Describing Acids and Bases

Properties of Acids In order to identify an acid, you can test its properties. Acids are compounds whose characteristic properties include the kinds of reactions they undergo. An acid is a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus paper red.

Properties of Acids Sour Taste If you have ever tasted a lemon, then you have had first-hand experience with the sour taste of acids. Can you think of other fruits that sometimes taste sour or tart? Citrus fruits are acidic—they all contain citric acid.

Properties of Acids Reactions with Metals Acids react with certain metals to produce hydrogen gas. When they react, the metals seem to disappear in the solution. This observation is one reason acids are described as corrosive, meaning they “eat away” at other materials.

Properties of Acids Reactions with Indicators Litmus paper is an example of an indicator, or a compound that changes color when in contact with acids or bases. Vinegar, lemon juice, and other acids turn blue litmus paper red.

Properties of Bases Bases are another group of compounds that can be identified by their common properties. A base is a substance that tastes bitter, feels slippery, and turn red litmus paper blue. Bases are the opposite of acids. Examples include: Sodium hydroxide, calcium hydroxide, and ammonia.

Properties of Bases Bitter Taste Bases taste bitter like soaps, shampoos, and detergents (if you have ever gotten these in your mouth by mistake!) Slippery Feel Bases feel slippery (like when using soaps and shampoos) Some bases can irritate or burn your skin

Properties of Bases Reactions with Indicators Bases turn red litmus paper blue. An easy way to remember: “B” for BASE and “B” for BLUE

Uses of Acids and Bases Uses at Home: Ammonia solutions, drain cleaners, and glass cleaners are all bases used for cleaning Baking soda is a base that is used for cooking, it reacts with acids to produce gas bubbles (making your food light and fluffy!)

Uses of Acids and Bases Uses in Industry: Mortar and cement are manufactured using the bases calcium oxide and calcium hydroxide Gardeners sometimes add calcium oxide to soil to make the soil less acidic for plants

Strength of Acids and Bases Acids and bases may be strong or weak. Strength refers to how well an acid or base produces ions in water. Strong acids react to form hydrogen ions (H+), in a solution, while weak acids produce very few ions. Similarly, strong bases react to produce many hydroxide ions (OH-), while weak bases produce very few.

Measuring pH Knowing the concentration of hydrogen ions is the key to knowing how acidic or basic a solution is. To describe concentration of ions, chemists use a numeric scale called pH. The pH scale is a range of values from 0 to 14. It expresses the concentration of hydrogen ions (H+) in a solution.

Measuring pH The most basic substances are at the higher end of the scale. A low pH tells you that the concentration of hydrogen ions is high. In contrast, a high pH tells you the concentration of hydrogen ions is low.

Using Acids and Bases Safely You can find pH of a solution by using indicators, or paper that turns a different color. Strength determines how safe acids and bases are to use. People often say that a solution is weak when they mean it is dilute.

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