Changes in Matter Review 9th

PHYSICAL PROPERTIES Characterize the physical state and physical behavior of a substance Each substance has unique physical properties Examples – Sulfur appears as a yellow powder – The boiling point of water is 100 o C – Carbon monoxide is odorless

CHEMICAL PROPERTIES Describe ways pure substances behave when interacting with other pure substances. Examples – Iron reacts with oxygen to form rust. – Platinum does not react with oxygen at room temperature.

Chemical vs. Physical Change – Physical Change: A change that can occur without changing the identity of the substance. – Ex. Solid, Liquid, Gas (Phase change) – Chemical Change: Process by which a substance becomes a new and different substance – Ex. Burning

STATES OF MATTER Solid Liquid Gas Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

WATER AND ITS STATES OF MATTER

CHANGES IN STATE Melting: Solid to liquid Boiling: Liquid to gas Sublimation: Solid to gas – The above three require input of energy Condensation: Gas to liquid Freezing: Liquid to solid Deposition: Gas to solid – The above three release energy

PHYSICAL CHANGES Do not alter the chemical identity of the substance – Examples include: Any change in the state of matter (e.g. freezing or boiling water) Sawing wood Crushing a tablet Bending a wire Dissolving salt in water

CHEMICAL CHANGES Changes the identity of the substance as the chemical composition changes. – Also called chemical reactions Examples: – Tarnishing of silver (Ag forms AgS) – Rusting of iron (Fe forms Fe 2 O 3 )

Chemical Reactions Chemical Reaction: a process in which the physical and chemical properties of the original substance change as new substances with different physical and chemical properties are formed Chemical Reaction: a process in which the physical and chemical properties of the original substance change as new substances with different physical and chemical properties are formed

CHEMICAL REACTIONS Are expressed using chemical equations. Rusting of iron: 4 Fe + 3 O 2  2 Fe 2 O 3 (rust) reactants products Meaning: Four atoms of iron react with three molecules of oxygen to form two molecules of rust

Mixtures and Solutions

A mixture is a combination of two or more components that are NOT chemically combined, and retain their identities. Mixtures can be physically separated. The identities of the substances DO NOT change. A homogeneous mixture is also called a solution.

Mixtures When a mixture’s components are easily recognizable, such as pizza, it is called a heterogeneous mixture. In a homogeneous mixture such as chocolate milk, the component particles cannot be distinguished, even though they still retain their original properties.

TYPES OF MIXTURES Heterogeneous Mixtures – A mixture that does not blend smoothly throughout – Individual components are distinct from one another Exe: Salad Dressing, fresh squeezed OJ Homogeneous Mixtures – Has uniform composition – Single phase – AKA: Solutions Exe: Chocolate Milk, Steel,

Separating Mixtures Common Techniques for Separating Mixtures Distillation – separates a mixture based on boiling points of the component. Examples : saltwater crude oil into gasoline and kerosene Magnet – separates iron from other objects. Centrifuge – spins and separates according to densities.

Solutions A mixture that appears to be a single substance but is composed of particles of two or more substances that are distributed evenly amongst each other. A solution may be liquid, gaseous, or solid. Examples of solutions Liquid - seawater Gas - air Solid - alloys

Solutions Dissolving – The process in which particles of substances separate and spread evenly amongst each other. Solute – substance that is dissolved. A solute is soluble, or able to dissolve. A substance that is insoluble is unable to dissolve, forms a mixture that is not homogeneous, and therefore NOT a solution. Solvent – substance in which solute dissolves into.

Solubility Solubility is the ability of a solid, liquid, or gaseous chemical substance called a solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance determines the amount of solute needed to make a saturated solution using a given amount of solvent at a certain temperature. Solubility is usually expressed in grams of solute per 100 ml of solvent (g/100ml) What does saturated mean? Three (3) methods that affect solubility – Mixing, stirring, or shaking – Heating – Crushing or grinding

Suspension A mixture in which particles of a material are dispersed through- out a liquid or gas but are large enough that they settle out. – Particles are insoluble, so they DO NOT dissolve in the liquid or gas. – Particles can be separated using a filter. Examples: Salad dressing Medicines that say “shake well before use”

Colloids A mixture in which the particles are dispersed throughout but are not heavy enough to settle out. Made up of solids, liquids and gases. –E–Examples : Mayonnaise Stick deodorant milk

CLASSIFICATION OF MATTER

ELEMENTS Pure substances contain only one type of atom The smallest building blocks of matter are called atoms There are 115 known elements today, 90 which occur naturally The periodic table displays the elements

The Periodic Table (+/-)

ELEMENTS (Cont) Each element has a unique symbol – The first letter is always capitalized, the second letter is always lower case Fluorine is F, not f Cobalt is Co, not CO (which is carbon monoxide) The smallest unit of an element is the atom

COMPOUNDS Substances containing more than one type of atom bonded together in fixed ratios. – NaCl (table salt) Contains sodium (Na) and chlorine (Cl) NaCl is the chemical formula – H 2 O (water) Contains 2 atoms of hydrogen (H) and 1 atom of oxygen (O) H 2 O is the chemical formula Elements in compounds are combined in a definite ratio – H 2 O is water but H 2 O 2 is hydrogen peroxide

COMPOUNDS (cont) Are the molecules H 2 and O 3 considered elements or compounds? Why?

Answer Pure chemical elements are not considered chemical compounds, even if they consist of molecules that contain only multiple atoms of a single element (such as H 2, S 8, etc.), which are called diatomic molecules or polyatomic molecules.

CLASSIFICATION OF MATTER Classify the following as an element, compound, homogeneous mixture, or heterogeneous mixture. a.Fog b.Gasoline c.Helium d.Sulfuric acid (H 2 SO 4 ) e.Orange juice from squeezed oranges

CLASSIFICATION OF MATTER Classify the following as an element, compound, homogeneous mixture, or heterogeneous mixture. a.Fog b.Gasoline c.Helium d.Sulfuric acid (H 2 SO 4 ) e.Orange juice from squeezed oranges

CHEMICAL REACTIONS (Cont) Zn + 2 HCl  ZnCl 2 + H 2 Zinc hydrochloric acid zinc chloride hydrogen gas Meaning: One atom of zinc reacts with two molecules of hydrochloric acid to produce one molecule of zinc chloride and one molecule of hydrogen gas.