pH & Acid Rain

What is an Acid?

• An acid is a substance which, when dissolved in water, releases protons. ([H+] ions)

• The amount of protons ([H+] ions) released is a measure of the strength of the acid.

• For example, HCl (hydrochloric acid) is a strong acid, because it dissociates completely in water, generating [H+] and [Cl-].

What is a Base?

• A base is a substance, when dissolved in water, releases hydroxide ions. ([OH-])

• The amount of the OH- ions released measures the strength of the base.

• For example NaOH is a strong base because it dissociates completely in water, generating [Na+] and [OH-].

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• Most living cells have a very narrow range of tolerance for pH.

•Acids are represented with a pH of 0-6.

•Bases are represented with a pH of 8-14.

•Neutral substances have a pH of 7. • Each pH unit represents a factor of 10 difference in [H+].

The pH scale goes from 0 to 14—because [H+][OH-] = 10-14

pH

10-2

10-3

10-5

10-4

10-8

10-7

10-6

[H+] M

10-10

10-9

10-11

10-12

10-13

10-14

10-1

100 A strong acid

A strong base

SOURCE: http://en.wikipedia.org/wiki/Image:PH_scale.png#file

How Can You Actually Determine the pH of a Solution?

• Use a pH meter—read the number.

• Use pH paper.– Acids turn litmus paper red.– Bases turn litmus paper blue.

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What is Acid Rain?

• Acid rain is rain that has been made acidic by certain pollutants in the air.

• Normal Rain = 5.6 pH• Acid Rain = >5.0 pH

What causes Acid Rain?

• Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide (SO2)and nitrogen oxides (NO) are released into the air.

• These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

What causes Acid Rain?

• Human activities are the main cause of acid rain. – Power plants - sulfur dioxide and nitrogen oxides

when they burn fossil fuels, such as coal, to produce electricity.

– The exhaust from cars, trucks, and buses releases nitrogen oxides and sulfur dioxide into the air.

Why is Acid Rain harmful?

• Can cause respiratory problems in humans.

• Can harm forests by seeping into ground.

• Can damage buildings and objects.

• Can damage lake and river life.

• http://www.epa.gov/acidrain/education/site_students/acid_anim.html

• http://www.epa.gov/acidrain/education/site_students/foodweb.html