Print bookPrint book

2.5 Acids, Bases and Salts

Site: Cowichan Valley School District - Moodle
Course: Science 10 with CSS teacher
Book: 2.5 Acids, Bases and Salts
Printed by: Guest user
Date: Friday, 9 May 2025, 8:05 AM

Description

chemistry

Table of contents

General Information

Acids and bases are very common.

  • Many familiar compounds are acids or bases.
  • Classification as acids or bases is based on chemical composition.

Acids and bases can be very dangerous!

  • Both can be very corrosive.
    • NEVER try to identify an acid or base by taste or touch!

The strength of acids and bases in measured on the pH scale

  • pH below 7 = acidic, pH above 7 = basic, pH 7 = neutral
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
AcidsNeutralBases
  • Each decrease of 1 on the pH scale indicates 10X more acidic
    • For example, pH 4 is ten times more acidic than pH 5
    • pH 3 is 1000X more acidic than pH6

Check out pH scale PhET simulation below.
(If you drag the pH meter into the container you can change the solution using the drop down menu to see the pH of different things. You can also add water and remove some of the solution to see how that affects the pH.)

pH Indicators

The pH of acids and bases cannot be determined by sight.
  • Instead, pH is measured by other chemicals called indicators, or by a pH meter that measures the electrical conductivity of the solution.
pH indicators change colour based on the solution they are placed in.
  • Litmus is the most common indicator, used on litmus paper.
  • Two colours of litmus paper: Blue = basic and Red = acidic.
  • Blue = pH above 7, Red = pH below 7
  • Universal indicator contains many indicators that turn different colours at different pH values (can be in liquid form, or on paper strips like litmus)
  • A pH meter uses electrical probes to measure how solutions conduct electricity
  • Indicators change colour at different pH values, so different indicators are used to identify different pH values
  • Bromothymol blue for pH 6 - 7.6, phenolphthalein for pH 8.2 - 10
  • Many natural sources, such as beets and cabbage, are also indicators

Acids

If you know a compound's chemical formula, you may be able to identify it as an acid.

  • Acids often behave like acids only when dissolved in water
  • Therefore, acids are often written with subscript (aq) = aquatic = water
The chemical formula of an acid usually starts with Hydrogen (H-).
  • Acids with a carbon usually have the C written first.
    • HCl(aq) = hydrochloric acid, HNO3(aq) = nitric acid, CH3COOH(aq)= acetic acid
Naming acids
  • For Acids formed from Hydrogen + a single element from the periodic table:
Hydrogen + …-ide = Hydro…ic acid
    • HF(aq) = hydrogen fluoride = hydrofluoric acid

  • For Acids formed from Hydrogen plus a polyatomic molecule ending in -ate.
Hydrogen + …-ate = …ic acid
    • H2CO3(aq) = hydrogen carbonate = carbonic acid

  • For Acids formed from Hydrogen plus a polyatomic molecule ending in -ite.
Hydrogen + …-ite = …ous acid
    • H2SO3(aq) = hydrogen sulphite = sulphurous acid

Naming Acids

Bases

If you know a compound's chemical formula, you may be able to identify it as a base.

  • Bases, like acids, often behave like bases only when dissolved in water
  • Therefore, bases are often written with subscript (aq) = aquatic = water
The chemical formula of a base usually ends with hydroxide (-OH).
Examples of common bases
  • NaOH(aq)
  • Mg(OH)2(aq)
  • Ca(OH)2(aq)
  • NH4OH(aq)

Naming Bases

  • To name a base you simply name the cation (metal) and then add hydroxide
    • NaOH (aq) - Sodium hydroxide
    • Mg(OH)2 (aq) - Magnesium hydroxide

Production of Ions

Acids and bases can conduct electricity because they release ions in solution.

  • Acids release hydrogen ions, H+(aq)
  • Bases release hydroxide ions OH–(aq)

The pH of a solution refers to the concentration of ions it has.

  • Square brackets are used to signify concentration, [H+(aq)], [OH–(aq)]
    • High [H+(aq)] = low pH, very acidic
    • High [OH–(aq)] = high pH, very basic
  • A solution cannot have BOTH high [H+(aq)] and [OH–(aq)]; they cancel each other out and form water. This process is called neutralization.
  • H+(aq) + OH–(aq)--> H2O(l )

ion table

Properties of Acids & Bases

acids and bases

Practice on Acid Formulas

Write the formula for the following common acids:
Hints:
- identify as binary or polyatomic
- ate becomes "ic", ite becomes "ous"

  1. Hydrofluoric
    Answer

  2. Nitric
    Answer

  3. Sulfuric
    Answer

  4. Phosphoric
    Answer

  5. Carbonic
    Answer

  6. Acetic
    Answer

  7. Oxalic
    Answer

  8. Boric
    Answer

  9. Silicic
    Answer

  10. Chloric
    Answer

Acid/Base Review

Check your understanding of acids and bases here.

Acids and Bases Practice Quiz

Complete this quiz to help you prepare for your assignments and the Chemistry Test.

Salts

Salts are ionic compounds formed when acids and bases react.
  • Salts are also produced when oxides or carbonates react with acids, or when metals react with acids.
Table salt, NaCl, is found in seawater, salt lakes or rock deposits.
  • Salt was once very valuable as a commodity.
  • Iodine is now added to salt to minimize goiter (a disease of the thyroid)
NaCl is only one kind of salt
  • A salt is made up of a positive ion from a base and negative ion from an acid.
  • Salts are found in many things
    • In batteries, explosives and fertilizers
    • In multivitamins
    • In many living cells

Neutralization

Neutralization reactions occur when an acid and a base react to produce a salt and water.
  • HCl(aq) + NaOH(aq) --> NaCl(s) + H2O(aq)
acid + base --> salt + water

Metal and Non-metal oxides

Metal oxides react with water to form bases.
  • Na2O(s) + H2O( l) --> 2NaOH(aq)
Non-metal oxides react with water to form acids
  • SO2(g) + H2O( l) --> H2SO3(aq)
  • Non-metal oxides are formed from the burning of fossil fuels
    • §Add water in the atmosphere = acid precipitation

Acid Reactions with Metals and Carbonates

Acids and Metals
  • The most reactive metals, at the bottom of groups 1 and 2, react vigorously with water and acids.
  • All other metals are less reactive than those in groups 1 and 2.
  • When metals do react with acids, H2gas is usually released
  • 2HCl(aq) + Mg(s) --> MgCl2(s) + H2(g)
Acids and Carbonates
  • Carbonates (-CO3) neutralize acids, protecting locations with natural carbonate supplies from acid precipitation.
  • H2SO4(aq) + CaCO3(s) --> CaCO4(s) + H2O(aq) + CO2(g)

sulphuric acid + calcium carbonate --> calcium carbonite + water + carbon dioxide

Salts Review

Check your understanding of Salts here.

Salts Practice Quiz

Complete this quiz to help you prepare for your assignments and the Chemistry Test.