C8 Flashcards
What is a pure substance?
A single element or compound, not mixed with any other substance
What is a formulation?
A mixture designed as a useful product
What are some examples of formulations?
Fuels; cleaning agents; paints; medicines; alloys; fertilisers and foods
What can chromatography be used for?
To separate mixtures and can give information to help identify substances.
What is the stationary phase in chromatography?
Chromatography paper
What is the mobile phase in chromatography?
The solvent (that travels up the paper)
What’s the equation to work out the Rf value?
distance moved by substance / distance moved by solvent. Always between 0 and 1
How to do chromatography?
- Draw a pencil line about 1cm from the bottom of the paper. 2. Add ink spots to the line. 3. Place the paper in a solvent but the dots must be above the solvent. 4.Allow solvent to move up the paper. 5. Leave to dry and measure distance the ink and solvent travelled to work out the Rf value.
What is the test and positive result for hydrogen?
Put a lit splint near the gas. Squeaky pop occurs.
What is the test and positive result for oxygen?
Glowing splint relights if oxygen is present.
What is the test and positive result for carbon dioxide?
Lime water goes cloudy / milky.
What is the test and positive result for chlorine?
DAMP litmus paper is bleached / turns white.
What can flame tests identify?
Some metal ions.
What flame is visible for lithium ions?
Crimson
What flame is visible for calcium ions?
Red / orange
What flame is visible for sodium ions?
Yellow
What flame is visible for copper ions?
Green
What flame is visible for potassium ions?
Lilac
What happens if there is a mixture of ions?
Some may be masked and not seen.
How can you identify some metal ions (cations)?
Add sodium hydroxide solution
Once you’ve added sodium hydroxide; which ions form white precipitate and what are the equations?
Aluminium - Al3+ + 3OH- —> Al(OH)3. Aluminium dissolves though in excess solution! Calcium - Ca2+ + 2OH- –> Ca(OH)2. Magnesium - Mg2+ +2OH- —> Mg(OH)2
Once you’ve added sodium hydroxide; which ion forms blue precipitate and what is the equation?
Copper II - Cu2+ + 2OH- —> Cu(OH)2
Once you’ve added sodium hydroxide; which ion forms green precipitate and what is the equation?
Iron II - Fe2+ + 2OH- —> Fe(OH)2
Once you’ve added sodium hydroxide; which ion forms brown precipitate?
Iron III - Fe3+ + 3OH- —> Fe (OH)3
What do carbonates and dilute acids form once they’ve reacted?
Carbon dioxide. Check with limewater test.
What do you add to identify a halide ion?
Add a few drops of dilute nitric acid and silver nitrate solution
What are the results for halide ions?
Chloride —> white precipitate of silver chloride. bromide —> cream precipitate of silver bromide. Iodide —> yellow precipitate of silver iodide.
How do you identify sulfate ions?
Add a few drops of HCl to solution and then a few drops of Barium Chloride solution - a white precipitate of barium sulphate should form.
How can elements and compounds detected and identified and why this?
Instrumental methods because they are accurate sensitive and rapid.
What is an example an instrumental method?
Flame emission spectroscopy - analyses metal ions.
How does flame emission spectroscopy work?
The sample is put into a flame and the light given out is passed through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.
