READ: Acids and Bases

READ: Acids and Bases

Introduction

We interact with acids – (compounds that produce hydrogen ions (H⁺) when dissolved in water) on a daily basis without even realizing it. For example, the chemical names for aspirin and vitamin C are acetylsalicylic acid and ascorbic acid because they are both acidic. Acetic acid (HC₂H₃O₂) is the primary component in vinegar, and formic acid (HCO₂H) is what causes ant bites to sting.

Hydrochloric acid (HCl) is stomach acid, phosphoric acid (H₃PO₄) is commonly found in dark soft drinks, and sulfuric acid (H₂SO₄) is used in car batteries. As you work your way through this chapter, try to notice how the properties of acids and bases manifest themselves in everyday situations.

Properties of Acids

One property that is common to all acids is a sour taste. You are probably most familiar with this in relation to citric acid, which is what makes lemons and other citrus fruits taste sour. In fact, sour taste buds are essentially just complicated H⁺sensors. The fact that one of our primary tastes is concerned solely with determining the acidity of what goes in our mouths further underscores the importance of acids in our lives.

However, testing whether something is acidic by taste is generally not a good idea. Another way to test for acidity is to use an indicator (a substance that can be used to determine the relative acidity or basicity of a solution, generally through a very distinct color change).

One common type of indicator is litmus paper. If a piece of blue litmus paper turns red when dipped into a solution, it means that the solution is acidic.

Another property common to many acids is that they can react with certain metals to form hydrogen gas. Examples of this type of reaction are shown below. Note that these are all single replacement reactions where a pure element reacts with a compound.

Zn(s)+2 HCl(aq)→ZnCl2(aq)+H2(g)Mg(s)+2 HCl(aq)→MgCl2(aq)+H2(g)

Properties of Bases

Bases (compounds that produce hydroxide ions (OH^-) when dissolved in water) also have a number of characteristic properties. Most bases are slippery and quite bitter (though not all bitter compounds are basic). Caffeine and milk of magnesia (chemical formula Mg(OH)₂) are two bases that you may have had the opportunity to taste, although the bitterness is generally masked by other flavors when these compounds are consumed. Other common bases are found in a number of cleaning products, including Drano (sodium hydroxide, NaOH) and Windex (ammonium hydroxide, NH₄OH).

Like acids, bases can be identified by the use of an indicator. For example, if red litmus paper is dipped into a basic solution, it will turn blue.

Summary

• Acids turn blue litmus paper red, taste sour, and react with metals to produce hydrogen gases.
• Bases turn red litmus paper blue, have a bitter taste, and are slippery to the touch.
• We can use indicators to test for acidity/basicity.

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