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 149
• Preparation of a gaseous product, nonsoluble in water, by water displacement from at least one reactant in solution page 151
• Distillation of a liquid page 199
• Titration page 263

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).

Figure 15.1 Preparation of Ammonia

1. SEPARATION OF A MIXTURE BY CHROMATOGRAPHY. SEE FIGURE 39.

Figure 15.2 Chromatography Setup

 

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.

1. MEASURING POTENTIALS IN ELECTROCHEMICAL CELLS. SEE FIGURE 40.

Figure 15.3 Potentiometer Setup for Measuring Potential

 

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 half-cell 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.

1. REPLACEMENT OF HYDROGEN BY A METAL. SEE FIGURE 15.4.

Figure 15.4 Eudiometer Apparatus

 

Example

Measure the mass of a strip of magnesium with an analytical balance to the nearest 0.001g. Using a coiled strip with a mass of about 0.040g produces about 40mL of H₂. Pour 5mL of concentrated HCl 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.)