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Units of Measurement

Units of Measurement. Section 2.2. Vocabulary. Measurement: dimensions , quantity, or capacity as ascertained by comparison with a standard . Quantity: something that has magnitude, size, or amount

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Units of Measurement

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  1. Units of Measurement Section 2.2

  2. Vocabulary • Measurement: dimensions, quantity, or capacity as ascertained by comparison with a standard. • Quantity: something that has magnitude, size, or amount • Example: the quantity represented by a teaspoon is volume, the teaspoon is a unit of measurement

  3. Standard Measurement • Nearly every measurement is a number plus a unit • There has to be an agreement on measurement standards

  4. SI Measurement • Le Systeme International d’Unites • Adopted in 1960 • Has seven base units with other units derived from these seven • Are standard measurements

  5. SI Base Units found on page 34

  6. SI Prefixes • These are the most commonly used prefixes (“unit” can be grams, liters, etc): • 1 unit = 100 c units • 1 unit = 1 000 m units • 1 unit = 1 000 000 µ units • 100 units = 1 h unit • 1 000 units = 1 k unit • 1 000 000 units = 1 M unit

  7. Mass and Length • A measure of the quantity of matter • Weight: a measure of the gravitational pull on matter • Length is frequently measured in cm or km

  8. Derived SI Units (page 36) • Volume: the amount of space occupied by an object • The derived SI unit of volume is m3 • cm3 is often used in chemistry • A non-SI unit of volume is the liter, L • A smaller non-SI unit of volume is the mL • 1cm3 = 1mL

  9. Density • Density: the ratio of mass to volume, or mass divided by volume • D = m/V • Units are expressed as kg/m3, g/L, g/mL or g/cm3(or any other mass/volume units)

  10. More about Density • Density is a characteristic physical property • It is an intensive property • Can be used to help identify a substance • See the table on page 38

  11. Conversion Factors • A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other • The following steps will help you use conversion factors for the rest of chemistry….they don’t ever go away!

  12. Steps for Using Conversion Factors • Determine which is the smaller unit • How many of the smaller units are in one of the larger units • Set up the conversion factors as fractions • Write what you are given, then a multiplication sign, then a fraction bar • Choose a conversion factor that will make the units of the given value cancel diagonally • Solve the problem.

  13. Practice Problem • Convert 42.6 cm to meters. • cm is smaller, so 100 cm = 1 meter. • 100 cm or ___1 m__ 1 m 100 cm • 42.6 cm ● __1 m__ 100 cm • This is a division problem of 42.6 divided by 100. Answer is 0.426 m

  14. More Practice • Convert: • 1.843 m to km • 96.3 hg to g • 0.0013 Mg to mg (two step problem, go to grams first, then to mg) • 4863 µL to L • 1.4 x 105 g to µg

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