Chapter 3 Matter Properties and Changes

DENSITY Density is a ratio that compares an objects mass to its volume. The unit for density is g/ L or g/ cm 3. A large piece of Styrofoam has the same mass as a quarter, but the quarter has a smaller volume. The quarter has a greater density, because there is a greater amount of mass contained in a smaller space.

1)A 5-mL sample of water has a mass of 5 g. What is the density of water? 2)An object with a mass of 7.5 g raises the level of water in a graduated cylinder from 25.1 mL to 30.1 mL. What is the density of the object? 3)The density of aluminum is 2.7 g/mL. What is the volume of 8.1 g?

Section 3.1 Matter is anything that has mass and takes up space. Matter that has a uniform and unchanging composition is called a substance. Common examples of substances include salt and water.

Matter has specific properties. Properties of matter can be physical or chemical. Physical properties are properties that can be observed or measured without changing the composition of the substance. Physical properties include density, color, odor, hardness, melting/ freezing/ boiling points.

Physical properties can be described as extensive or intensive. Extensive properties depend on the amount of the substance present. Length, for example is an observable, extensive physical property. Intensive properties do not depend on the amount of substance. Density, for example is an intensive physical property, because the density of a substance does not change, no matter how much of the substance is present.

Chemical properties of matter allow a substance to change composition as a result of contact with another substance or because of the application of thermal or electrical energy. If a substance is not reactive with another substance, HCl and Copper, that is a chemical property, also. Examples of chemical properties include the ability to rust, burn, release gas, absorb or give off energy.

All matter exists as either a solid, liquid, or a gas. Plasma is also a form of matter, but is only present on earth in lightning bolts. These are called STATES OF MATTER. States of matter are physical properties. Vapor is NOT the same as a gas!! A vapor is a word used to describe when a substance that is a solid or liquid at room temperature is heated enough to take a gaseous form.

SolidLiquidGas Definite shape Definite volume Particles held tightly together Particles expand when heated Takes shape of container, but does not have to fill it Definite volume Particles held close, but not tight Particles expand when heated Takes shape of containers and fills it completely No definite volume Particles are far apart, so it can be compressed

Section 3.2 Physical changes are changes which alter a substance without changing its composition. Examples are breaking glass, tearing paper, melting ice. Changes of state are physical changes. When energy is added to solid water, it changes to liquid water, when more energy is added, it is changed to gaseous water. All the time it is still water. Only a physical change has taken place.

Melting and boiling points are intensive physical properties. They do not change when the amount of substance changes. These intensive physical properties can be used to identify unknown substances.

Chemical change is defined as one or more substances combining to become one or more new substances. AKA chemical reaction Examples of common chemical reactions include burning wood, rusting iron, fermenting of barley and hops to make beer, and explosions.

Signs that a chemical reaction have taken place include: Thermal energy is given off or absorbed Light is produced Precipitate is formed Color has changed permanently Gas is formed

The Law of Conservation of Mass states that mass is neither created nor destroyed in any process, it is conserved. Mass of reactants = Mass of products A student carefully placed 15.6 g of sodium in a reactor supplied with an excess quantity of chlorine gas. When the reaction was complete, the student obtained 39,7 g of sodium chloride. How many grams of chlorine gas reacted? How many grams of sodium reacted?

24.1 g of chlorine gas is used in the reaction. Because the sodium reacts with excess chlorine, all of the sodium (15.6 g) is used in the reaction.

Law of Conservation of Energy In any chemical reaction or physical process, energy can be converted from one form to another, but it is neither created nor destroyed.

Classify each of the following as examples of physical or chemical changes 1.Crushing an aluminum can 2.Recycling used aluminum cans to make new cans 3.Aluminum combining with oxygen to form aluminum oxide

Section 3.3 A mixture is a combination of two or more pure substances in which each pure substance retains its individual chemical properties. The composition of a mixture is variable. Mixtures can be heterogeneous or homogeneous.

A heterogeneous mixture is one in which the substances still remain distinct. Examples include sand/ water, Skittles, fruit salad, vegetable soup. The existence of two or more distinct areas indicate a heterogeneous mixture.

A homogeneous mixture has a consistent composition throughout. It exists in one phase. Examples include salt and water, Kool- Aid, gold jewelry. Homogeneous mixtures are often referred to as solutions.

SystemExample Gas-gas Air is primarily a mixture of nitrogen, oxygen, and argon gasses Gas-liquid Carbonated beverages contain carbon dioxide gas in solution Liquid-gas Moist air contains water droplets in air Liquid-liquid Vinegar contains acetic acid in water Solid-liquid Sweetened powder drink contains sugar and other solid ingredients in water Solid-solid Steel is an allow of iron containing carbon

A mixture is a combination of substances physically combined. Physical separation methods take advantage of known physical properties of individual components of a mixture. Filtration uses a solid barrier to separate heterogeneous mixtures of a a solid and a liquid (sand & water). Distillation uses differences in boiling points to separate a homogeneous mixture.

Crystallization separates a mixture and forms a solid that is pure. Like making rock candy. Chromatography separates components of a mixture on the basis of the tendency of each to travel or be drawn across the surface of another material.

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Section 3.4 Elements are substances that cannot be broken down any further by either chemical or physical methods. Elements are pure substances. Elements have a unique name and chemical symbol. The symbol consists of one, two or three letters. The first letter is always capitalized and any following letters are lowercase.

The elements are grouped by patterns in their physical and chemical properties. In 1869, Dmitri Mendeleev organized the elements in rows and columns based on their masses. That was the first version of the periodic table. One of the greatest aspects of Mendeleev’s table was that it left spaces for elements not yet discovered.

The horizontal rows in the periodic table are called periods and the vertical columns are called groups or families. The table is called a “periodic” table, because the elements have patterns of similar properties as you move from period to period.

Compounds are two or more elements chemically combined. The names of compounds are written by using the element’s symbols. Salt is written NaCl, water is written H 2 O, hydrochloric acid is written HCl. Compounds can be broken down into simpler substances, unlike elements. In order to do that, electrical or heat energy must be added.

Compounds do not resemble the elements from which they are made. For example, salt, NaCl, is made from sodium (a silvery metal that burns when exposed to water), and chlorine (a greenish, poisonous gas). However, when these two combine, they form simple table salt that flavors food. m/search/assetDetail.cfm?guidAssetI D=E22926C5-4A5C A- 03E240843BD4

Law of Definite Proportions Regardless of the amount, a compound is always composed of the same elements in the same proportions by mass. The ratio of the mass of each element to the total mass of the compound as a percentage is called the percent by mass. Percent by mass % mass = mass of element x 100 mass of compound