Solutions of Acids and Bases Chapter 3 Section p. 68 – 71 Vocabulary: 1. neutralization reaction 2. pH 3. salt

Strengths of Acids and Bases p. 68 Acids and bases can be strong or weak. The strength of an acid or base is not the same as the concentration of an acid or base. The strength of an acid or base depends on the number of molecules that break apart when the acid or base is dissolved in water. As an acid dissolves in water, the acid’s molecules break apart and produce hydrogen ions, H +. If all of the molecules of an acid break apart, the acid is called a strong acid. Strong acids include sulfuric acid, nitric acid, and hydrochloric acid. If only a few molecules of an acid break apart, the acid is a weak acid. Weak acids include acetic acid, citric acid and carbonic acid.

Strong Vs. Weak Bases p. 69 When all molecules of a base break apart in water to produce hydroxide ions, OH -, the base is a strong base. Strong bases include sodium hydroxide, calcium hydroxide, and potassium hydroxide. When only a few molecules of a base break apart, the base is a weak base, such as ammonium hydroxide and aluminum hydroxide. Sodium Hydroxide is found in products like Drano. Ammonium hydroxide is used in products like ammonia

Acids, Bases and Neutralization p. 69 When the base in an antacid meets stomach acid, a reaction occurs. The reaction between acids and bases is a neutralization reaction. 3. Neutralization reaction: the reaction of an acid and a base to form a neutral solution of water and a salt. If you’ve ever had an upset stomach like this boy, you may have taken an antacid tablet. An antacid is a weak base that neutralizes a strong acid in your stomach.

3. pH – a value that is used to express the acidity or bacisity (alkalinity) of a system. To describe how acidic or basic a solution is, the pH scale is used. The pH of a solution is a measure of the hydronium ion concentration in the solution. A solution that has a pH of 7 is neutral (pure water). Basic solutions have a pH greater than 7. Acidic solutions have a pH less than 7. Each one-point step on the pH scale represents a ten times difference in acidity or basicity.

Using Indicators to Determine pH p. 70 This picture shows strips of pH paper, which contain several different indicators. These strips were dipped into different solutions. The pH of each solution is found by comparing the colors on the each strip with their colors on the indicator scale provided. This kind of indicator is often used to test the water in pools and aquariums.

pH and the Environment p. 70 Some plants, such as pine trees, prefer acidic soil that has a pH between 4 and 6. Other plants, such as lettuce, need basic soil that has a pH between 8 and 9. Many organisims living in lakes and streams need a neutral pH to survive. Most rain has a pH between 5.5 and 6. Most acid rain has a pH between 4 and 4.5, but some can be as low as 3!

Salts p. 71 When an acid neutralizes a base, a salt and water are produced. A salt is an ionic compound formed from the positive ion of a base and the negative ion of an acid. Sodium chloride, or table salt, is only one example of a salt. 4. salt – an ionic compound that forms when a metal atom replaces the hydrogen in an acid. Salts have many other uses, too. It is used to make the compounds lye and baking soda. Sodium nitrate is a salt that is used to preserve food, and calcium sulfate is used to make wallboard. As we have seen this past winter, salt is also used to melt the snow and ice on the streets.

Quiz Time 1. What is the difference between a strong acid and a weak acid? In a strong acid, all of the molecules break apart when dissolved in water. In a weak acid, only a few of the molecules break apart when dissolved in water. 2. A solution of pH 3 is ten times as acidic as a solution of pH 4, and a solution of pH 9 is ten times as basic as a solution of pH 8. How much more acidic than a solution of pH 6 is a solution of pH 2? (6 – 2 = 4) so 10 4 = 10,000 times as acidic 3. How do indicators determine pH? They turn a different color at different pH levels. Compare them to the indicator scale to determine their pH.

4. Would you expect the pH of a sample of acid rain to be 4 or 9? Why? 4, because it is acidic. 9 is basic. 5. A neutralization reaction: A. includes an acid and a base B. produces a salt C. forms water D. all of the above D Science Humor… 6. If H 2 0 is water, what is H 2 0 4? Drinking! Ha, Ha, Ha!