General Chemistry (LAB)
Beaker
- can be used for the transfer, mixture, and heating of liquids, or for reactions - however, beakers are not accurate and should not be used for measurements - it is not volumetric - it is not calibrated or graduated in a way that indicates very precise volumes. Beakers are cylindrical in shape and can vary in size
Erlenmeyer flask
- is used for the transfer of liquids, mixture of liquids, or for reactions - but is not accurate and should not be used for measurements - it is not volumetric - it is not calibrated or graduated in a way that indicates very precise volumes. - since it has a narrower neck than a beaker, it helps prevent splashing outside of the container (this is particularly useful during titrations, where a liquid is being dropped into a solution).
Buret
- is used for the transfer of very precise amounts of liquid - primarily in titrations to deliver specific, precise amounts of the titrant. - it contains a stopcock along its side that allows one to deliver solution gradually. Once the endpoint is reached, the stopcock is closed and the markings on the buret can be ready to determine the precise amount of liquid that was delivered to the solution. While a buret could be used to accurately measure 8.7 mL of a solution, it would not be the ideal choice compared to a graduated pipet. - while a pipet can easily draw up 8.7 mL from a solution (as it is a more portable device), a buret is a stationary piece of equipment that is loaded from the top as the solution must be poured in from above. - it is the ideal choice for transferring solution during a titration where an unknown amount needs to be measured accurately, but in most other situations where accuracy is desired, a pipet is preferable.
A student measures the mass of a compound to be 9.01 g and its volume to be 11.0 mL. What is the density in g/mL?
0.819 D = m/V We have 3 significant figures in 9.01g and 3 significant figures in 11.0mL, so our answer must have 3 significant figures.
Significant figures
1. Zeroes between digits are significant: 1005 (4 s.f.), 7.03 (3 s.f.) 2. Zeroes at the beginning of the number are NEVER significant: 0.02 (1 s.f.), 0.0026 (2 s.f.) 3. Zeroes at the end of the number are significant if the number has a decimal point: 0.0200 (3 s.f.), 3.0 (2 s.f.)
During a titration experiment, the titrant placed in which of the following?
Buret The titrant is the stock or known solution. The concentration (molarity) of the titrant is known, however the concentration (molarity) of the titrand (solution being titrated) is unknown. The titrant is poured into the buret and the volume is recorded before titration begins. The titrand is measured and added to an Erlenmeyer flask along with a pH indicator (commonly phenolphthalein) before the beginning of the titration experiment.
Test tube
can be used for the transfer, mixture, and heating of liquids, or for reactions - however, test tubes are not accurate and should not be used for measurements it is not volumetric - it is not calibrated to indicate very precise volumes, and test tubes are generally not graduated in any way
Filtration
is an effective technique to separate a solid from a liquid. (ex: sand in an aqueous solution of KCl and water) by passing the mixture through a filter with pores of the appropriate size (small enough to prevent sand from passing through, but large enough to allow the aqueous solution - the filtrate - to pass), the sand particles will be retained on the filter.
Evaporation
is the transition at the surface of a liquid from liquid to gas. It is very similar to the phase change of vaporization, but unlike vaporization (which occurs throughout the entirety of a liquid and only at or above the boiling point of the liquid), evaporation only occurs at the surface and can occur at any temperature. Example: It would be useful to separate the water from the KCl after it is filtrated, leaving behind salt crystals.
Liquid Column Chromatography
is used to differentiate liquids in a solution on the basis of differences in polarity. Method: A test tube or burette is filled with highly polar beads. The solution is then poured through. The more polar component of the solution will spend more time bound to the more polar beads, while the less polar component (being less attracted to the polar beads) will run through more quickly and have a faster elution time. This technique is generally more effective at analytically checking the purity of a solution than it is for separation.
Crystallization
is used to purify solid compounds on the basis of differences in solubility. during crystallization, a solid compound is added to a solvent (usually boiling). The solvent is then slowly cooled to room temperature, and then cooled again in an ice bath. As solubility of solids in solution generally lowers with temperature, as the solution cools the less soluble portion of the solid compound will crystallize and separate from the more soluble portion. This technique is also ineffective when the components of the solid compound are similar in solubility.
Distillation
is used to separate two liquids in a solution it separates based on differences in boiling point - if two liquids in a solution have boiling points that are similar, this technique would not be very effective. in simple distillation, a solution is heated and the component with the lower boiling point boils off first, then cools down and condenses into another apparatus.
Precise
measurement produces consistent results
Accuracy
measurement taken is close to the true value
Pipet
used for the measurement and transfer of very precise amounts of liquid. it may be graduated (with several markings for varying volume) or volumetric (a single marking for a set volume). unlike a buret, a pipette is portable and a graduated pipette could easily be used to accurately measure a desired amount of solution it is important when transferring liquid with a pipette not to "blow out" or force any remaining liquid at the very end of the pipette after the initial transfer - a pipette is calibrated to account for this remaining liquid.
