Acid & Base Titrations PDF

Acid & Base Titrations Standard Solution  A standard solution is a solution whose concentration is accurately known.  A primary standard is a water-soluble substance that is stable & is available in pure form.  Anhydrous sodium carbonate (Na2CO3) is a common primary standard. Procedures to ensure...

Acid & Base Titrations Standard Solution  A standard solution is a solution whose concentration is accurately known.  A primary standard is a water-soluble substance that is stable & is available in pure form.  Anhydrous sodium carbonate (Na2CO3) is a common primary standard. Procedures to ensure accurate titrations BURETTE: 1. washed out with DI water 2. It is then washed out with the solution it is to contain 3. The solution is added to the burette using a funnel. 4. The tap of the burette is opened briefly to fill the part of the burette below the tap. 5. The burette is topped up above the 0cm3 mark. 6. The funnel is removed. 7. The tap is opened and solution released until the bottom of the meniscus rests on the 0cm3 mark. PIPETTE: 1. The pipette is washed out with DI water 2. It is then washed out with the solution it will transfer 3. A pipette filler is used to bring the solution into the pipette. 4. The solution is filled until the bottom of the meniscus rests on the graduation mark when viewed from eye level. 5. The solution is fully released & then the tip of the pipette is placed against the inside of the conical flask for about 3 seconds (note: the pipette is designed to hold a small amount of the liquid after delivery). CONICAL FLASK: 1. The conical flask is washed out with DI water only 2. The pipette then transfers the solution into the conical flask. 3. A few drops of indicator are added 4. A white tile is placed under the conical flask 5. During the titration, the sides of the conical flask may be washed down from time to time EXP 1: Making a standard solution of Anhydrous Na2CO3 Steps in making a standard solution 1. Weigh 2. wash the solute into a clean beaker. 3. Use a stirring rod to dissolve the solute. 4. Pour the solution into a volumetric flask using a funnel.  Rinse the beaker and add washings  Using a dropper, add DI water until the bottom of the meniscus rests on the graduation mark, when viewed at eye level.  Stopper the solution and invert the flask 10 times in order to fully mix the solution volatile: HCl vapour escapes when a concentrated bottle is opened HNO3 is volatile: hydroscopic: H2SO4 This means that it will absorb water vapour from the air Exp 2 : HCL vs Sodium Carbonate   Indicator used: Colour change: Methyl Orange Yellow  Peach Pink Exp 3: Vinegar vs. NaOH  Vinegar = ethanoic acid.  The bottled vinegar is usually diluted.  If it were not diluted a colour change would occur after a very small volume of acid was added from the burette – this would result in a large % error.   Indicator used: Colour change: Phenolphthalein Pink  Colourless (base) (acid) Steps in solving vinegar titration questions: 1. Work out the concentration of titrated vinegar 2. Take account of the dilution factor 3. Multiply concentration by this 4. Convert mol/L into g/L 5. x Mr 6. Convert g/L into % w/v Exp 4: Water of Crystallisation Sodium carbonate can either be 1. Anhydrous  contains no water 2. Hydrated  contains water in its crystalline structure Hydrated sodium carbonate is represented as Na2CO3.xH2O Where x = 2,3,4…etc.    Reactants Used: Indicator Used: Colour Change: Na2CO3.xH2O vs. standardised HCl Methyl Orange Yellow -> Peach Pink Solving water of Crystallisation Q’s  In reactions involving Na2CO3.xH2O, only the sodium carbonate part of the compound takes part in the reaction. Steps in solving question: 1. Find the conc of the base 2. Convert M  g/L…….x Mr 3. Use actual volume to get mass of anhydrous base 4. Get mass of H2O 5. Hydrated mass – Anhydrous mass……express as a % 6. Find Mr of hydrated base