Chemistry Chapter 3 Notes

Section 3.1: Properties of Matter

Section 3.1: Properties of Matter

1) Matter is anything that has mass and takes up space. If the matter has a uniform composition, then it is called a substance.

Uniform

Not Uniform

Section 3.1: Properties of Matter

1) Matter is anything that has mass and takes up space. If the matter has a uniform composition, then it is called a substance, or pure substance. [This includes all elements, like iron, carbon, and oxygen, and compounds of the elements, like salt, water, and acetic acid.]

[Explain why salt and water are both substances, but seawater (salty water) is not.]

2) Matter is identified by it’s properties - physical and chemical.

a) Physical properties - can be observed or measured without changing the sample’s composition [(chemicals that make it up). (For example, if you rip a piece of paper, you’ve changed the size, but it’s still paper.)]

Two classifications of physical properties - extensive and intensive.

i. Extensive physical properties depend on how much of the sample you have, like mass and volume.

i. Extensive physical properties depend on how much of the sample you have, like mass and volume.

ii. Intensive physical properties do not depend on how much of the sample you have, they will still be the same, like density. [the density of a piece of copper is 8.92 g/cm3 whether you have a little piece or if you have a truckload.]

b) Chemical properties describe the sample’s ability to combine with or change into other substances. [If iron (an element - a substance) combines with oxygen (an element - a substance) it will form iron oxide (a compound - a substance), which we usually call rust.]

*Try to classify each of the following properties as a physical or chemical property. *If it is a physical property, also state if it is extensive or intensive.

SizeDensityColorFlammable

•Corrosive•Phase of Matter

3) [There are five phases of matter (also called states of matter.) Each phase has specific physical properties associated with it. Solid, liquids, and gases are by far the most common on earth, but plasmas (extremely high electrical energy - like lightening bolts) are the most common in the universe as all stars are made up of plasma. The fifth phase does not occur naturally anywhere in the universe and is still undergoing laboratory research.]

a) [Solids have a definite shape and a definite volume. The atoms in a solid are usually packed very close together and are often locked into a geometric shape (crystal). The atoms can only vibrate a little.]

b) [Liquids do not have a definite shape, but they still have a definite volume. The atoms in a liquid are still close together, but are free to slide around each other - making them a fluid (able to flow). ]

c) [Gases do not have a definite shape or a definite volume. The atoms spread apart as much as possible and move very fast.]

d) Plasmas are similar to gases, electrons get ripped loose of atoms.

Section 3.2: Changes in Matter

Section 3.2: Changes in Matter

1) two types of changes - physical and chemical.

a) Physical changes alter a substance without changing its composition. [Common physical changes involve change in shape and size - in other words, changes to a physical property. ]

i. Phase changes are ALWAYS physical changes. [The composition of the substance does not change, just how close the atoms are to each other and how much they can move. This includes melting, freezing, evaporation, vaporizing (boiling), and condensing. ]

b) Chemical changes alter the composition of a substance. [Thus chemical changes always alter physical properties. ]

b) Chemical changes alter the composition of a substance. Thus chemical changes always alter physical properties.

i. [Evidences of chemical changes include changes in color, texture, odor, the appearance or disappearance of a solid, and possibly a change in magnetic ability.]

[Note: it can be very tricky to tell physical and chemical changes apart just by the appearance. For instance, if you paint a piece of paper orange, it is a physical change, but if iron turns to orange rust, it is a chemical change. ]

[You cannot even think that physical changes can be easily reversed and chemical changes cannot, for it would be hard to “unpaint” the orange paper, but the orange rust can be turned back into iron by rubbing it with aluminum foil.]

[With each change, you must ask yourself if you’ve changed the chemical composition of the original substance or not. If you did, then it is a chemical change. If you did not, then it is a physical change. ]

2) The Law of Conservation of Matter applies to physical and chemical changes. The mass of the parts will be the same in the beginning and in the end. [ If you rip a piece of paper into 4 parts, the mass of all 4 parts must equal the mass of the original piece of paper. Also, the mass of all substances before a chemical change must equal the mass of all new substances after the chemical change.]

[When burning a log in a fireplace, you start with a large piece of wood and get just a little bit of ashes left over. If the law of conservation of mass is true (and it is), what happened to the rest of the mass?]

Section 3.3: Mixtures of Matter

Section 3.3: Mixtures of Matter

1) A mixture

is a combination of two or more substances in which each retains their individual chemical properties. [Mixtures can be separated into the substances that make them up by physical means.]

There are two types of mixtures - heterogeneous and homogeneous.

a) Heterogeneous mixtures

have an uneven spreading of the substances, and the distinct parts of the mixture are often easily distinguished. There are two types of heterogeneous mixtures - suspensions and colloids. [remember paraphrasing!

example

Heterogeneous – uneven distribution two types

suspensions & colloids]

i. Suspensions

heterogeneous mixtures in which the different parts can settle upon standing. Anything that tells you to shake well before using is a suspension, like orange juice with pulp and italian salad dressing.

II. Colloids are heterogeneous mixtures in which the different parts do not settle, like smoke and fog. Colloids will scatter light, a property called the Tyndall Effect.

Tyndall Effect

b) Homogeneous mixtures

have an even spreading of the substances, [making the parts of the mixture somewhat difficult to distinguish, which is the idea behind “homogenizing” milk - making it the same from the first glass to the last.] Homogeneous mixtures are often also called solutions. The two parts of a solution are the solute (thing being dissolved, or in lesser amounts) and the solvent (thing doing the dissolving, or in greater amount).

2) Mixtures must be separable by physical means. [ This could be simple, like using a magnet to pull iron out of sand, or using your fingers to pull marshmallows out of Lucky Charms Cereal, but often mixtures are harder than that to separate. Depending on the actual mixture,] chemists often use one of four basic ways to separate mixtures - filtration, distillation, crystallization, and chromatography.

a) Filtration

uses a filter to remove large, undissolved particles from a heterogeneous mixture. [The particles get trapped by the filter as the rest of the mixture travels through the filter. ]

b) Distillation uses the different boiling

temperatures of the liquid parts of a homogeneous mixture to separate the parts. [The part with the lowest boiling point will vaporize (boil out) first, and if desired can be collected and condensed back into a liquid. This process can be repeated until only one part of the original mixture is left. ][they do this to liquor to make it stronger!]

c) Crystallization removes the liquid part(s) of a homogeneous mixture to leave the solid part(s) behind. The liquid is removed by evaporation, or if time is an issue, vaporization.

d) Chromatography separates a homogenous mixture based on how far it can travel through a certain area. There are many, many types of chromatography that can do everything from separate dyes in an ink pen to separate the parts of DNA.

Section 3.4: Elements and Compounds

Section 3.4: Elements and Compounds

1) Pure substances can be classified into two groups - elements and compounds.

a) Elements contain atoms that are all the same, and cannot be broken down by physical or chemical means (it takes nuclear means). There are 91 naturally occurring elements, and several more that have been made by scientists. The best way to check if a substance is an element is to find it on the Periodic Table of the Elements.

b) Compounds contain atoms of two or more elements arranged in a specific ratio that is always the same. Unlike mixtures, compounds cannot be separated by physical means; separation can only be done chemically. [When a compound is formed, its properties are usually nothing like the properties of the atoms that make it up. Because the atoms of a compound must always be of the same whole number ratio, many different rules can be established. ]

i. The law of definite proportions says that no matter how much of the

compound you have, the ratio of the masses of the elements is always the same. [This means, for example, that water always has two hydrogens and one oxygen.]

ii. The law of multiple proportions says that elements can combine in different whole number ratios to make different compounds. [ For example, water has a ratio of 1 oxygen atom to 2 hydrogen atoms, while peroxide has a ratio of 2 oxygen atoms to 2 hydrogen atoms. There is no molecule with a half an element. ]

Matter

Mixtures Substances

HomogeneousHeterogeneous

Colloids Suspensions

Solutions

Elements Compounds