DAT General Chemistry Lab Techniques

____________ is used to measure the change in heat (released or absorbed) during a chemical reaction.

Calorimetry

The setup for _______ generally consists of a Styrofoam cup with a sealed lid and hole for thermometer to measure the change in temperature during the reaction.

calorimetry

___________ is used to separate solids and liquids in heterogenous mixtures.

Centrifugation

Successful separation (centrifugation) results in the solid portion, ______, at the bottom of the centrifuge tube and the liquid portion, ________, above it.

pellet; supernatant

When using a centrifuge, it is important that it remains ____________ at all times -- any tube being spun should have one of equal volume placed in the opposite slot.

balanced

Proper ____________ ___________ methods ensure that the entire quantity of a substance has been transferred.

quantitative transfer

When transferring powders, the ______ should first be measured on creased weighing paper.

mass

After weighing the mass of a powder on creased weighing paper, the paper should carefully be _____ and tipped into its destination. A spatula should then be tapped against the paper to:

folded; dislodge any remaining powder

(Final step of weighing a powder) Finally, the paper should be __________ to ensure full transfer of the powder.

rinsed into a beaker

When transferring a liquid, after it is poured into its destination, the sides of the vessel it was poured from should be rinsed with ______ and continue to be poured into the destination to ensure that all of the liquid has been transferred.

solvent

_____________ allows for one to determine the endpoint of a reaction and the quantity of reactant used to achieve it.

Titration

Tools for a titration:

buret (to deliver precise amounts of the titrant) and a flask (generally an Erlenmeyer flask) containing the solution

What is used to determine when the equivalency point has been crossed during a titration?

an indicator that changes color, sometimes a pH meter

_________ is used to separate solids from liquids in a mixture.

Filtration

In some cases, filtration entails pouring the solution through filter paper set in a ________ over a flask.

Buchner funnel

To filter more effectively, a _____ _____ is used in combination with a ______ _______ to suck the liquid solution through the filter paper (vacuum filtration)

filter flask; vacuum outlet

When measuring volume in graduated glassware, always read a meniscus from:

the bottom of the curve

Some glassware can be placed in an oven for drying, but _____ glassware should never be placed in an oven -- the heat can ruin the calibration.

volumetric glassware (pipets, burets, volumetric flasks, graduated cylinders)

Once glassware is cleaned with soap or detergent in tap water, it should be rinsed with ________ to avoid potentially contaminating future solutions with small concentrations of residual ions.

deionized water

_______ can be used for the transfer of liquids, mixture of liquids, or for reactions; however, they are not accurate and should not be used for measurements.

Beakers

A ___________ ________ can be used for the transfer of liquids or for general measurements (with accuracy varying based on the extent of volume indications present). They are not the most accurate measure of transferring liquids, a pipette or buret is better suited when very high accuracy is needed.

graduated cylinder

Like a beaker, an _________ can be used for the transfer of liquids, mixture of liquids or for reactions, but is not accurate and shouldn't be used for measurements. Since it has a narrower neck than a beaker, it helps prevent splashing outside of the container.

Erlenmeyer flask

A __________ ____ is used as a container for liquid of a known, precise amount (or the creation of a mixture to a known volume). These flasks have a very narrow neck along which there is a mark for the precise amount the flask holds.

volumetric flask

A _______ flask is used during vacuum filtration. It is similar in appearance to an Erlenmeyer flask, but the side of the neck contains a protruding "side arm" along which a vacuum hose can be fixed to create suction.

filter

Like beakers, ____ ____ can be used for transfer of liquids, mixture of liquids or for reactions, but are not accurate for measurements of volume. They are generally useful for the transfer of smaller quantities of liquid.

test tubes

A ______ is used for the measurement and transfer of very precise amounts of liquid. They may be graduated or volumetric.

pipet

A _____ is used for the transfer of very precise amounts of liquid; they are primarily used in titrations to deliver specific, precise amounts of the titrant.

buret

Used during gravity filtration. Does not form the necessary seal for vacuum filtration.

Gravity filter funnel

Used to separate immiscible liquids.

Separatory funnel

Used to add liquid reagents one drop at a time to a flask.

Dropping funnel

Used for adding solid reagents to a flask.

Powder funnel

___________ errors are errors that resulted from flawed equipment or experimental design. They can be detected and corrected for. They can still be precise, but will not necessarily be accurate.

Systematic

__________ errors are errors that result from human interpretation of data. They can affect both precision and accuracy.

Random

________ is useful for separating a solid from a liquid.

Filtration

________ is used to separate 2 liquids in a solution based on boiling point differences.

Distillation

_________ purifies based on solubility differences.

Crystallization

____________ differentiates liquids in solution based on differences in polarities (check solution purity).

Liquid Column Chromatography

________ is the process used to remove the top layer of a liquid after the precipitate has settled to the bottom.

Decantation

Filters and Separatory Funnels are often used for separating _______ mixtures.

Heterogenous

Homogenous mixtures are often separated by ________. The mixture is boiled until one of the compounds evaporates. The evaporated compound is then cooled using a condenser.

Distillation

________ techniques rely on using polar and nonpolar solvents (organic layer usually on top except for chlorinated solvents)

Extraction

For carboxylic acids, use ____ or ______ to extract.

NaOH, NaHCO3

For phenols, extract with aqueous ______.

NaOH

For amines, extract with aqueous ______.

HCl

_______ separates mixtures of two or more volatile liquids.

Distillation

__________ _____ is used when the two volatile liquids have boiling points that are around 25 C apart.

Fractional Distillation

__________ dissolves an impure compound in hot solvent and gradually precipitates the pure compound as the solution cools down.

Recrystallization

_____ _______ _____________ is used to determine the relative abundance of each compound in a liquid mixture (separates components in liquid mixture by boiling point).

Gas-liquid chromatography

_______ separates compounds by their solubility in the solvent (polarity) Most soluble compound travels the furthest up the plate.

TLC (Thin Layer Chromatography)

TLC usually uses a ______ plate and ______ solvent.

polar, nonpolar

In TLC, the compound that travels the furthest with the nonpolar solvent is the most ________ compound.

nonpolar

In column chromatography, the most nonpolar compound travels the _____.

fastest