Physical Science

Experiment 4-5



Background Information

Humans have a built-in detector of acids:  they taste sour.  But tasting unknown substances can be hazardous to life!  While we can select tangy foods and beverages as acids to investigate, it will be useful to find other ways to identify whether other substances are acids.  Some dyes such as that in goldenrod-colored paper are indicators that change color depending on acidity.  Purple cabbage and tea also contain such dyes.

Many animals use acid to help digest proteins in food.  It has long been known that stomach fluids from humans and other animals contains a substance called muratic acid.  Such acids have the ability to dissolve some materials that water and alcohols do not dissolve.  Muratic acid can be purchased at hardware stores for cleaning away grout and etching cement.  Chemists, having determined its molecular composition (HCl), call it hydrochloric acid.

The alchemists discovered that a few minerals would produce acid when heated.  One colorful rock called green vitriol produces a mineral acid originally named oil of vitriol.  Chemists, having determined its molecular composition (H2SO4), call it sulfuric acid.  Today it has wide industrial use and is the corrosive fluid in the rechargeable batteries used in cars, trucks, and other vehicles.

The alchemist Rhazes (860 to 925 A.D.) discovered some substances are capable of neutralizing (cancelling) the properties of acids.  These became know as alkalies or the equivalent word bases.  These taste bitter, a sensation that gives clue that they are undesirable for eating due to their ability to corrode living tissue.  Alkalies react with fats and oils to make soap.  Thus basic solutions feel slippery to the touch as they convert to soap the oils in cell membranes of our skin.

Many acids and bases are water soluble.  How reactive each is depends partly on its concentration and partly on molecular composition.  But generally all can be made less hazardous (such as in the case of a spill) by diluting with large volumes of water.


Purpose:  This experiment investigates acids and bases as solvents.

Materials needed:


Prepare for any potential accident BEFORE it happens!  Since acids and bases are corrosive (the more concentrated the more corrosive), be prepared to dilute any spill with lots of water.  If not too extensively damaged, skin will regenerate.  But be prepared to wash off any spill of corrosive material on skin as soon as possible.  Since eyes do NOT REGENERATE, wear eye protective goggles that fit tightly against the face on all sides for the full duration of preparation, experimentation, and disposal.  Clothing also won't regenerate, but spill damage can be minimized by promptly removing and thoroughly rinsing both underlying skin and the clothing with water.  In case of an accident, it is wiser to save living tissue than to save your modesty!  That said, remember that while the chemical damage will start immediately upon contact, no acid or base (or any other corrosive material) will instantly consume your body.  Remain calm and in control.  Don't procrastinate, but proceed to minimize further damage to living tissue while avoiding making matters worse in panic.  Even if you do get a corrosive material in an eye, start immediately rinsing constantly with comfortable water for 15 minutes, then seek further medical attention. Initial stinging of an eye is an indication of the presence of a corrosive substance, but the end of stinging may indicate nerve damage rather than the substance has been totally removed.  You will probably have to hold eye lids open with your fingers because washing an eye tickles a lot.  These directions are not exclusively for this experiment but should be learned for working with corrosive materials the rest of your life whether cleaning a clogged drain at home, or working with hazardous materials on a job!
  1. Place small samples to be tested for solubility in solutions of acids and bases.  It might be useful to also put samples in plain water as a control.  Look for bubbles, color changes, size changes and other changes to the samples.  The reactions probably won't be instantaneous so give an extended period of time if no changes are apparent within a couple minutes. Occasional mixing by light shaking might speed any change.

  2. Dip samples to be tested as indicators in the acids, bases, and water looking for color changes. Look for patterns where an indicator turns one color in all acids but a different color in all bases.


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revised 1/31/2004
by D Trapp
Mac made