Mixtures and Solutions: The Sugar in the Tea by Emily Sohn and Joseph Brennan

Transcription

1 Readers Mixtures and Solutions: The Sugar in the Tea by Emily Sohn and Joseph Brennan Science Objective This book introduces children to some basics of chemistry as they explore the atoms and molecules that form the basic structure of matter. Children learn how substances can be combined into mixtures, solutions, and compounds. Different types of matter have different properties. Substances can undergo physical or chemical changes when they are combined. iscience Puzzle: How Much Sugar Can You Put in Tea? This science puzzle offers children four solutions to finding out how much sugar was put in glasses of hot tea and iced tea. Children will investigate the properties of liquids, including how they can change state. They will learn how and why some solutions can be separated into their components and others cannot. In the end, they will be able to use what they have learned to prove there is the same amount of sugar in both glasses of tea. Objectives Children will: learn that all matter is formed of atoms, which combine to form molecules. understand and give examples of mixtures, solutions, and compounds. explain the differences between physical changes and chemical changes. explore how to separate substances that have been combined. describe the properties of metals and other elements and substances. Teacher Notes 1

2 Lesson Plan Before Reading Bring in some mixtures, such as salt and pepper or tea with sugar. Ask children to name other mixtures. List some responses on the board. Ask: Do the parts of each mixture change or stay the same when they are mixed with the other parts? Can the parts be separated after they have been mixed? Accessing prior knowledge gets children thinking about the topic. Tell children they will learn that different kinds of matter have different properties. When substances combine and keep their own properties, they form a mixture. When substances combine and do not keep their own properties, they form a compound. Children will explore some physical and chemical changes that matter can go through. During Reading pp. 6 9: Discuss each option. Have children predict which one would work. pp : Explain that the salt-and-water mixture is called a solution. Ask: What do you think will happen over the 10 to 14 days? pp : Review the terms atom, molecule, and element. Go over the Glossary definitions. Be sure children understand that: Elements are pure substances made of only one kind of atom. Atoms are the smallest particle of an element that have the properties of the element. Molecules are made of two or more atoms chemically bonded together. The atoms may be of the same kind of element (such as a molecule of oxygen O 2 ) or of different kinds of elements (such as a molecule of carbon monoxide CO). You may wish to revisit this material when you reach pages When a substance like sugar dissolves in a liquid, it forms a solution. Some solutions can be separated into their components through settling, filtering, or evaporation. Some dissolved solutes can be retrieved by evaporating the solvent. Every substance or material is made of matter, including air, which you cannot see or smell. Matter can be in one of three states: solid, liquid, or gas. Each form of matter has its own properties. Substances can be changed to make new substances. Teacher Notes 2

3 During Reading (continued) pp : Refer to the list you made on the board in the Before Reading section. Ask: Which groupings are mixtures? Which are compounds? Encourage children to add new responses to the categories as they work through the book. p. 18: Revisit the list on the board. Ask: Which mixtures do you think can be separated by filtering? Which with a magnet? pp : Ask children to find out what metals pennies are currently made of. Ask: Which metal gives pennies their color? Their strength? pp : Have children make a list of any random things they can think of. Encourage them to include solids, such as books, liquids, such as milk, and gases, such as air. Tell them that all substances and materials known in the universe are made from some combination of only a hundred or so elements. The same element can be in many different kinds of substances. For example, the element hydrogen in rocket fuel is the same as the element hydrogen in water. p. 25: Revisit the parts of an atom on page 22 in context of the paragraph here that starts with: Atoms react with each other through their electrons. pp : Break a pencil in two or rip some paper to show a physical change. The paper is still paper even after being torn. Bring in a rusty nail to show a chemical change. Rust is a new substance formed when air combines with iron. p. 28: Present the Law of Conservation of Mass in terms of a cake. The cake batter contains flour, sugar, eggs, salt, oil, and other ingredients. When the batter is baked, it changes into a cake. All of the original flour, sugar, eggs, salt, and oil are still there; they have just combined chemically in the presence of heat to form something different from the batter. Mixtures, including solutions, are formed by physically combining two or more substances. Compounds are formed when a chemical reaction takes place between two or more substances. Matter can change form and properties through chemical reactions. Mixtures can be separated in many ways, including by density, gravity, filtering, or evaporation, or with a magnet. Elements have different properties, including hardness, strength, color, electrical conductivity, malleability, and resistance to wear. Elements are substances made of only one type of atom. There are fewer than 100 naturally occurring elements. All substances that are combined chemically are combined through the electrons of their atoms. Physical changes include changes that may involve the shape or form of a substance, or the state of matter the substance is in. Physical changes do not result in changes to the properties of a substance. Chemical changes make new substances out of the initial substances. The new substances have different properties from the original substances. The Law of Conservation of Mass says that the mass of the substances present before a chemical reaction equals the mass of the new substances created in the reaction. Put another way, all of the atoms present in the substances before a chemical reaction are still present in the substances created in the reaction; they are just arranged differently. Teacher Notes 3

4 During Reading (continued) pp : Have children think about the Discover Activity from the beginning of the book. Ask: What kind of mixture was the salt-and-water substance? Does it represent a physical change or a chemical change? How do you know? If children have a difficult time answering the last question, let them take a look at the yarn now. pp : Discuss the terms concentration and saturation. Refer back to the Discover Activity once again. Ask: Why could you see some salt in the bottom of the cup after it had been stirred into the water? pp : After reading these pages, ask: Which method of separating a solution did you use in the Discover Activity? Can you think of mixtures or solutions that can be separated with a filter? With a magnet? pp : Focus children s attention on the salty yarn from the Discover Activity. Ask: If you didn t have a faucet or other source of water and you wanted to remake the salt-and-water solution with the salt on the yarn, what could you do? Then ask: Can you think of other uses for evaporation and condensation besides desalination and distillation? A solution is a type of mixture. It is made up of one substance, called a solute, dissolved in another substance, called a solvent. Like other mixtures, solutions can be separated back into their original components. Solubility is the measure of the amount of one substance that will dissolve in another substance. Solubility is affected by temperature and size of particles. The more solute that is dissolved in a solvent, the more concentrated the solution. Soluble particles will dissolve until the solution reaches its saturation point. Different separation methods will work with different mixtures and solutions. Condensation and evaporation are opposites. While evaporation can recollect a solute from a solvent, or collect a solvent from a solution, condensation can help remake the solution. Teacher Notes 4

5 After Reading Restate the key ideas in this book. Everything known to people is made of about a hundred types of elements. Elements are made up of atoms. Atoms can be combined chemically into molecules. Molecules and atoms can be combined chemically into compounds. Mass is the amount of matter, or number of atoms, a substance contains. Mass is conserved during chemical reactions. All substances have properties unique to the substance. New substances with different properties are formed through chemical changes. Substances can be combined into mixtures, solutions, and compounds. Substances in liquids dissolve at different rates. When no more solid can dissolve in a liquid, the solution is saturated. Have children design an experiment to investigate how much of different solids will dissolve in the same amount of water. Then have children use water of a different temperature and repeat the same experiment. Be sure they write down their procedure, and record all data from each trial. Children can share their results with the rest of the class. Understanding Science Scientific investigation involves experimentation, observation, recording data, and analysis. Teacher Notes 5