1. Chemistry Lesson # 8
Acids & Bases

2. Definitions
Acids are substances that release hydrogen - H+ ions in aqueous solutions.
Bases are substances that release hydroxide - OH- ions in aqueous solutions.
An indicator is a substance that changes colour in the presence of an acid or a base

3. Comparisons & Tests

4. The pH Scale
Chemists use a pH scale to represent how acidic or basic a solution is. It ranges from 0 – 14.
pH stands for the “power of hydrogen” which is the indicator of acidity – the concentration of hydrogen ions in solution.
A very acidic solution has a low pH and a very basic solution has a high pH.
A neutral solution, like water, has a pH around 7.

5. pH Scale

6. pH (continued)
pH is based on a logarithmic scale, which means that every change of one unit on the scale represents a tenfold effect on the concentration of the solution.
For example, a pH of 2 is 10 times greater than a pH of 1.
A pH of 3 is 10x10 = 100 times greater than a pH of 1.
A pH of 4 is 10x10x10 = 1000 times greater than a pH of 1, etc.

7. Neutralization
An acid and a base neutralize each other to produce water and a soluble salt.
It is a type of double displacement reaction.
The hydrogen in the acid (H+) and the hydroxide (OH-) in the base create H2O, which is neither acidic nor basic.
Practical Use: neutralize soil to keep plants healthy from acid rain, cure acid indigestion with TUMS (a weak base), balance soap and shampoo (“pH balanced”) from being too basic and irritating skin, increase acidity in foods so they keep longer.

8. Examples Hydrochloric Acid + Sodium Hydroxide →
Sulfuric Acid + Aluminum Hydroxide →

9. Soil pH & Acid Precipitation
The pH of soil affects the availability of nutrients in the soil to plants. When the pH of a soil is altered, it can have a detrimental effect on plant life and the entire food chain that relies on those plants.
A major issue is acid precipitation, which is rain, snow, or dew that has a pH of less than 5.6.
Two main causes of acid precipitation are sulfur dioxide and nitrogen oxides in the atmosphere. They are usually formed from coal power plants, metal production, paper production, or car engines.
When these acids enter the atmosphere, and eventually build up in clouds, and fall as rain, it can change the pH of the soil in forests, or change the pH in bodies of water. This will cause both plant and animal life to die.
Scrubbers need to clean the smokestacks of factories to ensure that sulfur dioxide and nitrogen oxides are not released into the environment. We also are finding cleaner ways of burning fuel and running cars.

10. Heavy Metals
Heavy metals are elements that have a high atomic mass, such as arsenic, copper, mercury, and zinc.
Accumulation in the body can result in kidney disease, lung disease, bone defects, and damage to the nervous system.
Many heavy metals are found at abandoned mine sites. In the past, the environmental standards were not very high, and waste, or tailings, from the mines, were just dumped into open pits or even poured into the surrounding bodies of water.
These excess metals tend to decrease the pH of the soil and water surrounding the area.
Now there are strict methods of disposing of heavy metals, such as lined landfills, and they are never allowed to be dumped in water. There are also frequent water and soil testing around the mine to ensure environmental standards are being upheld.