Chemistry 3 Unit 4
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What is the flame test?
This is the identification of positive ions using sodium hydroxide solution
Name the flame colours for lithium, sodium, potassium, calcium, barium ion precipitates
- Lithium = Crimson
- Sodium = Yellow
- Potassium = Lilac
- Calcium = Red
- Barium = Green
Which ions produce white precipitates with sodium hydroxide?
Aluminium calcium magnesium ions
What happens when excess sodium hydroxide is added to the solution?
Aluminium hydroxide dissolves
Name the flame colours for Copper(||), iron (||), iron(|||) ion precipitates
- Coper (||) = blue
- Iron (||) = green
- Iron (|||) = brown
What test identifies carbonate ions?
Carbonates react with dilute hydrochloric acid to form carbon dioxide. Carbon dioxide produces a white precipitate with limewater and turns limewater cloudy
What test identifies halide ions?
- Adding dilute nitric acid and silver nitrate solution to halide ions.
- Chloride = white
- Bromide = Cream
- Iodide = Yellow
What test identifies sulphate ions?
Adding dilute hydrochloride acid and then barium chloride solution. If a white precipitate forms, sulphate ions are present
What's the function of titrations?
Titrations are used to find the volumes of solutions that react exactly
Describe the process of titration
- A pipettes is used to measure accurately the volume of alkali that is put in the conical flask
- An indicator is then added to the alkali
- A but d'être is filled with acid which is then added gradually to the flask
- When the indicator changed colour the end point has been reached
When a reversible reaction occurs in a closed system, when is equilibrium reached?
When a reversible reaction occurs in a closed system, equilibrium is reached when the rare of forward reaction is equal to the rate of the reverse reaction
What does the amount of reactants and products depend on?
The relative amounts of reactants and products at equilibrium depend on the conditions of the reaction
What conditions affect the amount of reactants and products?
How does concentration affect the amount of reactants and products?
Of the concentration of a reactant is increased, more products are formed as the system tries to achieve equilibrium
How does pressure affect the amount of reactants and products if the forward reaction produces more molecules of gas?
- An increase in pressure decreases the amount of product formed
- A decrease in pressure increases the amount if products formed
How does pressure affect the amount of reactants and products if the forward reaction produces fewer molecules of gas?
- An increase in pressure increases the amount of products formed
- Decreasing the pressure decreases the amount of product formed
How does temperature affect the amount of reactants and products if the forward reaction is exothermic?
- An increase in temperature decreases the amount of product formed
- A decrease in temperature increases the amount if product formed
How does temperature affect the amount of reactants and products if the forward reaction is endothermic?
- An increase in temperature increases the amount if product formed
- A decrease in temperature decreases the amount if product formed
Describe the harber process in the manufacturing of ammonia
- Nitrogen from the air and hydrogen, usually from natural gas, are purified and mixed in the correct proportions
- The gasses are passed over a catalyst of iron at temperatures of 450•c and pressures of 200 atmospheres
- Ammonia is then liquified by cooling to be separated from nitrogen and hydrogen which are recycled
Why are high pressures needed in the Harber process?
The products have fewer molecules of gas than the reactants so the higher pressure the greater the yield of ammonia
What is the disadvantage of the high pressure used in the Harber process?
- High pressures need strong reaction vessels and pipes which increase costs
- The higher the pressure the more energy is needed to compress the gas
Why is there optimum pressure for the Harber process?
A pressure of 200 atmospheres is used as a compromise between the cost and yield
Why are low temperatures needed in the Harber process?
The forward reaction is ectothermic so the lower the the temperature the greater the yield of ammonia
What is the disadvantage of the low temperatures used in the Harber process?
The lower the temperature, the lower the reaction rate therefor the the iron catalyst becomes ineffective and process of producing ammonia is longer
Why is there optimum temperature for the Harber process?
A compromise of 450•c is used to give a reasonable yield in a short time
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