Laboratory Concepts

Dani Klingert

Accuracy

When titrating, rinse the buret with the solution to be used in the titration instead of with water. If you rinse the burette with water, you might dilute the solution, which will cause the volume added from the buret to be too large

Allow hot objects to return to room temperature before weighing. Hot objects on a scale create convection currents that may make the object seem lighter that it is.

Accuracy

Don’t weigh reagents directly on a scale. Use a glass or porcelain container to prevent corrosion of the balance pan.

When collecting a gas over water, remember to take into account the pressure and volume of the water vapor.

Accuracy

Don’t contaminate your chemicals. Never insert another piece of equipment into a bottle containing a chemical. Instead you should always pour the chemical into another clean container. Also, don’t let the inside of the stopper for a bottle containing a chemical touch another surface.

When mixing chemicals, stir slowly to ensure distribution.

Accuracy

Be conscious of significant figures when you record your results. The number of significant figures you use should indicate the accuracy of your results.

Be aware of the difference accuracy and precision. A measurement is accurate if it is close to the accepted value. A series of measurements is precise if the values of all of the measurements are close together.

Lab Procedures- Methods of Separation

FiltrationDistillationChromatography

Filtration-

Solids are separated from liquids when the mixture is passed through a filter. Typically, porous paper is used as the filter. To find the amount of solid that is filtered out of a mixture, the filter paper containing the solid is allowed to dry and then weighed. The initial weight of the clean, dry filter is then subtracted from the weight of the dried filter paper and solid.

Distillation-

Use of the differences in the boiling points of liquids to separate them. The temperature of the mixture is raised to a temperature that is greater than the boiling point of the more volatile substance and lower than the boiling point of the less volatile substance. The more volatile substance will vaporize, leaving the less volatile substance.

Chromatography-

When substances are separated by the differences in the degree to which they are absorbed onto a surface. The substances are passed over the absorbing surface, and the ones that stick to the surface with greater attraction will move slower than the substances that are less attracted to the surface. This difference in speeds separates the substances. The name chromatography came about because the process is used to separate pigments.

Lab Procedures-Measuring Concentration

TitrationSpectrophotometer

Titration-

An acid-base neutralization reaction is used to find the concentration of an unknown acid or base. It takes one mole of hydroxide ions (OH-, base) to neutralize one mole of hydrogen ions (H+, acid), so the concentration of an unknown acid solution can be found by calculating how much of a known basic solution is required to neutralize a sample of given volume.

Titration-

The most important formula in titration experiment is derived from the definition of molarity. Molarity = Moles / Liters Moles = (Molarity) (Liters)

The moment when exactly enough base has been added to the sample to neutralize the acid present is called the equivalence point. In the lab, an indicator is used to tell when the equivalence point had been reached.

Titration-

An indicator is a substance that is one color in an acid solution and a different color in basic solution. Two popular indicators are phenolphthalein, which is clear in acidic solution and pink in basic solution, and litmus, which is pink in acidic solution and blue in basic solution.

Indicators

Spectrophotometer-

Measures slight variations in color. It can be used to measure the concentration of ions that produce colored solutions. The concentration of the ions will be directly proportional to the absorbance of the solution measured by the spectrometer.

Lab Equipment

beaker safety goggles thermometer buret burner crucible tongs

Lab Equipment

dropper pipette evaporating dish ring clamp graduated pipette Erlenmeyer flask Mortar and pestle

Lab Equipment

Volumetric pipette Forceps Funnel Metal spatula Florence flask Rubber policeman

Lab Equipment

Pipette bulb Graduated cylinder Test tube Platform balance (triple beam) / Electric

Balance