--- title: "What goes in, what comes out?" subtitle: "Years 9 and 10 Chemistry · Equations and conservation of mass · Lesson 6" --- # What goes in, what comes out? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A gas stove burns methane with a blue flame. Hold a cold spoon above it and drops of water appear. Where did the water come from? :::teacher-note **In one sentence:** Students identify reactants and products, explain that products are new substances with different properties, and write word equations that include every product (AC9S9U07, nodes 1 and 3). **Students should be able to say:** I can name the reactants and products of a reaction. I can write a word equation that includes every product. I can say what a word equation shows and does not show. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **Methane (natural gas) burns in air. Which word equation names everything that goes in and comes out?** ☐ methane + oxygen → carbon dioxide + water ☐ methane + oxygen → smoke + heat ☐ methane + oxygen → carbon dioxide ☐ methane → carbon dioxide + water My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** methane + oxygen → carbon dioxide + water. Methane contains carbon and hydrogen: the carbon ends up in carbon dioxide and the hydrogen in water (the drops on the cold spoon). Oxygen from the air is a reactant too. Heat is energy given out, not a substance, so it is not in the equation. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: reactants and products :::keep-together ### Reactants and products **methane + oxygen → carbon dioxide + water. Reactant or product?** Groups: Reactant, Product - methane: {{field-15}} - oxygen: {{field-15}} - carbon dioxide: {{field-15}} - water: {{field-15}} ::: :::teacher-note **Answer:** methane → Reactant; oxygen → Reactant; carbon dioxide → Product; water → Product ::: :::keep-together ### The arrow **What does the arrow in a word equation mean?** ☐ Is mixed with ☐ Reacts to make ☐ Equals: the two sides are the same substances ::: :::teacher-note **Answer:** Reacts to make Reactants → products: read the arrow as 'react to make'. ::: :::keep-together ### New substances **Why are carbon dioxide and water counted as new substances, and not just methane and oxygen in a new shape?** ☐ They have different properties: methane burns and water puts fires out ☐ They are heavier ☐ They are gases ::: :::teacher-note **Answer:** They have different properties: methane burns and water puts fires out A product is a new substance with its own properties. The atoms are the same; how they are joined is different (next lesson). ::: :::keep-together ### Signs of a reaction **Is it a sign that a chemical reaction has made a new product?** Groups: Sign of a reaction, Not on its own - Bubbles of a new gas: {{field-15}} - A colour change in a mixture: {{field-15}} - A solid forming when two clear solutions mix: {{field-15}} - Ice melting into water: {{field-15}} - Sugar disappearing in tea: {{field-15}} ::: :::teacher-note **Answer:** Bubbles of a new gas → Sign of a reaction; A colour change in a mixture → Sign of a reaction; A solid forming when two clear solutions mix → Sign of a reaction; Ice melting into water → Not on its own; Sugar disappearing in tea → Not on its own ::: :::keep-together ### What it leaves out **What does a word equation NOT tell you?** ☐ How many particles of each substance react, or which atoms they contain ☐ Which substances react ☐ Which substances are made ::: :::teacher-note **Answer:** How many particles of each substance react, or which atoms they contain Word equations name the substances only. Formulas and balanced equations (two lessons on) show the atoms and amounts. ::: ## word equations :::keep-together ### Magnesium **Magnesium burns in oxygen with a bright white flame, leaving white magnesium oxide.** ☐ magnesium + oxygen → light ☐ magnesium + oxygen → magnesium oxide ☐ magnesium oxide → magnesium + oxygen ☐ magnesium → magnesium oxide ::: :::teacher-note **Answer:** magnesium + oxygen → magnesium oxide magnesium + oxygen → magnesium oxide. ::: :::keep-together ### Neutralisation **Hydrochloric acid neutralises sodium hydroxide, making salt (sodium chloride) and water.** ☐ hydrochloric acid + sodium hydroxide → sodium chloride ☐ hydrochloric acid + sodium hydroxide → water ☐ sodium chloride + water → hydrochloric acid + sodium hydroxide ☐ hydrochloric acid + sodium hydroxide → sodium chloride + water ::: :::teacher-note **Answer:** hydrochloric acid + sodium hydroxide → sodium chloride + water acid + base → salt + water. ::: :::keep-together ### Displacement **A zinc strip is put in blue copper sulfate solution. Copper forms on the zinc, and zinc sulfate is left in solution.** ☐ zinc + copper sulfate → zinc sulfate + copper ☐ zinc + copper → zinc sulfate ☐ zinc + copper sulfate → copper ☐ zinc sulfate + copper → zinc + copper sulfate ::: :::teacher-note **Answer:** zinc + copper sulfate → zinc sulfate + copper Zinc takes the place of copper: zinc + copper sulfate → zinc sulfate + copper. ::: :::keep-together ### Fizzing marble **Hydrochloric acid is added to marble chips (calcium carbonate). It fizzes. The products are calcium chloride, water and carbon dioxide.** ☐ calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide ☐ calcium carbonate + hydrochloric acid → carbon dioxide ☐ calcium carbonate → calcium chloride + water + carbon dioxide ☐ calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide ::: :::teacher-note **Answer:** calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide Acid + carbonate → salt + water + carbon dioxide (the fizz). ::: :::typical ## Elaborate: magnesium burning :::keep-together ### The heavier ash **The white ash after burning magnesium is heavier than the magnesium ribbon was. Why?** ☐ Oxygen from the air joined the magnesium to make magnesium oxide ☐ Burning makes new atoms ☐ The ash soaks up water ::: :::teacher-note **Answer:** Oxygen from the air joined the magnesium to make magnesium oxide The word equation shows it: magnesium + oxygen → magnesium oxide. The product contains the oxygen as well. ::: ::: :::wider ## Elaborate: why sodium hides :::keep-together ### Sodium in nature **Sodium is never found as a pure metal in nature, but there is plenty of sodium chloride in seawater. Why?** ☐ Sodium dissolves in seawater as a metal ☐ Sodium is a rare element ☐ Sodium reacts so readily that any sodium has long since reacted, leaving it in compounds ::: :::teacher-note **Answer:** Sodium reacts so readily that any sodium has long since reacted, leaving it in compounds Reactive elements end up as products. Getting sodium (or iron, or aluminium) back as the element takes another reaction, and usually a lot of energy. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - In a chemical reaction the **reactants** are used up and new substances, the **products**, are made. Products have different properties. - A **word equation** names them: reactants → products. Read the arrow as "react to make". - Include every reactant and product: burning a fuel that contains hydrogen makes water as well as carbon dioxide; oxygen from the air is a reactant. - Heat and light are energy, not substances, so they are not in the equation. - A word equation shows no amounts and no atoms: formulas and balanced equations do. ## Exit ticket :::keep-together **Iron reacts with oxygen and water to make rust (hydrated iron oxide). Write the word equation and label the reactants and products.** {{lines-3}} ::: :::teacher-note **Answer:** iron + oxygen + water → hydrated iron oxide (rust). Reactants: iron, oxygen, water. Product: hydrated iron oxide. :::