C3 - Analysis & Synthesis Flashcards
What are the two main methods for testing for positive ions?
- Flame test
- Reaction with sodium hydroxide.
How is a flame test carried out?
- The compound is put on a cleaned wire loop
- The loop is then held in a Bunsen burner.
- The colour of the flame can be used to identify a positive ion.
What colour flame does lithium produce?
Crimson
What colour flame does sodium produce?
Yellow
What colour flame does potassium produce?
Lilac
What colour flame does calcium produce?
Red
What colour flame does barium produce?
Green
What possible elements are present if a white precipitate forms in sodium hydroxide?
Al3+, Ca2+, Mg2+
How is it possible to distinguish between Al, Ca and Mg ions?
- Adding more NaOH causes aluminium ions to dissolve.
- Calcium can be identified with a flame test.
Which ions produce a blue precipitate with NaOH?
Copper(II)
Which ions produce a green precipitate with NaOH?
Iron(II)
Which ions produce a brown precipitate with NaOH?
Iron(III)
How can negative carbonate ions be identified?
- Adding dilute acid produces CO2 gas.
- Limewater is then turned cloudy.
How can negative halide ions be identified?
- Nitric acid then silver nitrate solution is added.
- If a precipitate forms, halides are present.
Which ions produce a white precipitate with silver nitrate?
Chloride
Which ions produce a cream precipitate with silver nitrate?
Bromide
Which ions produce a yellow precipitate with silver nitrate?
Iodide
How can negative sulfate ions be identified?
- Hydrochloric acid then barium chloride is added.
- If a white precipitate forms, sulfate ions are present.
What is titration used for?
To measure how much acid and alkali react completely.
What is the end-point of a reaction?
The point at which the acid and alkali have reacted completely.
What is a pipette used for?
Measure out a fixed solution.
What is a burette used for?
Measuring the volume added.
How is the concentration of a solution calculated?
- Calculate the mass in 1cm3 of solution.
- Calculate mass of solute in 1000cm3 of solution.
- Convert the mass to moles.
How is the mass of solute calculated?
- Calculate the mass of the solute in 1dm3.
- Calculate mass in 1cm3.
- Calculate the mass in the given volume.
What technique is used to analyse DNA?
Gel electrophoresis
Give two examples of chemical analysis in medicine.
- DNA can be matched to find suitable donors.
- Metal concentrations can be analysed to indicate joint failures.
What is the point of equilibrium?
When the rate of forward and reverse reactions are equal.
What happens when a system of equilibrium is changed?
When a system of equilibrium is subjected to a change then the position of equilibrium will shift to oppose the change.
How does changing the pressure affect reversible reactions involving gases?
- Increasing the pressure favours the reaction with the least number of molecules of gas formed.
- Decreasing the pressure favours the reaction with the greater number of molecules of gas formed.
How does changing the temperature affect reversible reactions?
- Increasing the temperature favours the endothermic reaction.
- Decreasing the temperature favours the exothermic reaction.
If the forward reaction of a reversible reaction is exothermic, what must the reverse reaction be?
Endothermic
Give five examples for the uses of ammonia.
- Dye
- Fibre making
- Nitric acid
- Fertiliser
- Explosives
What makes the Haber process so efficient?
- Unreacted hydrogen and oxygen are reused.
- Steam is used to turn generators.
How is the nitrogen for the Haber process obtained?
Hydrogen is burned with air to give nitrogen and water.
How is the ammonia gas collected?
It is condensed into a tank.
How can the yield of ammonia be changed?
Increasing the pressure.
Why does an increase in pressure increase the yield of ammonia?
There are four molecules going in and two going out meaning the pressure favours the forward reaction.
What pressure is the Haber process undertaken at?
200atm
Why is the Haber process done at the given pressure?
It gives a high yield at a lesser expense.
What temperature is the Haber process carried out at?
200C
Why can’t the Haber process be carried out at a lower temperature?
The rate of reaction would be too slow.
Why can’t the Haber process be carried out at a higher temperature?
- The forward reaction is exothermic.
- A lower temperature favours the forward reaction.
What is used as a catalyst in the Haber process?
Iron
What does the presence of a catalyst do in the Haber process?
- Doesn’t increase yield.
- Forms ammonia faster.
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