Acids and Bases Everywhere

Every liquid you see will probably have either acidic or basic traits. One exception might be distilled water. Distilled water is just water. That's it. The positive and negative ions in distilled water are in equal amounts and cancel each other out. Most water you drink has ions in it.

Acids and Bases Everywhere

Those ions in solution make something acidic or basic. In your body there are small compounds called amino acids. Those are acids. In fruits there is something called citric acid. That's an acid, too. But what about baking soda? When you put that in water, it creates a basic solution. Vinegar? Acid.

PH Scale

Scientists use something called the pH scale to measure how acidic or basic a liquid is. Although there may be many types of ions in a solution, pH focuses on concentrations of hydrogen ions (H+) and hydroxide ions (OH-).

PH Scale

The scale goes from values very close to 0 through 14. Distilled water is 7 (right in the middle). Acids are found between a number very close to 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. They are either a little below or a little above that mark.

PH Scale

When you start looking at the pH of chemicals, the numbers go to the extremes. If you ever go into a chemistry lab, you could find solutions with a pH of 1 and others with a pH of 14. There are also very strong acids with pH values below one such as battery acid. Bases with pH values near 14 include drain cleaner and sodium hydroxide (NaOH). Those chemicals are very dangerous.

Names to Know

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).

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.

What really happens..

That pH scale we talked about 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.

What really happens..

Acid or Base?

Acids are substances which free hydrogen ions (H+), when they are mixed with water. Bases are substances which free hydroxide ions (OH-) when they are mixed with water.

Acids and Bases

Substances with pH lower than 7 are considered acids, those with pH equal to 7 are considered neutral, and those with pH higher than 7 are considered bases. .

Acids and Bases

Litmus Paper

How to Measure PH

Litmus is a substance obtained from certain lichens. It has the property of changing its color to red with acidic substances and to blue with basic ones. On the packet of the litmus paper, there is a color scale which indicates the color assumed by the paper as a function of the pH

Litmus Paper

pH Meter

The pH meter is an electronic instrument supplied with a special bulb which is sensitive to the hydrogen ions which are present in the solution being tested.

The signal produced by the bulb is amplified and sent to a liquid-crystal or an analog meter display.

These instruments are much more precise and convenient to use than the indicating papers

As we have seen, acids and bases have the property of modifying the color of certain substances. This is the case with the juice of the red cabbage. This liquid has a blue-violet color, but when it comes in contact with acidic substances it becomes red, while in contact with basic substances it becomes green and even yellow.

Red Cabbage Juice

Red cabbage juice mixed with baking soda (left) and with vinegar (right).

On the top, a drop of unmixed juice.

Red Cabbage Juice

Soaking cards with red cabbage juice..

Preparing red cabbage pH papers.

Drying the cards.

Preparing red cabbage pH papers.

Cutting the strips

Preparing red cabbage pH papers.

Lemon Juice Baking soda

Preparing red cabbage pH papers.

Color of the scale in cabbage papers

Corrosive ('burns' your skin) Sour taste (lemons, vinegar) Contains hydrogen ions (H+) when dissolved in

water Has a pH less than 7 Turns blue litmus paper to a red color Reacts with bases to form salt and water Reacts with metals to form hydrogen gas

Properties of Acids

* Hydrochloric acid (HCl) in gastric juice

* Sulphuric acid (H2SO4)

* Carbonic acid in softdrink (H2CO3)

* Uric acid in urine

* Ascorbic acid (Vitamin C) in fruit

* Citric acid in oranges and lemons

* Acetic acid in vinegar

* Tartaric acid (in grapes)

Examples of Acids

* Sodium hydroxide (NaOH) or caustic soda

* Calcium hydroxide ( Ca(OH)2 ) or limewater

* Ammonium hydroxide (NH4OH) or ammonia water

* Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia

* Many bleaches, soaps, toothpastes and cleaning agents

Examples of Bases

Soapy feel Has a pH more than 7 Turns red litmus paper to a blue color Many alkalis (soluble bases) contain hydroxyl

ions (OH-) Reacts with acids to form salt and water

Properties of Bases

Every team must bring the following:

1. Lemon

2. Mayonnaise

3. Mustard

4. Ketchup

5. Sprite or Coke

6. Sauce (botanera)

7. Aspirin

HOMEWORK

I need ONLY 1 person to bring the following:

1. Egg

2. Slice of white bread

3. Apple

4. Orange

HOMEWORK

I will bring the following:

1. Baking soda

2. Vinegar

3. Bathroom cleaner

4. Vinegar

5. Hydrochloric Acid

6. Sugar

7. Salt

8. Detergent

9. Zinc

10. Oil

11. Tums

12. Alcohol

13. Pepto Bismol

14. Sunscreen Lotion