Topic 12 - Chemical Analysis Flashcards
How is a pure substance defined?
A pure substance is one that is made up of only one substance, this substance being either an element or a compound.
What are fixed points of an element?
Melting and boiling points.
Why are fixed points useful for chemical analysis?
Since you can heat a mixture to identify substances if you know their fixed points in relation to other substances.
What are formulations?
A formulation is a mixture that has been designed to produce a useful product. Many consumer products are formulations.
How are formulations used in medicine?
Medicinal drugs are formultions, often containing 5-10% of the active drug, which helps the body relieve sickness. If taken in tablet form, they can contain colourants, sweetners, smooth coatings amongst other things to aid swallowing.
What two phases do chromatograms always contain?
A mobile phase and stationary phase.
How does the mobile phase of a chromatogram work?
The mobile phase moves through the stationary phase, carrying the components of the mixture up with it. Each component will have a different attraction for the mobile and stationary phases. A substance with stronger forces of attraction between itself and the mobile phase than the stationary phase will be carrie a greater distance within a given time.
What is the line drawn at the top of the chromatogram called?
The solvent front.
What is an Rf value?
The retention factor value is a ratio calculated by dividing the distance a spot moves by the distance the solvent moves.
How do you calculate Rf value?
Rf = distance moved by substance / distance moved by solvent
What is the reaction for the test for hydrogen?
Zinc + Sulphate Acid –> Zinc Sulphate + Hydrogen
What is the hydrogen test?
Hold a lighted splint where the hydrogen gas is meant to go and the splint will ‘pop’
What is the reaction for the test for oxygen?
Hydrogen Peroxide ———-> Water + Oxygen
Manganese (IV) Oxide
What is the oxygen test?
Take a glowing splint near to where the oxygen should come out of the apparatus, the glowing splint should relight.
What is the reaction for the test for carbon dioxide?
Calcium Carbonate + Hydrochloric Acid –> Calcium Chloride + Water + Carbon Dioxide
What is the carbon dioxide test?
Funnel the products of the reaction between marble chips and HCl into a limewater solution. If carbon dioxide is present the limewater will turn cloudy.
What is the test for chlorine gas?
If you hold damp blue litmus paper where the chlorine gas will come out, it will turn white as it becomes bleached.
In a flame test, what colour do Lithium ions (Li+) turn a bunsen flame?
Crimson/red
In a flame test, what colour do Sodium ions (Na+) turn a bunsen flame?
Yellow
In a flame test, what colour do Potassium ions (K+) turn a bunsen flame?
Lilac/purple
In a flame test, what colour do Calcium ions (Ca2+) turn a bunsen flame?
Orange/red
In a flame test, what colour do Copper ions (Cu2+) turn a bunsen flame?
Green
How do you do a flame test?
A nichrome wire loop should be dipped in concentrated hydrochloric acid and then heated to clean it first.
Then it should be dipped in the acid again before dipping it into the metal compound.
Then hold the loop in the roaring blue flame of a Bunsen burner.
Use the colour of the flame to identify the metal ion in the compound.
How does the precipitate reaction work?
Reacting unknown compounds with sodium hydroxide solution leads to a type of precipitate forming.
What precipitate is formed in the precipitate reaction when Copper (II) ions are present?
A blue precipitate.
What precipitate forms in the precipitate reaction when Iron (II) ions are present?
A green precipitate.
What precipitate is formed in the precipitate reaction when Iron (III) ions are present?
A brown precipitate.
What three ions form a white precipitate in the precipitate reaction when they are present?
Al3+ ions, Mg2+ ions, Ca2+ ions.
How do you distinguish between Al3+ ions, Mg2+ ions and Ca2+ ions (since they all form a white precipitate)?
If the solution dissolves in the precipitation reaction they are Al3+ ions. If not then you test for them in the flame test. If there is no colour they are Mg2+ ions, if there is an orange/red colour they are Ca2+ ions.
What is the general equation for carbonate reactions?
If you add a dilute acid to a carbonate, it fizzes and produces carbon dioxide gas.
What do impurities tend to do to a substance’s fixed points?
It lowers melting point and increases boiling point
What do paints contain?
A pigment to provide colour
A binder to help attach itself to an object and form a protective film
A solvent to help the pigment spread well
What do washing-up liquids contain?
A surfactant, to remove grease
Water, to thin out the mixture
Colouring and fragrance additives to improve the appeal of the product
Rinse agent to help water drain off crockery
What examples of formulations do you need to know?
Fuels, alloys, fertilisers, pesticides, cosmetics and food products
What is the formula for testing Iron (II) chloride with sodium hydroxide?
FeCl2 (aq) + 2NaOH (aq) –> 2NaCl(aq) + Fe(OH)2 (s)
What is the ionic equation for testing iron (II) chloride?
Fe2+ (aq) + 2OH- (aq) –> Fe(OH)2 (s)
What is the reaction between magnesium carbonate and hydrochloric acid?
Magnesium carbonate + hydrochloric acid –> magnesium chloride + water + carbon dioxide
What is the ionic equation for the reaction between magnesium carbonate and hydrochloric acid?
CO3 2- (s) + 2H+ (aq) –> CO2 (g) + H2O (l)
Which ion forms a yellow precipitate in the reaction between halide ions and dilute nitric acid?
Iodide ions
Which ion forms a cream precipitate in the reaction between halide ions and dilute nitric acid?
Bromide ions
Which ion forms a white precipitate in the reaction between halide ions and dilute nitric acid?
Chloride ions
What is the equation for the reaction between Potassium Sulfate and Barium Chloride?
K2SO4 (aq) + BaCl2 (aq) –> 2KCl (aq) + BaSO4 (s)
What is the ionic equation for the reaction between Potassium sulfate and Barium Chloride?
Ba2+ (aq) + SO4 2- (aq) –> BaSO4 (s)
What are the advantages of using modern instrumental methods of analysis?
-they are highly accurate and sensitive
-they are quicker
-they enable very small samples to be analysed
What are the disadvantages of using instrumental methods?
-the equipment is very expensive
-it takes special training to use
-gives results that can only be interpreted by comparison with other substances
How does flame emission spectroscopy work?
The sample is heated in a flame
The energy provided excites electrons in metal ions making them jump to higher energy levels
When they fall back to lower energy levels, the energy is released as light energy
What can a spectrometer do in flame emission spectroscopy?
The wavelengths of light produced can be analysed by passing it through a spectroscope.
Each ion absorbs and gives out its own characteristic pattern of radiation.
These patterns are called a line spectrum which can be compared with other ions.
Where else are flame emission spectrometers used?
The steel industry to control the amount of trace metals present.
