Stoichemetry Flashcards
What is a titration reaction
A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution. Typically, the titrant (the know solution) is added from a buret to a known quantity of the analyte (the unknown solution) until the reaction is complete.
Chromatography is used in the what what and what of components in a mixture
Separation, purification and identification
What is chromatography paper made of
Cellulose fibres, insoluble carbohydrates with OH that water bonds to
What does chromatography paper comprise in paper chromatography
Stationary phase
What happens to the substance which is analysed in chromatographic analysis first
Dissolved into a suitable solvent and spotted onto stationary phase
What does the movement of compounds in chromatography depend on
Their polarity eg more polar substances will be attracted to the polar -OH group
What is the formula for energy released and what is the units
M(water) x 4.18 x Delta T
Joules
How to convert joules to kilojoules
Divide by 1000
Two approximations in combustion reactions
That the density of the solution is the same as the density of water
The specific heat of the solution is equal to the specific heat of water
3 assumptions of combustion reactions
Any temp change is instantaneous
No heat is lost or gained
All of any solid is dissolved
3 reasons in ethanol combustion etc the value is lower than the true value
Heat is lost to surroundings
Ethanol evaporates on wick
Incomplete combustion
Why are polystyrene cups used in combustion reactions
Good insulator and doesn’t react with liquids
Why is stirring carried out
Ensures complete and fast reaction to minimise heat lost also ensures even distribution of heat
What are fuels
Substances that releases heat energy when burnt or combusted
3 types of fossil fuels
Coal, gas, oil
3 biofuels
Ethanol (fermentation)
Biodiesel
Biogas
3 advantages of biofuels
Plant based hence renewable, carbon neutral (no NET change in CO2 levels), less emissions
3 disadvantages of biofuel
Biodiesel conceals at very low temperatures
Land is cleared to grow crops to produce leading to higher food prices
Fossils fuels are used to manufacture biofuels
What is the energy conversion in galvanic cells
Spontaneous chemical reactions that produce chemical energy
In a copper aluminium galvanic cell what are three observations
Copper deposit at cathode
Fading of blue Colour
Al corrosion
In a copper aluminium galvanic cell why is aluminium the anode
Because it is more reaction and therefore oxidises which always occurs at the cathode
What is the electron flow in galvanic cells
More to less reactive electrode
In galvanic cells where do the anions and cations go
Anions -> anode
Cations -> cathode
What are fuel cells
A special type of voltaic cell
In a fuel cell does oxygen react at the anode or cathode
Cathode as its been reduced
Reduction reaction in fuel cells with oxygen
O2 + 4H^+ + 4ē -> 2H2O
Oxidation reaction in fuel cells with methane
CH4 + 2H2O -> CO2 + 8H^+ + 8ē
What is an electrolytic cell
Cell that converts electrical energy to chemical energy using a power supply
Two reactions for the electrolysis of water
Oxidation - 2H2O -> O2 + 4H^+ + 4ē
Reduction - 2H2O + 2ē -> H2 + 2OH^-
In a car battery during discharge what type of cell is it
VOLTAIC
In a car battery during recharging what type of cell is it
ELECTROLYTIC
Why are most metals found combined with other metals
Most metals are reactive and have the tendency to lose electrons
Two forms of metal production
Chemical reduction and electrolysis
Formula for electrolysis in the production of aluminium
Al3^+ + 3ē -> Al
4 steps of the production of zinc
1) Ore is crushed to fine dust
2) Mineral is dried and roasted in air
3) ZnO is dissolved in H2SO4
4) Electrolysis of ZnSO4 (Zn^2+ + 2ē -> Zn) to produce Zinc metal
Why and how are metal ions such as Pb2+ and Cd2+ removed during zinc production
Displacement using Zn, removed as they would be preferentially reduced during electrolysis
In zinc production what is the byproduct of SO2 used for
Used to make sulphuric acid
What is dynamic equilibrium
Reaction continues with no net change
What is the significance of Kc
If the Kc is large it favours the forward reaction and if it is small if favours the back reaction
4 ways to increase yield in the haber process
High pressure
Low temperature
Increased N2 / H2
Remove ammonium as it’s produced
What is the catalyst in the haber process
Iron powder
How to convert kJmol^-1 to kJg^-1
Divide by molar mass of specified reactant
Equation for heat energy released or absorbed
n x molar enthalpy of reaction (q x n x delta H
What does q stand for
Heat energy transferred
2 sources of systematic error in combustion
Not all of the heat energy released is absorbed by the water
Combustion is incomplete as portion of alcohol undergoes incomplete combustion
2 sources of random errors in combustion
Measuring cylinder doesn’t not have high resolution
Flame wasn’t concentrated at the same point throughout the experiment due to draughts
How to achieve delta H values of a higher accuracy
Use a bomb calorimeter
4 steps when using polystyrene cup
Measure out
What factor effects Kc
Temperature
2 ways to save energy costs in production
Catalyst
Run process continually
What’s the charge of the anode and cathode in galvanic (voltaic) cells
Anode Negative
Cathode positive
What’s the charge of the anode and cathode in electrolytic cells
Anode positive
Cathode negative
Oxidation is a … In oxidation number
Increase
Reduction is a. … In oxidation number
Decrease
In half cells will the more reactive metal become the anode or cathode
Anode
The direction of movement of cations in the salt bridge will be towards?
The cathode
The direction of movement of anions in the salt bridge will be towards the?
Anode
3 advantages of fuel cells
They continuously produce an electric current so long as fuel and oxidant is continuously supplied
They have a high operating efficiency
Do not produce pollutant gases
Electrodes and electrolyte are not consumed during operation
3 disadvantage of fuel cells
High purity fuels and oxidants are costly
Medium to high temperatures are needed for the cells to function most effectively
Metal electrode catalysts such as platinum and palladium are very costly
In exothermic reactions in energy profile diagrams is the bump near the left or the right
Left
In endothermic reactions in energy profile diagrams is the bump near the left or the right
Right
6 factors that effect reaction rate
Concentration of reactants Pleasure Temperature of reaction mixture Surface area of solid reactants Catalysts Intensity of light for photochemical reactions
What conditions are needed for a reversible chemical reaction to reach equilibrium
A closed system that’s at a constant temperature
What is Le châtelier’s principle
If an external change is made to the reaction conditions of a system at equilibrium so that it is no longer at equilibrium a net reaction will occur in the direction that counteracts the change
According to Le Chateliers principle what will happen if the concentration of a reactant is increased
Equilibrium shifts to the right
According to Le Chateliers principle what will happen if the concentration of the reactants decreases
Equilibrium shifts to the left
According to Le Chateliers principle what will happen if the concentration of the products increases
The equilibrium shifts to the left
According to Le Chateliers principle what will happen if the concentration of the products decreases
The equilibrium shifts to the right
What’s froth floatation
Powder from the grinding mill is mixed with water in large floatation tanks to form a slurry . Frothing agents such as pine oil are added with water soluble substances called collectors, air is blown through aqueous suspension of ground ore
Why is froth floatation Carried out
To concentrate desired minerals
What a are commonly used collectors referred to as
Xanthates
Describe the structure of a xanthate ion
Ionic head and non polar tail
4 steps in producing zinc
Roasting zinc sulfide
Leaching zinc oxide
Purification of zinc surface
Electrolysis
The degree of difficulty of reduction to the metal increases as the … Increases
Reactivity of the metal
