Finding Out about Matter2.1-2.6

2-1:What You Know about Matter
-water is one of the most familiar kinds of matter.
-water samples collect from a muddy stream and the ocean are different
-they dont look the same,taste the same, or boil at the same temperature, and different densities
-the temperature at which matter changes from a liquid to a gas, its boiling point, is still another property that you use to identify matter.


2-2:Purifying Matter
-Mixture---two or more kinds of matter that have separate identities.
-Matter that is easily separated into component parts is called a mixture or said to be impure.
-Mixtures like salt water or sugar water that look uniform throughout and do not scatter light are called solutions
-Mixtures are matter that can be separated into component parts that have a separate identity
-Distillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction.
-Many mixtures are extremely difficult to separate. Much of the recent awareness of air pollution, water pollution, carcinogens in foods, and similar environmental concerns have come about because new and better techniques have been found to detect those impurities.


2-3:Characteristics of Pure Substances
-Characteristics of Mixture: if you boil the water collected in this way, you will find that the temperature will remain constant from the time the water first boils until it all disappears.
-Characteristics of Pure Substances: have a constant boiling point; mixtures ordinarily do not
-but a few have a constant boiling point, because the water and grain alcohol cannot be separated by distillation is that a mixture containing 95.6% ethanol and 4.4% water has a constant boiling point of 78.2℃
-the temperature at which a liquid changes o a solid is called its freezing point(melting point), the temperature at which a solid becomes a liquid.


2-4: Chemical and Physical Change
-Density is a property of matte that describes its mass per unit volume.
-Changes that produce a new kind of matter with different properties are called chemical changes. This particular chemical change is called a decomposition because one kind of matter comes apart(decomposes) to form two or more kinds of matter.
-melting is therm used to describe the change of a solid to a liquid without the formation of any new kind of matter
-Change that didnt produce new kinds of matter and reversible are called Physical changes. Boiling is a physical change


2-5:Compounds and Elements
-Ex: when salt is melted and an electric current is passed through the melt ,the salt decomposes to form sodium metal at the negative electrode and chlorine gas at the positive electrode. The process just described is called electrolysis. Electrolysis involves passing an electric current through a substance, causing into decompose into new kinds of matter.
-Decomposition of a pure substance and distillation of a mixture are both processes in which matter is separated into components, but in thinking about what happens you see that they are fundamentally different processes
-In decomposition, a single , pure substance with constant, characteristic properties is somehow changed into new substances with different properties. Decomposition represents a chemical change
-Pure substances that can be decomposed into new kinds of matter are called compounds
-the elements building blocks of all kinds of matter and are called elements
-109 known elements
-Virtually all matter on Earth is made of obly 85 elements, and just eight of these account for 99% of the Earthe's crust. All other elements in Earth's crust make up ony 1% of its mass

2-6: Compounds Have a Definite Compositon
-not all combinations of elements are compounds.
-The law of definite composition states that all samples of a compound have the same composition— the same proportions by mass of the constituent elements.
-The law of multiple proportions states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers
-CHEM THEME:Any sample of a given compound contains the same percentage by mass of each element. Samples of compounds which contain the same elements but in different percentages by mass are defferent.