# Ch. 3, Scientific Measurement

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Ch. 3, Scientific Measurement

Measurement Measurement: A quantity that has a number and a unit. Like 52 meters.

Scientific Notation Writing long numbers as smaller ones to a power of ten. 1,400, = x = E6 = x 10 — = 5.6E-4 15,093,000 = x = E7 ----- Meeting Notes (9/4/14 11:04) ----- Rules - decimal after first number

Accuracy vs. Precision *Accuracy: How close a measurement comes to the correct value. *Precision: How close a series of measurements are to one another.

Determining Error of a measurement
Error = Experimental Value - Accepted Value Can be positive or negative Percent Error = error / accepted value * 100% or Always positive Example, you measured 99 cm, but it is 100 cm. ----- Meeting Notes (9/4/14 11:04) ----- define experimental and accepted.

Significant Figures: The digits in a measurement that are known plus one that is not known.
Filled 43.1 mL

Rules for Sig Figs Non-Zero Numbers are always significant
Ex) .236 m has 3 sig figs. Zeros between non-zero numbers are significant. Ex) 7003 m and m each have 4 sig figs. Leftmost zeros are not significant Ex) m, 0.42 m, and .073 m each have 2 sig figs. Rightmost zeros are significant if they come before or after a period. Ex) m, m, and m each have 4 sig figs.

Rules for Sig Figs Rightmost zeros with no decimal points are no significant. Ex) 300 m has 1 sig fig. Exactly defined quantities have an unlimited number of sig figs. Seen most when converting between measurements. 60 min = 1 hour, cm = 1 m each have an unlimited number of sig figs.

Is a Zero a Significant Number or Not?
504 L .06 mL 50.0 m 7,000 km

Sig Figs in Calculations:
Calculations cannot be more precise than the least precise measurement. Addition or subtraction - Round the final answer to the same number of decimal places as the measurement with the least number of decimal places. the last “shared column”. 13.4 m m = 18.7 m

Sig Figs in Calculations:
Multiplication or Division - The final answer should have the same number of sig figs as the measurement that has the least number of sig figs. m x 8.4 m = 21 m

In this class, delay rounding until the very end.
(3.449L L) * 8.779L / 5.2L = 17L

International System of Units
How much of something you have is given by Units. Like centimeters, kilometers, etc. SI is the standard measurement system for science.

* The five SI units used most by chemists are:
Distance = meter (m) Mass = kilogram (kg) Temperature = kelvin (K) Time = second (s) Volume = liter (L) Amount = mole (mol).

Prefixes can be used in front of units for powers of 10.

Mass = how much “stuff” is in something
Mass = how much “stuff” is in something. How much matter is in something. Weight = the pull on something by gravity. If I go to the moon, which changes and which stays constant? -Weight changes, mass stays the same.

Temperature: Celsius and Kelvin are units of temperature that are the same, just shifted. K = C + 273 Water freezes at 0 C and at 273 K. Absolute Zero = 0 K; a K value will never be negative.

*Energy * Energy - The ability to do work or produce heat.
Joule (J) is the SI unit of energy. Calorie (cal) is another unit of energy. 1 J = .239 cal

Conversions Convert 7 mm to m. Convert 12.4 Mm to cm.

Convert 7 km/ms to m/s An experiment asks students to measure 1.50 g of Cu wire. All we have is a 40.0 g spool of Cu. How many students can do the experiment?

*Density *Density = mass / volume
What is the density of 2 g of salt in a volume of 4 L? What is the density in g/L of 5 kg of salt in a volume of 6 mL?

If silver has a density of 10
If silver has a density of 10.5 g/L, what is the volume of a silver coin that has a mass of 14 g?

Density decreases as temperature increases.
D=m/v As T increases, V increases. Therefore, density decreases.

Example Problems!!!

1. How many sig figs in: * E3 2. Perform these calculations and come up with answers that have the correct number of sig figs: E3 / E3 * 3 3. Convert 3.4 ng into kg. 4. Convert 7E3 cm into Mm. 5. What is the mass if a substance with a density of g/L has a volume of 3 L?

6. How many sig figs in: 7. Convert 3 kg into g Convert 34 cm into m Convert 4 m into cm. 8. You have a 4 kg box. You measure it to be 5.8 kg. What is the error? The % error? 9. What is the difference between mass and weight? Accuracy and precision?

11. Put 5,009,000,000 into Scientific Notation
13. Put 8.7 * 10-4 into a regular number.

14. Which is the largest amount?
A. 2*102 g B. 30 kg C. 45 mg D g 15. Convert 40 Kelvin into Celsius 16. Convert 99 Celsius into Kelvin.