Topic 6 - Quantitive Analysis, Dynamic Equilibria, Calcularions Involving Volumes Of Gases, Chemical Cells and Fuel Cells Flashcards
actual yeild
The amount of product obtained when you carry out experiment
Percentage yield equation
percentage yield = (actual yield / theoretical yield) x100
reasons why the yield is less than expected
- reaction may be incomplete so not all the reactants are used up - possibly because the reaction has not been left for long enough or the reaction may reach equilibrium
- some of the products are lost
- there may be other unwanted side reactions taking place
atom economy
mass of the product you want as a % of the mass of all the products you make
atom economy equation
atom economy = (Relative formula mass of useful product /sum of relative formula masses of all the reactants) x 100
% yeild
amount of product you actually make as a % of the amount you should theoretically make
% yeild
amount of product you actually make as a % of the amount you should theoretically make
How do you make a solution?
The solid is dissolved in distilled water and then made up to graduation mark before suffering and then shaking the flask
Concentration of a solution
The amount of solute dissolved in a state volume of solution
In centimetres cubed, how much is 1 decimetre cubed?
1000cm3 = 1dm3
How do you work out concentration in g/dm3?
concentration in g/dm3 = mass of solute in g / volume of solution in dm3
how do u work out concentration in mol/dm3 (2 equations)
concentration in mol/dm3 = number of moles of solute / volume of solution in dm3
concentration in mol/dm3 = concentration in g/dm3 / RFM of solute
Acid-alkali Titration
Used to find the exact volume of an acid that neutralises a fixed volume of alkali or vice versa
method for an acid-alkali titration (CORE PRACTICAL)
- Rise a burette with hydrochloric acid to fill the burette with the acid
- Record initial volume of the acid in the burette
- Rinse pipette with sodium hydroxide solution then fill the pipette to the 25.0cm3 mark and empty the solution in a conical flask
- Add a few drops of methyl orange indicated to the flask on a white tile underneath the burette
- At the acid to the sodium hydroxide solution while swirling the flask
- When the indicator starts to change colour rinse the tip of the burette and the sides of the flask with a small amount of distilled water from a wash bottle to ensure that all the acid is in the mixture and add the acid drop by drop until the end point is reached.
- Record the final volume of acid in the burette
- Repeat the experiment apart from the initial rinsing of the burette and pipette until concordant results are obtained.
concordant result
if the results are within 0.2cm3 of each other
End point
The point at which the indicator changes colour in an acid- base titration
Avogadros Law
If the temperature and pressure are the same, equal volume of different gases contain an equal number of molecules
Molar gas volume
The volume occupied by one mole of molecules of any gas (24dm3 at room temp and pressure)
amount of gas equation (at rtp)
moles of gas = volume of gas (dm3) / 24
How is ammonia manufactured?
Through the Haber process
Haber process
Process in which nitrogen and hydrogen reacts together in a reversible reaction
ammonia symbol equation
What conditions are used in the Haber process?
- 450°C
- 200 atmospheres pressure
- iron catalyst
What conditions are used in the Haber process?
- 450°C
- 200 atmospheres pressure
- iron catalyst
What happens to the equilibrium position when temperature is increased?
The equilibrium position shifts in the direction of the endothermic reaction
What happens to the position of equilibrium if pressure is increased in a reaction involving gases?
The position of equilibrium moves towards the side of the balanced equation with the fewer molecules of reacting gas
What happens to the position of equilibrium if the concentration of a reacting substance increases?
The position of equilibrium moves away from the reacting substance in the balance equation
What factors affect equilibrium?
- temp.
- pressure
- concentration
When making ammonia is the forward reaction exo or endothermic
Exothermic
When making ammonia is the backward reaction exo or endothermic
Endothermic
When making ammonia why is it at 450°C?
Because low temperatures increase the equilibrium yield of ammonia but reduces the rate of reaction so 450°C is a compromise that gives an acceptable yield of ammonia in an acceptable time
When making ammonia, why is it done at 200 atmospheres (pressure)?
High pressures increase equilibrium of ammonia and increase the rate of reaction so 200 atm is a compromise because it’s very high pressure too expensive to maintain
When making ammonia, why is there an iron catalyst?
Because it does not change position of equilibrium, but it does increase the rate of reaction
How is your reaction pathway chosen - what factors does it take into account?
- Availability and cost of raw materials and energy supplies
- The rate of reaction and the equilibrium position
- Atom economy, yield and usefulness of byproducts
What is a byproduct?
An accidental or secondary product made in the manufacture of synthesis or something else
What components does a chemical cell contain?
- Two different metals each dipped into a solution of one of their salts
- a ‘salt bridge’ to allow dissolved ions to pass from one solution to another
What does it mean to the voltage if the two metals are further apart in the reactivity series? (Chemical cell)
The voltage is greater when the two metals are further apart in the reactivity series
What three elements do plants need to grow well?
- Nitrogen, phosphorus and potassium
Artificial fertilisers (NPK fertilisers)
chemical compounds which contain these elements - they need to be soluble so that the ions dissolve and are easily absorbed by plant
How are ammonium salts made?
A neutralisation of ammonia with acids
Haber process diagram
What ammonium salts are used as fertilisers?
- Ammonium sulphate and ammonium nitrate
What is a batch process?
A method of completing tell us all the groups or a lot rather than individually or in real time
What do fertilisers do?
They replace the mineral ions needed by plants and so promote plant growth
hydrogen fuel cells
are electrochemical devices like batteries, which produce electricity by converting hydrogen and oxygen into water
Fuel cell
Electricity produced when they are supplied with fuel and oxygen from outside
What happens at each electrode in a hydrogen-oxygen fuel cell?
- hydrogen atoms lose electrons and form hydrogen ions
- electrons flow through the external circuit to the positive electrode (anode)
- hydrogen ions pass through a membrane to the right hand side electrode where they gain electrons and react with oxygen to produce water
How do you calculate the theoretical yield?
Calculate the relative formula masses and a multiplied by the balancing number (total RFM)
What are the two methods of making ethanol
- fermentation
- Reaction of ethene w steam
Compare fermentation and reaction of ethene with steam
What is a continuous process?
A process in which reactants are constantly fed into the reactors and products are removed
Advantages of continuous process
+ automated - need fewer people to make a given amount of product
daniell cell
an electrochemical cell that converts chemical energy into electrical energy
How is hydrogen mostly manufactured?
by the reaction of steam with coal or natural gas -> these processes do release carbon dioxide as a byproduct
when increasing temp, what happens to the yield of products and rate of reaction
idk
when increasing pressure, what happens to the yield of products and rate of reaction
when increasing conc, what happens to the yield of products and rate of reaction
explain why the mixture is stirred
so that the mixture is evenly mixed to help the elements to collide and react to see the change of colour
explain the effect of any that traces of water in the pipette after rinsing could have on the titration result
- less hydroxide used -> more dilute
- less acid used in titration -> titration result decreased
explain the effect of any that traces of water in the conical flask after rinsing could have on the titration result
no change in volume or conc of hydroxide solution added to flask
-> no change in result
state the colour change of phenolphthalein at the end point when the barium hydroxide solution has just be neutralised
pink to colourless
describe an experiment to obtain a sample of pure dry barium sulphate from the contents of the conical flask after a titration
- filter the barium sulphate (precipitate)
- wash precipitate with water
- dry precipitate in warm oven on filter paper
