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Introduction to Chemistry

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No eating or drinking! Wear goggles at all times! Use common sense!

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All of the “stuff” in the universe is made of MATTER Chemistry is the study of matter and the changes it undergoes. “Why is chemistry important to me?”

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Matter, all the “Stuff” in the universe, has many different forms. All matter has mass This is different than weight. On earth a person with a mass of 70 kg weights 154 lbs On the moon the same 70 kg person only weights 25.5 lbs.

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Scientific Methods: ◦ Any systematic approach used in scientific study. ◦ An organized process used by scientists to do research. The most important part of any scientific method is making observations. Qualitative data: Descriptive Quantitative data: Measurements After making observations scientists then come up with a hypothesis. A hypothesis is a proposed explanation for what is being observed.

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Experimentation An experiment is a set of controlled observations that test the hypothesis. scientists must carefully plan experiments in order to test their hypothesis. In any experiment there are many different variables.

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Variables are quantities or conditions that can be changed. A control is used by scientists as a basis for comparison.

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A Theory is an explanation of a natural phenomenon based on many observations and investigations over time. A Law is based on scientific facts. Law of Gravity.

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All scientists around the world us the SI system. This ensures that all scientific findings are reported in the same way. An SI base unit is a defined unit in the SI system that is based on an object or event in the physical world.

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There are seven SI base units. Time: ◦ Seconds (s) Length: ◦ Meter (m) Mass: ◦ Kilogram (kg) Temperature: ◦ Kelvin (K) ◦ The formula to convert from Celsius to kelvin is ◦ K = o C + 273

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Amount of a substance: ◦ mole (mol) Electric current: ◦ Ampere (A) Luminous intensity: ◦ Candela (cd)

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Not all things can be measured directly using SI base units. For example to SI unit for speed is m/s. We need to measure both time and length at the same time to get speed. Volume: The derived SI unit for volume is the Liter.

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Density is also a derived unit of measurement. Density = Mass/Volume

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To record very small or very big numbers scientists use SCIENTIFIC NOTATION.

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The diameter of the sun is 1,392,00 km

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In order to add and subtract numbers in scientific notation, the exponents must be the same. 2.840 x 1018 J 3.146 x 1018 J 3.60 x 1017 J 1.50 x 1017 J 6.9 x 1016 J 6.565 x 1018 J

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For multiplication, multiply the numbers and then add the exponents. (2 x 10 3 ) x (3 x 10 2 ) 2 x 3 = 6 3 + 2 = 5 6 x 10 5 For division, divided the numbers and then subtract the exponent of the divisor from the exponent of the dividend. (9 x 10 8 ) ÷ (3 x 10 -4 ) 9 ÷ 3 = 3 8 – (-4) = 8 +4 = 12 3 x 10 12

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Dimensional Analysis is a systematic approach to problem solving that uses conversion factors to move, or convert, from one unit to another. How many pizzas do you need to order if 32 people will attend a party, each person eats 3 slices of pizza, and each pizza has 8 slices?

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We can do the same types of conversions with SI units. We just need to know the relationship between the units we want to convert. Examples: We know that there are 1000 m in 1 km. We can rewrite this as: 1000m/1km or 1km/1000m Then if we are given and number of meters or kilometers we can convert. Convert 48 km into meters.

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All measurements contain uncertainties that affect how a calculated or measured result is presented. Each teaspoon you measure in the kitchen contains some error. 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.

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When we make a measurement we always measure to the last known marking on our tool and then we make one guess. The significant figures in these measurements are all of the known digits plus our one guess.

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When there is liquid in a graduated cylinder we can only know the exact measurement for sure up to a certain value. This picture shows us definitely 50mL, definitely 51mL, and definitely 52mL. The actual volume is somewhere between 52 and 53. We are allowed and MUST make our best estimation of the actual volume.

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1. Zeros between nonzero digits are always significant. ◦ 1005 kg – Has 4 significant figures 2. Zeros at the beginning of a number are never significant. ◦ 0.02 g – Has one sig. fig. ◦ 0.0025 - Has two sig. figs. 3. Zeros at the end of a number are significant only if there is a decimal in the number. ◦ 0.0200 g – Has three sig. figs. ◦ 3.0 cm – Has two sig. figs. ◦ 100 cm – Has only one sig. fig.

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When we use measured quantities to do calculations, the least certain measurement limits the certainty of our calculation. Therefore the number of significant figures in our answer is determined by the number of sig figs in the least certain number. Rules: ◦ For addition and subtraction: The answer has the same number of decimal places as the number with the least amount of decimal places. ◦ 20.42 + 1.322 + 83.1 = 104.842, we round to 104.8 ◦ For multiplication and division: The answer has the same number of sig figs as the number with the smallest number of sig figs. ◦ 6.221 x 5.2 = 32.3492, we round to 32

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