Unit 3 – Acids and BasesDeveloped by Trevor Boehm

Hutterian Interactive TV SystemPrairie Rose School Division

Science 20F

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Unit 3 Overview

Properties of Acids and Bases (Text Topic 8.2)

The pH Scale (Text Topic 8.3) pH indicators Elements and Oxides (Text Topic 8.6) Acid Precipitation (Text Topic 8.7) Neutralization Reactions (Text Topic 8.10)

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What is an Acid?

An acid is a substance which produces hydrogen ions (H+) when dissolved in water.

Most acids contain hydrogen in their formulas.

Acids are sour tasting. The word 'sauer' in German means acid and is pronounced almost exactly the same way as 'sour' in English.

Acids react with certain metals (for example, Zn and Fe) to produce hydrogen gas.

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Examples of Acids

Citric Acid (from certain fruits and veggies, notably citrus fruits)

Ascorbic Acid (vitamin C, from certain fruits) Vinegar (5% acetic acid) Carbonic Acid (for carbonation of soft drinks) Lactic Acid (in milk) Battery Acid (from car batteries) Stomach Acid (inside our stomachs, we have HCl).

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What is a Base?

A base is a substance which produces hydroxide (OH-) ions when dissolved in water.

Bases are sometimes called alkalines. Bases feel slippery. Bases taste bitter.

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Examples of Bases

Baking Soda (Sodium bicarbonate) Bleach Ammonia (found in many cleaners) Drain Cleaner Many soaps

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(aq) = Aqueous

Because both acids and bases exist in water (the definition “forms H+ / OH- ions in water solution”), we always write (aq) after the formula for an acid or base. Hydrochloric acid = HCl (aq) Sodium Hydroxide = NaOH (aq)

(aq) = in water Also: (s) = solid, (l) = liquid, (g) = gas

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Important Uses forAcids and Bases

Antacids treat heartburn by neutralizing the acidity in the stomach. They usually contain magnesium hydroxide Mg(OH)2 and/or aluminum hydroxide Al(OH)3.

Sulfuric acid is used in the manufacture of many car batteries.

Hydrochloric acid (also called Muriatic acid) can be used to clean deposits in pipes, to clean cement, etc.

When baking soda is combined with moisture and an acidic ingredient (yogurt, chocolate, buttermilk, honey), the resulting chemical reaction produces bubbles of carbon dioxide that expand under oven temperatures, causing baked goods to rise.

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The pH Scale

The pH scale is a way of measuring how acidic or basic a chemical is. pH stands for “Power of Hydrogen”. pH measures the concentration of

hydrogen ions in water. A solution with a pH of 0 to just under 7 is acidic. The closer the pH is

to 0, the stronger the acid. A solution with a pH of just over 7 to 14 is basic. The closer the pH is

to 14, the stronger the base. A solution with a pH of 7 is neutral.

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The pH Scale (Cont’d)

The pH scale is a logarithmic scale. This means that every change of 1

on the pH scale is a change of 10 in the strength of the acid or base.

Using the diagram on the right and this information… Tomatoes are 10 times more acidic than

coffee. Battery acid is 10,000 times more acidic

than tomatoes. Blood is 5 times more basic than distilled

water. Blood is 10 times more basic than milk.

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The pH Scale (Diagram)

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pH Indicators

Indicators are chemicals which change colour in response to pH.

Indicators change colour at different pH values.

Four common indicators are listed below.

Indicator pH

Colour in

Acid

Colour in

Base

Litmus 7.0 Red Blue

Phenolphthalein 9.7 Colourless Red/Pink

Methyl Orange 3.7 Red Yellow

Bromophenol Blue 4.0 Yellow Blue

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pH Indicators (Pictures)

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Elements and Oxides

Non-metal oxides dissolve in water to produce acids. Nonmetal oxide + water acid Carbon dioxide + water carbonic acid CO2(g) + H2O(l) -> H2CO3(aq)

Metal oxides dissolve in water to produce bases. Metal oxide + water base Calcium oxide + water calcium hydroxide CaO(s) + H2O(l) Ca(OH)2(aq)

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Acid Precipitation

Acid precipitation is rain, snow or fog that is polluted by acid in the atmosphere and damages the environment.

Two common air pollutants acidify rain: sulphur dioxide (SO2) and nitrogen oxides (NOx). NOx combines with water to form nitric acid

(HNO3). SO2 combines with water to form sulfuric

acid (H2SO4). When these substances are released into

the atmosphere, they can be carried over long distances by prevailing winds before returning to earth as acidic rain, snow, fog or dust.

Pollution created in one area can cause acid precipitation far away.

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Acid Precipitation (Diagram)

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Effects of Acid Precipitation

Excessive acidity in a stream or lake can affect all organisms living in that ecosystem:

Fish will die if the acidity of the water is too high. Acidity can also affect the ability of fish to reproduce

(killing fish eggs). When the fish die, this removes the main source of

food for birds. Plant life (forests etc.) is affected if acidity of

precipitation is too high: Needles and leaves can turn brown and fall off. Trees can also suffer from stunted growth or have

damaged bark and leaves, which makes them vulnerable to weather, disease, and insects.

Plant life can be exposed to acid precipitation directly (as it falls) or through absorption of water from the soil.

Buildings, statues, etc. can be eroded by acidic precipitation, particularly those made of limestone (a base).

Acid precipitation can damage the paint of cars, houses, etc.

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Effects of Acid Precipitation(Photos)

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Neutralization Reactions

When an acid and a base are mixed, a neutralization reaction takes place.

Some neutralization reactions occur very rapidly and can be violent.

The word equation for a neutralization reaction is: Acid + Base Water + Salt

For example: HCl (aq) + NaOH (aq) H2O + NaCl

The paper mache volcano above

“erupts” because of a neutralization reaction between baking soda

and vinegar. Red food colouring gives the “lava” a realistic

appearance.

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Review for Unit 3

At the end of this unit, you should be able to… Define acid and base, and give examples of each. Explain how both acids and bases are used in daily life. Describe the pH scale, the positions of strong/weak acids

and strong/weak bases, and compare the strength of different substances on the pH scale.

Identify different indicators which can be used to test the pH of a substance.

Explain how metal oxides form bases and how nonmetal oxides form acids.

Explain how acid precipitation is formed, and describe its effects on the environment.

Explain the general form of a neutralization reaction, and recognize neutralization reactions.