1 What is pH?

Some of our favorite foods make our tongue curl up because they are SOUR. Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases

Bitter! Some foods have a “bite” of their own because they’re somewhat bitter. Some foods have a “bite” of their own because they’re somewhat bitter. WHY? WHY?

Acids and Bases Chemicals may be classed as acids or bases. Chemicals may be classed as acids or bases. Things that are neither acids nor bases are neutral. Things that are neither acids nor bases are neutral. pH measures how acidic or basic a solution is. pH measures how acidic or basic a solution is.

Acids Often taste sour * Often taste sour * Is a measure of the concentration of hydrogen ions in a solution Is a measure of the concentration of hydrogen ions in a solution Strong acids can burn skin & eyes Strong acids can burn skin & eyes Strong acids can dissolve metals Strong acids can dissolve metals Examples: Examples: Lemon juice Lemon juice Vinegar Vinegar Car battery acid Car battery acid (dangerous!) *Never test an unknown acid by tasting it!

Bases Can taste bitter, sweetish, or salty * Often feel slippery or “soapy” * Strong bases can burn skin & eyes Bases react more easily with protein than with metal; they are often used for cleaning Examples: Milk Baking soda Soap Drain cleaner (dangerous!) *Never test an unknown base by touching or tasting it!

How Do We Measure pH? We measure pH by using special strips of paper called pH paper or litmus paper. We measure pH by using special strips of paper called pH paper or litmus paper.

How Does It Work? The paper is treated with chemicals that change color to show the pH. The paper is treated with chemicals that change color to show the pH. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base. When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.

Acid Any substance which has a pH of value of less than 7 is considered an acid Any substance which has a pH of value of less than 7 is considered an acid Acid Neutral Base Acid Neutral Base

Base Any substance which has pH value greater than 7 is a base Any substance which has pH value greater than 7 is a base Acid Neutral Base Acid Neutral Base

pH 7 A pH of 7 is called neutral—neither acid nor base. A pH of 7 is called neutral—neither acid nor base Acid Neutral Base Acid Neutral Base

Acidic or Basic If the number is less than 7 the substance is acidic If the number is less than 7 the substance is acidic If the number is more than 7 the substance is basic If the number is more than 7 the substance is basic

The pH Scale pH scale ranges from pH scale ranges from pH 7 is neutral; neither acid nor base, pH 7 is neutral; neither acid nor base, Pure water is pH 7 Pure water is pH 7 Below 7 is acid, above 7 is base. Below 7 is acid, above 7 is base. Low pH = acid Low pH = acid High pH = base High pH = base The closer to the ends of the scale, the stronger the solution is The closer to the ends of the scale, the stronger the solution is

The pH Scale

Each pH unit is 10 times as large as the previous one Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic A change of 2 pH units means 100 times more basic or acidic Each pH unit is 10 times as large as the previous one Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic A change of 2 pH units means 100 times more basic or acidic x10x100

The pH Scale Careful measurement is important Careful measurement is important A mistake of one pH unit means too much or too little! A mistake of one pH unit means 10 times too much or too little! x10x100

Why is pH important? Soil has to be in a certain pH range for plants to grow and stay healthy. Fish can’t live if the pH is too high or too low

Learning Check AB1 Describe the solution in each of the following as: acid base or neutral. A. ___soda B. ___soap B. ___soap C. ___coffee D. ___ wine E. ___ water F. ___ grapefruit F. ___ grapefruit

Solution AB1 Acid, Base or Neutral a. Soda b. Soap c. Coffee d. Wine e. Water f. Grapefruit acid base acid neutral acid

One Paper Tells All 20 One pH paper has the ability to detect the strength of an acid or a base in a substance. - Place the strip of pH paper in the liquid and quickly remove it. Let it dry. As it dries, the color of the paper changes denoting either an acid or base.

We will also be using LITMUS PAPER Litmus paper is blue or red paper that will test the pH of a substance. Red litmus paper will turn blue in a base and STAY RED in an acid Blue litmus paper will turn red in an acid and STAY BLUE in a base In other words, RED means ACID BLUE means BASE (basic blue)

Neutralizing The Effects of Acid Rain - Ordinary rainwater is naturally slightly acidic. When it mixes with pollution it can have a pH as low as 3. When acid rain falls, it changes the pH of soil and water and can have devastating effects on the organisms and the environment in which they live. - Acidic lakes are sometimes treated with lime (calcium hydroxide) to neutralize them. A chemical reaction takes place between this limewater, which is a base and the dilute sulfuric acid of the lake’s water. - The reaction produces calcium sulfate (a salt) and water. If all the acid and all the base are used up, the solution becomes neutral.

The equation for the neutralization of an acid and base is: Ca(OH) 2 (aq) + H 2 SO 4 (aq) CaSO 4(s) + 2H 2 O (l) calcium + sulfuriccalcium + water hydroxide acidsulfate (SALT) Base + Acid Salt + Water