Assignment. 1. Complete Problems: 2. Read Chapter for Friday. 3. Don t fall behind!

Transcription

1 Assignment 1. Complete Problems: 1,4,6,7,13,14,16,18,20,24,27,30,34,38,40, 42,45,47, (more to follow) 2. Read Chapter for Friday. 3. Don t fall behind!

2 Useful Conversions 365 days = 1 year 1 day = 24 hrs 1000 ms = 1 s 60 min = 1 hrs 60 sec = 1 min 10 6 um = 1 m 10 9 nm = 1 m 1000 mg = 1 gram 1 mile = 5280 ft 12 in = 1 ft 100 cm = 1 m 1000 m = 1 km 10 6 µs = 1 s sec = 1 ps grams = lb lb = 1 kg 1 oz = g 1000 cm 3 = 1 L 3.78 L = 1 gallon 1000 ml = 1 L

3 Length Conversions Metric Units 5280 ft = 1 mile 3 ft = 1 yd 12 in = 1 ft

4 Mass Conversions Metric Units 2,200 lb = 1 metric ton 16 oz = 1 lb

5 Volume Conversions Metric Units 4 qt = 1 gal 3.78 L = 1 gal 2 pts = 1 qt 16 oz = 1 pt

6 Some Problems The speed of light in a vacuum is 2.99 X cm per second. What is this speed in km/hr?

7 Some Problems The speed of light in a vacuum is 2.99 X cm per second. What is this speed in km/hr? cm sec cm min cm hr m hr km hr km hr cm = sec 1m 10 2 cm 1 km 10 3 m 60 sec 1 min 60 min 1 hr km hr = 2.99 cm 1010 sec 1 m 10 2 cm 1 km 10 3 m 60 sec 1 min 60 sec 1 hr

8 Problem The record for the Kentucky Derby is held by the 1973 Triple Crown winner Secretariat, who ran the 10 furlongs in 1 minute, 59.4 seconds. 1 furlong is 1/8 of a mile in English Units. Calculate this remarkable horse s average speed in km per hour.

9 Example with volume The small block Chevrolet 350 cubic inch race engine is arguably the most famous race engine in US auto racing history. How many liters is this small-block Chevy workhorse?

10 A Systematic Approach to Solving Chemistry Problems Problem statement Clarify the known and unknown. Plan Suggest steps from known to unknown. Prepare a visual summary of steps. Solution Check Comment and Follow-up Problem

11 International computer communications are often carried by optical fibers in cables laid along the ocean floor. If one strand of optical fiber weighs 1.19 x 10-3 lbs/m, what is the total mass (in kg) of a cable made of six strands of optical fiber, each long enough to link New York and Paris (8.84 x 10 3 km)? PLAN: The sequence of steps may vary but essentially you have to find the length of the entire cable and convert it to mass. length (km) of fiber 1 km = 10 3 m length (m) of fiber 1 m = 1.19x10-3 lb mass (lb) of fiber 6 fibers = 1 cable mass (lb) of cable lb = 1 kg SOLUTION: 8.84 x 10 3 km x 8.84 x 10 6 m x mass (kg) of cable 10 3 m km 1.19 x 10-3 lbs m 6 fibers 1.05 x 10 4 lb x cable 6.30x 10 4 lb cable = = 8.84 x 10 6 m = 1.05 x 10 4 lb 6.30x 10 4 lb cable 1kg x = lb 2.86x10 4 kg cable

12 Temperature Kelvin Celsius Fahrenheit

13 Temperature Conversions Kelvin is the SI unit for temperature. To convert from C to Kelvin memorize: Kelvin = C C = 5 9 ( F 32) F = ( C 9 )

14 Rick s Noise Limiter The highest and lowest temperatures on record for San Bernardino, CA USA are 118 and 17 F, respectively. What are these temperatures in C and in K? 1) What is the question asking: C and K equivalents 2) What do we know---can we make a picture to help?

15 What is Density? Density is the ratio of a mass of an material to its volume in kilograms per liter. Chemists typically use as units grams/ml or g/cm 3, or g/ml. Density = mass (grams) volume (ml)

16 Densities of Some Common Substances * Substance Physical State Density (g/cm 3 ) Hydrogen Gas Oxygen Gas Grain alcohol Liquid Water Liquid Table salt Solid 2.16 Aluminum Solid 2.70 Lead Solid 11.3 Gold Solid 19.3 * At room temperature(20 0 C) and normal atmospheric pressure(1atm).

17 Specific Gravity Specific Gravity is the ratio of density of a substance compared to water at 25 C (Density of Water (25 C) =1 g/cm 3 ). S.G. = Density X (g/cm3 ) Density W ater (g/cm 3 )

18 Using Density A piece of platinum metal with a density (d) of 21.5 g/cm 3 has a volume (V) of 4.49 cm 3. What is its mass? Density = mass (g) V olume (cm 3 ) Rearranging : m = D V Substituting : m = 21.5 g cm cm 3 = 96.5 g 3 SF 3 SF 3 SF

19 Better Problem What is the diameter of the moon in kilometers if the moon has a mass of 7.4 X kg and its density is 3.3 g/cm 3? Don t think about memorizing formulas.

20 II. Uncertainty in Measurements Accuracy is correctness Precision is reproducibility

21 Chemistry In Action On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mar s atmosphere 100 km lower than planned and was destroyed by heat. 1 lb = 1 N 1 lb = 4.45 N This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.

22 Uncertainty in Measurements Accuracy describes how well a measurement agrees to a standard or a known true value (how valid it is). A measurement is accurate if it is near the true value. Precision is how well a number of repeated independent measurements agree with each another, its reproducibility regardless of how accurate the measurement is. Note that neither tells us how accurate or precise an instrument is---they come about as a result of the measurement.

23 Precision and accuracy in the laboratory. precise and accurate precise but not accurate

24 Errors and Uncertainty All measurements are uncertain and subject to error. Why?! Random errors- errors that tend to lead to values both above and below the true value. More measurements needed to average out. Leads to a decrease in precision.!systematic errors - errors that normally affect accuracy in one direction (high or low). Examples include poor calibration of instruments, human error in reading measurement.

25 Random vs Systematic Error random error systematic error

26 Accurate or Precise Suppose the true value of a measurement is the bulls eye Systematic Error Random Error accurate & precise precise but not accurate not accurate & not precise