Illustrated Guide to Home Chemistry Experiments

Chapter 7 Laboratory: Solubility and Solutions 125

SvABLET ERSUS UNSTABLE

Before you make up a stock solution—particularly a

standardized stock solution—check to make sure that

the chemical is stable in solution. Some chemicals break

down in solution, and others react with the container

or air. For example, sodium hydroxide solutions absorb

carbon dioxide from the air, which converts some of the

sodium hydroxide to sodium carbonate. Sodium hydroxide

solutions also dissolve glass containers, further changing

the concentration and introducing contaminants. The best

practice is to make up solutions of such chemicals only as

needed. If you must make up stock solutions of unstable

chemicals, at least make the minimum amounts possible

and store them in inert plastic accordion bottles, such as

those sold by photography supply stores. Opaque, screw-

cap Nalgene bottles are also good for storage.

EvdRE y Ay SoLUTIoNS

We’re surrounded by solutions, quite literally, because

the atmosphere itself is a solution. You can find many

other examples of commonplace solutions just by

looking around you:

• An average home contains hundreds of solutions,
  from beverages, vinegar, lemon juice, maple syrup,
  and vanilla extract in the kitchen to the bleach
  and fabric softener in the laundry room and the
  medicines and personal care products in the
  bathroom.


• When you turn the key to start your car, the power
  needed to crank the engine is supplied by a solution
  of sulfuric acid in the car battery. When the engine
  starts, it’s fueled by gasoline, which is a complex
  solution of hydrocarbons and additives.


• When you record a television program to a rewritable
  DVD, your DVD recorder stores that program by
  melting small pits into the complex solid solution
  of rare-earth metals that makes up the recording
  surface of the disc.


• Our bodies are made up largely of water, which
  serves as the solvent for the many complex solutions
  that serve various functions in our bodies. For
  example, our blood plasma is a complex solution of
  proteins, salts, glucose and other carbohydrates,
  amino acids, hormones, vitamins, gases, and
  metabolic waste products. Cytosol, the fluid inside
  our cells, is a similarly complex solution.