Calibration of Volumetric Equipment Volumetric Flask (TC: to contain) Buret (TD: to deliver) Pipet (TD: to deliver) –Volumetric (or transfer) –Mohr (or graduated) (not calibrated) Thermometer

CLEANING GLASSWARE Do not rinse at de-ionized water tap – take flask back to own sink to rinse. For glassware, rinsing with de-ionized water should leave no droplets. Droplets indicate the need for cleaning. For open and easily rinsed containers such as beakers and flasks, use a cleansing powder, elbow grease, and test tube brush; then rinse with tap water and finally with de-ionized water. For burets, pipets, volumetric flasks, etc., use special liquid detergent along with buret brush, then rinse with tap water and finally with de-ionized water. NEVER use cleansing powder; it is too hard to get out and in the case of burets it will usually score the Teflon stopcocks.

Time After Delivery Volume Change After Drainage with Different Buret Free Delivery Times 30 sec100 sec 1 min0.01 mL0.00 mL 10 min0.10 mL0.02 mL Buret Drainage Times: (Buret should drain within seconds) Buret Check Duplicate Runs by Approximate Method V W  = V - W Run l ml g 0.18 Run ml g 0.15 Δ 1 – Δ 2 ≤.03 Run l ml g 0.16 Run ml g 0.19 etc.

Buoyancy Correction:  B= buoyancy correction d a = g/cm 3 (density of air at room temperature) d w = 8.4 g/cm 3 (density of calibration weights) d o = 1.00 g/cm 3 (density of water to 3 sig. fig.) o =object (water) w w = mass read on balance (mass of weights) w o = actual mass of object =w w +  B Archimedes’s Principle: an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced. If an object is larger in volume than the weights that balance it, then it displaces more air and is buoyed up by a greater force. ΔB = d a w w [1/d o – 1/d w ] Mass of air displaced by object Mass of air displaced by weights

Volumetric Pipet Uncertainty of a SINGLE MEASUREMENT Thermometer Quartz thermometer Should be within 0.5  C

Storage of buret and pipet: Fill with de-ionized H 2 0 Cork in top of buret (if old obtain a new cork) Rubber policeman on tips Loosen stopcock of buret slightly for storage. Remember to retighten when you use buret again. Store in buret cabinet