C6 (Chemistry): Chemical Synthesis
Overview
Synthesis provides many of the chemicals that people need for food processing, health care, cleaning and decorating, modern sporting materials and many other products. The chemical industry today is developing new processes for manufacturing these chemicals more efficiently and with less impact on the environment.
In this context, the module explores related questions that chemists have to answer: ‘How much?’ and ‘How fast?’ in the context of the chemical industry. Quantitative work includes the calculation of yields from chemical equations and the measurement of rates of reaction.
A further development of ionic theory shows how chemists use this theory to account for the characteristic behaviours of acids and alkalis. Energy level diagrams are used to describe the exothermic and endothermic nature of chemical reactions.
Topics
C6.1 Chemicals and why we need them
- The scale and importance of the chemical industry; acids, alkalis and their reactions
- Neutralisation explained in terms of ions
C6.2 Planning, carrying out and controlling a chemical synthesis
- Planning chemical syntheses
- Procedures for making pure inorganic products safely
- Comparing alternative routes to the same product
- Calculating reacting quantities and yields
- Measuring purity by simple titration
- Controlling the rate of change
Detailed specification
C6.1 Chemicals and why we need them
1. understand the importance of chemical synthesis to provide food additives, fertilisers, dyestuffs, paints, pigments and pharmaceuticals
2. interpret information about the sectors, scale and importance of chemical synthesis in industry and in laboratories
3. recall the formulae of the following chemicals: chlorine gas, hydrogen gas, nitrogen gas, oxygen gas, hydrochloric acid, nitric acid, sulfuric acid, sodium hydroxide, sodium chloride, sodium carbonate, sodium nitrate, sodium sulfate, potassium chloride, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium chloride, magnesium sulfate, calcium carbonate, calcium chloride and calcium sulfate
4. work out the formulae of ionic compounds given the charges on the ions
5. work out the charge on one ion given the formula of a salt and the charge on the other ion
6. recall the main hazard symbols and be able to give the safety precautions for handling hazardous chemicals (limited to explosive, toxic, corrosive, oxidizing, and highly flammable). NOTE: See Appendix H for guidance on recent changes to hazard labelling
7. recall examples of pure acidic compounds that are solids (citric and tartaric acids), liquids (sulfuric, nitric and ethanoic acids) or gases (hydrogen chloride)
8. recall that common alkalis include the hydroxides of sodium, potassium and calcium
9. recall the pH scale
10. recall the use of litmus paper, universal indicator and pH meters to detect acidity and
alkalinity, and the use of universal indicator and pH meters to measure pH
11. recall the characteristic reactions of acids that produce salts, to include the reactions with metals and their oxides, hydroxides and carbonates
12. write word equations when given appropriate information
13. interpret symbol equations, including the number of atoms of each element, the number of molecules of each element or covalent compound and the number of ‘formulas’ of ionic compounds, in reactants and products. NOTE: In this context, ‘formula’ is used in the case of ionic compounds as an equivalent to molecules in covalent compounds; the concept of the mole is not covered in the specification
14. balance unbalanced symbol equations
15. write balanced equations, including the state symbols (s), (l ), (g) and (aq), to describe the characteristic reactions of acids and other reactions when given appropriate information
16. recall the state symbols (s), (l ), (g) and (aq) and understand their use in equations
17. recall that the reaction of an acid with an alkali to form a salt is a neutralisation reaction
18. explain that acidic compounds produce aqueous hydrogen ions, H+ (aq), when they dissolve in water
19. explain that alkaline compounds produce aqueous hydroxide ions, OH–(aq), when they dissolve in water
20. write down the name of the salt produced given the names of the acid and alkali
21. write down the formula of the salt produced given the formulae of the acid and alkali
22. explain that during a neutralisation reaction, the hydrogen ions from the acid react with hydroxide ions from the alkali to make water:
H+(aq) + OH−(aq) → H2O(l )
23. understand the terms endothermic and exothermic
24. use and interpret simple energy level diagrams for endothermic and exothermic reactions
25. understand the importance of the energy change during a reaction to the management and control of a chemical reaction.
C6.2 Planning, carrying out and controlling a chemical synthesis
1. identify the stages in a given chemical synthesis of an inorganic compound (limited to acidalkali reactions), including:
- a. choosing the reaction or series of reactions to make the required product
- b. carrying out a risk assessment
- c. working out the quantities of reactants to use
- d. carrying out the reaction in suitable apparatus in the right conditions (such as temperature, concentration)
- e. separating the product from the reaction mixture (limited to filtration)
- f. purifying the product (limited to evaporation, crystallisation and drying in an oven or desiccator)
- g. measuring the yield and checking the purity of the product (by titration)
2. understand the purpose of these techniques: dissolving, crystallisation, filtration, evaporation, drying in an oven or desiccator
3. understand the importance of purifying chemicals and checking their purity
4. understand that a balanced equation for a chemical reaction shows the relative numbers of atoms and molecules of reactants and products taking part in the reaction
5. understand that the relative atomic mass of an element shows the mass of its atom relative to the mass of other atoms
6. use the Periodic Table to obtain the relative atomic masses of elements
7. calculate the relative formula mass of a compound using the formula and the relative atomic masses of the atoms it contains
8. substitute relative formula masses and data into a given mathematical formula to calculate reacting masses and/or products from a chemical reaction
9. calculate the masses of reactants and products from balanced equations
10. calculate percentage yields given the actual and the theoretical yield
11. describe how to carry out an acid-alkali titration accurately, when starting with a solution or a solid to be dissolved to make up a solution. NOTE: Making up of standard solutions is not required
12. substitute results in a given mathematical formula to interpret titration results quantitatively
13. understand why it is important to control the rate of a chemical reaction (to include safety and economic factors)
14. explain what is meant by the term ‘rate of chemical reaction’
15. describe methods for following the rate of a reaction (for example, by collecting a gas, weighing the reaction mixture or observing the formation or loss of a colour or precipitate)
16. interpret results from experiments that investigate rates of reactions
17. understand how reaction rates vary with the size of solid particles, the concentration of solutions of chemicals and the temperature of the reaction mixture. NOTE: A qualitative treatment only is expected
18. understand that catalysts speed up chemical reactions while not being used up in the reaction
19. interpret information about the control of rates of reaction in chemical synthesis
20. use simple ideas about collisions to explain how chemical reactions take place
21. use simple collision theory and ideas about collision frequency to explain how rates of reaction depend on the size of solid particles and on the concentration of solutions of dissolved chemicals. NOTE: The effect of temperature on collision frequency is not considered since activation energy has a greater influence
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