Edexcel GCSE 9-1 Chemistry: SC14/15/16 - Quantitative analysis, Dynamic equilibria, Chemical + Fuel cells

5.8C Calculate the concentration of solutions in mol dm–3 and convert concentration in g dm–3 into mol dm–3 and vice versa

5.8C Calculate the concentration of solutions in mol dm–3 and convert concentration in g dm–3 into mol dm–3 and vice versa

1. work out how many moles of the 'known' substance you have using the formula:
number of moles = concentration (mol dm-3) x volume (dm-3)

2. write down the balanced equation of the reaction and work out how many moles of the 'unknown solution' you must have had.

3. work out the concentration of the 'unknown' substance using the formula:
concentration (mol dm-3) = number of moles / volume (dm3)

5.10 Carry out simple calculations using the results of titrations to calculate an unknown concentration of a solution or an unknown volume of solution required

1) write balanced equation
2) add data given in question under reactants in equation
3) calculate amount in mol of reactant with all data given
4) use balanced equation to determine amount in mol of other reactant
5) calculate unknown concentration of reactant

5.11C Calculate the percentage yield of a reaction from the actual yield and the theoretical yield

% yield = (actual yield / theoretical yield) * 100

5.12C Describe that the actual yield of a reaction is usually less than the theoretical yield and that the causes of this include:

a) incomplete reactions

b) practical losses during the experiment

c) competing, unwanted reactions (side reactions)

• incomplete reactions: reaction has not been left for long enough or the reaction may have reached equilibrium

• practical losses during the experiment: during transfers - a liquid may be left on the walls of the container

• side reactions: reactants may react to make a different product which can compete with the main reaction

5.13C Recall the atom economy of a reaction forming a desired product

The measure of the amount of starting materials that end up as useful materials

5.14C Calculate the atom economy of a reaction forming a desired product

% AE= (relative formula mass (M_r ) of desired product / sum of M_r of all reactants) * 100

5.15C Explain why a particular reaction pathway is chosen to produce a specified product, given appropriate data such as… (5)

Atom economy, yield, rate, equilibrium position and usefulness of by-products

5.16C Describe the molar volume, of any gas at room temperature and pressure… 24dm³

The volume occupied by one mole molecules of any gas temperature and pressure
24dm³

5.17C Use the molar volume and balanced equations in calculations involving the masses of solids and volumes of gases

gas volume / number of moles

5.18C Use Avogadro’s law to calculate volumes of gases involved in a gaseous reaction, given the relevant equation

vol = amount of gas moles * 24dm³ mol^-1

5.19C Describe the Haber process as a reversible reaction between nitrogen and hydrogen to form ammonia

The Haber process is a reversible, EXOTHERMIC reaction between nitrogen and hydrogen to form ammonia.

Predict how the rate of attainment of equilibrium is affected by:

a) changes in temperature

• increase in temp = shifts =m in endothermic reaction (backwards / left)→ expensive!

• decrease in temp = shifts =m in exothermic reaction (forwards / right)

Predict how the rate of attainment of equilibrium is affected by:

b) changes in pressure

• increase pressure - shifts to side of least gas moles (limit due to safety, specialist equipment + cost)

• decrease pressure - shifts to side of most gas moles

Predict how the rate of attainment of equilibrium is affected by:

c) changes in concentration

• increase reactant: cause forward reaction to speed up to get rid of additional reactant, yield increase → quicker

• decrease reactant: reactant has to work longer due to less conc, yield decreases → slower

Predict how the rate of attainment of equilibrium is affected by:

d) use of catalyst

• doesn’t affect the RATE of equilibrium

• but affects the SPEED of equilibrium

5.21C Explain how, in industrial reactions, including the Haber process, conditions used are related to:

a) the availability and cost of raw materials and energy supplies

b) the control of temperature, pressure and catalyst used produce an acceptable yield in an acceptable time

• in the Haber Process the raw materials are readily available and inexpensive to purify:

• nitrogen - from the air

• hydrogen- from natural gas

• if the cost of extraction of raw materials is too high or they are unavailable then the process is no longer economically viable

• many industrial processes require huge amounts of heat and pressure which is very expensive to maintain

• atom economy

• cost of energy

• yield of product

• rate of reactions

• equilibrium position

• usefulness of by-products

5.22C Recall that fertilisers may contain nitrogen, phosphorus and potassium compounds to promote plant growth

Fertilisers may contain:

- nitrogen compounds
- phosphorus compounds
- potassium compounds

5.23C Describe how ammonia reacts with nitric acid to produce a salt that is used as a fertiliser

NH₃ + HNO₃ → NH₄NO₃ (salt)

5.24C Describe and compare:

a) the laboratory preparation of ammonium sulphate

b) the industrial production of ammonium sulphate

• lab - made small scale by batches for experimental purposes

• factory - made large scale, continuously for commercial purposes

5.25C Recall that a chemical cell produces a voltage until one of the reactants is used up

a chemical cell produces a voltage until one of the reactants is used up

5.26C Recall that in a hydrogen–oxygen fuel cell, hydrogen and oxygen are used to produce a voltage and water is the only product

in a hydrogen–oxygen fuel cell, hydrogen and oxygen are used to produce a voltage and water is the only product

5.27C Evaluate the strengths and weaknesses of fuel cells for given uses

adv:

• low maintenance

• quiet in comparison to an engine

• does not produce greenhouse gases

disadv:

• hydrogen is flammable

• extraction of hydrogen releases CO₂