Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Reactions and FormulasIn this unit, we will learn about the characteristics of different types of reactions, as well as how to name compounds and balance chemical formulas.

Assessment Statements Write word and formula equations using accepted conventions. Apply appropriate state symbols to reactants and products in reactions Annotate the conditions required for a reaction (such as heat or presence of a catalyst) above and/or below the

arrow in a reaction. Identify and name ionic and covalent compounds Outline the characteristics of major types of reactions, with examples. Balance simple formula equations and show your working.

Quiz Quizzes to complete: 3.1 Types of Reactions (http://www.quia.com/quiz/3644575.html) 3.2 Naming ionic and covalent compounds (http://www.quia.com/quiz/3644603.html)

Self-assessment: Attitudes in ScienceLevel Level descriptor

0 The student does not reach a standard described by any of the descriptors below.

1–2 The student requires some guidance to work safely and some assistance when using material and equipment.The student requires some guidance to work responsibly with regards to the living and non-living environment.When working as part of a group, the student needs frequent reminders to cooperate with others.

3–4 The student requires little guidance to work safely and little assistance when using material and equipment.The student works responsibly with regards to the living and non-living environment.When working as part of a group the student cooperates with others on most occasions.

5–6 The student requires no guidance to work safely and uses material and equipment competently.The student works responsibly with regards to the living and non-living environment.When working as part of a group, the student cooperates with others.

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Synthesis Reactions In these reactions, one or more reactants are combined to form one product. These can be simplified as A + B AB

Let’s use the example of magnesium reacting with oxygen to learn about how to write equations.

Ignite a piece of magnesium in the Bunsen roaring flame, using tongs. Safety: goggles, tongs. DO NOT LOOK DIRECTLY AT THE REACTION. Follow the demonstration.

This is not burning or combustion.

State symbols are shown subscripted in brackets next to each element or compound. This is important information which tells us about the phase or state of the chemical.

(s) represents solids. This includes precipitates which form, such as in suspensions.(g) represents gases. These could be observed as bubbles or smelled as fumes. (l) represents liquids. These are substances in their liquid state – not solutions. (aq) represents aqueous solutions. This means a solute dissolved in water.

Balancing Formula EquationsRemember the Law of Conservation of Mass? Atoms can neither be created nor destroyed. This means that there must be the same number of atoms of each element on the products side as on the reactants side.

Use the method outlined below and show your working. Adjust the symbol equation above. 1. List and count the elements and groups on each side of the reaction. Don’t split polyatomic ionc. 2. Identify the compound with the greatest number of atoms. 3. Balance the atoms in this compound on both sides of the equation, without changing the compound!4. Balance any groups (such as polyatomic ions). 5. Finish up with H and O.

Mg + O2 -----------> MgOReactants Products

MgO

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Another synthesis reactionBlow gently into a flask of water while measuring the pH. Safety: Blow gently, don’t drink. Use goggles.

“reversible reaction”

CO2 (g) + H2O (l) H2CO3 (aq)

carbon dioxide (g) + water (l) carbonic acid (aq)

Observations: What happens to the pH of the water as you blow into the flask?

Is the formula equation balanced? Use the method we practiced.

CO2 + H2O -----------> H2CO3

Reactants Products

COH

Why is CO2 called carbon dioxide? Naming ionic and covalent compounds. 1. Identify if the compound is ionic or covalent. 2. Name it, using the rules below.

Naming ionic compounds Naming covalent compoundsPick the ion names from the list. Put the cation before the anions. You do not need to use ‘mono-‘ ‘di-‘ etc.

The ending of the last element in the compound usually becomes –ide.They are in the same horizontal order as the periodic table, except H comes before O.Prefixes are given based on the number of atoms: mono: 1. di: 2. tri: 3. tetra: 4. penta: 5. hexa: 6.Mono- is not often used with the first element in the compound if it is a single atom.

Name these examples:1. CH4 - ---------------------------------

2. CaS ---------------------------------

3. N2H4 ---------------------------------

4. MgI2 ---------------------------------

5. FeO iron (II) oxide6. Fe2O3 ---------------------------------

Complete Quia Quiz 3.1: Naming compounds

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Decomposition Reactions

These can be simplified as AB A + BWhere a single reactant breaks down into component elements or compounds.

Decomposition of hydrogen peroxide using a catalyst Add a small amount of the catalyst MnO2 to about 10ml H2O2

Use a flame test to determine which gas is produced. Safety: goggles. Take care with the flame test.

H2O2 (aq) ----------->

hydrogen peroxide (aq) ----------------->

Observations, changes and evidence that a chemical reaction has taken place.

MnO2 is not included as a reactant or product. Where should it be written in the reaction? Add it.Describe the role of a catalyst in chemical reactions.

Balance the formula equation.

Heating copper(II) sulphate pentahydrate Heat the blue crystals in a boiling tube, over a bunsen flame Observe the changes in the test tube carefully.

Safety: goggles, tongs. DO NOT POINT AT ANYONE!

CuSO4.5H2O -----------> CuSO4 + H2O

copper (II) sulphate pentahydrate ----------------->

Observations, changes and evidence that a chemical reaction has taken place.

Think: why is the reactant called copper (II) sulphate (what’s the (II) for?)Add the conditions for the reaction above the arrow.What happens when you add water to the tube again?

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Combustion ReactionsHydrocarbons contain – wait for it… hydrogen and carbon. They react with oxygen in the presence of heat through the process of combustion. When combustion is complete (there is no hydrocarbon left), all that remains is carbon dioxide and water.

We combust a hydrocarbon in our science lab all the time – propane!Safety: flame safety.

C3H8 + O2 ----------->

propane + oxygen ----------------->

Observations, changes and evidence that a chemical reaction has taken place.

Which of the products we’ve made so far could be used to test if the condensation in this reaction really is water?

Using the naming conventions we’ve learned, suggest an alternative name for propane.

Balance it!Reactants Products Don’t forget to complete the

word and formula equations and add state symbols.

CHO

Alcohols can also be combusted. Observe the demonstration with methanol.

CH3OH + O2 ----------->

methanol + oxygen ----------------->

Balance it!Reactants Products Don’t forget to complete the

word and formula equations and add state symbols.

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Single Replacement Reactions

These can be simplified as AB + C A + BCAn element or ion has changed places with another element or ion.

Reaction 1: Copper sulphate solution and iron (II) Get this one going early. It takes a while. Mix iron powder and copper sulphate solution in a test tube and wait.

CuSO4 (aq) + Fe (s) -----------> FeSO4 + Cu

copper sulphate + iron ----------------->

Observations, changes and evidence that a chemical reaction has taken place.

Reactants Products Sulphate is a polyatomic ion, so it must remain together.

Check the word equation and state symbols.

CuSO4

Fe

Reaction 2: Magnesium and hydrochloric acid. Add a piece of magnesium to about 10ml HCl.

Safety: goggles. Take care with the flame test.

Mg + HCl -----------> H2 + MgCl2

magnesium + hydrochloric acid ----------------->

Explain why the formula for hydrogen chloride HCl, but magnesium chloride is MgCl2. (Think: ions!)

Reactants ProductsCheck the word equation and

state symbols.MgHCl

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Double Replacement Reactions

These can be simplified as AB + CD AD + CBWhere the anions and cations of two compounds trade places.

Reaction 1: Sodium chloride solution and silver nitrate solution Pour the NaCl solution into the AgNO3 solution

Safety: goggles.

NaCl + AgNO3 ----------->----------------->

The white precipitate formed is a suspension. What does this mean?

Reactants ProductsAgain, polyatomic ions must

remain together.

Complete the word and symbol equations, with state

symbols.

Reaction 2: Potassium iodide and lead nitrate Set up a petri dish with a thin layer of water Very carefully add the two solids to opposite ends of the dish

Safety: goggles. Give the finished reaction to MrT to dispose of carefully.

KI + Pb(NO3)2 -----------> KNO3 + PbI2

potassium iodide + lead nitrate ----------------->

Observe the diffusion and reaction. Deduce which of the solids was which. Explain your reasoning.

Reactants ProductsAgain, polyatomic ions must

remain together.

Complete the word and symbol equations, with state

symbols.

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Neutralisation ReactionsThese can be simplified as HA + BOH H20 + ABWhere the acid (HA) is neutralized by the base (BOH), giving water and a salt (AB).

Reaction 1: hydrochloric acid (with universal indicator) and sodium hydroxide Add the NaOH solution, dropwise, to the HCl solution.

Safety: goggles!

HCl + NaOH -----------> H2O + NaCl

hydrochloric acid + sodium hydroxide ----------------->

Observations, changes and evidence that a chemical reaction has taken place.

How could you prove experimentally that the salt produced is sodium chloride?

Reactants ProductsComplete the word and

symbol equations, with state symbols.

HCl

NaO

Reaction 2: A special case: hydrochloric acid and sodium hydrogencarbonate Add the NaHCO3 to the flask of HCl Safety: goggles!

HCl + NaHCO3 -----------> H2O + NaCl + CO2

hydrochloric acid + sodium hydroxide ----------------->

Note: baking soda (sodium hydrogencarbonate) is amphoteric. It acts as a base or as an acid. Cool.Carbon dioxide is not normally produced in simple acid-base reactions.

Reactants ProductsComplete the word and

symbol equations, with state symbols.

HCl

NaO

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Identifying and balancing reactions practiceIn each case, identify the type of reaction (circle it) and explain your choice. Complete the word and symbol equations. Balance the symbol equation and show your working.

Reaction 1: Inside our cells!

C6H12O6 + O2 -----------> CO2 + H2O

glucose + oxygen ----------------->

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Reaction 2: electrolysis of water

H2O -----------> H2 + O2

water ----------------->

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Reaction 3: making ethane from acetylene

C2H2 + H2 -----------> C2H6

acetylene + hydrogen -----------------> ethane

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Reaction 4: using the ethane

C2H6 + O2 -----------> CO2 + H2O

+ ----------------->

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Reaction 5: reaction of iron (II) sulphide with hydrochloric acid

FeS + HCl -----------> FeCl2 + H2S

+ ----------------->

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Explain why iron bonds with two chlorides and two hydrogens are needed to bond with one sulphur.

Reaction 6: sulphuric acid and potassium hydroxide

H2SO4 + KOH -----------> K2SO4 + H2O

+ -----------------> Potassium sulphate + (a salt)

Type: synthesis decomposition combustion single-replacement double-replacement neutralizationReason:

Balance it:

Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______

Six Main Types of Chemical Reaction

Indicators of a chemical change: Precipitate Formation (a new solid is formed, or the solution becomes very cloudy as tiny new solid

particles are suspended in the solution) Temperature Change

Exothermic – gets hotter. Energy is released as bonds between atoms are broken. Endothermic – gets colder. Energy is taken in to make new bonds.

Colour Change (no colour = “colourless”) Gas Production (bubbles – think about how you would test the gas) Change in odor (smell) – be sure to check this safely

The Law of Conservation of Mass “Matter can neither be created nor destroyed” This means that the same number of atoms of each element must exist on the reactants side and on the products side. If not, it needs to be balanced!