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UNIT 2: Chemical Reactions Chapter 3: Chemical Names, Formulas, and Equations Chapter 4: Classifying Compounds and Chemical Reactions

Chapter 4: Classifying Compounds and Chemical Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Chapter 4: Classifying Compounds and Chemical Reactions Airbags on motorcycles are a fairly recent safety innovation, but airbags have been in cars since the 1980s. Airbags inflate when a chemical reaction occurs, and a gas is produced. What are some of the properties that the reactants must have to be useful in airbags? The reactants must produce a lot of gas very quickly. The reactants must be stable in a variety of temperature extremes because they sit unused for long periods of time. The reaction must be reliable. The gas produced must be safe. TO PREVIOUS SLIDE

4.1 Types of Chemical Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 4.1 Types of Chemical Reactions Chemists have developed a classification system for chemical reactions using the following categories: combination reactions decomposition reactions single replacement reactions double replacement reactions combustion reactions Potassium reacts with water to produce potassium hydroxide and hydrogen gas. TO PREVIOUS SLIDE

Combination Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Combination Reactions A combination reaction is a chemical reaction in which two or more reactants combine to form one new product. A combination reaction can be expressed pictorially as shown below. The reactants can be elements or compounds, but the product is always a compound. The combination reaction between liquid hydrogen and liquid oxygen propelled space shuttles into orbit. 2H2(ℓ) + O2(ℓ) → 2H2O(g) TO PREVIOUS SLIDE

Decomposition Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Decomposition Reactions A decomposition reaction is a chemical reaction in which a single compound breaks down into two or more products. A decomposition reaction can be expressed pictorially as shown below. The products may be a combination of elements and compounds, but the reactant is always a compound. In hydrolysis, energy is used to decompose water into hydrogen gas and oxygen gas. 2H2O(ℓ) → 2H2(g) + O2(g) TO PREVIOUS SLIDE

Reviewing Combination and Decomposition Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Reviewing Combination and Decomposition Reactions What are the seven diatomic molecules that you need to know when writing chemical equations for combination reactions? In the electrolysis of water, what is the purpose of the battery and what are the products of the reaction? H2(g), N2(g), O2(g), F2(g), Cl2(g), Br2(ℓ), and I2(s) The battery supplies the electric current needed to break the bonds between the hydrogen and oxygen in water to form hydrogen gas and oxygen gas. TO PREVIOUS SLIDE

Single Replacement Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Single Replacement Reactions A single replacement reaction is a chemical reaction in which one element takes the place of another element in a compound. A single replacement reaction can be expressed pictorially as shown below. Chlorine gas in the flask on the left bubbles through an aqueous solution of sodium bromide. In a single replacement reaction, the chlorine replaces the bromine in the sodium compound. 2NaBr(aq) + Cl2(g) → 2NaCl(aq) + Br2(ℓ) TO PREVIOUS SLIDE

Double Replacement Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Double Replacement Reactions A double replacement reaction is a chemical reaction in which the positive ions of two different compounds exchange places, resulting in the formation of two new compounds. A double replacement reaction can be expressed pictorially as shown below. In aqueous solution, the reacting compounds have more contact area and the particles are free to move around. This increases the efficiency of the reaction. A red precipitate, Ag2CrO4(s), forms when two ionic solutions, AgNO3(aq) and K2CrO4(aq), undergo a double replacement reaction. TO PREVIOUS SLIDE

Reviewing Single and Double Replacement Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Reviewing Single and Double Replacement Reactions Do metals or non-metals undergo single replacement reactions? Both metals and non-metals undergo single replacement reactions. In aqueous solution, the reacting compounds have more contact area and the particles are free to move around. This increases the efficiency of the reaction. Why would it be more efficient for double replacement reactions to occur in aqueous solution rather than the reaction occurring between two solid compounds? TO PREVIOUS SLIDE

Combustion Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Combustion Reactions A combustion reaction is a chemical reaction in which a compound or element reacts with oxygen to form compounds called oxides. The general equation of a combustion reaction is CxHy + O2  CO2 + H2O Heat and light are often produced in a combustion reaction. What are two examples of combustion reactions? What is incomplete combustion, and why is it hazardous when it occurs in homes? 1. when methane combusts in a gas stove; 2. when our bodies combust glucose Incomplete combustion occurs when the supply of oxygen is too low, and carbon monoxide and soot are produced in the reaction. Incomplete combustion is hazardous when it occurs in homes (which are usually closed systems) because carbon monoxide is an odourless, poisonous gas. TO PREVIOUS SLIDE

Summary of Reaction Types UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Summary of Reaction Types TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.1 Section 4.1 Review Chemical reactions can be classified as combination, decomposition, single replacement, double replacement, or combustion reactions. Combustion reactions may be complete or incomplete. Incomplete combustion of organic compounds such as hydrocarbons produces the toxic compound carbon monoxide. TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 4.2 Acids and Bases Some compounds are classified as an acid or a base. Citrus fruits, vinegar, soaps, and baking soda are examples of acids and bases. What does this whip scorpion have to do with acids and bases? The whip scorpion uses a mist of acid as a defense mechanism. TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Acids An acid is a chemical that produces hydrogen ions when dissolved in water. An acidic solution has a pH of less than 7. Acids taste sour. Many acids are corrosive, and they will react with many substances. How are hydrofluoric acid and this glass globe related? Hydrofluoric acid was used to create the etching in this glass globe. Remind students to never taste a chemical in the laboratory. TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Bases A base is a chemical that produces hydroxide ions when dissolved in water. A basic solution has a pH greater than 7. Bases taste bitter, and they have a slippery feel. Many bases are corrosive, and they are often used in cleaning products. Hydrogen and oxygen make up a hydroxide ion. Remind students to never taste a chemical in the laboratory. Consumer products such as cleaners often contain bases. Which two elements make up a hydroxide ion? TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 The pH Scale The pH scale is a numerical scale that is used for identifying a solution as acidic, basic, or neutral. Acid solutions have a pH of less than 7. The lower the pH number, the higher the concentration of hydrogen ions. Basic solutions have a pH of greater than 7. The higher the pH number, the greater the concentration of hydroxide ions. A neutral solution has a pH of 7 and approximately the same number of hydrogen ions and hydroxide ions. It is acidic. Is a tomato that has a pH of about 4 acidic or basic? TO PREVIOUS SLIDE

The pH Scale UNIT 2 Section 4.2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 The pH Scale TO PREVIOUS SLIDE

Differences in pH Values UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Differences in pH Values The concentration of hydrogen ions associated with a value on the pH scale differs from the value above it or below it by a power of 10. A solution that has a pH of 4 has a concentration of hydrogen ions that is 10 times greater than a solution that is pH 5. The pH of a solution can be measured using pH paper or a pH meter. If grapes have a pH of 3 and a banana has a pH of 5, how much greater is the concentration of hydrogen ions in grapes than in the banana? The concentration of hydrogen ions in the grape is 100 times greater than the hydrogen ion concentration in the banana. TO PREVIOUS SLIDE

Identifying Acids and Bases UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Identifying Acids and Bases An acid-base indicator is a chemical that has a characteristic colour when in the presence of an acid or a base. Red and blue litmus papers can be used to determine if a solution is an acid or a base. Red litmus paper turns blue in a basic solution, and blue litmus paper turns red in an acidic solution. The solution tested with the pH paper is basic; the solution tested with the pH meter is acidic. The pH paper on the left and the pH meter on the right both determine the pH of a solution. Are the solutions that were tested acidic or basic? TO PREVIOUS SLIDE

A Summary of Acid and Base Properties UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 A Summary of Acid and Base Properties TO PREVIOUS SLIDE

Names of Acids HF(aq) H2SO4(aq) UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Names of Acids Two categories of acids are binary acids and oxoacids. Binary acids are composed of two elements—hydrogen and a non-metal. Oxoacids are composed of hydrogen, oxygen, and another element. HF(aq) hydrofluoric acid H2SO4(aq) sulfuric acid Binary Acids Rules: The root of the non-metal name is used. The prefix hydro- is added to the root name. The ending –ic acid is added to the root name. Oxoacids Rules: Write the name of the polyatomic ion, without the –ate or –ite ending. If the ion name ended in –ate, replace it with –ic at the end of the name. If the ion name ended in –ite, replace it with –ous at the end of the name. Add the word acid. What are the rules for naming a binary acid and an oxoacid using the classical method? TO PREVIOUS SLIDE

Chemical Formulas of Acids UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Chemical Formulas of Acids The chemical formula of an acid can be considered composed of a certain number of hydrogen ions and the negative ion. The negative ion is identified by the name of the acid. TO PREVIOUS SLIDE

Names and Chemical Formulas of Bases UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Names and Chemical Formulas of Bases Bases are ionic compounds composed of metal ions and hydroxide ions. Their names are written following the IUPAC guidelines for ionic compounds. The chemical formula for a base includes enough hydroxide ions in the formula to make the total charge of the compound zero. TO PREVIOUS SLIDE

Acids in the Atmosphere and Waterways UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Acids in the Atmosphere and Waterways Rainwater is naturally acidic and normally has a pH of between 5.6 to 5.8. Various human activities release compounds into the air that lower the pH of precipitation. What human activities add to acid precipitation? Why is acid precipitation a problem? Operating cars releases nitrogen oxides into the atmosphere; these contribute to the nitric acid in acid precipitation. Smelting and energy production using coal and natural gas contribute to sulfuric acid in acid precipitation. Acid precipitation causes plankton, crustaceans, fish, and other organisms to die, which disrupts all ecosystems. TO PREVIOUS SLIDE

Neutralization Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Neutralization Reactions Neutralization is a chemical reaction between an acid and a base that results in production of a salt and water. A salt, such as sodium chloride, is an ionic compound. The increased pH of waterways due to acid precipitation can be temporarily reduced by adding calcium carbonate (lime) to the water. Why is liming waterways a temporary solution to the problem of the effects of acid precipitation? Liming is a temporary solution because it deals with the current results of acid precipitation instead of the causes. TO PREVIOUS SLIDE

Salts Formed From Neutralization Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Salts Formed From Neutralization Reactions Different salts formed in the neutralization reactions between acids and bases have a variety of uses. Commercially important salts include sodium chloride, magnesium acetate, and calcium acetate. What might be the original source of the underground salt deposits in Canada? The salt deposits shown on the map were formed many million years ago when ancient seas evaporated. TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Section 4.2 Review Acids and bases are two important classes of compounds with their own characteristic properties. The pH scale tells you how acidic or basic a substance is. Acids have pH values below 7. Bases have pH values above 7. Neutral solutions have a pH of 7. Universal indicator, pH paper, and a pH meter are all tools for determining the pH of a solution. Acids have both IUPAC and classical names. There are special rules for naming binary acids and oxoacids. TO PREVIOUS SLIDE Continued…

Section 4.2 Review (continued) UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.2 Section 4.2 Review (continued) Bases are named using IUPAC guidelines for ionic compounds. Rainwater is naturally acidic, but human activities can lower the pH of rainwater further. This is called acid precipitation, and it can severely damage ecosystems. When most acids and bases react, they form a salt and water. The reaction between an acid and a base is called neutralization. Antacids and the liming of lakes are examples of applications of neutralization reactions. TO PREVIOUS SLIDE

4.3 Rates of Chemical Reactions UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.3 4.3 Rates of Chemical Reactions Reaction rate is a measure of how fast a reaction occurs. Some reactions, such as the process of rusting, occur slowly and some reactions, such as the deployment of air bags, occur quickly. Is the reaction shown in this photo occurring slowly or quickly? The rusting process is a slow reaction. TO PREVIOUS SLIDE

Factors That Affect the Rate of a Reaction UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.3 Factors That Affect the Rate of a Reaction There are four main factors that affect reaction rates. Higher temperatures result in an increase in frequency and energy of collisions among particles. Increased surface area results in more collisions that result in a reaction. Glow sticks are powered by a chemical reaction. Why might the glow stick on the left be brighter? The glow stick on the left is at a higher temperature than the stick on the right. Surface area is the measure of how much area of an object is exposed. TO PREVIOUS SLIDE Continued…

Factors That Affect the Rate of a Reaction UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.3 Factors That Affect the Rate of a Reaction A greater concentration of particles increases the chances that a collision will result and a reaction will occur. Catalysts lower the energy required for a reaction to occur. How could you increase the reaction rate between the wood and oxygen in the air? You could increase the reaction rate between the wood and oxygen by fanning the flames to increase the amount of oxygen that is available in the reaction. A catalyst is a substance that increases the rate of a chemical reaction without being used up in the reaction. TO PREVIOUS SLIDE

UNIT 2 Chapter 4: Classifying Compounds and Chemical Reactions Section 4.3 Section 4.3 Review Chemical reactions occur at different rates. For example, rusting is a slow reaction. The combustion of propane is a fast reaction. Rates of reaction are affected by a number of factors, including temperature, surface area, concentration, and the presence of a catalyst. TO PREVIOUS SLIDE