SAT Chemistry The Laboratory - Laboratory Safety Rules

SAT Chemistry The Laboratory - Laboratory Safety Rules

The Ten Commandments of Lab Safety
The following is a summary of rules you should be well aware of in your own chemistry lab.

1. Dress appropriately for the lab. Wear safety goggles and a lab apron or coat. Tie back long hair. Do not wear open-toed shoes.
2. Know what safety equipment is available and howto use it. This includes the eyewash fountain, fire blanket, fire extinguisher, and emergency shower.

3. Know the dangers of the chemicals in use, and read labels carefully. Do not taste or sniff chemicals.
4. Dispose of chemicals according to instructions. Use designated disposal sites, and follow the rules. Never return unneeded chemicals to the original containers.
5. Always add acids and bases to water slowly to avoid splattering. This is especially important when using strong acids and bases that can generate significant heat, form steam, and splash out of the container.
6. Never point heating test tubes at yourself or others. Be aware of reactions that are occurring so that you can remove them from the heat if necessary before they “shoot” out of the test tube.
7. Do not pipette anything by mouth! Never use your mouth as a suction pump, not even at home with toxic or flammable liquids.
8. Use the fume hood when dealing with toxic fumes! If you can smell them, you are exposing yourself to a dose that can harm you.
9. Do not eat or drink in the lab! It is too easy to take in some dangerous substance accidentally.
10. Follow all directions. Never haphazardly mix chemicals. Pay attention to the order in which chemicals are to be added to each other, and do not deviate!

SOME BASIC SETUPS
Throughout this book, drawings of laboratory setups that serve specific needs have been presented. You should be familiar with the assembly and use of each of these setups. The following list, with page references, will enable you to review them in context with their uses:

• Preparation of a gaseous product, nonsoluble in water, by water displacement
  from solid reactants......................................................................................... page 137

• Preparation of a gaseous product, nonsoluble in water, by water displacement
  from at least one reactant in solution................................................................. page 139

• Distillation of a liquid..................................................................................... page 180
• Titration....................................................................................................... page 249

The following are additional laboratory setups with which you should be familiar:

1. PREPARATION OF A GASEOUS PRODUCT, SOLUBLE IN WATER AND LIGHTER THAN
   AIR, BY THE DOWNWARD DISPLACEMENT OF AIR. SEE FIGURE 38.

Example _________________________________________________

Preparation of ammonia (NH₃).
2NH₄Cl(s) + Ca(OH)₂(s) → CaCl₂(s) + 2H₂O(g) + 2NH₃(g)



Example _________________________________________________

Chromatography is a process used to separate parts of a mixture. The component parts sepa­rate as the solvent carrier moves past the spot of material to be separated by capillary action. Because of variations in solubility, attraction to the filter paper, and density, each fraction moves at a different rate. Once separation occurs, the fractions are either identified by color or removed for other tests. A usual example is the use of Shaeffer Skrip Ink No. 32, which separates into yellow, red, and blue streaks of dyes.

3. MEASURING POTENTIALS IN ELECTROCHEMICAL CELLS. SEE FIGURE 40


Example _________________________________________________

The voltmeter in this zinc-silver electrochemical cell would read approximately 1.56V. This means that the Ag to Ag⁺ half-cell has 1.56V more electron-attracting ability than the Zn to Zn²⁺ half-cell. If the potential of the zinc half-cell were known, the potential of the silver half­cell could be determined by adding 1.56V to the potential of the zinc half-cell. In a setup like this, only the difference in potential between two half-cells can be measured. Notice the use of the salt bridge instead of a porous barrier.

4. REPLACEMENT OF HYDROGEN BY A METAL. SEE FIGURE 41.

Example _________________________________________________

Measure the mass of a strip of magnesium with an analytical balance to the nearest O.OOlg. Using a coiled strip with a mass of about 0.040g produces about 40mL of H₂. Pour 5mL of concentrated HC1 into a eudiometer, and slowly fill the remainder with water. Try to minimize mixing. Lower the coil of Mg strip into the tube, invert it, and lower it to the bottom of the beaker. After the reaction is complete, you can measure the volume of the gas released and calculate the mass of hydrogen replaced by the magnesium. (Refer to Chapter 5 for a discus­sion of gas laws.)

I. SUMMARY OF QUALITATIVE TESTS


II. Identification of Some Negative Ions


III. Identification of Some Positive Ions


IV. Qualitative Tests of Some Metals

FLAME TESTS. Carefully clean a platinum wire by dipping it into dilute HNO₃ and heating in the Bunsen flame. Repeat until the flame is colorless. Dip heated wire into the substance being tested (either solid or solution), and then hold it in the hot outer part of the Bunsen flame.


HYDROGEN SULFIDE TESTS. Bubble hydrogen sulfide gas through the solution of a salt of the metal being tested. Check color of the precipitate formed.