Chemical Analysis - C12 Flashcards
What is a pure substance
It is a substance that is made up of just one type of element or compound.
How do the MP and BP change when a substance becomes impure
If a substance is impure then the melting point will be lower and the boiling point higher than the same pure substance.
what is a formulation.
It is a mixture that has been designed to produce a useful product. Each part of the mixture plays some role for example helping absorption or changing the taste of the mixture. Each product is carefully mixed.
What are the two parts of chromatography
The mobile phase and the stationary phase
In paper chromatography, the paper is the stationary phase and the water (or other solvent) is the mobile phase.
What is a Rf value
It is a value for how soluble a substances is
a larger Rf value means that the component is more soluble in the mobile phase and a smaller Rf value means the component is less soluble.
What is the equation for Rf value
Distance travelled by component/Distance travelled by solvent
What factors affect Rf value
Each substance has a specific Rf value depending on the solvent and temperature used
why does the solvent needs to be below the base line when developing a chromatogram.
Because if the solvent is above the base line then the food colouring’s will be washed away off the page and there will be no results.
why does a chromatogram need to be removed from the solvent before the whole of the paper has become moist.
Because if the whole paper gets moist, then a Rt value cant be calculated for each of the components as you wont get the true distance that the components moved.
why is the base line drawn in pencil not pen.
Because if the base line is in pen, then the ink from the pen could mix with the food colouring’s which would make the results invalid.
What are instructions for a chromatography
- Get your chromatography paper and draw a horizontal baseline in pencil 1 cm above the bottom of the paper using a ruler.
- Place crosses on the pencil line where you are going to put the food colouring’s
- Use the capillary tubes to place a few small drops of the food colouring’s on the crosses
- Clip the wooden splint to the top of the paper and then place the paper elevated into the large beaker making sure the water line is below the pencil line.
- Leave the equipment for until the water reaches 1 cm below the top of the paper
- Quickly mark on the solvent front where the water stopped
- Allow it to dry
- Use the equation to calculate the Rt values.
What is the test for hydrogen
Squeaky pop test
What is the test for oxygen
Relighting a glowing splint
What is the test for chlorine
Damp litmus paper will turn red then white
What is the test for Carbon dioxide
Lime water turns milky and cloudy
Explain why hydrogen pops with a lighted splint
Because the hydrogen is burning very quickly with the oxygen in the air in a small explosion helped by the energy from the splint.
Explain why oxygen relights a glowing splint.
Because oxygen is one of the key parts of combustion and there is a much higher concentration of oxygen meaning the splint can relight.
Explain why lime water goes milky when carbon dioxide is bubbled through it
Because when the carbon dioxide and lime water react, it produces a calcium carbonate which is white and insoluble.
Explain why litmus paper goes white when in contact with chlorine.
Because chlorine is a bleach so when it comes in contact with the paper it bleaches it.
What does the flame test identify
Positive metal ions
What colour does the flame go for lithium
Crimson red
What colour does the flame go for Sodium
Yellow
What colour does the flame go for Potassium
Lilac purple
What colour does the flame go for Calcium
Orange-red
What colour does the flame go for copper (ll)
Green
When added with sodium hydroxide what colour is the precipitate for magnesium
White
When added with sodium hydroxide what colour is the precipitate for calcium
White
When added with sodium hydroxide what colour is the precipitate for Aluminium
White then clear when added in excess
When added with sodium hydroxide what colour is the precipitate for Iron (ll)
Green
When added with sodium hydroxide what colour is the precipitate for Iron (lll)
Rust brown
When added with sodium hydroxide what colour is the precipitate for copper (ll)
Blue
What is the test and result for Chloride ion
Nitric acid + silver nitrate
White precipitate - Silver chloride
What is the test and result for Bromide ion
Nitric acid + silver nitrate
Cream precipitate - Silver bromide
What is the test and result for Iodide ion
Nitric acid + silver nitrate
Yellow precipitate
What is the test and result for sulphate ion
Barium sulphate and hydrochloric acid
White precipitate
What is the test and result for Carbonate ions
Add hydrochloric acid
Fizzing - Carbon dioxide
What is a flame emission spectroscopy.
It is a technique used to monitor the composition of materials such as steel
It can see the elements present and the quantity of them
How does flame emission spectroscopy.
Each element emits light of certain specific wavelengths so the wavelengths of the spectral lines reveal the identities of the elements present. In addition, the intensity of the light emitted reveals the quantity of each element in the sample
What are the advantages of flame emission spectroscopy.
very accurate
can spot very small changes in the composition of materials
very fast
uses small samples
What are the disadvantages of flame emission spectroscopy
very expensive
the people operating it need specialist training
The results need to be compared to data from known substances
