IGCSE 0620 Acid Base Salts Notes PDF

IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Proton transfer, strong & weak acids IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Proton transfer  Acids are proton donors as they ionise in solution producing protons, which...

IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Proton transfer, strong & weak acids IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Proton transfer  Acids are proton donors as they ionise in solution producing protons, which are H+ ions  These H+ ions make the aqueous solution acidic  Bases are proton acceptors as they accept the protons which are donated by the acid Proton transfer between hydrochloric acid and water Diagram showing the role of acids and bases in the transfer of protons - here water acts as a base as it accepts a proton What is a strong acid?  Acids can be either strong or weak, depending on how many H+ ions they produce when dissolved in water  Strong acids completely dissociate (or ionise) in water, producing solutions of a very low pH  Strong acids include HCl and H2SO4  Example of a strong acid: hydrochloric acid HCl (aq) → H+ (aq) + Cl- (aq) What is a weak acid?  Weak acids partially dissociate (or ionise) in water and produce pH values which are closer to the middle of the pH scale, whilst still being below 7  For weak acids, there is usually an equilibrium set-up between the molecules and their ions once they have been added to water  Example of a weak acid: propanoic acid CH3CH2COOH ⇌ H+ + CH3CH2COO-  The equilibrium lies to the left, indicating a high concentration of intact acid molecules, with a low concentration of H+ ions in the solution  Another example of a weak acid is ethanoic acid which will react with alkalis such as sodium hydroxide to form ethanoate salts IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi ethanoic acid + sodium hydroxide → sodium ethanoate + water CH3COOH + NaOH → CH3COONa + H2O Effect of concentration on strong and weak acids  A concentrated solution of an acid is one that contains a higher number of acid molecules per dm3 of solution  It does not necessarily mean that the acid is strong though, as it may be made from a weak acid which does not dissociate completely  For example a dilute solution of HCl will be more acidic than a concentrated solution of ethanoic acid, since most of the HCl molecules dissociate but very few of the CH3COOH do  IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Important Definitions: An acid is proton (H+)donor A base is proton (H+)acceptor Examples of the names of salts from specific acids and metals Acid Name of products Equation for reaction Hydrochloric acid Magnesium chloride and hydrogen Mg + 2HCl → MgCl2 + H2 Sulfuric acid Magnesium sulfate and hydrogen Mg + H2SO4 → MgSO4 + H2 Nitric acid Magnesium nitrate and hydrogen Mg + 2HNO3 → Mg(NO3)2 + H2  IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Examples of reactions between acids and bases Acid Name of products Equation for reaction Hydrochloric acid Magnesium chloride and water Mg(OH)2 + 2HCl → MgCl2 + 2H2O Sulfuric acid Magnesium sulfate and water MgO + H2SO4 → MgSO4 + H2O Mg(OH)2 + 2HNO3 → Mg(NO3)2 + Nitric acid Magnesium nitrate and water H2O IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Examples of reactions between acids and carbonates Acid Name of products Equation for reaction Magnesium chloride, carbon MgCO3 + 2HCl → MgCl2 + CO2 + Hydrochloric acid dioxide and water H2O Magnesium sulfate, carbon MgCO3 + H2SO4 → MgSO4 + CO2 + Sulfuric acid dioxide and water H2O Magnesium nitrate, carbon MgCO3 + 2HNO3 → Mg(NO3)2 + Nitric acid dioxide and water CO2 + H2O A proton acceptor IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi What are indicators?  Two colour indicators are used to distinguish between acids and alkalis  Many plants contain substances that can act as indicators and the most common one is litmus which is extracted from lichens  Synthetic indicators are organic compounds that are sensitive to changes in acidity and appear different colours in acids and alkalis  Thymolphthalein and methyl orange are synthetic indicators frequently used in acid-alkali titrations What are synthetic indicators?  Synthetic indicators are used to show the endpoint in titrations as they have a very sharp change of colour when an acid has been neutralised by alkali and vice-versa  Litmus is not suitable for titrations as the colour change is not sharp and it goes through a purple transition colour in neutral solutions making it difficult to determine an endpoint  Litmus is very useful as an indicator paper and comes in red and blue versions, for dipping into solutions or testing gases 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: o pH 0-2 = strong acid  Extremely acidic substances can have values of below 1 IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi o pH 3-6 = weak acid  The higher the pH then the more alkaline the solution is: o pH 8-11 = weak alkali o pH 12-14 = strong alkali  A solution of pH 7 is described as being neutral  The pH scale  The pH scale and hydrogen ions We have already seen that acids are substances that contain hydrogen ions in solution The more hydrogen ions the stronger the acid, but the lower the pH The higher the concentration of hydroxide ions in a solution the higher the pH So pH is a measure of the concentration of H+ ions in solution, but they have an inverse relationship Exam Tip Acid strength is reflected in how many hydrogen ions are in solution. The more hydrogen ions the lower the pH and vice-versa. How is universal indicator used? Universal indicator is a mixture of different indicators which is used to measure the pH A drop is added to the solution and the colour is matched with a colour chart which indicates the pH which matches specific colours IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi Neutralization reaction: IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi IGCSE 0620: TOPIC ACID, BASE SALTS NOTES Compiled by Iram Shahzadi