CHEM 100 CH 2 Notes
CHEM 100 CH 2 Notes Chem 100
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This 6 page Class Notes was uploaded by Carly Holliday on Friday February 5, 2016. The Class Notes belongs to Chem 100 at Indiana State University taught by Dr. Jeewandara in Summer 2015. Since its upload, it has received 23 views.
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Date Created: 02/05/16
KEY Sections ON the Syllabus Sections NOT on the Syllabus CHEMISTRY IN FOCUS CHEM 100 CHAPTER 2 NOTES Introduction: In this chapter, you will learn how to use some chemists’ tools. Just as a carpenter learns to use a hammer and a screwdriver to build a cabinet, so you must learn to use the tools of measurement and problem solving to build chemical knowledge. 2.1 Curious about Oranges The importance of curiosity in science cannot be overstated. If early scientists had not cared about why matter is as it is, science would not exist. Therefore, as a student of science, the first tool you must develop is your curiosity. Suppose you become curious about why some oranges are sweeter than others. To study the problem you begin with observation. You must observe or measure the sweetness of oranges as well as other properties that may be related (sweetness, size, and color). How would you measure an orange’s size? Level of sweetness? Color? The measurements must be accurate. They must also use a standard unit of measurement. You cannot merely classify the oranges as large or small, sweet or sour, orange or green. You must be able to show others what the difference is between the oranges. After completing your measurements, you might have to perform some calculations (converting your measurements from one unit to another). Then, you could put your results in a table or graph, which allows you and others to see correlations between properties. You might summarize this trend with a general statement such as, “In oranges, sweetness increases with increasing size.” If this statement had no exceptions, it would be a scientific law. The next step in the scientific method is to devise a hypothesis explaining why the bigger oranges are sweeter. 2.2 Measurement The ability to give a quantity allows us to go beyond saying that this object is hot and that one is cold or that this one is large and that one small—it allows us to actually quantify the difference. Uncertainty: All measuring devices have limitations; therefore, measurements always involve some uncertainty. Whether you are using a ruler or a graduated cylinder, you will always have one uncertain number in your measurement (ten’s place or hundredth place). It usually depends on the tool’s limitations. Significant figures: Are used when trying to preserve certainty in measurements. They are all of the certain digits followed by one uncertain digit in a measurement. 2.3 Scientific Notation A shorthand number to make computing easier when dealing with very large numbers and very small numbers. Positive n: When you have a positive exponent, your expanded number will be very large. You get your answer by moving the decimal point to the RIGHT. 10 = 1 1 10 = 1x10=10 10 =1x10x10=100 10 = 1x10x10x10 = 1,000 4 10 = 1x10x10x10x10 = 10,000 Negative n: When you have a negative exponent your expanded answer will be a very small number. You get your answer by moving the decimal point to the LEFT. 1 1 10 = 10 = 0.1 1 10 = 10 x10 = 0.01 1 3 10 = 10 x10x10 = 0.001 1 10 4= 10 x10x10x10 =0.0001 Expressing a number in scientific notation 0.000062 6.2 x 10 Negative 172,000,000 1.72 x 10 Positive 2.4 Units of Measurement Unit: A fixed, agreedupon quantity by which other quantities are measured Length centimeter, meter, inch, yard, mile, Kilometer…etc. 1 meter = 39.4 inches Temperature Fahrenheit, Celsius, Kelvin Temp. Kelvin Temp. Celsius K = C + 273.15 C = K – 237.15 1 Mass Gram = kg, Kilogram (standard unit), ounce, pound…etc. 1000 Volume Milliliter, Liter, cubic centimeter (cm )…etc. Time second, minute, hour…etc. Fun Fact: Today, a second is defined by an atomic standard using a cesium clock. 2.5 Converting Between Units When using measured quantities, you often have to convert a quantity expressed in one unit into another unit. To perform these calculations, you need to know the numerical relationships between units. When converting a quantity from one unit to another, the units themselves help to determine the correctness of the calculation. Units are multiplied, divided, and canceled like equations in algebra. Conversion factor: a fraction with the units you are converting to on the top and the units you are converting from on the bottom. Conversion factors can be constructed from any two quantities known to be equal. 60s 1m EX: 60 seconds= 1 minute 1m or 60s 12∈¿ ¿ 1 ft 12 inches = 1 foot 12∈ 1 ft ¿ ¿ 1000kg ∨ 1g 1000 kilograms = 1 gram1g 1000kg Since all of the above are equal to each other, each quantity can be on the top or bottom of a fraction and it will still be true! Equation to remember: (quantity given) x (conversion factor(s)) = quantity sought You may have to take two steps to get to the unit you desire EX: Convert 120 seconds to hours. s∗1minute ∗1hour 120 60s = 1 hours 60minutes 30 2.6 Reading Graphs To see trends in numerical data, scientists often display data in graphs. Understanding graphs is an important tool, not just for the science student but for any educated reader. Graph: A set of points representing collected data over a period of time. Always be aware about where the Axis of a graph starts. Most graphs begin at zero, but some do not. In order to read the graph correctly you must check out the both axis’ first. You can read many things on one graph. Percentage increased or decreased Average yearly increase or decrease How much change occurred over a certain period of time How many years data was collected change∈y y2−y1 Slope: the steepness of a live or curve. It is representchange∈x x2−x1 EX: If you are given two points: (3,6) (7,2) your slope equation will be: 2−6 4 7−3 →Then you simplify→− =−4 This is your slope If you were to plot (3,6) and (7,2) your live would be declining instead of inclining. This tells you that your slope is negative. Slope is represented by the letter “m” in the equation: Y=mx+b Yintercept: This is where the line touches or crosses the yaxis (the vertical one). Represented by the letter “b.” You can find “b” if you are given a point: EX: Point: (3,2) Equation: y = 6x + b 2 = 6(3) + b 2 = 18 + b 16 = b Your new equation will be: y = 6x – 16 2.7 Problem Solving Sometimes getting started with a problem is hard, so here are some steps that work for most problems you will have to solve. 1. Look at the quantities that are given to you and do something to label them. 2. Think about what quantities you need to find and label them differently. 3. Write down your conversion factors 4. Start with the given info then multiply by the conversion factor then cancle units and you will have your answer. 5. Round your answer to the nearest tenth or thousandth. 2.8 Density Some people call density “the level of compactness.” That means how much stuff can be put in a certain area. Density(d)= Mass(m) The Ratio of Mass to Volume: Volume(V) You can use density to convert between Volume and Mass. Here is a fun little trick I like to use: Steps: Cover up the unit you want to find ÷ M ÷ Then do what the table tells you. D V *Don’t forget your units!! X
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