Analysis And Synthesis Flashcards
What flame colour do lithium ions give
Crimson red
What flame colour do sodium ions give
Yellow
What flame colour do potassium ions give
Lilac
What flame colour do calcium ions give
Red
What flame colour do barium ions give
Green
Give the lithium and calcium give the same flame test colours how can we distinguish between them
With sodium hydroxide solution will show which is which because calcium ions will form a white precipitate but lithium will not
Which hydroxides are mostly insoluble in water
Ones with ions of 2+ and 3+ charges
What happens when sodium hydroxide is added to a solution of insoluble ions
A precipitate of a metal hydroxide is formed
Which 3 metals form white precipitate
Aluminium, calcium, magnesium
What happens to the aluminium hydroxide precipitate when excess sodium hydroxide solution is added
The precipitate of aluminium hydroxide dissolves
What colour is calcium hydroxide
Blue
What colour is iron (II) hydroxide
Green
What colour is iron (III) hydroxide
Brown
What can we use to show the reactions of positive ions with sodium hydroxide solution
Balanced ionic equations
What are the 3 test for negative ions
Carbonate ions
Halide ions
Surfate ions
Describe the test for carbonates (negative ion test)
Add dilute HCL to the substance to see if it fizzes. If it does and the gas produces turns limewater cloudy, the substance contains carbonate ions
Describe the test for halide ions (negative ions)
Add dilute nitric acid and then silver nitrate solution different negative ions form different coloured precipitates
In the test for negative halide ions what colour precipitate do chloride ions form
A white precipitate
In the test for negative halide ions what colour precipitate do bromide ions form
A cream coloured precipitate
In the test for negative halide ions what colour precipitate do iodide ions form
A yellow precipitate
Describe the test for surface ions (negative ions)
Add dilute hydrochloride acid and then barium chloride solution. If a white precipitate forms, sulfate ions are present
Why must nitric acid be added and not HCL or sulphuric acid when testing with silver nitrate solution for halides?
HCL contains chloride ions and sulphuric acid contains sulfate ions which both give precipitates with silver nitrate solution
How can positive ions be identified
Using a flame test
Using sodium hydroxide solution
What is titration
A method for measuring the volumes of 2 solutions that react together
What is used to measure accurately the volume of alkali put into a conical flask
A pipettes
What is added to the alkali which is in the conical flask
Indicator
What is used to gradually add the acid to the alkali in a titration experiment
A burette
What is the difference between a pipette and a burette
A pipette measures a fixed, has a single graduation, and has no tap; a burette measures different volumes, has graduations, has a tap
When is the end point of titration reached
The indicator changes colour
How is repeatability of the titration experiment improved
The titration should be done several times
What can concentration be measured in
Grams per decimetre cubed (g/dm3)
Moles per decimetre cubed (mol/dm3)
What do we need to calculate concentration
The mass or the number of moles dissolved in a given volume of solution
What can be used to calculate mass or number of moles of a substance in any volume of solution
The volume of a solution and its concentration
How do you calculate the concentration of a solution in g/dm3
1) to calculate what 1cm3 of the solution contains divide the value of the NAMED solution (in grams) by the value of the unnamed solution (in cm3)
2) to calculate what 1dm3 contains, times the answer to the previous step by 1000
How do you calculate the concentration of a solution in mol/dm3
1) calculate the value of 1 mole of the named solution (relative formula mass)
2) divide the previously worked out concentration of the solution in g/dm3 by the relative formula mass of the the named solution
What are the steps to calculate the mass of a solution (with the concentration stated) which is dissolves in another solution
1) to calculate what 100cm3 contains, 100 x the concentration value/1000
2) calculate the relative formula mass of the solution
3) times the relative formula mass by the previous worked out answer
What is needed so the concentration of solution be calculated in a titration experiment
If the concentration of one of the solutions is known and the volumes that react together are known
How are the concentrations calculated in titration
Using balanced symbol equations and moles
What are the steps in calculating an unknown concentration in a titration calculation
1) write the balanced equation
2) understand that the given concentration (eg. 0.5) means the value given in divided by 1000 0.5/1000
3) times the volume of the acid/ solution with a given concentration by the concentration value (0.5/1000)
4) from the equation work out how many moles of the unknown substance will react with what value of the Unknown (concentration) solution eg 0.010 mol of HCL will react with 0.010 mol of sodium hydroxide
5) so the concentration is the value calculated from step 5 divided by the stated volume of the Unknown (concentration) solution x 100
What purposes may chemists analyse substances for
Environmental, medical, forensic investigations
What are qualitative tests
Tests which simply find out if a substance is in a sample, such as testing the ions
What can titration so tells you
How much of a substance is in a sample
What are examples of quantitative methods
Mass spectrometry and gas chromatography
When is it necessary to use quantitative analysis
When we need to know the quantity of a substance in a sample
What can a large data base build up
help identify substances in samples, individuals or to monitor changes in amounts of substances over time
Why is it important to have a large database for DNA analysis to identify individuals
Because everyone’s DNA is different
When is equilibrium reached for a reversible reaction in a closed system
When the rate of the forward reaction is equal to the rate of the reverse reaction
What happens in equilibrium
Both reactions continue to happen but the amounts of reactants remain constant
How can the amounts of the reactants and products for a reversible reaction be changed
By changing the reaction conditions
How will increasing the concentration of the reactant name the amount of product produced
It will cause more product to be formed as the system tries to achieve equilibrium
What happens if a product is removed in a equilibrium reaction
More reactants will react to try to achieve equilibrium and so more product is formed
To make SO3, the reaction 2SO2 + O2 2SO3 is done in a reactor over a heated catalyst. Why is the SO3 removed from the reactor as soon as it is made
So more of the reactants react and more SO3 is produced
What happens if the conditions of a system change at equilibrium
The position of equilibrium changes as if to try to cancel out the change
How does increasing the pressure favour the equilibrium
UIf the pressure is increased the equilibrium will shift to try to reduce the pressure favouring the reaction that produces fewer molcules of gas
If the forward reaction produces more Molecules of gas…..
An increase in pressure decreases the amount of products formed
A decrease in pressure reduces the amount of products formed
If the forward reaction produces fewer molecules of gas
An increase in pressure increases the amount of products formed
A decrease in pressure decreases the amounts of products formed
Increasing the pressure …….. The amount in the mixture at equilibrium
Increases
Reversible reaction are ……. In one direction and …… In the other
Exothermic
Endothermic
Increasing the temperature favours which reaction
The endothermic reaction, the equilibrium shifts as it to lower the temperature by taking in energy
Decreasing the temperature favours which reaction
Exothermic reaction
If the forward reaction is exothermic…
An increase in temperature decreases the amount of products formed
A decrease in temperature increases the amount of products formed
If the forward reaction is endothermic….
An increase in temperature increases the amount of products formed
A decrease in temperature decreases the amount of product formed
What is the habet process used to make
Ammonia
What is ammonia used as
Fertilisers, other chemical s
Where is hydrogen and nitrogen obtained from
Natural gas
How is nitrogen and hydrogen from the air turned into ammonia
They are purified and mixed in the correct proportions
What are the conditions for the habet process
Iron catalyst
450 degrees
200 atmospheres, pressure
Why are those conditions for the haber process chosen
They give a fast rate of reaction
Reasonable yield of ammonia
What is the balanced symbol equation for the haber process
N2 + 3H2 2NH3
The haber process is ………..
Reversible
What is the yield of the haber process and why is this
15% as some of the ammonia breaks down into nitrogen and hydrogen
How is the ammonia obtained at the end of the haber process
The gases are cooled so the ammonia condenses
The liquid ammonia is separated from the unreacted gases
What is done in the haber process to conserve raw materials
The unreacted gases are recycled and not wasted
Why does increasing the pressure increase the yield of ammonia
The products have fewer molecules of gas than the reactants so the higher the pressure the greater the yield
What is bad about the higher pressure needed for the haber process
More energy is needed to compress the gas
Stronger reaction vessels and pipes are needed
Which all increase the cost
Why is a pressure of 200 atmospheres used in the haber process
It is a compromise between the cost and yield
What type of reaction if the forward reaction in the haber process
Exothermic
Because the forward reaction of the haber process Is exothermic what type of temperature will increase the yield of ammonia
A lower temperature
Why is a temperature of 450 degrees used for the haber process
A lower temperature, although it would increase the yield, the reaction rate decrease as the temperature is lowered and the iron catalyst becomes ineffective so it would take longer to produce ammonia
