CHEM 123 - Lab final UBC Questions And Answers Rated A+

[A] = -kt + [A]0 - 0th order integrated rate law 1/[A] = kt + 1/[A]0 - 2nd order integrated rate law accuracy - how close a measured value is to the true value acid buffer capacity - the number of moles of H3O + per litre of buffer which are required to lower the pH by 1 unit (units = M) analytical balance - - used to determine a precise mass to the nearest +/- 0.0001 g - masses are always reported to 4 decimal places Are you allowed to change the flow rate after you've set it? - no you cannot - it will change the drop size and thus the volume base buffer capacity - the number of moles of OH- per litre of buffer which are required to raise the pH by 1 unit (units = M) beaker - - measuring volumes of liquids and transporting chemicals - not very precise briefly describe the method of initial rates - various reaction rates are measured for multiple experimental trials where the concentration of one reactant is kept constant and the other is changed to determine the order of reaction with respect to the test variable buret - - graduated glass tube with a tap at one end and is used for delivering known volumes of a liquid (good for titrations) - long, graduated, glass tube with stopcock at lowered end and has a tapered glass tipceramic tile - - for resting hot objects on to cool (protects bench top) - can also be placed under an Erlenmeyer flask during a titration to make it easier to determine the end point Describe the steps for weighing by difference - - place clean empty weigh boat on top loading balance - tare top loading balance & weigh boat to 0.00g - add approximate mass (+/- 20%) of chemical to weigh boat - close all doors on analytical balance and tare it to 0.0000g - weigh the sample & weigh boat and record the value (1) - transfer weighed sample into beaker (from weigh boat) - weigh the emptied weigh boat and record the value (2) Subtract value 2 from value 1 to get the mass of the chemical describe the steps to take when preparing a standard solution (in a volumetric flask) - - weigh & dissolve the solid compound (using weigh by difference) - clean the volumetric flask, funnel, and stopper 3x with deionized water - quantitatively transfer the dissolved sample into the volumetric flask (using and funnel and rinsing beaker/stir rod with deionized water) - fill volumetric flask to a few centimetres below the calibration mark (do not go above this line) - use a dropper to add water dropwise to volumetric flask until the bottom of the meniscus is resting on the calibration line (if you go past calibration mark, you must start over) - stopper the flask and invert the flask 20x does an analytical balance or top-loading balance need to be recorded to 4 decimal places? - analytical balance drop counter - - has a sensor that counts the number of drops coming out of the drop dispenser - must be lined up with the drop dispenserdrop dispenser - - used to hold liquids and has a knob that controls the flow - special tip is used to create drops Erlenmeyer flask - - good for storing, swirling, and heating liquids - used for titrations (helps prevent liquid from splashing out due to its long neck) funnel - for quantitative transfer of solutions glass stir rod - used for mixing solutions graduated cylinder - used for general measuring of liquids (not used for quantitative analysis, as it isn't very precise) hot plate - used to heat solutions and helps to dissolve solids how can we monitor the rate of a reaction? - by the decrease in concentration of the reactants (disappearance of the dye's colour) how do we know if something is a standard solution? - if it has a known concentration to at least 4 significant figures) how do we know what the order is with respect to dye given its kinetic trace? - whatever plot (0th, 1st, or 2nd order) produces a linear plot will correspond to the order with respect to dye how do you determine the order with respect to bleach? - by plotting kinetic traces using the constant concentration of dye and higher concentration of bleach to see which rate law the data follows how do you determine the order with respect to dye? - by plotting kinetic traces using the constant concentration of dye and lower concentration of bleach to see which rate law the data followsHow do you fill a volumetric pipette? - - hold the pipette near the very top (blunt end) with one hand and the bulb with the other) & make sure the tip is submerged below the surface of the solution & bulb is not yet on the pipette - completely squeeze all air out of pipette bulb & gently put tip of bulb into top of the pipette (never pipette by mouth) - slowly release pressure on the pipette bulb to allow the solution to rise into the pipette (fill to at least 2 cm above calibration line, keep pipette tip in solution to avoid bubbles from entering pipette) - remove the bulb quickly and cover the top of pipette with index-finger of the hand holding the pipette (not with thumb) - drain solution down to calibration (slowly move index finger covering the top of the pipette to drain solution to get meniscus resting on the calibration line) - remove any suspended drops from the pipette by touching it to the side of the beaker how do you prepare a volumetric pipette? - clean with deionized water and then rinse with solution that will be pipetted (the sample) How much KIO3 should be used in the titration to maintain 4 significant figures in the measurements? - at least 10 mL of KIO3 (usually recommended to use 25 mL) How to calibrate drop dispenser - - fill the drop dispenser with deionized water - open the valve & turn the flow rate knob - slow the rate to a drop every half a second & make sure the light is flashing with each drop - press start on microlab and make sure drops are going up in ones how to calibrate pH probe - - place probe in buffer solution with pH of 7 & record the voltage produced - Microlab related voltage to measured pH value & calculates the corresponding pH value to each measured voltage & displays it on the monitor How to calibrate the drop counter - - immerse the pH probe in the solution & set computer to take pH reading whenever a drop is added- we calibrate microlab by measuring the volume of approximately 100 drops of solution delivered from a drop dispenser - drop counter is selected from microlab's sensor menu & the formula tool is used to convert drops to volume in mL (so graph reads directly in volume) - volume = (counter reading in drops)(mL of solution measured by difference)/100 drops how to clean a pipette - - pour at least 25ml of deionized water into a clean beaker - use pipet bulb to half-fill the pipette with deionized water - hold pipette horizontally and role around to coat the inside with water - discharge the water through the tip into the sink or waste beaker - repeat the wash 2 times with deionized water - transfer 25 mL of the solution to be pipetted into a clean & dry beaker - draw approximately 5 mL of solution into the pipet and hold in horizontal position and coat inside with solution - discharge liquid into the sink/waste beaker how to clean the burette - - use clean funnel over the sink & add 5-10mL of deionized water with the stopcock closed - hold in horizontal position and roll to coat insides with water - drain water through tip by opening the stopcock - repeat 2x - close stopcock again and use clean funnel & add 5-10mL of solution into burette - hold horizontally and coat sides of burette with solution & drain through stopcock into sink or waste beaker