 "> | This chapter MAY be much easier if you were to follow my method. The first thing you always have to learn in acid base and salt is to IDENTIFY them. I know its tough to memorise and master them, but its the best way to identify acid, its basically very simple all u hav to rmb theres an H or H2 in front of the formulae. these are different acids u have to learn to identify Identification: any front can go with any back in the formula ignore acid Front - Back H Cl H NO3 H2 CO3 H2 SO4 Organic Acid [Time Taken to master: 10seconds] Front Back CH3 COOH Heres bases, the key here is jus simply having O or HO behind the formula. The following below are only soluble base. Other bases that are not mention here are all insoluble Soluble Bases [Time Taken to master: 5mins] Front - Back K...........O Na.........OH Li NH4 NH3 Note: For NH3, it is alone, and it is not bonded with O or OH, NH3 itself is a soluble base. For NH4, it is uses only wif O or OH eg: NH4OH (aqueous ammonia) Form when ammonia is dissolved into water Furthur identification of bases [Time Taken to master: 5mins] Acidic Oxide Front - Back Non-Metal + O2 Basic Oxide Front - Back Metal + O Amphoteric Oxide/Hydroxide Front - Back Pb........O Al........ OH Zn There are only 3 amphoteric oxide, other metal + oxygen are basic oxde Neutral oxide Front - Back Non-metal + O [only 1 oxygen plus a non-metal will be neutral oxide] {Eg: CO, SO, H2O} Solublilty in Salts [Time Taken to master: 10mins] Whenever u see nitrate, sulphate, halogen and carbonate in the formulae, its a salt. Type of Salt - Soluble ......................- Insoluble Nitrate.........- All metals.................... - None Sulphate.....- Almost all metals......... - Ca, Pb, Ba Chloride..... - Almost all metals......... - Ag, Pb Carbonate.. - Group I metals/NH4...... - Mostly all .............................................................Metals [Eg: CaSO4 is a sulphate salt, and its insoluble] Memory Guide in General: Whenever you see NITRATE ,Group I metal and Ammonium in the formula, its soluble Memory Guide in Salt: If you DO NOT see nitrate and there is only Pb, it is insoluble the rest are up to ur hardworkingness :) When you have master the idenfication of ABS, you can proceed to learn preparation of salt 1st step: IDENTIFY the ABS 2nd step: IDENTIFY SOLUBILITY 3rd step: Decide the methods to use in preparation of salts For TITRATION IMPORTANT: this is ONLY for preparing group I and ammonium salt because both during titration, both reactants are in aqueous solution hence, excess acid or alkaline have to be removed 1. Use a pipette to draw an accurate fixed volume of acid to a conical flask 2. Add 2 to 3 drops of methyl orange into the flask 3. Titrate drop by drop of alkali from the burette into the acid. Swirl the solution each time a drop of alkali is added 4. When the first appearance of orange colour observed in the solution, stop the titration and note the volume of alkali used 5. Repeat the experiment using the exact volume of acid and alkali from the first experiment without the indicator (so that the salt is free from contamination of indicator) 6. The salt solution is purified by crystallisation process Note: Universal Indictor is not suitable because the colour change cannot be observed distinctly For Filtration IMPORTANT: This is ALSO to produce soluble salts but not Group I metal or ammonium salt. In filtration, one of the REACTANT IS SOLID 1. Excess 'solid reactant' is added to a fixed volune of dilute acid to make sure all acid is used up in this reaction ( important ) 2. Filter the solution to remove the excess 'solid reactant' from the 'salt formed' solution 3. Evaporate the filtrate until it becomes saturated so that the salt crystals can be formed easily 4. Let the solution cool so salt crystal can be formed 5. Wash the salt crystals with little bit of water and let it dry For Precipitation method This is easy however, yet confusing. This method is for preparing INSOLUBLE salt. how do u know which + which to get you insoluble salt? Hence, mastering the solublity salt is a MUST. there are two ways, acid + soluble salt or soluble salt+ soluble salt. Depending on what salt the question asked u to prepare, you have to know how to split the insoluble salt into its ion form in order to see their reactants. Eg: AgCl an insoluble salt split into its ion form, Ag+ and Cl- now, this gives you a clue of the two soluble salts you shld use. Look, the 1st salt should contains Ag and the 2nd salt should contains Cl Since you are looking for soluble, nitrate salt is the best since all nitrate salt are soluble. Hence: The 1st salt can be AgNO3 Now, u can use ANY POSITIVE element for Cl salt EXCEPT for Pb and Ag, remember? and since group I metal or ammonium salt are always soluble, lets take Na Henece: The 2nd salt can be NaCl So now, contruct the equation: AgNO3 + NaCl ----> AgCl + NaNO3(just form the 2nd salt in the product with whatever u are remaining. In this case, you are left with NO3 and Na after getting AgCl) Another example with Acid + Soluble Salt AgNO3 + HCl ----> AgCl + HNO3 finally, 3easy steps to memorise 1. Add the salt solution/acid to a beaker containing 'another salt solution you have chosen' 2. Stir the solution. A whte precipitate of the 'Insoluble Salt' is formed 3. Filter off the precipitate, wash with a little cold water and leave the precipitate to dry Take Note for ABS: IONIC EQUATION is very likely to be tested, hence if the substance is soluble, be sure the state is in AQ state! now lets proceed to reaction with metals,carbonates,ammonium salt, acid and bases. These are the list of equation you have to memorise in order to score well and construct its equation. 1. Acid + Metal Carbonate ----> Salt + Carbon Dioxide + Water 2. Acid + Base/Alkali ----> Salt + Water 3. Base/Alkali + Ammonium salts ----> Ammonia + Salt + Water 4. Acid + Metal ----> Salt + Hydrogen gas 5. Acid + Metal oxide/hydroxide ----> Salt + Water 6. Metal + Water ----> Metal Hydroxide + Hydrogen gas 7. Metal + Steam ----> Metal Oxide + Hydrogen gas 8. Metal Carbonate + Heating ----> Metal Oxide + Carbon Dioxide These are the total number of equation you have to memorise. It is combined with another chapter, metals The last part is just properties of the acid and bases you have to memorise, also indicators and its respective colour change Acidic Oxide - Reacts with bases to form salt and water - Reacts with water to form acid Basic Oxide - Reacts with acids to form salt and water - Reacts with water to form alkali Amphoteric Oxide - Can behaves like basic oxide or acidic oxide Neutral Oxide - They behave neither like Basic oxide nor Acidic oxide For emergency cases where you forgot the product of equations: - When there is just a metal in the reactant, there will be hydrogen gas in product, the other product will be whatever left behind - When you see the element CARBON(exclude acid), in any circumstances, there will be carbon dioxide in the product - When you see ammonium, there will always be ammonia in the products - If you manage to get the salt first, the remaining elements left, are hydrogen and oxygen, it will be water. Long? yeah, to master ABS u need hours of 'training' LOL you may copy post if you wan to. the main problem in ABS is only the identification part and solublity after that, its easy to learn ABS jus endure for 1-2hr memorising it =\ kekeke |
