Edexcel IGCSE Chemistry: Double Science PDF

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Chemistry: Your notes Double Science Acids, Bases & Salt Preparations Contents Solubility Rules Acids, Bases & Pro...

Head to www.savemyexams.com for more awesome resources Edexcel IGCSE Chemistry: Your notes Double Science Acids, Bases & Salt Preparations Contents Solubility Rules Acids, Bases & Protons Reactions of Acids Bases Prepare a Soluble Salt Practical: Prepare Copper(II)Sulfate Page 1 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Solubility Rules Your notes Solubility rules Ionic compounds are generally soluble in water compared to covalent substances, but there are exceptions A knowledge of the solubility of ionic compounds helps us to determine the most appropriate method for the preparation of salts The solubility of common ionic compounds is shown below: Solubility of the common salts Salts Soluble Insoluble Sodium, potassium and All None ammonium Nitrates All None Chlorides Most are soluble Silver and lead(II) Sulfates Most are soluble Barium, calcium and lead(II) Carbonates of sodium, Carbonates Most are insoluble potassium and ammonium Hydroxides of sodium potassium and ammonium Hydroxides (calcium hydroxide is sparingly Most are insoluble soluble) Note that calcium hydroxide is slightly soluble in water Exam Tip Calcium hydroxide solution is more commonly know as limewater and is used to test for carbon dioxide. Page 2 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Acids, Bases & Protons Your notes Acids, bases & protons Proton transfer The earlier definition of an acid and a base can be extended In terms of proton transfer, we can further define each substance in how they interact with protons Acids Acids are proton donors as they ionize in solution producing protons, H+ ions These H+ ions make the aqueous solution acidic Example: hydrochloric acid HCl (aq) → H+ (aq) + Cl– (aq) Bases (Alkalis) Bases (alkalis) are proton acceptors as they ionize in solution producing OH- ions which can accept protons These OH- ions make the aqueous solution alkaline Example: sodium hydroxide NaOH (s) → Na+ (aq) + OH– (aq) Page 3 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Reactions of Acids Your notes Reactions of Acids Reactions of acids with metals Only metals above hydrogen in the reactivity series will react with dilute acids The more reactive the metal then the more vigorous the reaction will be Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids When acids react with metals they form a salt and hydrogen gas The general equation is: metal + acid ⟶ salt + hydrogen Some examples of metal-acid reactions and their equations are given below: Table of acid-metal reactions Metal Sulfuric acid Hydrochloric acid Magnesium Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) Zinc Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g) Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g) Iron Fe (s) + H2SO4 (aq) → FeSO4 (aq) + H2 (g) Fe (s) + 2HCl (aq) → FeCl2 (aq) + H2 (g) In general, we can summarise the reaction of a metal that forms a +2 ion as follows: Acids-Metals Summary Table Acid Name of products Equation for reaction Hydrochloric acid Metal chloride and hydrogen M + 2HCl → MCl2 + H2 Sulfuric acid Metal sulfate and hydrogen M + H2SO4 → MCl2 + H2 Reaction of acids with bases When an acid reacts with a base, a neutralisation reaction occurs In all acid-base neutralisation reactions, a salt and water are produced: Page 4 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources acid + base ⟶ salt + water The identity of the salt produced depends on the acid used and the positive ions in the base Your notes Hydrochloric acid produces chlorides, sulfuric acid produces sulfate salts and nitric acid produces nitrates Metal oxides and metal hydroxides act as bases The following are some specific examples of reactions between acids and metal oxides / hydroxides: 2HCl + CuO ⟶ CuCl2 + H2O H2SO4 + 2NaOH ⟶ Na2SO4 + 2H2O HNO3 + KOH ⟶ KNO3 + H2O In general, we can summarise the reaction of metals and bases as follows: Acids and Metals Oxides or Hydroxides Summary Table Acid Name of products Equation for reaction Hydrochloric acid Metal chloride and water MOH + HCl ⟶ MCl + H2O Sulfuric acid Metal sulfate and water MO + H2SO4 ⟶ MSO4 + H2O Nitric acid Metal nitrate and water MO + HNO3 ⟶ MNO3 + H2O Reactions of Acids with Metal Carbonates Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the presence of effervescence caused by the carbon dioxide gas Acids & Metal Carbonates Reactions Table Acid Name of Products Equation for Reaction Metal chloride, carbon dioxide and Hydrochloric acid water MCO3 + 2HCl ⟶ MCl2 + CO2 + H2O Metal sulfate, carbon dioxide and MCO3 + 2H2SO4 ⟶ MSO4 + CO2 + Sulfuric acid water H 2O Metal nitrate, carbon dioxide and MCO3 + HNO3 ⟶ M(NO3)2 + CO2 + Nitric acid water H 2O Page 5 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The following are some specific examples of reactions between acids and metal carbonates: Your notes 2HCl + Na2CO3 ⟶ 2NaCl + H2O + CO2 H2SO4 + CaCO3⟶ CaSO4 + H2O + CO2 Exam Tip If in an acid-base reaction there is effervescence produced then the base must be a metal carbonate which produces carbon dioxide gas. Page 6 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Bases Your notes Bases What makes a base act like a base? Bases are substances which can neutralise an acid, forming a salt and water The term base and alkali are not the same A base which is water-soluble is referred to as an alkali So, all alkalis are bases, but not all bases are alkalis Alkalis have pH values of above 7 In basic (alkaline) conditions red litmus paper turns blue Bases are usually oxides, hydroxides or carbonates of metals The presence of the OH- ions is what makes the aqueous solution an alkali One unusual base is ammonia solution When ammonia reacts with water it produces hydroxide ions Some common alkalis and the ions they contain Name of alkali Formula Ions formed in water Sodium hydroxide NaOH Na+ + OH- Potassium hydroxide KOH K+ + OH- Aqueous ammonia NH3 (+ H2O) NH4+ + OH- Exam Tip Aqueous ammonia and ammonium hydroxide are the same thing. When ammonia gas dissolves in water it forms ammonium hydroxide. Be careful to use the correct terminology: ammonia is the gas, NH3, ammonium is the ion present in ammonium compounds, NH4+ Page 7 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Prepare a Soluble Salt Your notes Prepare a soluble salt A soluble salt can be made from the reaction of an acid with an insoluble base During the preparation of soluble salts, the insoluble reactant is added in excess to ensure that all of the acid has reacted If this step is not completed, any unreacted acid would become dangerously concentrated during evaporation and crystallisation The excess reactant is then removed by filtration to ensure that only the salt and water remain Since all of the acid has reacted and the excess solid base has been removed then the solution left can only be salt and water The water is evaporated by heating until small crystals begin to appear This is typically once half of the water is left Allowing the filtered solution to evaporate slowly over a period of days results in the formation of larger crystals If a carbonate was used as the solid base instead of an oxide or hydroxide, then any carbon dioxide gas produced would have been released into the atmosphere A common example is the preparation of copper(II) sulfate which can be made with copper(II) oxide and dilute sulfuric acid: CuO (s) + H2SO4 (aq) ⟶ CuSO4 (aq) + H2O (l) Copper sulfate crystals After filtering and heating copper sulfate crystals will form. Larger crystals will form if the water in the solution is left to evaporate slowly Photo by Wikimedia commons The acid could also be reacted with a metal to produce the salt, as long as the metal is above hydrogen in the reactivity series and not too reactive so that a dangerous reaction does not take place Page 8 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes Exam questions often ask why the solid oxide is added in excess. This is done to avoid leaving any unreacted acid which would become dangerously concentrated during evaporation and crystallisation. Page 9 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Practical: Prepare Copper(II)Sulfate Your notes Practical: Prepare Copper(II)Sulfate Aim To prepare a pure, dry sample of hydrated copper(II) sulfate crystals Materials 1.0 mol / dm3 dilute sulfuric acid Copper(II) oxide Spatula & glass rod Measuring cylinder & 100 cm3 beaker Bunsen burner Tripod, gauze & heatproof mat Filter funnel & paper, conical flask Evaporating basin and dish. Diagram Preparation of a soluble salt from an insoluble base and acid Page 10 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 11 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The preparation of copper(II) sulfate by the insoluble base method Method 1. Add 50 cm3 dilute acid into a beaker and warm gently using a Bunsen burner 2. Add the copper(II) oxide slowly to the hot dilute acid and stir until the base is in excess (i.e. until the base stops dissolving and a suspension of the base forms in the acid) 3. Filter the mixture into an evaporating basin to remove the excess base Page 12 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4. Gently heat the solution in a water bath or with an electric heater to evaporate the water and to make the solution saturated 5. Check the solution is saturated by dipping a cold glass rod into the solution and seeing if crystals form Your notes on the end 6. Leave the filtrate in a warm place to dry and crystallise 7. Decant excess solution and allow the crystals to dry Practical Tip The base is added in excess to use up all of the acid, which would become dangerously concentrated during the evaporation and crystallisation stages Results Hydrated copper(II) sulfate crystals should be bright blue and regularly shaped Exam Tip Make sure you learn the names of all the laboratory apparatus used in the preparation of salts. Page 13 of 13 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers