C8 - Chemical Analysis Flashcards
What are Pure Substances?
Give Examples of Pure Substances?
Single element or compound, not mixed with any other substance
They Melt and boil over a fixed temperature
What happens to when you increase the temperature of a pure substance compared to an impure substance?
Whereas, in impure substances the water melts over a range of temperatures.
What are Formulations?
Give me Examples of Formulations?
Facts to know about Formulations:
Formulations
A formulation is a mixture that has been designed as a useful product. Many products are complex mixtures in which each chemical has a particular purpose. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
Examples include:
- *- Fuels
- Cleaning products
- Paints
- Medicines
- Alloys
- Fertilisers
- Food**
Give two examples of useful Formulations
- An everyday example of a formulation is paint
- Paint contains the following substances in exact quantities:
- Pigment: gives the paint colour
- Binder: forms a film that holds the pigment in place
- Solvent: used to dissolve the other components and alter the viscosity
- Formulations are very important in the pharmaceutical industry where the exact ratios of each component must be precise
- By changing the formulation of a particular medicine chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it’s safe to consume and has an adequately long shelf life
- The information on the packaging of some products tells you the formulation as a percentage composition
What is chromatography?
What is Rf value?
All separation techniques are physical processes so there are no chemical reactions and no new substances are made.
Paper Chromatography allows us to separate substances based on their solubilities.
The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent can be expressed as its Rf value
How does chromatography take place?
- We take a piece of special paper called chromatography paper
- We draw a pencil line near the bottom
- Then we add a dot of our first colour and next to it we do the dot for the second colour
- Place the bottom of the paper into a solvent (A liquid that will dissolve substances).
- The solvent then makes it way up the paper and it dissolves the ink in the dots. These are now carried up the paper
- After a while the paper will look like this:
Why does paper chromatography work?
What will happen to chemicals strongly attracted to the stationary phase?
What will happen to Chemicals that are weakly attracted?
Chromatography works because Each chemical will be attracted to the stationary phase to a different extent.
Chemicals attracted strongly to the stationnary phase will not move very far
Chemicals weakly attracted will move far
What do we call the paper and why?
What do we call the solvent and why?
What will a pure chemical produce?
Why do we draw our starting line in pencil?
- We call the paper the stationary phase because it does not move.
- We call the solvent the mobile phase** because it moves.
- A pure chemical will produce a single spot whereas a mixture will separate into different spots depending on the solvent.
- We draw our starting line in pencil because if we drew it in pen the ink would travel up the paper.
How do we test for Oxygen?
To test for oxygen we:
- *1. Relight a glowing splint**
- *2. If placed in a test tube of oxygen**
- *3. The splint will relight**
How do we test for Carbon Dioxide?
To test for CO2 we:
- We use limewater(An aqeous soloution of calcium hydroxide)
- Draw some of the gas into a plastic pipette
- Then bubble the gas through limewater
- If repeated the limewater may turn cloudy indicating the presence of carbon dioxide
How do we test for Hydrogen?
To test for hydrogen we:
- We remove the bung from the test tube and insert a burning splint
- Hydrogen gas burns rapidly and produces a pop sound
How do we test for Chlorine
To Test for chlorine we:
- Insert damp litmus paper into the mouth of the test tube.
- Chlorine bleaches the litmus paper and bleaches it white.
What are Flame tests used for?
How do we conduct a flame test?
How do we clean the wire?
Flame tests are used to identify metal ions.
You can conduct a flame test by:
1. Place a small amount of our chemical onto wire mounted in a handle.
- Then place the end of this into a blue Bunsen burner flame
- The colour of the flame can be used to work out metal ion present
- lithium compounds result in a crimson flame
- sodium compounds result in a yellow flame
- potassium compounds result in a lilac flame
- calcium compounds result in an orange-red flame
- copper compounds result in a green flame.
- Dip the loop of an unreactive metal wire such as nichrome or platinum in dilute acid, and then hold it in the blue flame of a Bunsen burner until there is no colour change
- This cleans the wire loop and avoids contamination
- This is an important step as the test will only work if there is just one type of ion present
- Two or more ions means the colours will mix, making identification erroneous
What ion produces a crimson flame?
What ion produces a yellow flame?
What ion produces a lilac flame?
What ion produces a orange/red flame?
What ion produces a green flame?
- Lithium produces a crimson flame.
- Sodium gives a yellow flame.
- Potassium produces a lilac flame.
- Calcium produces orange/red flame.
- Copper ion produce a green flame.
Why is a flame test not reliable?
The colour of the flame test can be difficult to distinguish espicially if there is a low concentration of a metal.
Having a mixture of metals can mask the flame
So we use flame emission spectroscopy
What type of method is FES and why is this method better?
They are instrumental methods.
- They are more Rapid
- They are more Sensitive will work with small sample.
- They are more Accurate as flame tests can be subjective.
- They are automated and can perform multiple simultaneous sampling and testing
Remember u add sodium hydroxide
Metal Hydroxide Precipitates:
What metal ions form a white precipitate
How do you work out which one is aluminium?
How do you work out which one is calcium?
To get the precipitate you need to add sodium hydroxide.
Calcium, magnesium & aluminium are all white precipitates.
For aluminium you need to add excess sodium hydroxide and it will redissolve so we know which is aluminium
For Calcium you need to do a flame test.
Which metal ion produces a blue precipitate.
Which metal ion produces a green precipitate?
Which ion produces a brown Precipitate?
Copper 2 produces a blue precipitate
Iron 2 produces a green precipitate
Iron 3 produces a brown precipitate
How do you identify Non-metal halide ion?
What colour precipitate does Chloride form?
What colour precipitate does Iodide form?
What colour precipitate does Bromide form?
To test for halides we:
- Add Dilute nitric acid to the sample
- Add dilute silver nitrate solution
- Halide ions produce a precipitate of the silver halide. Each halide makes a different coloured precipitate.
- *Chloride** makes a white precipitate
- *Iodide** makes a yellow precipitate
- *Bromide** makes a cream precipitate
How can metal cations in aqueous solutions be identified?
- Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide
- If only a small amount of NaOH is used then normally the metal hydroxide precipitates
- In excess NaOH some of the precipitates may dissolve
- For this reason just a few drops of NaOH are added at first and very slowly
- If it is added too quickly and the precipitate is soluble in excess, then you run the risk of missing the formation of the initial precipitate which dissolves as quickly as it forms if excess solution is added
- A small amount is thus added, very gradually and any colour changes or precipitates formed are noted
- Then the NaOH is added in excess and the reaction is observed again
- Ca2+ and Mg2+ ions can be distinguished from Al3+ as calcium hydroxide and magnesium hydroxide precipitates do not dissolve in excess NaOH but aluminium hydroxide does
- Another test could be used to distinguish between the Ca2+ and Mg2+ ions, for example a flame test
- Most transition metals produce hydroxides with distinctive colours
What is the effect of adding NaOH on:
- Aluminium
- Magnesium
- Calcium
- Copper
- Iron II
- Iron III
