AQA GCSE Combined Science: Trilogy: Chemistry Revision Notes Exam code: 8464

Strong & Weak Acids  (AQA GCSE Combined Science: Trilogy): Revision Note Exam code:  8464 Strong & weak acids Higher tier only Acids can be either  strong  or  weak,  depending on how many ions they produce when they dissolve in water When added to water, acids ionise or  dissociate  to produce H +  ions For example, the general acid HX dissociates to form H +  and X – HX ⟶ H +  + X – What is a strong acid? Strong acids dissociate  completely  in water This produces a solution with a high concentration of H +  ions  This means that strong acids have a  low  pH, typically pH 1 - 3  Examples of strong acids include: Hydrochloric acid, HCl HCl (aq) → H +  (aq) + Cl –  (aq)   Nitric acid, HNO 3   HNO 3  (aq) → H +  (aq) + NO 3 –  (aq) Sulfuric acid, H 2 SO 4   H 2 SO 4  (aq) → H +  (aq) + SO 4 2–  (aq) What is a weak acid? Weak acids...

The pH Scale & Neutralisation  (AQA GCSE Combined Science: Trilogy): Revision Note Exam code:  8464 Did this video help you? Acids & bases When  acids  are added to water, they form positively charged  hydrogen ions  (H + ) The presence of H +  ions is what makes a solution acidic When  alkalis  are added to water, they form negative hydroxide ions (OH – ) The presence of the OH –  ions is what makes the aqueous solution an alkali The pH scale is a numerical scale which is used to show how  acidic  or  alkaline  a solution is It is a measure of the amount of the hydrogen ions present in solution The pH scale What is the pH scale? The pH scale goes from 1 – 14  All acids have pH values of  below  7 All alkalis have pH values of  above  7 The  lower  the pH then the  more acidic  the solution is pH 1-3 = strong acid Extremely acidic substances can have values of ...

Required Practical: Preparation of a Soluble Salt  (AQA GCSE Combined Science: Trilogy): Revision Note Exam code:  8464 Required practical 1: Preparation of a soluble salt Objective: To prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a Bunsen burner and dilute acid Hypothesis: A salt can be prepared and separated by an acid-base neutralisation reaction Materials: 1.0 mol/dm 3  dilute sulfuric acid Copper(II) oxide Spatula & glass rod Measuring cylinder & 100 cm 3  beaker Bunsen burner Tripod, gauze & heatproof mat Filter funnel & paper, conical flask Evaporating basin and dish. The steps in the preparation of a soluble salt 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 Method: Add 50 cm 3  dilute acid into a beaker and warm gently using a Bunsen burner Add the insoluble oxide slowly to ...

Soluble Salts  (AQA GCSE Combined Science: Trilogy): Revision Note Exam code:  8464 Did this video help you? Preparing soluble salts 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...