Burette and Balance

BURETTE AND BALANCE

HOW TO USE BURETTE

Rinse and fill each burette with solution as you were shown in the Lab Techniques Experiment.

waste

Discard the rinsing solution into the 400 mL beaker labeled waste.

No air bubbles in tip

Use a burette reading card to take all readings from the burette. Results are dependent on making accurate measurements.

Avoid Parallax

When reading a buret it is important that your line of sight be in a direction perpendicular to the buret column. Variability of the background does not always offer such visibility. The bottom of the mensicus is lightened by random reflections in the laboratory. Such variability can produce errors of several hundredths of a milliliter.

Avoid Parallax

From below

From above

A 50 mL buret can be read to 0.01 mL, but in order to be able to interpolate to the last digit, the perpendicular line of sight must be followed with meticulous care.

Use a Buret Card

Just right A buret card ought to have a black streak with a distinct horizontal zone of black against white. the upper limit of the black streak ought to be placed just under the meniscus, so that the bottom of the meniscus can be seen distinctly placing the black streak just under the meniscus is more repeatable than at some variable distance, the close

Too low

Keep Clean

Pipettes and burettes accumulate inert solid material which must be removed from time to time. You may have to use a wire to clean out this material. It is best to do it with the stopcock valve removed so that when you do a reverse wash, the material can be washed out at the point of the valve instead of at the other end of the burette cylinder

Keep Clean

This buret has droplets which stick to the inner wall. If your buret shows such droplets, use one of the buret brushes and Alconox to wash the inner surface. If that doesn't improve the drainage, rinse with some dichromate/sulfuric acid cleaning solution into the buret for more thorough cleaning.

Avoid poor drainage.

Avoid Air Bubbles

A bubble in the nozzle of a buret will produce an inaccurate volume reading if the bubble escapes during a titration. Bubbles may be large and visible as shown above or so small as not to be seen. During a titration such small bubbles typically begin to move in the direction of the nozzle .

Buret Buret A buret is used to deliver solution in precisely-measured, variable volumes. Burets are used primarily for titration, to deliver one reactant until the precise end point of the reaction is reached. Using a Buret To fill a buret, close the stopcock at the bottom and use a funnel. You may need to lift up on the funnel slightly, to allow the solution to flow in freely.

Buret You can also fill a buret using a disposable transfer pipet. This works better than a funnel for the small, 10 mL burets. Be sure the transfer pipet is dry or conditioned with the titrant, so the concentration of solution will not be changed. Before titrating, condition the buret with titrant solution and check that the buret is flowing freely. To condition a piece of glassware, rinse it so that all surfaces are coated with solution, then drain. Conditioning two or three times will insure that the concentration of titrant is not changed by a stray drop of water.

Buret Rinse the tip of the buret with water from a wash bottle and dry it carefully. After a minute, check for solution on the tip to see if your buret is leaking. The tip should be clean and dry before you take an initial volume reading

Buret When your buret is conditioned and filled, with no air bubbles or leaks, take an initial volume reading. A buret reading card with a black rectangle can help you to take a more accurate reading. Read the bottom of the meniscus. Be sure your eye is at the level of meniscus, not above or below. Reading from an angle, rather than straight on, results in a parallax error.

Buret Deliver solution to the titration flask by turning the stopcock. The solution should be delivered quickly until a couple of mL from the endpoint.

Buret The endpoint should be approached slowly, a drop at a time. Use a wash bottle to rinse the tip of the buret and the sides of the flask.

Quantitative Chemistry Analytical Balance needed for: Preparation of Standard Solutions Gravimetric Analysis: Suspended Solids (fixed and organic) Sludge Solids (fixed and organic) Dissolved Solids (fixed and organic)

Analytical Balance An analytical balance measures masses to within 0.0001 g. Use these balances when you need this high degree of precision. Turn the balance on by pressing the control bar. The display lights up for several seconds, then resets to 0.0000.

Analytical Balance Place creased, small weighing paper on the balance pan. Close the sliding glass doors. Wait for the green dot on the left to go out. This is the stability indicator light, indicating that the weight is stable.

Analytical Balance Press the control bar to cancel out the weight of the container or paper. The display will again read 0.0000.

Analytical Balance Carefully add the substance to be weighed up to the desired mass. Do not attempt to reach a particular mass exactly.

Analytical Balance Before recording the mass, close the glass doors and wait until the stability detector lamp goes out. Record mass of solid.

Analytical Balance Use the brush provided to clean spills in the weighing chamber. Discard any disposable tare containers, weighing paper, or Kimwipes in the nearest wastebasket.