The Chemistry of Acids and Bases

For thousands of years people have known that vinegar, lemon juice and many other foods taste sour. However, it was not until a few hundred years ago that it was discovered why these things taste sour - because they are all acids. The term acid, in fact, comes from the Latin term acere, which means "sour".

In the seventeenth century, the Irish writer and amateur chemist Robert Boyle first labeled substances as acids or bases. Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and less acidic when mixed with bases. Bases feel slippery, change litmus paper blue and become less basic when mixed with acids. While Boyle and others tried to explain why acids behave the way they do, the first reasonable definition of acids and bases would not be proposed until 200 years later.

Acids are compounds that break into hydrogen (H+) ions and another compound when placed in an aqueous solution. Bases are compounds that break up into hydroxide (OH-) ions and another compound when placed in an aqueous solution.

If you have an ionic compound and you put it in water, it will break apart into two ions. If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solution is basic. There are other ions that make acidic and basic solutions, but we won't be talking about them here.

The pH scale is actually a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the pH is very low. If there are a lot of OH- ions, that means the number of H+ ions is very low, so the pH is high.

Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with metals to produce hydrogen gas. Can produce carbon dioxide gas Have a bitter taste. Feel slippery. Many soaps contain bases. Bases

Some Properties of Acids Produce H+ Taste sour Corrode metals Conduct Electricity React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red

Some Common Acids Vinegar Soda Oranges

Some Properties of Bases Produce OH- ions Taste bitter Feel soapy, slippery pH greater than 7 Turns red litmus paper to blue “Basic Blue”

Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Mg(OH)2magnesium hydroxideMilk of magnesia Al(OH)3aluminum hydroxideMaalox (antacid)

Acid/Base definitions Acids – Has H+ ions Bases – Has OH- ions (hydroxide)

What is the difference between a strong acid and a weak acid? A strong base and a weak base?

The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+

Over 7 = base 7 = neutral Under 7 =acid pH

Paper testing Paper tests like litmus paper and pH paper place a drop of the solution from the end of the stirring rod onto a piece of the paper Read and record the color change. Note what the color indicates

pH meter Tests the voltage of the electrolyte Converts the voltage to pH Very cheap, accurate

pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Some dyes are natural, like radish skin or red cabbage

Acid: A solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour". Base: A solution that has an excess of OH- ions. Another word for base is alkali. Aqueous: A solution that is mainly water. Think about the word aquarium. AQUA means water. Strong Acid: An acid that has a very low pH (0-4). Strong Base: A base that has a very high pH (10-14). Weak Acid: An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (3-6). Weak Base: A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10). Neutral: A solution that has a pH of 7. It is neither acidic nor basic.

The pH Scale

THE pH SCALE pH is something that effects your life alot! Look on shampoo and conditioner bottles, and you ’ll see that some are “pH formulated” for the best hair care! We want drinking water and soil in the garden and a multitude of other stuff “pH correct”! So what’s this pH stuff all about? Good question. pH is a number used by chemists to indicate the concentration of hydrogen ions in a solution. The pH scale tells us how acidic or basic a substance is. The scale ranges from 0 (maximum acidity) to 14 (maximum alkalinity). The middle of the scale, 7, represents the neutral point. The acidity increases from neutral toward 0, with 1-6 being acidic and and the alkalinity increases from neutral toward 14, with 8-14 being basic (or alkaline). A substance with a pH of 7 is neutral, meaning that it is not an acid or a base. Mixing acids and bases can result in a neutral solution because the two neutralize each other. The pH scale is logarithmic. This means that a difference of one pH unit represents a tenfold change. For example, the acidity of a sample with a pH of 5 is ten times greater than that of a sample with a pH of 6. A difference of 2 units, from 6 to 4, would mean that the acidity is one hundred times greater, and so on.

pH Lab Procedure: 1. Put your safety glasses on You will be testing several items to determine the pH of them. Be sure you can identify each item that is to be tested. Make a prediction as to whether each item is an acid or a base. Be sure to record you predictions on the data sheet. 2. Choose one of the liquid test items to test first. Measure 10 ml of the liquid to be tested into one of the small plastic testing cups. 3. Use one of the eye droppers and add cabbage indicator solution to the test liquid, drop by drop. Continue this until there is no further color change. 4. Use the pH chart and determine where the color “fits” onto the chart. Determine the pH number that corresponds to the color on the scale. This is the pH of your test liquid. Record your results on the data sheet provided. 5. Repeat this process for all test items. 6. What do you think happens when you mix an acidic substance and an alkaline substance together? Try it! Be sure to record your experiments and results! 7. When you are finished testing the liquids, clean up and answer the lab questions. Due Thursday is your lab packet. Cover sheet, procedure, data sheet, lab questions answered in complete sentences.

BSBaking Soda Solution AApple Juice AmAmmonia FFantastic/409 Cleaner LLemon Juice MMMilk of Magnesia WDistilled Water VVinegar BBleach 1Rain water sample 1 2Rain water sample 2 Testing Items Before going to the lab table..... Predict for each item: Acid Neutral Base

What happens when you put an acid with a base? Be sure and do some experiments to determine the answer to this question that you will be answering after completing your lab work.

What happens when you put an acid with a base?

pH Values of Common Household Materials butter 6.4 cow’s milk human saliva maple syrup 7.0 distilled water human blood egg whites 8.3 baking soda 9.2 borax 10.5 milk of magnesia 11.0 laundry ammonia 12.0 lime water 13.0 lye battery acid (sulfuric acid) limes lemon juice 2.2 vinegar (acetic acid) fruit jellies apple juice, cola acid rain strawberries 3.7 orange juice tomatoes 5.6 unpolluted rain peas corn

When fossil fuels are burned, sulfur dioxide and nitrous oxides are released. When these gases react with water, they produce sulfuric and nitric acids, respectively. H O O H O O + sulfur dioxide and nitrous oxides + sulfuric acid nitric acid acid rain Fossil fuels are fuels that originated from decaying plants and animals such as oil, coal and natural gas. Pull here Fossil fuels are fuels that originated from decaying plants and animals such as oil, coal and natural gas. sulfur dioxide and nitrous oxides

When fossil fuels are burned, sulfur dioxide and nitrous oxides are released. These toxic gases react with water in the atmosphere. Sulfuric and nitric acid are produced. The rain is now has a lower pH and is acidic. This is known as acid rain. Click here for the answer Click here for the answer pH is a measure of acidity. The lower the pH the more acidic. The higher the pH the more alkaline. A pH of 7 is considered neutral. Pull here pH is a measure of acidity. The lower the pH the more acidic. The higher the pH the more alkaline. A pH of 7 is considered neutral. Rearrange the sentences to describe how acid rain is caused.

When fossil fuels are burnt sulfer dioxide and nitrous oxides are released. These toxic gases react with water in the atmosphere. Sulfuric and nitric acid are produced. The rain is now has a lower pH and is acidic. This is known as acid rain. Description of how acid rain is formed. Click here for causes of acid rain.

Which of these cause acid rain? Click on the image to see if you are correct. Car Lightning Plants Volcanoes Windmills Power stations Which of these cause acid rain? Click on the image to see if you are correct.

This does not cause acid rain. Click here to go back Click here to go back

This causes acid rain. Click here to go back Click here to go back

This causes acid rain, but its effect is minor. Click here to go back Click here to go back

Arrange the following effects of acid rain in order of significance. Deterioration of buildings Damage to lakes, streams and rivers Soil and tree-root damage Effects on human health Arrange the following effects of acid rain in order of significance.

Acid rain lowers the pH of lakes and ponds. pH is a measure of acidity. The lower the pH the more acidic. The higher the pH the more alkaline. A pH of 7 is considered neutral. Pull here pH is a measure of acidity. The lower the pH the more acidic. The higher the pH the more alkaline. A pH of 7 is considered neutral. An ecosystem is a community of organisms that interact with each other and the environment they live in. Pull here An ecosystem is a community of organisms that interact with each other and the environment they live in. Explain how this can have adverse effects on an entire ecosystem. Click here for the answer Click here for the answer

One of the most dangerous effects of acid rain is on the human respiratory system. Sulfur dioxide and nitrous oxides are toxic gases and can cause respiratory problems such as asthma. Why do think the respiratory system is at high risk from these gases? Click here for the answer Click here for the answer Why do think the respiratory system is at high risk from these gases?

Acid rain can have a detrimental effect on buildings. Over time, it gradually dissolve parts of the building. The building material most effected by this is limestone. Limestone is made from calcium, carbon and oxygen. When it reacts with acid it produces carbon dioxide. Pull here Limestone is made from calcium, carbon and oxygen. When it reacts with acid it produces carbon dioxide. How do you think the effect of acid rain on limestone could effect quality of life? Click here for the answer Click here for the answer

Many historic buildings and statues are made from limestone. The effects of acid rain can wear away these historic structures. Limestone is made from calcium carbonate. When it reacts with acid, it produces carbon dioxide. This adds to the greenhouse effect. Click here to go back Click here to go back The greenhouse effect is a natural phenomenon where heat is trapped inside the Earth's atmosphere. Pull here The greenhouse effect is a natural phenomenon where heat is trapped inside the Earth's atmosphere.

In an ecosystem like a pond, food webs are intertwined. If the pH level falls too low, plants cannot survive. The fish that eat the plants then begin to die off. When the fish die off, the predators that feed on them will also have less food. Click here to go back Click here to go back

Through the respiratory system, humans inhale gases. Since the gases produced from burning fossil fuels are toxic, it is the respiratory system that is most at risk from direct contact with these gases. Click here to go back Click here to go back

Where do sulphur dioxide emissions come from? Sulphur dioxide (SO2) is generally a byproduct of industrial processes and burning of fossil fuels. Ore smelting, coal- fired power generators and natural gas processing are the main contributors. In 2000, for instance, U.S. SO2 emissions were measured at 14.8 million tonnes - more than six times greater than Canada's 2.4 million tonnes. But the sources of SO2 emissions from the two countries are different. In Canada, 68% of emissions come from industrial sources and 27% comes from electric utilities (2000). In the U.S., 67% of emissions are from electric utilities (2002).