CH 3: The Metric System

1. CH 3: The Metric System Renee Y. Becker CHM 1025 Valencia Community College

2. The Metric System • The English system was used primarily in the British Empire and wasn’t very standardized. • The French organized a committee to devise a universal measuring system. • After about 10 years, the committee designed and agreed on the metric system. • The metric system offers simplicity with a single base unit for each measurement.

3. Metric System Basic Units

4. SI unit • SI units • In 1960 International System of Units (SI) adopted • This system has 7 SI base units that all other units can be derived from • Metric system is a decimal system • We use SI prefixes • Indicates a power of 10

5. Measurement and Units SI Units

6. Metric Prefixes 1 kilometer = 1 x103 meter 1 km = 1000 m

7. Measurements and Units • Dimensional-Analysis method uses a conversion factor to express the relationship between units. Original quantity x conversion factor = equivalent quantity Example: express 2.50 kg  lb. Conversion factor: 1.00 kg = 2.205 lb 2.50 kg x 2.205 lb = 6.00 lb 1.00 kg Then multiply by the conversion factor Always start with the original quantity

8. Measurements and Units • Remember that anything divided by itself =1 • This is how we can get rid of units!!! They cancel out!! • So remember when setting up dimensional analysis to always divide the units you are trying to get rid of. And multiply by the unit you want to keep!

9. Example 1 • What unit will the answer have for the following? 12 bird x 3 dog x 12 cat = 108 4 bird 1 dog 13 g CO2 x 1 mole CO2 = .30 44 g CO2 56 clowns x 2 doctors x 10 doctors = 3 x 101 12 clowns 3 cops

11. Example 2: Metric Conversion • 1.267 km  m  cm • .784 L  mL • 3.67 x 105 cm  mm

12. Example 3: English Conversion • 79 oz  lb. • 9.63 x 10-3 ft  in

13. Example 4: Metric-English Conversion • 1.34 x 1012 in  cm • 4.67 x 10-7 lb  g • 10.5 gal  L

14. Example 5: Measurement with Compound Units I am traveling 32 mi/hr, how fast am I traveling in km/hr? 1 mi = 1.61 km

15. Volume by Calculations V = L x w x h Length, width, and height have to be in the same unit Example: a box has L = 12 cm, w = 42 cm, h = 32 cm • What is the volume of the box? V = L x w x h = 12 cm x 42 cm x 32 cm = 1.6 x 104 cm3 • don’t forget to multiply the units as well as the #’s!!! • If the units are not the same you will have to convert so that they are!!

16. Volumes of Solids, Liquids, Gases

17. Volume by Displacement • How we can find density in the lab!! • If the jade has a mass of 21.3 g what is the density?

18. Gas Volume by Displacement You want to measure the volume of gas given off in a chemical reaction. The gas produced displaces the water in the flask into the beaker. The volume of water displaced is equal to the volume of gas.

19. The density of an object is a measure of its concentration of mass. Density is defined as the mass of an object divided by the volume of the object. Density = Mass/Volume M = DxV V = M/D Density

20. Density • Density is expressed in different units. It is usually grams per milliliter (g/mL) for liquids, grams per cubic centimeter (g/cm3) for solids, and grams per liter (g/L) for gases.

21. Density

22. Density • We can estimate the density of a substance by comparing it to another object. • A solid object will float on top a liquid with a higher density. • Object S1 has a density less than that of water, but larger than that of L1. • Object S2 has a density less than that of L2, but larger than that of water.

23. Example 6: Density • What is the density(in g/mL) of unknown substance that has a volume of 20 mL and a mass of 10 g?

24. Example 7: Density • What is the density (in g/cm3) of a platinum nugget that has a mass of 224.50 g and a volume of 10.0 cm3 ?

25. Example 8: Volume • What is the volume (in mL) of an unknown substance if it’s mass is 0.125 g and it’s density is 1.873 g/mL?

26. Example 9: Mass • What is the mass (in g) of an unknown substance if it’s density is 2.578 g/mL and it’s volume is 4.23 mL?

27. Temperature • Temperature is a measure of the average kinetic energy of the individual particles in a sample. • There are three temperature scales: • Celsius • Fahrenheit • Kelvin • Kelvin is the absolute temperature scale.

28. Temperature Temperature Conversions: The Kelvin and Celsius degree are essentially the same because both are one hundredth of theinterval between freezing and boiling points of water.

29. Temperature • Temperature Conversions: • Celsius (°C) — Kelvin temperature conversion: Kelvin (K) = °C + 273.15 • Fahrenheit (°F) — Celsius temperature conversions: C = 5/9 (F -32) F = (9/5 * C) + 32

30. Example 10: Temperature Carry out the indicated temperature conversions: (a) –78°C = ? K (b) 158°C = ? °F (c) 375 K = ? °C (d) 98.6°F = ? °C (e) 98.6°F = ? K

31. Temperature Scales • On the Fahrenheit scale, water freezes at 32 °F and boils at 212 °F. • On the Celsius scale, water freezes at 0 °C and boils at 100 °C. These are the reference points for the Celsius scale. • Water freezes at 273K and boils at 373K on the Kelvin scale.

32. Heat • Heat is the flow of energy from an object of higher temperature to an object of lower temperature. • Heat measures the total energy of a system. • Temperature measures the average energy of particles in a system. • Heat is often expressed in terms of joules (J) or calories (cal).

33. Heat vs. Temperature • Although both beakers below have the same temperature (100 ºC), the beaker on the right has twice the amount of heat, because it has twice the amount of water.