Unit B Chemical Reactions. Copyright © 2010 Pearson Canada Inc. B - 1 Acids and Bases An acid is a...

Unit B

Chemical Reactions

Copyright © 2010 Pearson Canada Inc. B - 2

Acids and Bases

• An acid is a substance that produces hydrogen ions when dissolved in water

• A base is a substance that produces hydroxide ions when dissolved in water


Acids/Bases and Human Digestion

Parts Secretion Acid/base

mouth saliva basic

stomach Mucus HCl

liver Bile Base

pancreas Sodium bicarbonate

Base


Organs in Human Digestive System


Identifying Acids and Bases

• The more hydrogen ions H+, the more acidic; and the lower the pH.

• The more the hydroxide ions OH-, the more basic; and the higher the pOH

• The abbreviation “pH” stands for “power of hydrogen”.

• The pH scale is a number scale that indicates how acidic or basic a solution is


pH Scale


Examples,

• 1. lemon juice contains citric acid and ascorbic acid (vitamin C). It has a pH of

2-3, and so it is moderately acidic.

• 2. The more basic a substance is, the higher the pH. e.g. Sodium hydrogen carbonate (baking soda)


Aid to Remember Acids and Bases


Calculating pH values

• One unit of change on the pH scale is a 10 times change in how acidic or basic a solution is.

• For example, the hydrochloric acid in your stomach has a pH of 1. This is 10 times more acidic than lemon juice (pH 2).

• Difference between pH 2 and pH 5 is a 1000 times stronger i.e. 5-2 = 3

=103

1000 times more acidic


Acid-Base Indicators

• Indicators are used to test if a solution is an acid or a base

• They are substances that change colour in the presence of an acid or a base. e.g. litmus papers and universal indicator

• Red litmus paper turns blue when it is dipped into a basic solution.

• Blue litmus paper turns red when it is dipped in an acidic solution.


A pH meter can precisely measure the pH of an acidic or basic solution


• Universal indicator is a mixture of chemicals that changes colour through a wide range of pH values

• Other types of indicators

• Natural Indicators• Red cabbage juice; tea; Rose petals

• Commercial Indicators

• Phenolphthalein; Bromothymol blue• Congo red; Sudan IV• Litmus paper; Universal indicator paper stripes

Testing litmus paper


Properties of Acids and BasesSee text book Pg 198

http://www.youtube.com/watch?v=DQk7f6DksN8

http://www.youtube.com/watch?v=DQk7f6DksN8


Identifying and Naming Acids

• The chemical formula of acids start with H+

• The formula of some acids end with COOH- (mainly weak acids)


Naming Acids That Contain Hydrogen and a Non-Metallic Element

Classical names IUPAC Names

• HCl (aq) hydrochloric aqueous hydrogen acid chloride• HF (aq) hydrofluoric acid aqueous hydrogen fluoride

Name These:HBr (aq)

HI (aq)

H2S (aq)


Naming Acids That Contain Polyatomic Ions

with Oxygen Atom

• e.g. Nitrate,NO3-;

sulphate,SO42- ;phosphate,PO4

3-; chlorate, ClO3

-


Identifying and Naming Bases

• Name starts with a metallic ion (or ammonium ion) and ends with hydroxide

• the chemical formula ends with OH- (called a hydroxyl group)

• For example NaOH (s), KOH (s), NH4OH (aq)

• Sodium hydroxide (NaOH) is commonly found in drain cleaners and oven cleaners


Naming BasesStep Examples

KOH (aq) NH4OH (aq)

1. Write the name of the positively

charged metallic ion

potassium Ammonium

2. Add the word

“hydroxide.”

potassium

hydroxide

Ammonium hydroxide


Chemical & Common Names, Chemical Formula

Chemical Names

Common Names

NaOH (aq) Sodium Hydroxide

caustic soda

NH4OH (aq) ammonium

hydroxide ammonia solution

Ca(OH)2 (s)

calcium

hydroxide slaked or hydrated lime

Mg(OH) 2(s) magnesium

hydroxide milk of magnesia


5.2: Neutralization

• Neutralization is a chemical reaction between an acid and a base that produces water (H2O) and a salt.

• The salts formed may be soluble in water or can be insoluble.

• If a salt is insoluble, a precipitate will form. A precipitate is a suspension of small, solid particles formed during a chemical reaction.


Neutralization reactions:

• acid + base → salt + water

• HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

• H2SO4 (aq)+ NaOH (s) → Na2SO4 (aq)+ H2O (l)


Practice Problems

1. When HBr (aq) reacts with KOH (aq), a neutralization reaction occurs. The products are KBr (aq) and H2O (l). What is the balanced chemical equation for this reaction,

including states?

2. When H2SO4 (aq) reacts with Mg(OH)2 (aq), the products are MgSO4 (aq) and liquid water. Write the balanced chemical equation for this neutralization reaction, including states.


Applications of Neutralization Reactions

1. In pharmaceutical manufacturing, the pH of a solution may be changed from acidic to basic (or vice versa) so that the desired product forms a precipitate. Precipitate can be purified to produce

medications.

2. The calcium carbonate enters into a neutralization reaction with some of the acid in the soil water, and the soil pH becomes more basic.

3. Acid reflux and antacids (Bases)


4. Food industries uses neutralization reactions to adjust the pH of products for preservation.

5. Bee stings can also be treated using a neutralization reaction

Bee stings contain methanoic acid, treated with solutions that contain ammonia (base)


Neutralization Reactions and

Environment • Acid precipitation is rain, snow, fog, or dew that

has a pH less than 6.

• Two main causes of acid precipitation are

sulphur dioxide (SO2) and nitrogen oxides ( NO, NO2, N2O, N2O3) in the atmosphere.

• Sulphur dioxide is converted to sulphuric acid by the following two chemical reactions:


• 2SO2 (g) + O2 (g) → 2SO3 (g)

• SO3 (g) + H2O (l) → H2SO4 (aq)

• Nitrogen dioxide gas dissolves in water droplets in the atmosphere to form nitric acid and fall as acid

precipitation.

• Acid precipitation changes the pH of the soil which causes leaching


Neutralizing Acidic Lakes

• most lakes are naturally protected from the effects of acid precipitation because they are surrounded by limestone (CaCO3).

• Most Ontario lakes do not contain limestone and have greater risk of acidification, due to nitric acid and sulphuric acid.


• One way to raise the pH of heavily acidified lakes is by adding a substance called lime (CaO).

• When lime mixes with water, the base calcium hydroxide (Ca(OH)2) is formed.

• Calcium hydroxide can neutralize both the sulphuric acid and the nitric acid

Unit B Chemical Reactions. Copyright © 2010 Pearson Canada Inc. B - 1 Acids and Bases An acid is a...

Documents

Transcript of Unit B Chemical Reactions. Copyright © 2010 Pearson Canada Inc. B - 1 Acids and Bases An acid is a...