Scientific Measurement

1. Scientific Measurement Objective: To understand the importance of measurements in Chemistry

2. Measurements • Quality with both number and a unit • History • 4000Bc- Egyptians used knotted cords- kite • 1700Bc- Babylonians used cubits-elbow to finger tip • 500Bc- Phoenicians used Zebo-finger width • 300Bc- Romans used a soldiers Boot as a unit-equal to width of 12 fingers • 900AD- due to trade a standard unit of measurement was needed -Fathom- finger tip to finger tip (Vikings) • 1500AD- Tudor rules create a furlong= 220cyd Queen Elizabeth I- Roman mile= 5280 ft= 8 furlongs 1790AD- Metric system was proposed- base 10 system, meter basic uni1 1875AD- Renamed International System of Units (SI)

3. Scientific Notation • Since we deal w/ numbers very small and large 5.75 x 104 Coefficient Base Exponent • 1. The coefficient must be greater than or equal to 1 and less than 10.2. The base must be 10.3. The exponent must show the number of decimal places that the decimal needs to be moved to change the number to standard notation.  A negative exponent means that the decimal is moved to the left when changing to standard notation. Positive to the right

4. Accuracy/Precision • Accuracy- a measure of how close a measurement comes to the actual or true value of whatever is measured • Precision- a measure of how close a series of measurements are to one another • How do we test accuracy?? • How to we test precision?? • Dart board example

5. Error • Accepted Value-correct value based on reference sources • Experimental Value- measured in the lab • Error = EV-AV • Percent Error = [ error] x 100% Accepted value

6. What are Significant Figures? • All the digits that can be known precisely in a measurement, plus a last estimated digit. • “Guess Digits” • 10 mL graduated cylinder=8.29 • 25 mL graduated cylinder=20.55 • 100 mL graduated cylinder= 55.5 • Cm Ruler = 2.55

7. Why do we use Sig Figs? • We need to know how precise our measurements are. • Our calculations can not be more precise than the instruments we used to measure them • When working in the chemistry lab it is important to understand where your measurement came from

8. Significant Figure Rules! • 1. Every non-zero digit in a reported measurements is assumed to be significant • 27.3 m = 3 significant figures 0.734m = 3 Sig Figs • 2. Zeros appearing between nonzero digits are significant • 2703 m = 4 Sig Figs 70003 m = 5 Sig Figs • 3. Left most zeros appearing infront of nonzero digits are not significant, they act as placeholders • 0.0056 = 2 Sig Figs 0.4202 = 4 Sig Figs

9. Cont. • 4. Zeros at the end of the number and to the right of the decimal point are always significant. • 43.00 = 4 Sig Figs 1.0110= 5 Sig Figs • 5. Zeros at the rightmost end of a number but to the left of the decimal are not significant, they act as place holders • 21,800 = 3 Sig Figs 7,000 = 1 Sig fig

10. Atlantic/Pacific Method • Another way of looking at it………. Pacific Side Atlantic Side (Decimal is Present) (Decimal is Absent) NUMBER If the decimal is Present you come in from the left hand side and count every digit as significant starting with the first nonzero digit • 1.002 = 4 Sig Figs 108.008 = 6 Sig Figs

11. Atlantic/Pacific Cont. • If the decimal is Absent, then you come in from the right hand side and count every digit as significant starting with the first nonzero digit • 1239 = 4 Sig Figs 12000 = 2 Sig Figs 300 = 1 Sig Fig

12. Significant Figures when Adding or Subtracting • Think…”You are only as strong as your weakest link” • Your answer can only have the same number of decimal places as the number with the least amount of decimal places • 3.0001 + 2.33 Weakest link 5.3301 Since our weakest link only has 2 decimal places our answer can only have 2 decimal places…….so round the answer to 5.33

13. Significant figures when multiplying or dividing • Again..think, “Your only as strong as your weakest link” • Your answer needs to have the same amount of significant figures as the number with the least amount of sig figs • 3.444 x 2.04 = 7.02576 Since our “weakest link” only has 3 sig figs, our answer can only have 3 sig figs Weakest Link

14. Final Sig Fig Practice • How Many Sig Figs? • 1.oom = 3400 m = • 0.0078 g = 1.0900 x 103 = • 34009 g = 200 g = • Calculate: • 234.0g + 34.00g = • 34.555g – 18.9g = • 2.33m x 400m = • 25.000 / 4.09 =

15. Answers • How Many Sig Figs? • 1.oo m = 3 3400 m = 2 • 0.0078 g = 2 1.0900 x 103= 5 • 34009 g = 5 200 g = 1 • Calculate: • 234.0g + 34.00g = 268.0 g • 34.555g – 18.9g = 15.7 g • 2.33m x 400m = 900 m • 25.000m / 4.09m = 6.11 m

16. SI Units • Length- meter (m) • Mass- kilogram (kg) • Temperature- kelvin (K) • Time- second (s) • Amount of Substance- mole (mol)

17. Energy • Capacity to do work or to produce heat • Joule and calorie (quantity of heat that raises the temp of 1 g of pure water by 1° C) • 1 J = 0.2390 cal • 1 cal= 4.184 J

18. Metric System • Decimal system based on powers of 10 • See worksheet • Conversions: • Start with given value; move decimal one spot to left or right for each prefix -white board

19. Conversions Cont. • Use “conversion factor” – a ratio of equivalent measurements • When a measurement is multiplied by a conversion factor, the number may change, but the value stays the same 23 km x 106 mm = 2.3 x 107 mm 1 km conversion factor

20. Conversions • 234 m ____ cm • 23 km ____ mm • 0.0023 nm ____ Mm • 23 hm ____ dm • 100 g ____ mg • 78 ml ____ kl • 45 ml ____ cl • 345 g ____ kg

21. More practice w/ conversion factors • 24 Tm _____ pm • 6789.0 nm _____ km • 0.0038 Gm _____ μm • 230 cm _____ Mm • 0.000000780 Em _____ fm

22. Dimensional Analysis • Way at analyze and solve problems using the units, or dimensions, of the measurements • Converting between units How many hours are in 1 century? 1 century x 100 yrs x 365 d x 24 hr = 876000 hours 1 cent. 1 yr 1 d Known conversion factor

23. You try!!! • Mr. Focht is throwing a pizza party because all of his students studied and got “A”s on their chapter 3 test. However, Mr. Focht is poor from student loan payments. If a large pizza has 8 slices, how many students can Mr. Focht feed with 10 pizzas. (2 slice per student) 10 pizza. x 8 slice x 1 student = 40 students 1 pizza 2 slices

24. Little more difficult • Your car's gas tank holds 18.6 gallons and is one quarter full. Your car gets 16 miles/gal. You see a sign saying, "Next gas 73 miles." Your often-wrong brother, who is driving, is sure you'll make it without running out of gas. Figure out if you can make it to the gas station. 18.6 gallon x 1 tank x 16 miles = 74.4 miles 1 tank 4 quarter- tank gallon quarter tank

25. More Practice • If you are going 50 miles per hour, how many feet per second are you traveling? 50.0 miles x 5280 ft x 1 hour x 1 min = 73.3 ft hour 1 mile 60 min 60 sec sec

26. Warm Up • My car gets 33 miles to the gallon. How many miles can I travel if my car is currently holding 5.7 gallons of fuel. • You are driving down the road at 55 mph. How many feet will you travel in the next 3o min?

27. Density • Ratio of the mass of an object to its volume • D = m/v • How do we measure mass? • How do we measure volume? • Intensive property • As Temp. increases, density usually decreases • Exception???

28. Density of Water • Obtain a 100 ml graduated cylinder • Mass the graduated cylinder • Add 10.0 ml of water • Mass the cylinder • Add 30.0 ml of water • Mass the cylinder • Add 50.0 ml of water • Mass the cylinder • Plat your data on a graph using the graph paper provided • Add line of best fit