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UNITS OF MEASUREMENT

UNITS OF MEASUREMENT. The metric system. CHEMISTRY. You will be studying chemistry Chemistry is defines as “ the study of matter and its reactions ” Chemistry is a physical science so we need to discuss how we measure things. WHAT ARE UNITS OF MEASUREMENT?.

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UNITS OF MEASUREMENT

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  1. UNITS OF MEASUREMENT The metric system

  2. CHEMISTRY • You will be studying chemistry • Chemistry is defines as “the study of matter and its reactions” • Chemistry is a physical science so we need to discuss how we measure things

  3. WHAT ARE UNITS OF MEASUREMENT? • Units describe what aspect of matter is being measured • Qualitative: something that is described • Quantitative: something that is measured • Examples: • Unit of distance – mile • Unit of volume – gallon • Unit of time – hour • Unit of weight - pound

  4. SI UNITS OF MEASUREMENT • SI – Standards International • Set of units that are recognized by the scientific community • In science (unlike math), you need a unit for EVERY NUMBER • These are the units we will be using in this class – not English units

  5. BASE UNIT • Metric system is a base 10 system • A base unit is a unit that measures some sort of physical/chemical data • Distance – meter (m) • Mass – gram (g) • Volume – liter (L) • Time – second (s) • Temperature – degrees Celsius (°C) • Energy – Joules (J)

  6. MASS – A QUICK EXPLANATION • Mass and weight are different • Weight can change. It is not an absolute value • Weight depends upon the force of gravity • You weigh more on Earth than on the Moon • Mass cannot change. It is an absolute value • Mass depends on the amount of matter in a substance • Mass does not change with gravity

  7. PREFIXES (GET HANDOUT) • Look at the name of the prefixes and the abbreviation on the sheet • These prefixes work for all base units • The prefix tells you how the base unit can be changed • Example: • If you have a cg (centigrams), this means that the centigram is 1/100 of a gram. • If you have a cL (centiliter), this means that the centiliter is 1/100 of a liter.

  8. HOW DO WE CHANGE THE BASE UNIT? • How big the measurement is depends on the prefix from the metric system • You increase or decrease the size of the number by changing the prefix in front of the base unit • IMPORTANT NOTE: • When you go DOWN the chart, the number gets BIGGER • When you go UP the chart, the number gets SMALLER

  9. STEPS TO CONVERT : EXAMPLE: 100mm = _?_cm Step 1: Find the conversion on the last column of the handout (Look at the prefixes) • 100mm = _____ cm • m (milli): 1 meter = 1000 mm • c (centi): 1 meter =100 cm Step 2: Use the conversion from the last column to convert to the base unit. (We will use ratios) • We start with 100millimiters (mm) and we want to make it the base unit meters (m) • The base unit DOES NOT have a prefix • Therefore: 100 mm = ??? m

  10. MATH FOR THE STEP 2 • We look at the prefix conversion from the first step • 1m = 1000mm • We start with 100mm • So the equation is: 1m____ = (x) m____ 1000mm 100mm • Solve for x to find the number of meters • NOTE: The meters(m) are both on top and the millimeters(mm)are both on bottom

  11. ANSWER FOR STEP 2 • When you cross-multiply, you get the following: x = 0.1m

  12. STEPS TO CONVERT Step 3: Use the answer that you got from step 2, to calculate into the unit you are looking for (cm) • We have our answer from step 2 (0.1m) • We want to convert it to our second unit (cm) • Therefore, we want to turn 0.1m into centimeters (cm) • We will use the other conversion from the first step • 1meter (m) = 100 centimeters (cm)

  13. MATH FOR STEP 3 • 1m = 100cm • We start with 0.1m • So the equation is: 1m____ = 0.1 m____ 100cm (x) cm • Solve for x to find the number of centimeters • NOTE: The meters(m) are both on top and the centimeters (cm) are both on bottom

  14. ANSWER FOR STEP 3 • When you cross-multiply, you get the following: x = 10 cm • NOTE: I know most of you know how to move the decimal to get the answer. YOU have to do it this way for the homework and quizzes. THERE IS A REASON.

  15. ONE FINAL THING • The example we just did showed how to go from to numbers with prefixes in their units mm to cm • This process involved 2 math steps • If your problem only has 1 number with a prefix, you will only need 1 math step • Example: • 250 cm = ??? m

  16. MATH FOR EXAMPLE 100 cm = ??? m • Find the value in the final column for centimeters (cm) • 1meter (m) = 100 centimeters (cm) • Set up the ratio: 1m__ = (x) m__ 100 cm 250 cm • x = 2.5m

  17. PRACTICE • Try the following 3 conversions IN YOUR NOTES: • 1500 g = __?__ kg • 63.3 hL = __?__ mL • 1.22 km = __?__ nm

  18. ANSWERS • 1.500 g • 6,330,000 mL • 1,220,000,000,000 nm

  19. TRY THESE IN ON YOUR OWN • 0.25 hg = ________ g • 3200 cm = ________ m • 0.0036 kL = ________ mL • 33400nJ = _______ kJ • 225 dkg = ________ dg • 880 hm = ________ um • 1 nL = ________ kL

  20. SCIENTIFIC NOTATION • Some numbers are so big or small that you have to write too many numbers • Scientists have a short hand way to abbreviate these number called scientific notation • Let’s look at the current national debt • 13,600,000,000,000 dollars

  21. FORMAT • In scientific notation we use exponents to tell us how to move the decimal • Write the number (without any zeroes before or after it) • 136 • Put a decimal after the first digit • 1.36

  22. FORMAT • Count how many spaces before or after the decimal that you need to move the decimal to get to your original number • 1.36 • 13,600,000,000,000. • You have to move the decimal 13 spaces to the right

  23. FORMAT • Use the following convention that shows you moved the decimal 13 spaces • x 1013 • Put the original number from step 2 with step 4 • 1.36 x 1013 • This tells you to move the decimal 13 places to the right

  24. QUESTION • How do you show that we move the decimal to the left? • For example: • 0.00122

  25. ANSWER • Same method except you use a negative (-) number in the exponent to show that the decimal goes to the left • 1.22 x 10-3 • The (-)3 says to move the decimal 3 spots to the left in the number 1.22

  26. TRY THESE • What are the following numbers in scientific notation? • 356,000,000 • 0.0000125 • What are the following numbers written out as a numeral? • 2.50 x 102 • 7.77 x 10-3

  27. ANSWER • What are the following numbers in scientific notation? • 3.56 x 108 • 1.25 x 10-5 • What are the following numbers written out as a numeral? • 250 • 0.00777

  28. PRACTICE WITH CALCULATORS • You will need to know how to read and enter scientific notation on calculators • After receiving a calculator, we will practice some on the board.

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