Making salts titration-week 3
- 2. Demonstrate knowledge and understanding of preparation, separation and purification of salts as examples of some of the techniques specified in section 2.2.2 and the reactions specified in section 8.1
- 3. A soluble salt can be prepared by reacting an acid with a soluble reactant. This is usually a dilute solution of an alkali such as sodium hydroxide or ammonia. The main steps are: Carry out a titration. This is to determine the volumes of acid and alkali that must be mixed to obtain a solution containing only salt and water. Mix the acid and alkali in the correct proportions, as determined in step 1, but this time without including an indicator. Pure dry crystals can be produced by crystallisation, then filtration to remove excess solution, followed by drying on a watch glass or in a warm oven.
- 4. Apparatus 1. a pipette to accurately measure the volume of a reactant before transferring it to a conical flask 2. a burette to add small, measured volumes of one reactant to the other reactant Chemicals 1. a suitable indicator 2. Dilute solution of an aqueous acid. 3. Dilute solution of an alkali.
- 6. Method This is an outline method for carrying out a titration in which hydrochloric acid is added to sodium hydroxide solution. Use the pipette and pipette filler to add a measured volume of sodium hydroxide solution to a clean conical flask. Add a few drops of indicator and put the conical flask on a white tile. Fill the burette with hydrochloric acid and note the starting volume. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix. Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). Note the final volume reading. Repeat steps 1 to 5 until you get concordant titres(values within a certain range). More accurate results are obtained if acid is added drop by drop near to the end-point.
- 7. Titration must be used to know the amounts of an acid and an alkali for complete neutralisation. This is because there is no insoluble excess reactant that could be removed by filtration. Once we know how much acid/alkali reacts with a known amount of alkali/acid, experiment is repeated using these amounts without indicator
- 8. Titrations gives a solution of salt as a final product. To obtain salt crystals we must crystalise it. The salt solution is heated in an evaporating basin using a Bunsen burner and a tripod. Solution is heated until crystallization point. On cooling salt crystals are formed. Collect the crystals by filtering or decanting Dry the crystals by keeping in a warm dry place or between the folds of filter paper.
- 9. It is the time when cooling a hot saturated solution forms crystal. We can find it out by putting a drop of solution on glass slide using a glass rod. If it makes crystals on slide, the crystalisation point is reached.