Acidic, Basic and Neutral Solutions Chapter 9, Lesson 2

Acids An acid is a substance that releases a positively charged hydrogen ion, H+, in water. Acids taste sour and turn blue litmus paper red. The hydrogen ion from an acid combines with a water molecule in solution to form a hydronium ion, which has the formula H3O+ Because acid solutions contain ions, they conduct electricity.

Hydronium ion When an acid dissolves, it releases a hydrogen ion. The H+ ion combines with water to form H3O+, the positively charged hydronium ion. Hydrogen ion Water molecule Hydronium ion

What is a hydronium ion?

Uses of Acids Acids are important in several body processes, including breaking down food in the stomach. Acids are also used in making many products, such as fertilizers, detergent, and cleaners.

Bases A base is a substance that produces hydroxide ions when dissolved in water. The formula for the hydroxide ion is OH- Bases feel slippery on your skin, taste bitter, and turn red litmus paper blue. Most bases are ionic compounds.

Hydroxide ion In water, bases separate into a positive ion and the hydroxide ion (OH–). All the properties of bases are a result of the presence of hydroxide ions that form when the base is dissolved in water.

Uses of Bases Common bases include baking soda and cleaning agents. Bases are also used to produce new products, such as soap, paper, and plaster. Acids and Bases

What is pH? pH is a numerical scale used to indicate how acidic or basic a solution is. The pH scale runs from 0 to 14. Acids are below 7; strong acids are near 0. Bases are above 7; strong bases near 14. Neutral solutions have a pH of 7.

pH and Hydronium ion Concentration The higher the concentration of hydronium ions, the more acidic a solution is. All acid and base solutions contain both hydronium ions and hydroxide ions. In a neutral solution (pH=7) the hydronium and hydroxide ion concentrations are equal. A change in one pH unit represents a tenfold change in the acidity or alkalinity (how basic) of a solution.

Neutralization When an acid and a base are mixed, a neutralization reaction occurs. A neutralization reaction produces water and a salt. Stomach acid reacts with magnesium hydroxide in the following equation: 2HCl + Mg(OH)2 → MgCl2 + 2H2O Neither of the products is acidic or basic.

How is pH measured? An indicator is a compound that changes form one color to another within a particular pH range. Indicators can be used to determine approximate pH, simply whether something is acidic or basic.

How is pH measured?

pH strips Litmus is one of the simplest indicator test papers but also the least accurate. pH testing strips are a quick way of determining the approximate pH of a solution.

pH Meters pH meters are electronic instruments with an electrode that is sensitive to hydronium ions present in a solution. Accurately measures pH Requires an electric source to operate

pH Meters (cont’d)

Lesson Review 9-2 1. An acid with a pH of 3 is contains how many times as many hydronium ions as an acid with a pH of 6? A 1000 B 3 C 30 D 100

Lesson Review 9-2 2. When an acid and base are mixed, the products are ____ and ____. A water; a base B water; ammonia C water; salt D ammonia; salt

Lesson Review 9-2 3. Red litmus paper is dipped in a solution. The paper turns blue. The solution must have been ____. A acidic B homogeneous C basic D polar

Lesson Review 9-2 4. Blue litmus paper turns ____ in acid solutions. A red B orange C green D blue

Lesson Review 9-2 5. Which of the following is a hydroxide ion? A H3O+ B H+ C OH– D NH4+

Lesson Review 9-2 6. Which is a property of a base? A sour taste B produces OH– in water C produces H+ in water D reacts with metal to produce hydrogen gas

Lesson Review 9-2 7. What ions are present in the greatest amount in a solution with a pH of 2.5? A hydroxide B hydrogen C hydronium D oxygen

Lesson Review 9-2 8. What is the symbol for the hydrogen ion? A H3O+ B H2O C H+ D OH–