Objective: To understand the importance of measurements in Chemistry

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)

Scientific Notation Since we deal w/ numbers very small and large 5.75 x 10 4 CoefficientBaseExponent 1. The coefficient must be greater than or equal to 1 and less than The base must be 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

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

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

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= mL graduated cylinder= mL graduated cylinder= 55.5 Cm Ruler = 2.55

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

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 Figs70003 m = 5 Sig Figs 3. Left most zeros appearing infront of nonzero digits are not significant, they act as placeholders = 2 Sig Figs = 4 Sig Figs

Cont. 4. Zeros at the end of the number and to the right of the decimal point are always significant = 4 Sig Figs1.0110= 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

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 = 4 Sig Figs = 6 Sig Figs

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 Figs12000 = 2 Sig Figs300 = 1 Sig Fig

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 Weakest link Since our weakest link only has 2 decimal places our answer can only have 2 decimal places…….so round the answer to 5.33

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 x 2.04 = Since our “weakest link” only has 3 sig figs, our answer can only have 3 sig figs Weakest Link

Final Sig Fig Practice How Many Sig Figs? 1.oo m =3400 m = g = x 10 3 = g =200 g = Calculate: 234.0g g = g – 18.9g = 2.33m x 400m = / 4.09 =

Answers How Many Sig Figs? 1.oo m = m = g = x 10 3 = g = 5200 g = 1 Calculate: 234.0g g = g g – 18.9g = 15.7 g 2.33m x 400m = 900 m m / 4.09m = 6.11 m

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

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 = cal 1 cal = J

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

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 10 6 mm= 2.3 x 10 7 mm 1 km conversion factor

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

More practice w/ conversion factors 24 Tm _____ pm nm _____ km Gm _____ μm 230 cm _____ Mm Em _____ fm

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 = hours 1 cent. 1 yr 1 d Known conversion factor

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 pizza2 slices

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 gallon x 1 tank x 16 miles = 74.4 miles 1 tank 4 quarter- tank gallon quarter tank

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