Properties of Acids and Bases

Learning Objectives

  • List characteristics of acids.
  • List the properties of bases.


Properties of Acids

Is the coffee ready yet?

coffee-983955_640Many people enjoy drinking coffee. A cup first thing in the morning helps start the day. But keeping the coffee maker clean can be a problem. Lime deposits build up after a while and slow down the brewing process. The best cure for this is to put vinegar (dilute acetic acid) in the pot and run it through the brewing cycle. The vinegar dissolves the deposits and cleans the maker, which will speed up the brewing process back to its original rate. Just be sure to run water through the brewing process after the vinegar, or you will get some really horrible coffee.

Acids

Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food.

Acids are a distinct class of compounds because of the properties of their aqueous solutions. Those properties are outlined below:

  1. Aqueous solutions of acids are electrolytes, meaning that they conduct an electrical current. Some acids are strong electrolytes because they ionize completely in water, yielding a great many ions. Other acids are weak electrolytes that exist primarily in a non-ionized form when dissolved in water.
  2. Acids have a sour taste. Lemons, vinegar, and sour candies all contain acids.
  3. Acids change the color of certain acid-base indicators. Two common indicators are litmus and phenolphthalein. Blue litmus turns red in the presence of an acid, while phenolphthalein turns colorless.
  4. Acids react with active metals to yield hydrogen gas. Recall that an activity series is a list of metals in descending order of reactivity. Metals that are above hydrogen in the activity series will replace the hydrogen from an acid in a single-replacement reaction, as shown below:


text{Zn}(s)+text{H}_2text{SO}_4(aq)rightarrow text{ZnSO}_4(aq)+text{H}_2(g)

  1. Acids react with bases to produce a salt compound and water. When equal moles of an acid and a base are combined, the acid is neutralized by the base. The products of this reaction are an ionic compound, which is labeled as a salt, and water.


Properties of Bases

Have you ever had acid indigestion?

Perhaps you have eaten too much pizza and felt very uncomfortable hours later. This feeling is due to excess stomach acid being produced. The discomfort can be dealt with by taking an antacid. The base in the antacid will react with the HCl in the stomach and neutralize it, taking care of that unpleasant feeling.

Milk of magnesia can be used to help relieve acid indigestions

Bases

Phenolphthalein turns pink in basic solutions Figure 1. Phenolphthalein indicator in presence of base.


Bases have properties that mostly contrast with those of acids.

  1. Aqueous solutions of bases are also electrolytes. Bases can be either strong or weak, just as acids can.
  2. Bases often have a bitter taste and are found in foods less frequently than acids. Many bases, like soaps, are slippery to the touch.
  3. Bases also change the color of indicators. Litmus turns blue in the presence of a base while phenolphthalein turns pink.
  4. Bases do not react with metals in the way that acids do.
  5. Bases react with acids to produce a salt and water.


Please note that tasting chemicals and touching them are NOT good lab practices and should be avoided in other words, don’t do this at home.

Bases are less common as foods, but they are nonetheless present in many household products. Many cleaners contain ammonia, a base. Sodium hydroxide is found in drain cleaner. Antacids, which combat excess stomach acid, are comprised of bases such as magnesium hydroxide or sodium hydrogen carbonate.

Summary

  • Properties of acids are described.
  • The properties of bases are listed.


Practice

Acids

Watch the video at the link below and answer the following questions:



  1. Which of the four solutions are acids?
  2. Stop the video at 0:30 minutes and predict conductivities.
  3. What color did the acids turn when universal indicator was added?


Bases

Read this page about Chemical Properties of Bases and answer the following questions:

  1. What does the reaction between an acid and a base produce?
  2. What is this reaction called?
  3. What does the reaction of a base with an ammonium salt form?


Review

Acids

  1. Are all acids electrolytes in water?
  2. What color does blue litmus turn in the presence of an acid?
  3. What does the reaction of an acid and a base produce?


Bases

  1. Are bases electrolytes?
  2. What color does a base turn phenolphthalein?
  3. Do bases react with metals the same way that acids do?


Glossary

  • antacid: A commercial preparation that neutralizes stomach acid.


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