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**Homework Answers 1. 4.17 m/s 2. 22.36 m2 3. 13.5 g/L 4. 5712 cm3**

5. 60 kg·m/s N·m/s kg/cm2 mm3 kg·m/s2 N·m J/g·oC J/g mol/L 15. y/2 17. 3d3

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More answers… 18. X=11.5 22. X=3.5 23. X=2 24. X= H/WQ 25. X= T+6/Y 26. X=23FG-8 27. X=EF2/18KR 28. X=T/LS 29. X= -w+15G 30. X= T3KE4R/B2H5Y x105 x10-6 x107

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x1027 ,000 x10-7 x10-15 x102 x104 x10-15 x10-3 x1012

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**Scientific Measurement**

MAKE SURE YOU HAVE A CALCULATOR!! Scientific Measurement

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Units of Measurement SI Units System used by scientists worldwide

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**Prefixes used with SI units**

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1,000 100 kilo k 10 hecto h 1 deca dc 0.1 Meter Liter Gram Staircase Rule: The direction you slide your finger is the direction the decimal place goes! 0.01 deci d 0.001 centi c milli m

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**Derived Units A unit that is defined by a combination of base units**

Volume Density

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**Density A ratio that compares the mass of an object to its volume**

The units for density are often g/cm3 Formula:

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Example Problem Suppose a sample of aluminum is placed in a 25-mL graduated cylinder containing 10.5mL of water. The level of the water rises to 13.5mL. What is the mass of the sample of aluminum? Volume: final-initial13.5mL-10.5mL= 3.0mL Density: 2.7 g/mL (Appendix C) Mass: ????

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**Temperature Kelvin is the SI base unit for temperature**

Water freezes at about 273K Water boils at about 373K Conversion: 0C +273 =Kelvin

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**Using and Expressing Measurements**

A measurement is a quantity that has both a number and a unit. Measurements are fundamental to the experimental sciences. For that reason, it is important to be able to make measurements and to decide whether a measurement is correct.

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**Dimensional Analysis *Very Important***

A method of problem solving that focuses on the units to describe matter Conversion factor- a ratio of equivalent values used to express the same quantity in different units Example: 9.00 inches to centimeters Conversion factor: 1 in = 2.54 cm

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Scientific notation We often use very small and very large numbers in chemistry. Scientific notation is a method to express these numbers in a manageable fashion. Definition: Numbers are written in the form M x 10n, where the factor M is a number greater than or equal to 1 but less than 10 and n is a whole number. = 5 x 103 = 5 x (10 x 10 x 10) = 5 x 1000 = Numbers > one have a positive exponent. Numbers < one have a negative exponent.

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Example Ex. 602,000,000,000,000,000,000,000 Ex In scientific notation, a number is separated into two parts. The first part is a number between 1 and 10. The second part is a power of ten. 6.02 x1023 1.775 x10-3

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Examples 730,000 122,091

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ANSWERS 9.13x10-4 730,000 7.3x105 122,091 x105 1.24x10-3

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**Accuracy and precision**

Your success in the chemistry lab and in many of your daily activities depends on your ability to make reliable measurements. Ideally, measurements should be both correct and reproducible. Accuracy: a measure of how close a measurement comes to the actual or true (accepted) value of whatever is being measured. Precision: a measure of how close a series of measurements are to one another

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Good Accuracy Poor Precision Poor Accuracy Poor Precision Poor Accuracy Good Precision Good Accuracy Good Precision

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**Determining error Error**

- the difference between the accepted value and the experimental value Accepted Value: referenced/true value Experimental Value: value of a substance's properties found in a lab.

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Example A student takes an object with an accepted mass of 150 grams and masses it on his own balance. He records the mass of the object as 143 grams. What is his percent error?

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**% ERROR Accepted value: 150 grams Experimental value: 143 grams**

Error= 150grams – 143 grams = 7 grams % ERROR

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Significant Figures The significant figures in a measurement include all of the digits that are known, plus the last digit that is estimated. Measurements must always be reported to the correct number of significant figures because calculated answers often depend on the number of significant figures in the values used in the calculation. Instruments differ in the number of significant figures that can be obtained from their use and thus in the precision of measurements.

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**Rules for Determining Sig Fig’s**

Every nonzero digit in a reported measurement is assumed to be significant. The measurements 24.7 meters, meter, and 714 meters each express a measure of length to 3 significant figures. Zeros appearing between nonzero digits are significant. The measurements 7003 meters, meters, and meters each have 4 significant figures.

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3. Leftmost zeros appearing in front of nonzero digits are NOT significant. They act as placeholders. The measurements meter, and 0.42 and meter each have only 2 significant figures. By writing the measurements in scientific notations, you can eliminate such place holding zeros: in this case 7.1 x10-3 meter, 4.2x10-1 meter, and 9.9x10-5 meter.

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**4. Zeros at the end of a number to the right of a decimal point are always significant.**

The measurements meters, meters, and meters each have 4 significant figures. 5. Zeros at the rightmost end of a measurement that lie to the end of an understood decimal point are NOT significant if they serve as placeholders to show the magnitude of the The zeros in the measurements 300 meters, 7000 meters, and 27,210 meters are NOT significant.

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**6. There are two situations in which numbers have unlimited number of significant figures.**

The first involves counting. If you count 23 people in the classroom, then there are exactly 23 people, and this value has an unlimited number of significant figures. The second situation involves exactly defined quantities such as those found within a system of measurement. For example, 60 min= 1 hour, each of these numbers have unlimited significant figures.

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ABSENT DECIMAL Atlantic Ocean PRESENT DECIMAL Pacific Ocean

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**EXAMPLES 123 m: 9.8000 x104m: 0.07080 m: 40,506 mm: 22 meter sticks:**

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ANSWERS 123 m: 3 x104m: 5 m: 4 40,506 mm: 5 22 meter sticks: unlimited 98,000 m: 2

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**Rounding Rules: Addition/Subtraction**

When you add/subtract measurements, your answer must have the same number of digits to the RIGHT of the decimal point as the value with the FEWEST digits to the right of the decimal point Example: cm cm cm cm Rounded to cm Fewest Decimal places

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**Rounding Rules: Multiplication/Division**

When you multiply or divide numbers, your answer must have the same number of significant figures as the measurements with the FEWEST significant figures Example: 3.20cm x 3.65cm x 2.05cm= = cm3 Rounded = 23.9 cm3 Each has 3 sig fig’s

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** HOMEWORK Finish #2 and #3 from previous worksheet Page 29 #1-3,**

Pages #14-16 Page 38 #29-30 Pages #31-38

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Name_____________________ Block____ Chemistry - Chapter 3 Reading Measurements, Significant Figures, SI Units and Dimensional Analysis.

Name_____________________ Block____ Chemistry - Chapter 3 Reading Measurements, Significant Figures, SI Units and Dimensional Analysis.

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