Objectives:

After performing this lab, the student should be able to:

• Calculate grams of solute and correctly prepare a molar solution. • Prepare parallel and serial dilutions using C1V1 = C2V2 • Distinguish a parallel dilution from a serial dilution. • Determine whether a parallel or serial dilution should be used in a given situation. • Use a microcentrifuge to make a pellet.

Making Molar Solutions and Dilutions

A major job of any biotechnician is the preparation of solutions. Accuracy is of the utmost importance. An incorrectly prepared solution can destroy months of hard work or cost companies thousands of dollars. Therefore, several safeguards are in place in most SOPs (Standard Operating Procedures) to ensure that mistakes are minimized. First, all calculations are written down in the lab notebook, even though a calculator is used to do the arithmetic. Second, important calculations are double-checked by another person (and sometimes triple-checked). Third, the exact mass or volume of each reagent used in making the solution is recorded in the lab notebook. Fourth, this information and more, is recorded on a data sheet and on a label on the bottle itself.

Weight per volume is the simplest way of expressing a concentration. This is often used for small amounts of chemicals and specialized biological reagents. For example, enzyme concentrations are often given as weight per volume-- 1 mg/µL DNA.

Percents may be:

1) weight per volume percent which is the grams of solute per 100 mL of solution (for solids in liquids) 2) volume percent, the mL solute per 100 mL solution (for liquids in liquids) 3) weight percent which is the grams of solute per 100 g solution (for solids in solids) Note that in all cases a 100 mL (or 100 g) solution is used since percent means “out of 100”. Molarity is by far the most commonly used solution calculation in the lab. Molarity is equal to the number...

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