Reactions & Formulas Lab Sequence
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Reactions & Formulas Lab Sequence

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I use this lab sequence over a couple of lessons to get to grips with some basics of different types of reactions, balancing, writing formulas and problem-solving.

I use this lab sequence over a couple of lessons to get to grips with some basics of different types of reactions, balancing, writing formulas and problem-solving.

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    Reactions & Formulas Lab Sequence Reactions & Formulas Lab Sequence Document Transcript

    • Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______ Reactions and Formulas In 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 Science Level 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 Equations Remember 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 -----------> MgO Reactants Products Mg O
    • Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______ Another synthesis reaction Blow 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+ H2 O -----------> H2CO3 Reactants Products C O H 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 compounds Pick the ion names from the list. Put the cation before the anions. The ending of the last element in the You do not need to use ‘mono-‘ ‘di-‘ etc. 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) oxide 6. 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 + B Where 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) sulphatepentahydrate 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) sulphatepentahydrate -----------------> 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 Reactions Hydrocarbons 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. C3 H 8 + 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 C word and formula equations and add state symbols. H O 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 + BC An 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 coppersulphate + iron -----------------> Observations, changes and evidence that a chemical reaction has taken place. Reactants Products Sulphate is a polyatomic ion, so it must remain together. Cu SO4 Check the word equation and Fe state symbols. 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 Products Check the word equation and Mg state symbols. H Cl
    • Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______ Double Replacement Reactions These can be simplified as AB + CD  AD + CB Where 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 Products Again, 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 Products Again, 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 Reactions These can be simplified as HA + BOH  H20 + AB Where 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 Products H Complete the word and symbol equations, with state Cl symbols. Na O Reaction 2: A special case: hydrochloric acid and sodium hydrogencarbonate Add the NaHCO3 to the flask of HCl Safety: goggles! HCl+ NaHCO3 -----------> H2 O + 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 Products H Complete the word and symbol equations, with state Cl symbols. Na O
    • Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______ Identifying and balancing reactions practice In 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+ H2 O glucose + oxygen -----------------> Type:synthesis decomposition combustion single-replacement double-replacement neutralization Reason: Balance it: Reaction 2: electrolysis of water H2 O -----------> H2 + O2 water -----------------> Type:synthesis decomposition combustion single-replacement double-replacement neutralization Reason: Balance it: Reaction 3: making ethane from acetylene C2 H2 + H2 -----------> C2 H6 acetylene + hydrogen -----------------> ethane Type:synthesis decomposition combustion single-replacement double-replacement neutralization Reason: Balance it:
    • Grade 9 Introduction to Chemistry Student Name: _________________________Reactions & Formulas Date: _______ Reaction 4: using the ethane C2 H 6 + O2 -----------> CO2 + H2 O + -----------------> Type:synthesis decomposition combustion single-replacement double-replacement neutralization Reason: Balance it: Reaction 5: reaction of iron (II) sulphide with hydrochloric acid FeS+ HCl -----------> FeCl2 + H2S + -----------------> Type:synthesis decomposition combustion single-replacement double-replacement neutralization Reason: 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 neutralization Reason: 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!