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 oC– 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 Fe2O3)

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 REACTIONS• Are expressed using chemical equations.

• Rusting of iron:4 Fe + 3 O2 2 Fe2O3 (rust)

reactants products

Meaning: Four atoms of iron react with three

molecules of oxygen to form two molecules of rust

Mixtures and Solutions

Mixtures and Solutions

• A mixture is a combinationof two or more components thatare 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 asolution.

Mixtures• When a mixture’s components are easily

recognizable, such as pizza, it is called a heterogeneous mixture.

• In a homogeneous mixture suchas chocolate milk, the component particles cannot be distinguished,even though they still retain theiroriginal 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 :saltwatercrude 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 - seawaterGas - airSolid - 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 ofa material are dispersed through-out a liquid or gas but are largeenough 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.– 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 Table1+ 2+ 3+ 4(+/-) 3- 2- 1- 0

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

– H2O (water)• Contains 2 atoms of hydrogen (H) and 1 atom of oxygen (O)• H2O is the chemical formula

• Elements in compounds are combined in a definite ratio– H2O is water but H2O2 is hydrogen peroxide

COMPOUNDS (cont)

• Are the molecules H2 and O3 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 H2, S8, 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. Fogb. Gasolinec. Heliumd. Sulfuric acid (H2SO4)e. Orange juice from squeezed oranges

CLASSIFICATION OF MATTER

Classify the following as an element, compound, homogeneous mixture, or heterogeneous mixture.

a. Fogb. Gasolinec. Heliumd. Sulfuric acid (H2SO4)e. Orange juice from squeezed oranges

CHEMICAL REACTIONS (Cont)

Zn + 2 HCl ZnCl2 + H2Zinc 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.