# Chemistry Chapters 2&3

## Chapter 2 Teks

This chapter goes over Units of measurement, Scientific Notation and Dimensional Analysis, how reliable measurements are, and Representing Data.

## Si Units

Base units: Time, Length, and Mass. SI measurement units allow scientist to report data that can be reproduced by other scientist. Adding prefixes to SI units extends the range of possible measurements. Volume and Density have derived units. Density is the ration of mass to volume. Density can be used to identify a sample of matter.

## Scientific Notation

Scientific Notation- Expresses numbers as a multiple of two factors: a number between 1-10; and raised to a power or exponent. Scientific Notation makes it easier to handle extremely large or small measurements. Numbers expressed in scientific notation are a product of two factors: (1) a number between 1 and 10 and (2) ten raised to a power. Numbers added or subtracted in scientific notation must be expressed to the same power of ten. When measurements are multiplied or divided in scientific notation, their exponents are added or subtracted, respectively.

## Dimensional Analysis

Dimensional analysis is a method of problem solving that focuses on the units used to describe matter. For example, if you want to convert a temperature in degrees Celsius to a temperature in kelvins, you focus on the relationship between the units in the two temperature scales. Dimensional Analysis often uses conversion factors to solve problems that involve units. A conversion factor is a ration of equivalent values.

## Accuracy and Precision

Accuracy refers to how close a measured value is to an accepted value. Precision refers to how close a series of measurements are to one another. An accurate measurement is close to the accepted value. Precise measurements show little variation over a series of trials. The type of measurement instrument determines the degree of precision possible.

## Percent Error

Percent Error is the ratio of an error to an accepted value. Here is the formula:

Percent error= error/accepted value x100

Percent error compares the size of an error in experimental data to the size of the accepted value.

## Significant Figures

Significant figures include all known digits plus one estimated digit. There are a few rules for recognizing significant figures:

• Non zero numbers are always significant.
• Zeros between non-zero numbers are always significant.
• All final zeros to the right of the decimal place are significant.
• Zeros that act as placeholders are not significant. Convert quantities to scientific notation to remove the placeholder zeros.
• Counting numbers and defined constants have an infinite number of significant figures.
The number of significant figures reflects the precision of reported data. Answers to calculations are rounded off to maintain the correct number of significant figures.

## Representing Data

When you represent data you should use graphing i.e Circle graphs, Bar graphs, and Line graphs.

## Graphing

• Circle graphs: A circle graph is used for showing a certain percent out of 100. This is good to use when your trying to show things as a whole or combined to make one whole.
• Bar graphs: A bar graph is often used to show how a quantity varies with factors such as time, location, or temperature.
• Line graphs: In chemistry this is mostly what you will use. The points on a line graph represent the intersection of data for two variables. The independent variable is plotted on the x-axis and the dependent is on the y-axis.

## Chapter 3 Teks

Matter-Properties and Changes. This chapter goes over:

• Properties of Matter
• States of Matter.
• Physical Changes.
• Chemical Changes.
• Conservation of Mass
• Mixtures
• Separating Mixtures
• Elements
• Compounds

## Properties of Matter.

• Substances:Matter that has a uniform and unchanging composition is call a substance. i.e Table salt, water, and sand.
• Physical properties: A physical property is a characteristic that can be observed or measured without changing the samples composition.
• Extensive and intensive properties: Extensive properties are dependent upon the amount of substance present.Intensive properties are independent of the amount of substance.
• Chemical properties: The ability for a substance to combine into one or more other substances.

## Observing Properties of Matter

• Every substance has its own unique set of physical and chemical properties.
• States of matter:
• Solid: A solid is a form of matter that has its own definite shape and volume. i.e Wood, Metal, and paper.
• Liquids: A liquid is a form of matter that flows, has constant volume, and takes the shape of its container. i.e Water, blood, and mercury.
• Gases: A gas is a form of matter that flows to conform the shape of its container and fills the entire volume of its container. i.e neon, methane, and air.

## Changes in Matter

• Physical Changes: This alters a substance without changing its composition. i.e Bend, grind, crumble, split, and crush.
• Chemical Changes: A process that involves one or more substances changing into new substances. i.e wine making... you change grapes into wine.

## Conservation of mass

The Law of Conservation of Mass states that mass is neither created nor destroyed during a chemical reaction--- it is conserved. The formula is

Mass(reactants)=Mass(products)

## Mixtures of Matter

• Mixtures: A combination of two or more pure substances in which each pure substance retains its individual chemical properties. I.e sand, and water and table salt, and water.

## Types of Mixtures

• Heterogeneous mixture: One that does not blend smoothly throughout and in which the individual substances remain distinct.
• Homogeneous mixture: Has constant composition throughout; it always has a single phase. Also referred to as a solution.

## Separating Mixtures

• Filtration: A technique that uses a porous barrier to separate a solid from a liquid.
• Distillation: A separation technique that is based on differences in the boiling points of the substances involved.
• Crystallization: A separation technique that results in the formation of pure solid particles of a substance from a solution containing the dissolved substance.
• Chromatography: A technique that separates the components of a mixture on the basis of the tendency of each to travel or be drawn across the surface of another material.

## Elements and Compounds.

• An element is a pure substance that cannot be separated into simpler substances.
• A compound is a combination of two or more different elements that are combined chemically.