Matter: Properties and Changes Chapter 3
Chemistry is the Study of Matter What is Matter? • Matter is anything that takes up space and has mass. • Mass is the amount of matter in an object. • Volume is a measure of space taken up.
Matter is Diverse • All matter falls into two categories. • Pure Substance: element or compound • Or Mixtures (of substances) • We must describe and classify matter in order to understand it.
Pure Substance A substance is matter that has a uniform and unchanging composition Example: pure water No matter where it is found, a sample of water will have the same composition as any other sample of water Other Examples: Table Salt,
Types of Matter • Any element or any compound is a Pure Substance • Elements: H, C, Ne, Li • Compounds: sodium chloride, carbon dioxide, LiBr, C6H12O6 • Mixture- more than one kind of matter • Combinations of elements and compounds
How do we describe matter? Properties
Properties Characteristics and Behaviors • Physical Properties- can be observed and measured without changing the chemical composition of the substance. • Describes how a substance looks, feels, smells, tastes, etc. • Examples: color, density, hardness, texture, crystal size
Physical Properties • Intensive Physical Properties • Do not change when the sample size changes • Good for identification of matter • Density, odor, boiling pt, freezing pt • Extensive Physical Properties • Change as the sample size changes • Mass, volume, length, weight
States of Matter: Physical Properties • Solid- mater that can not flow and has definite volume. • Liquid- definite volume but takes the shape of its container (flows). • Gas- a substance without definite volume or shape and can flow. • Vapor- a substance that is currently a gas but normally is a liquid or solid at room temperature.
Condense Freeze Evaporate Melt Gas Liquid Solid
Chemical Properties A property that can only be observed by changing the type of substance. Describes the ability of a substance to combine with or change into one or more other substances. Describe how a substance behaves Describes how a substance interacts with other matter
Chemical Properties • Flammability • Reactivity • Explosiveness, • Ability to rust • Ability to burn or not burn
Non-reactivity is also chemical the inability to combine with most other substances is a chemical property of gold. • The inability of a substance to combine with another substance is also a chemical property.
Identify as chemical and physical property Silver tarnishes when it comes in contact with hydrogen sulfide in the air. A sheet of copper can be pounded into a bowl. Barium melts at 725°C. Helium does not react with any other element. A bar of lead is more easily bent than is a bar of aluminum of the same size. Potassium metal is kept submerged in oil to prevent contact with oxygen or water. Diamond dust can be used to cut or grind most other materials. Rocks containing carbonates can be identified because they fizz when hydrochloric acid is applied.
Mini Lab: Zinc and HCl Materials: Test tube Small piece of Zinc 10 mL of HCl Record the physical properties of the zinc metal. Record the physical properties of the HCl.
With the test tube in the test tube rack, drop the zinc into the HCl. • Observe. Be sure to touch the bottom of the tube. • Light a wooden splint and do a flaming splint test. Record your results. What gas does this result confirm?
Post Lab • 1. What is the gas a sign of? • 2. The equation for this reaction is Zn + HCl ??? What are the products? 3. What is the identity of the gas produced? Give two reasons to support your prediction. 4. Name a chemical property of Zinc and a chemical property for HCl.
More analysis Give some reasons you know that a chemical reaction happened when you added zinc to HCl What happens in the flaming splint test? Write the equation for the flaming splint test? Name something on a bigger scale that this flaming splint test is like.
Two Types of Changes in Matter Physical Changes or Chemical Changes
Physical Changes • A change that changes appearances, without changing the composition. • Changes that do not alter the composition of matter • Verbs used to indicate physical changes • Boil Melt Freeze • Dissolve Break Shatter • Tear Condense Crumple • Grind Split Crush
Grinding Coffee A physical change
Boiling Water Physical Change
Chemical Change Occurs when one or more substances change into new substances. also known as a chemical reaction. The appearance of new substances is the sign that a chemical reaction has occurred
Chemical Changes • Change where a new form of matter is formed. • Verbs used to indicate a chemical change • Burn Oxidize • Decay Ferment • Rot Rust • Reacts with Corrode • Decomposes Tarnish
Frying an Egg Chemical change
A rotting pumpkin A chemical change
A Chemical Reaction http://www.youtube.com/watch?v=awdbiiTiWKk&feature=plcp Combustion of Iron
Leaves Changing Colors in the Fall Fireworks
Chemical Reactions • When one or more substances are changed into new substances. • Reactants- materials you start with • Products- What you make • NEW PROPERTIES • Not easily reversed
Indicators of Chemical Reactions • Production of a gas (smell or bubbles) • Production of a solid (precipitate) • Color Changes • Changes in Energy (temperature)
Classify as Physical or Chemical Moisture in the air forms beads of water on a cold windowpane. An electric current changes water into hydrogen and oxygen. Yeast cells in bread dough make carbon dioxide and ethanol from sugar. Olive oil, vinegar, salt, and pepper are shaken together to make salad dressing. Molten bronze is poured into a mold and solidifies to form a figurine. A reactant decomposes to form two products
Lab Evidence of a Chemical Reaction
Law of Conservation of Mass • Mass Reactants =Mass Products • One of the greatest achievements of 18th century science • Antoine Lavoisier was one of the first to use an analytical balance to show this.
Conservation of Mass • Mass can not be created or destroyed in ordinary (not nuclear) changes. • All the mass can be accounted for.
Dalton's atomic theory addressed this when he said that chemical reactions involve the rearrangement of atoms and atoms are neither created nor destroyed in chemical reactions. This law is why chemical equations have to be Balanced.
Example Problem When 10 grams of calcium are burned in oxygen, 14 grams of calcium oxide are formed. How many grams of oxygen react?
Conservation of mass says that the sum of the masses of the reactants must be the same as the sum of the masses of the products Reactant Mass = Product Mass Calcium + oxygen calcium oxide 10 g Ca + ? gO2 = 14 g CaO 4 gO2
Example Problem • A thin strip of iron with a mass of 15.72 g is placed into a solution containing 21.12 g of copper (II) sulfate and copper begins to form. After a while, the reaction stops because all of the copper(II) sulfate has reacted. The iron strip is found to have a mass of 8.33 g. The mass of copper formed is found to be 8.41 g. What mass of iron(II) sulfate has been formed in the reaction?
Solution • Apply the Law of Conservation of Mass • Massreactant1 + Massreactant 2 = Massproduct 1 + Massproduct 2 • Rewrite the equation with the names of the reactants and products. • Massiron + Masscopper sulfate = Masscopper + Massiron sulfate • To find the mass of iron sulfate, rearrange the equation. • Massiron sulfate = Massiron + Masscopper sulfate - Masscopper • Then, determine the mass of iron that reacted. • Massiron = original mass of iron - mass of iron remaining • Massiron = 15.72 g - 8.33 g = 7.39 g • Finally, substitute the masses into the equation and solve. • Massiron sulfate = 7.39 g + 21.12 g - 8.41 g = 20.10 g iron sulfate • To check your work, make sure the sum of the masses of the reactants is equal to the sum of the masses of the products.
We also have to remember to put the units by each number; this helps us keep track of what's going on and also expresses to the reader that we are dealing with mass and not some other property.
Practice Problems A sealed glass tube contains 2.25 g of copper and 3.32 g of sulfur. The mass of the tube and its contents is 18.48 g. Upon heating, a reaction forms copper(II) sulfide (CuS). All of the copper reacts, but only 1.14 g of sulfur reacts. Predict what the mass of the tube and its contents will be after the reaction is completed. Explain your reasoning.