with stronger forces of attraction between itself and the mobile phase than between itself and the stationary phase will travel a greater distance in a given time because different components in the mixture will have different attractions for the mobile and stationary phase
What are the steps of chromatography
- Draw a base line in pencil (so it doesn’t dissolve in solvent) and draw crosses at equal distances
- Place drops of different dyes on the base line using a capillary tube
- Place paper in solvent with solvent below the base line
- Dry paper and calculate the distance moved by the solvent and the Rf (retention factor) value of each substance. The result of chromatography analysis is called a chromatogram
What is the Rf value and the formula
An Rf value is the ratio between the distance travelled by the dissolved substance (dilute) 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 a mixture
Run a pure sample of that substance (a reference) alongside the unknown mixture. If the Rf values match the substance may be present. Repeat this with different substances and if the Rf always matches then the reference compound is found in the mixture
The test for chlorine gas
Bleached damp blue litmus paper and turns it white
The test for oxygen
If you put a glowing splint inside a test tube contains oxygen, the oxygen will relight the glowing splint
The test for carbon dioxide
Bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) causes the solution to turn cloudy
What is the 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’. The noise comes from the hydrogen burning quickly in the oxygen in the air to form water
What ions do carbonates contain
CO3^2- ions
What is the test for carbonates
Use a dropping pipette to a dad a few drops of dilute acid to a test tube containing the mystery substance. Then connect the test tube to a test tube containing lime water. If carbonate ions are present, their reaction with the acid will release carbon dioxide which will turn the limewater cloudy as it bubbles through it
What ions do sulfates contain
SO4^2- ions
How to test for sulfate ions
Use a dropping pipette to add at couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution to a test tube containing the mystery solution. If sulfate ions are present a white precipitate of barium sulfate will form
Describe the test for halide ions
Add a couple of drops of dilute nitric acid followed by a couple of drops of silver nitrate solution to your mystery substance
Describe the results for different halide ions
- A chloride will give a white precipitate of silver chloride
- A bromide will give a cream precipitate of silver bromide
- An iodide will give a yellow precipitate of silver iodide
Describe how to carry out the flame test for metal ions
- Dip a nichrome wire loop in concentrated hydrochloric acid and heat it to clean it until the blue flame stays blue
- Then dip it in the acid again before dipping it in the metal compound being tested
- Hold the loop in the blue flame of the bunsen burner and record the colour of the flame
Results for the flame test
- Lithium ions (Li+), produce a CRIMSON flame
- Sodium ions (Na+) produce a YELLOW flame
- Potassium ions (K+) produce a LILAC aflame
- Calcium ions (Ca2+) produce a ORANGE-RED flame
- Copper ions (Cu2+) produce a GREEN flame
Describe the sodium hydroxide test to test for metal ions
Many metal hydroxides are insoluble and precipitate out of solutions when formed. Some of these hydroxides have a characteristic colour.
In this test add a few drops of sodium hydroxide to a solution of the mystery compound
Results of the sodium hydroxide test
- Calcium (Ca2+) forms a white precipitate
- Copper (II) forms a blue precipitate
- Iron (II) formed a green precipitate
- Iron (III) forms a brown precipitate
- Aluminium (Al3+) forms a white precipitate at first but then redissolves in excess NaOH to become colourless
- Magnesium (Mg2+) ions form a white precipitate
How does flame emission spectroscopy work
A sample is placed in a flame and as the ions heat up their electrons become excited and move to a higher energy level. When the electrons drop back to their original energy levels they release energy as light. This light passes through a. spectroscope which can detect different wavelengths of light to produce a spectrum. Every ion will have a different line spectrum and the intensity of the spectrum indicates the concentration of the ion in the solution
Pros of using instrumental analysis
- Small sample sizes can be analysed as they are very sensitive
- Very fast and tests can be automated
- Very accurate
Cons of using instrumental analysis methods
- Requires training to use
- Results often need to be compared to known substances
- Expensive
