1. measure of how a measurement comes to the or true value of whatever is Example: 2. measure of how close a of measurements are to Example:

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1 Chemistry Chapter 3: Metric, Measuring, Scientific Notation & Significant Figures. Name: 3-1 Measurements A. Scientific Notation: A number written as the product of two numbers: a and raised to a power. 3.6 x 10 4 = 8.1 x 10-3 = Try to express in scientific notation = Try to express 2.3 x 10 7 as a whole number = a. Multiplication: Multiply the coefficients, then add the exponents. (3.0 x 10 4 ) x (2.0 x 10 2 ) = (4.0 x 10-6 ) x (2.0 x 10 3 ) = Period: b. Division: Divide the coefficients, then subtract the exponent in the from the exponent in the. 3.0 x 10 4 = 2.0 x 10 2 c. Addition and subtraction: Simple, you can only add or subtract if the exponents are identical. If they are the same, you simply add or subtract the coefficients. 5.4 x x 10 3 = B. What is the Difference between Accuracy and Precision? 1. measure of how a measurement comes to the or true value of whatever is Example: 2. measure of how close a of measurements are to Example: 3. An accurate and precise measurement can the true value of whatever is being measured Example: Error Calculations 1. Error = value value. Sometimes error is also expressed as theoretical value - a. of the value tells whether or not the experimental value is too or too b. value correct value based on a reference c. value value measured in 2. Percent Error = Error x 100% Accepted Value

2 Example: Sulfur melts at 113 o C. In lab, you measure the temperature at which sulfur melts to be o C. What is the error and percent error in this measurement? Show your work. A. Significant Figures: When you measure anything, you know for certain ; however, you must estimate of your answer. i.e. Let s try it in the lab Record the masses of the 100 ml beaker and 100 ml graduated cylinder Pour 99 ml of water into the 100 ml beaker. Then pour the 99 ml of water into a 100 ml graduated cylinder. Record the masses of the containers with 99 ml of water. Since we know water has a density of 1g what should be the mass of the water? Show work below. 100 ml beaker Mass of empty container: Mass with 99 ml: Mass of water: Volume w/ precision. diagram 1mL 100 ml graduated cylinder Mass of empty container: Mass with 99 ml: Mass of water: Volume w/ precision. diagram % Error= % Error= 1. Show your work above for calculating the % error of the assuming the is more. Make your answer precise. 2. Put your answer on the whiteboard for the class to see. 3. Copy the answers on the overhead sheet and below. % error beaker % error grad cylinder Glane s Glane s 4. How closely were you able to measure the water with your graduated cylinder? 5. How closely were you able to measure the water with your beaker? 6. Can an answer be more precise than your measurement? Explain. 2

3 A. Math with Significant Figures: a. SIGNIFICANT FIGURE RULES 1. All non zero numbers are significant sig fig 34-2 sig fig sig fig sig fig 2. Zeroes between two non zero numbers are significant sig fig sig fig sig fig sig fig sig fig sig fig 3. Leading zeroes are not significant sig fig sig fig sig fig sig fig 4. Final or trailing zeroes are not significant UNLESS there is a decimal point in the number sig fig sig fig sig fig sig fig sig fig sig fig sig fig sig fig sig fig 5. Powers of ten are not significant X sig fig Practice problems: How many sig figs? a. 284 b c d e. 240 f. 285,000 g h i j k l. 3.2 x 10 2 b. When you perform or, your will need to round your answer to the number of sig figs as the with the. Or, your measurement will limit your x 2.20 = / 2 = x 4.24 = 6.8 x = / 2.0 = / 4.36 = 5.82 x 760 x 325 = 723 x 273 3

4 c. When you or, round your answer to the number of decimal places in your. *First add or subtract, then round the answer to the last decimal place they have in common International Measurement Units A. Basic Units (also called ) Quantity Unit Symbol Example Length Mass (We call it weight) Volume (size) Density (Heaviness) *Temperature Time Pressure Energy Amount of substance *Temperature: Basic Unit is. It is found by o is actually 273 degrees Kelvin. Lots of energy still there. o is equal to o is equal to This is called absolute. Everything Practice Problems 1. Antarctica can get as cold as -100 C. How many K is this? 2. If global warming continues, Earth could earn an average temperature of 423 K. How many degrees Celcius would this be. 4

5 B. Prefixes (from large to small) Prefix Symbol Meaning Factor Sci. Example Teragigamegakilodecicentimillimicro- Nano- Pico- 3-3 Converting Units notes are available in your Unit 1 notepack, or pages A. Practice: 1. An experiment requires that each student use an 8.5 cm length of magnesium ribbon. How many students can do the experiment if there is a 5.70 x 10-1 m piece of magnesium available? 2. What is 7.3 x 10-2 cm in micrometers? 3. Convert 2.00 m 3 to cm The density of manganese, a metallic element, is 7.21 x 10 3 mg/cm 3. What is the density in g/m 3? 5

6 3-4 Denisty: Density is i.e. Water Density =, Cork Density = A. The Formula for finding density is: Question: If you have two objects of the same size, and object A is more dense than object B, which one will have more mass? (diagram below) Practice Density calculations: 1. An object has a mass of 80 grams and a volume of 40 ml. What is it s density? 2. A liquid has a volume of 200 ml and a mass of 150 grams. What is it s density? 3. A rubber dog toy is perfectly square and measures 5 cm on each side. The package says is weighs 110 grams. What is the density of the toy? Can the person throw it in the water to play with the dog? 4. A clear liquid is poured into a graduated cylinder and reads 50 ml. The weight increased by 70 grams. What is the density? Is it water? 6