Presentation on theme: "Revision of C6 Chemical synthesis. Chemical synthesis: chemical reactions and processes used to get a desired product using starting materials called."— Presentation transcript:
Revision of C6 Chemical synthesis
Chemical synthesis: chemical reactions and processes used to get a desired product using starting materials called reagents. The products can be useful for a variety of purposes but tend to be either… C6.1 Chemicals are why we need them
Understand the importance of chemical synthesis to provide food additives, fertilisers,, paints, pigments and pharmaceuticals. Understand the importance of chemical synthesis to provide food additives, fertilisers, dyestuffs, paints, pigments and pharmaceuticals.
fine chemicals A chemical product that is made in relatively small quantities and is typically high in cost, e.g. a flavouring or vitamin, drugs etc. They are made to high levels of purity. Usually in laboratories. bulk chemicals A chemical product that is made in large amounts, very cheaply and often used to make other chemicals or to process other materials e.g. bleach, solvents, sulphuric acid etc. Usually made in industries. Interpret information about the sectors, scale and importance of chemical synthesis in industry and laboratory.
Recall the formulae of …. Gases: chlorine = Cl 2, hydrogen = H 2, nitrogen= N 2, oxygen = O 2 Acids: hydrochloric acid = HCl, nitric acid = HNO 3, sulfuric acid = H 2 SO 4, Alkalis sodium hydroxide = NaOH, magnesium hydroxide Mg(OH) 2
H ONLY : Work out the formulae of ionic compounds given the charges on the ions. CompoundPositive ionNegative ionFormula Sodium chloride Na + Cl - NaCl Magnesium chloride Mg 2+ Cl - MgCl 2 Calcium oxide Ca 2+ O 2- CaO Aluminium oxide Al 3+ O 2- Al 2 O 3 Magnesium sulfate Mg 2+ SO 4 2- MgSO 4
If magnesium forms Mg 2+ ions and sulfate forms SO 4 2- ions then identify the charges on the other ions in the following compounds… –MgO –MgCl 2 –MgNO 3 –Na 2 SO 4 –Al 2 (SO 4 ) 3 –CaSO 4 H ONLY Work out the charge on one ion, given the formula of a salt and the charge on the other ion.
harmful / irritant corrosive toxic highly flammable oxidising Recall the main hazard symbols, and understand the safety precautions to use when handling hazardous chemicals.
Recall examples of pure acidic compounds which are solid, liquids and gases. Solids =citric acid & tartaric acid Liquids =sulfuric, nitric and ethanoic acids Gases = hydrogen chloride
Recall the pH scale pH 1 to pH 3 shows that there is a STRONG ACID pH 4 to pH 6 shows that there is a WEAK ACID pH 7 shows that the substance is NEUTRAL pH 8 to pH 10 shows that there is a WEAK ALKALI pH 11 to pH 14 shows that there is a STRONG ALKALI
Recall the use of indicators and pH meters to measure pH. IndicatorColour in acid Colour in neutral Colour in alkali litmusRedBlue phenolphthaleincolourlesspink Universal (a mixture of indicators) RedGreenPurple
A pH meter.
Recall the reactions of acids that produce salts. Salts can be produced by reacting acids with….. metals metal oxides metal hydroxides metal carbonates Write balanced equations with state symbols to describe the characteristic reactions of acids
Metal + acid Metal + acid metal salt + hydrogen calcium + sulfuric magnesium + hydrochloric acid calcium sulfate + hydrogen magnesium chloride + hydrogen Ca(s) + H 2 SO 4 (aq)CaSO 4 (aq) + H 2 (g) Mg(s) + HCl(aq) MgCl 2 (aq) + H 2 (g)
Metal oxide + acid metal + acid metal salt + water copper + sulfuric magnesium + hydrochloric oxideacid oxideacid oxide copper sulfate + water magnesium chloride + water CuO(s) + H 2 SO 4 (aq) CuSO 4 (aq)+H 2 O(l) MgO(s)2HCl(aq)+MgCl 2 (aq)+H 2 O(l)
Metal hydroxide + acid metal + acid metal salt + water potassium + sulfuric sodium + hydrochloric hydroxide acid hydroxideacid hydroxide potassium sulfate + water sodium chloride + water 2KOH(aq) + H 2 SO 4 (aq) NaOH(aq) + HCl(aq)NaCl(aq)+ H 2 O(l) K 2 SO 4 (aq)+2H 2 O(l)
Metal carbonate + acid metal + acid metal salt + carbon + water copper + sulfuric magnesium +hydrochloric carbonateacid carbonateacid carbonatedioxide copper + carbon + water magnesium + carbon + water sulfatedioxide chloride CuCO 3 (s) + H 2 SO 4 (aq) CuSO 4 (aq) + CO 2 (g) + H 2 O(l) MgCO 3 (s) + 2HCl (aq)MgCl 2 (aq) + CO 2 (g) + H 2 O(l)
Recall that the reaction of acid with an alkali to form a salt is a neutralisation reaction. Explain what happens during a neutralisation reaction. When the number of H + ions is exactly matched by the number of OH - ions to form a pH of 7 H + (aq) + OH - (aq) H 2 O(l) An alkali can cancel out an acid to form a salt and the water (shown above) H + ions from the acid react with OH - ions from the alkali.
Acidic substances … Dissolve in water to form H + ions giving a pH of less than 7 Can be… –solids e.g. citric acid, tartaric acid –Liquids e.g. sulfuric acid, nitric acid, ethanoic acid –Gases e.g. hydrogen chloride Form salts with many other substances such as alkalis, hydroxides, carbonates, oxides, metals
Explain that acidic compounds…. Dissolve in water to produce aqueous hydrogen ions H + (aq) All acids contain hydrogen – HCl, H 2 SO 4, CH 3 COOH Explain that alkaline compounds…. Dissolve in water to produce aqueous hydroxide ions OH - (aq) Form solutions with pH lower than 7. Form solutions with pH higher than 7.
Write down the formula of the salt produced given the formula of the acid and the alkali. acidalkalisalt HClNaOHNaCl H 2 SO 4 KOHK 2 SO 4 HClCa(OH) 2 CaCl 2 H 2 SO 4 Mg(OH) 2 MgSO 4
C6.2 : Planning, Carrying out and controlling chemical synthesis 1. Identify the stages in the chemical synthesis of an inorganic compound. choosing the reaction or series of reactions risk assessment (chemical and procedural) working out the quantities of reactants to use carrying out the reaction in suitable apparatus in the right conditions (such as temperature, concentration or the presence of a catalyst) separating the product from the reaction mixture purifying the product measuring the yield and checking the purity of the product.
Understand the purpose of these techniques…. Dissolving… forming solutions to allow easy mixing of reactants Crystallisation… to purify a sample by the formation of pure crystals from a cooled (often saturated) solution, Filtration… to separate solid impurities from a solution, or to remove excess solid. Evaporation… to remove excess solvent from a solution Drying in an oven or dessicator… to remove water without the risk of wasting yield. Titration… to find the concentration of an acid (or alkali) using an alkali (or acid) of a known concentration AND an indicator
Understand the importance of purifying chemicals and checking their purity. There are three main grades of chemicals : 1. Analytical – this is the most pure (and most expensive!) If a product is to be used in foods/medicines then this grade is needed – eg. Table salt. 2. Laboratory – this is the ‘medium grade’. 3. Technical – this is low grade purity – eg salt for gritting roads.
Understand that a balanced equation for a chemical reaction shows the relative numbers of atoms and molecules of reactants and products. Mg(s) + 2HCl(aq) MgCl 2 (aq) +H 2 (g) Reactants : 1 x Magnesium atom 2 x Hydrogen atoms 2 x Chlorine atoms And, because the equation is balanced, the same number of atoms are present for the products side! The numbers in front of the formula tells you how many molecules there are of it. So above, there are 2 molecules of HCl, and 1 molecule of everything else.
Understand that the relative atomic mass of an element shows the mass of it’s atom relative to the mass of other atoms. Specifically, the RAM is compared to the mass of Hydrogen.
Be able to use the periodic table to obtain the relative atomic masses of elements. Look at the periodic table in your planners. The bottom number is the relative atomic mass.
Calculate the relative formula mass of a compound using the formula and the relative atomic masses of the atoms it contains. Periodic table : Ca = 40gC = 12gO = 16g CaCO 3 = 40+12+(3x16) = 40+12+48 = 100g What is the relative formula mass of calcium carbonate? Formula of calcium carbonate = CaCO 3
What is the relative formula mass of magnesium chloride? Formula of magnesium chloride = MgCl 2 From the periodic table: Mass of Mg = 24g Mass of Cl = 35.5g MgCl 2 = 24 + (2 x 35.5) = 24 + 71 = 95g
2Mg(s) + O 2 (g) 2MgO(s) 16g of oxygen (Relative formula mass = 32) is used to make magnesium oxide (relative formula mass = 40). How much magnesium oxide should we expect? 16/32 = 0.5 Ratio is 1:2 for oxygen to magnesium oxide 2 X 0.5 X 40 = 40g yield of magnesium oxide O 8 16 On periodic table
Mg(s) + 2HCl(aq) MgCl 2 (aq) +H 2 (g) 2.4g of magnesium (Relative atomic mass = 24) is used to make magnesium chloride (relative formula mass = 95). How much of this salt should we expect? 2.4/24 = 0.1 Ratio is 1:1 for magnesium to magnesium chloride 0.1 X 1 X 95 = 9.5g yield of magnesium chloride
Calculate percentage yields given the actual and theoretical yield. actual mass of pure sample X 100 theoretical mass expected Percentage yield = So if by experiment, 7.4g of magnesium chloride was made, when theoretically 9.5g was expected; what is the percentage yield? % yield = 7.4 9.5 X 100= 0.7789 x 100= 77.8 % yield.
An acid-base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid/base with an acid or base of known concentration. This allows for quantitative analysis of the concentration of an unknown acid or soluble base. It makes use of the neutralisation reaction that occurs between acids and bases and the knowledge of how acids and bases will react if their formulas are known. Acid-Base titrations can also be used to find percent purity of chemicals. Titrations
Open the tap to let the acid run into the flask Stop the tap at the first sign of a colour change Note the volume delivered (this is approximate) Repeat, but add drop by drop near the volume noted for greater accuracy. Record exact volume of acid needed to get colour change for neutral. Use the volumes of both solutions and the concentration of the acid to find the concentration of the alkali using a given formula (This could be a solid dissolved in water) Describe how to carry out an acid alkali titration accurately.
Substitute results in a given formula to interpret titration results quantitatively. In a titration, 50cm 3 of 2M sodium hydroxide was exactly neutralised by 30cm 3 of hydrochloric acid. What is the concentration of hydrochloric acid? Method 1. Write a balanced equation for the reaction. sodium hydroxide + hydrochloric acid sodium chloride + water NaOH(aq) HCl(aq) NaCl(aq)H 2 O(l) 2. Use the big numbers in front of the formulae ( if any) to work out the proportion of NaOH to HCl. In this case, it is 1:1 so 1 mole NaOH reacts with 1 mole HCl
3. Find out how many moles of sodium hydroxide are present. (moles = [concentration (in M) x volume (in cm 3 )] : 1000 The number of moles in 50cm3 of 2M sodium hydroxide = (2x50) : 1000 = 0.1 moles of sodium hydroxide. 4.From part 1 and 2 we know that 30cm3 of HCl also contains 0.1 moles. So to find the concentration of acid you rearrange the formula: concentration = (moles x 1000) : Volume Conc = (0.1 x 1000) : 30 = 3.33 M
Understand why it is important to control the rate of a chemical synthesis. If it is too fast it could make it unsafe. (eg could get too hot if exothermic; gas could be produced to quickly and pressure build up) If it is too slow, then product would be made too slowly, and yield low, so profit too low. (economic factors)
Explain the term ‘rate of chemical reaction’. This is the speed at which the reaction takes place. A reaction takes place when reactant molecules collide with enough energy.
Describe ways for following the rate of a reaction. 1. By collecting a gas. 2. Weighing the reaction mixture. 3. Observing colour change or precipitate.
Interpret results from experiments that investigate rate of reactions. Time (seconds) Mass lost (g) The reaction starts off quickly It slows down as it proceeds. It eventually stops when one of the reactant particles has run out.
Rate graphs and reactant concentrations Amount of product Time reactants product Reactant Concentration falls Rate of Reaction falls All product All reactant Mix of reactant And product Gradient of graph decreases
Rates and Graphs These show the increasing amount of product or the decreasing amount of reactant. Amount of product Time Amount of reactant Time Steep gradient Fast reaction Shallow gradient Slow reaction Steep gradient Fast reaction Shallow gradient Slow reaction
Time Mass lost Chips Powder Graph shows a faster reaction with powder. Same final volume of gas made. Increasing the temperature would have the same effect.
Recall that reaction rates vary with…. particle size (surface area) concentration temperature. Remember – to increase the rate of reaction, there needs to be more successful collisions per second.
Surface area The reactions of solids can clearly only take place at the surface of the solid. If we break a solid into smaller pieces we get more area and a faster reaction. Molecules collide with the surface of the solid Extra surface for molecules to collide with.
Reactions in solution involve dissolved particles that must collide before reaction is possible. The more crowded (concentrated) the solution, the faster the reaction because the frequency of successful collisions increases. Collisions infrequentCollisions frequent Use simple collision theory to explain how rates of reaction depend on the concentration of solutions of soluble chemicals.
Understand that catalysts speed up a chemical reaction while not being used up in the process. Because they are not used up, they are recyclable. For chemical reactions to occur: Existing bonds have to begin breaking so that new ones can be formed. The molecules have to collide in such a way that the reacting parts of the molecules are brought together. Catalysts can help with either or both of these processes.