C12 Chemical Analysis Flashcards
What is a pure substance
A sample containing only one element or compound
How is purity worked out
Pure substances have specific melting and boiling points
The closer the value of an experiment are to those in the data book, the greater the purity of a sample
What happens in the two phases of chromatography
Substances are picked up and carried by a mobile phase (liquid or gas)
The mobile phase then moves through a stationary phase (solid or viscous liquid)
How are substances separated in chromatography
They are distributed across the two phases
A substance moves far if it’s more attracted to the mobile phase
A substance doesn’t move far if it’s more attracted to the stationary phase
What happens in paper chromatography
Mixtures of soluble substances are separated
A solvent (mobile phase) is run through the mixture on paper (contains the stationary phase)
The substances will move up the paper at different rates
The most soluble substance will move the furthest
How is retention factor calculated
Distance travelled by substance / distance travelled by solvent
What is a reference substance
A pure substance run next to the tested substance to see if it’s a component in the mixture
This is evidence, not proof
What affects how far components travel in paper chromatography
The less attracted to the paper, the further it travels
The more soluble in the solvent, to further it travels
What does the process of chromatography produce that can be analysed?
Chromatogram
What can the number of spots produced by a mixture depend on
Solvent used
How is hydrogen tested for
Place a lit splint next to the mouth of the test tube
A squeaky pop shows the presence of hydrogen
This is produced due the rapid burning of hydrogen in the presence of oxygen to give H20
How is oxygen tested for
Insert a glowing splint into the test tube
The splint relighting shows the presence of oxygen
How is carbon dioxide tested for
Bubble the gas into an aqueous solution of lime water (calcium hydroxide)
The lime water going cloudy shows the presence of carbon dioxide
How is chlorine tested for
Insert damp litmus paper into the test tube
The paper bleaching shows the presence of chlorine
What is a flame test
Some positive metal ions produce characteristic flame colours that can be used to identify the ion
What does Li+ produce in a flame test
Crimson flame
What does Ca2+ produce in a flame test
Orange-red flame
What does Na+ produce in a flame test
Yellow flame
What does Cu2+ produce in a flame test
Green flame
What does K+ produce in a flame test
Lilac flame
Why is it problematic for interpreting the results of a flame test if a sample is made up of multiple ions?
If the sample consists of a mixture of metal ions, the flame colours of some may be masked, which can lead to incorrect interpretations
What metal hydroxides create white precipitates from aqueous solutions when reacted with sodium hydroxide
Calcium hydroxide
Ca2+
Magnesium hydroxide
Mg2+
Aluminium hydroxide
Al3+
Can dissolve in excess producing a colourless solution
What are precipitates
Insoluble solids
What metal hydroxides create coloured precipitates in aqueous solutions from a reaction with sodium hydroxide
Copper(II) hydroxide
Cu2+
Blue
Iron(II) hydroxide
Fe2+
Green
Iron(III) hydroxide
Fe3+
Brown
How are carbonates tested for
A reaction between a carbonate and a dilute acid produces carbon dioxide
We can use the standard carbon dioxide test to work out if an unknown substance is a carbonate
What ions are carbonates characteristic of
CO3 2-
What products are formed from carbonates and dilute acids
Salt
Carbon dioxide
Water
How are halides tested for
A reaction between halides and silver nitrate from a precipitate
The colour of the precipitate can determine what ions are present
What colour precipitate do chlorine ions produce when reacted with liver nitrate
White
What colour precipitate do bromine ions produce when reacted with sliver nitrate
Cream
What colour precipitate do iodine ions produce when reacted with sliver nitrate
Yellow
Why is dilute nitric acid added to a solution before testing for halides
This removes carbonate ions
These could disrupt results by forming a precipitate with silver ions
How are sulfates tested for
A reaction between sulfates and barium chloride forms a white precipitate
Why is dilute hydrochloric acid added to a solution before testing for sulfates
This removes carbonate ions
These could disrupt results by forming a precipitate with barium ions
What ions are sulfates characteristic of
SO4 2-
What ions do halogens typically form
Halide anions
E.g. K-, Br-
What are the disadvantages of instrumental methods
Instruments are often expensive
Need special training to operate
Results are only useful when compared to data from known substances
What are the advantages of instrumental methods
Greater sensitivity and accuracy
Quicker at producing results
Able to analyse tiny samples
What is flame emission spectroscopy
Instrumental method used to identify and find the concentration of metal ions present in a solution
How are flame emission spectroscopies carried out
Sample of metal solution is placed into a flame
The light that is given off is captured by a spectroscope
This instrument generates a line spectrum by distinguishing between light with different wavelengths
How are line spectra from flame emission spectroscopies analysed to identify ions
Each metal ion will generate a new line spectrum
This means that we can identify all ions present in a solution
How are line spectra from flame emission spectroscopies analysed to find the concentration ions
The concentration of an ion is indicated by the intensity of line spectra
What are reference spectra
A known spectrum from a specific metal ion used to analyse data through comparison
