Warm-up Complete the following conversions: 5days = _______ s 2.5 m = ______ cm

Chemistry Chapter 2 Scientific Measurement

3.1 Qualitative measurements measurements that give results in a descriptive, non-numerical form. Examples: He is tall Electrons are tiny

Quantitative measurements measurement that gives results in a definite form, usually as numbers and units. Examples: He is 2.2 m tall Electrons are 1/1840 times the mass of a proton

Scientific Notation a number is written as the product of two numbers: a coefficient and 10 raised to a power. Examples: = 5.67 X = 2.31 X 10 -3

Examples: Convert to or from Scientific Notation: 241 = 6015= = 0.512= 6.62 x 10 2 = 3.4 x = 2.41 x x x x

Tuesday, September 4 Bellwork Jenna burns a piece of firewood that has a mass of 1.29 kg. Later, she sweeps up the ashes and takes their mass. They only weigh 0.99 kg. What happened? Does this break the law of conservation of mass? Why or why not? How much mass was lost?

1. Give 3 examples of pure substances and a physical property of that example. 2. List the Phase(s) (S, L, G) below then match to the example on the left. _____ Heterogeneous Mixture Copper Wire _____ Homogenous Mixture Iced Tea _____ Element Sugar _____ Compound Soda 3. (circle one )When you did the fish lab you made qualitative and quantitative observations that were based on the (physical / chemical) properties. Homework Check Example: NaClColor: White

CALCULATOR PRACTICE (This is important to master!!!) 6.25 x x 10 2 = (2.15 x 10 3 )(6.1 x 10 5 )(5.0 x ) = 3.25 x 10 8 = 3.6 x x x 10 3 FYI: “EE” button on calc= typing “X10^”

3.2 Accuracy the measure of how close a measurement comes to the actual or true value of whatever is measured. how close a measured value is to the accepted value. Precision the measure of how close a series of measurements are to one another.

Accurate and Precise Precise Neither

Percent Error Formula: % Error = accepted value- experimental value x 100 accepted value *always a positive number- indicated by the absolute value sign* You will use this formula when checking the accuracy of your experiment.

Significant Figures – includes all of the digits that are known plus a last digit that is estimated. FYI: These rules are IMPORTANT and they will save you many points in the future if you learn them NOW! !

Rules for determining Significant Figures Rules for determining Significant Figures 1. All non-zero digits are significant. 1, 2, 3, 4, 5, 6, 7, 8, 9

2. Zeros between non-zero digits are significant. (AKA zero sandwich)

3. Leading zeros (zeros at the beginning of a measurement) are NEVER significant

4. Trailing zeros (zeros after last integer) are significant only if the number contains a decimal point

5. All digits are significant in scientific notation. 2.1 x x 10 23

Examples: How many significant digits do each of the following numbers contain: a) 1.2d) 4600 b) 2.0e) c) 3.002f) 6.02 x

Bellwork Tuesday, September 5 th Please take a reading of the volume in the graduated cylinder and the mass from the triple beam balance.

Exact numbers have unlimited Significant Figures Examples: 1 dozen = exactly people in this room Do not use these when you are figuring out sig figs…

Rounding Rules:  5 round up < 5 round down (don’t change) Examples: Round to 1 significant digit = Round to 3 sig. digs. = Round to 2 = Round 65,002 to 2 sig. digs. = ,000

The measurement with the fewest significant figures to the right of the decimal point determines the number of significant figures in the answer m m = m m = m m

The measurement with the fewest significant figures determines the number of significant figures in the answer m X m = m X 1.2 m = m / 2.2 m = 22.0 m 55 m 20. m

Measurement in Lab In lab, you record all numbers you know for sure plus the first uncertain digit. The last digit is estimated and is said to be uncertain but still considered significant. This graduated cylinder has markings to the nearest mL (milliliter) and you will determine volume to the nearest 0.1 mL because that is ONE DIGIT OF UNCERTAINTY.

International System of Units revised version of the metric system abbreviated SI All units, their meanings and values can be found on pgs. 63,64,65. Meter (m) – Liter (L) – Gram (g) – SI unit for length SI unit for volume SI unit for mass

-Mass – (g) amount of matter in an object -Volume – (mL) amount of space occupied by an object -Density – (g/mL) a ratio of mass to volume

Formula: D = m vm v Rewrite this formula to solve for m & v! What is the unit for Density???? Remember: A material has the same density no matter how big or small it is!

Example: A piece of metal has a volume of 4.70 mL and a mass of 57.3 g. What is the density? M = 57.3 g V = 4.70 mL D = M / V D = 57.3 g / 4.70 mL D = g/mL D = 12.2 g/mL

Trevor performed a lab about density in his chemistry class. He took the following measurements. Calculate Trevor’s density using correct significant figures. TrialMass (g)Volume (ml)Density g6.4 ml g6.9 ml g7.1 ml 2.9 g/mL 2.8 g/mL

Graphs of density and volume can be used to find the density of a substance. The slope of the line formed when mass and volume are plotted is the density. Remember “rise over run”.

Temperature – measurement of the average kinetic energy of a system.

Temperature Scales Celsius Sets the freezing point of water at 0  C and the boiling point at 100  C Kelvin Absolute zero is set as the zero on the Kelvin scale. It is the temperature at which all motion theoretically ceases.

To convert: K = ºC (Kelvin does not use “degrees”.) -273 º C = 0 K = absolute zero

Examples: Convert 25 º C to Kelvin. K = ºC K = 25ºC = 298 K

Three-step Problem Solving Approach 1. Analyze – determine how you will find the solution 2. Calculate – perform the calculation, this may involve measurements 3. Evaluate – does the answer make sense, and did you use correct units and significant digits

Ex. What is the mass, in grams, of a piece of lead that has a volume of cm 3 ? 1. Analyze: list the knowns and the unknown. Volume = cm 3 Density = mass/ volume Density = 11.4 g/cm 3 Mass = ? 2. Calculate: solve for the unknown. D = m / Vso…m = D x V Mass = cm 3 x 11.4 g/cm 3 = 226 g 3. Evaluate: does the result make sense? Would a piece of lead that is about the size of an eraser have a mass of 226 grams? Yes!

Practice: Solve the following using correct significant figures x = =

Practice What is the mass, in grams of a piece of lead that has a volume of 8.73 cm 3 ? Knowns V = 8.73 cm 3 D = 11.4 g/cm3 m = VD Unknowns m = ? To solve: m = (8.73 cm 3 )(11.4 g/cm 3 ) m = g = 99.5 g

Practice: What is the volume, in cm 3, of a sample of cough syrup that has a mass of 20.0g and a density of 11.4 g/cm 3 ? Knowns M = 20.0 g D = 11.4 g/cm 3 V = M / D Unknowns V = ? To Solve V = 20.0 g 11.4 g/cm 3 V = 1.75 cm 3

Dimensional Analysis To convert from one unit to another, we will use a problem solving method called dimensional analysis. This method uses equalities or conversion factors to change one unit into another. Example: If someone gives you 32 quarters, how many dollars do you have? How did you know this?

How many inches are there in 4 ft? 48 inches What did you have to know in order to figure that out? 1 ft = 12 inches 1 ft = 12 inches is a conversion factor. It can be written as a fraction where the numerator and the denominator are equivalent but have different units. For example, we can use the following conversion factors for changing between inches and feet: 12 inches1 foot 1 footor12 inches

Some Handy Conversions Let’s look at a meterstick and list all the conversions we can get from it. We can say that one meter is equal to… 10 dm 100 cm 1000 mm Now let’s use those prefixes to figure out how we can modify units for liters. A liter should contain _____ deciliters A liter should contain _____ centiliters A liter should contain _____ milliliters

Practicing with Dimensional Analysis 70 kg = ____ g 63 cm = ____ mm 2.5 L = _____ mL 1 m 2 = _____ cm 2

Practice: How many atoms are in 7.00g of gold? (1 atom of gold = x g) 7.00 g gold x g gold 1 atom gold= 2.14 x atoms gold

Some dimensional analysis problems require several steps How many seconds are in 5.0 days? 5.0 days24 hours60 min 60sec= 430,000 sec 1 day1 hour 1 min How many students are in a 10 room building if each classroom contains 25 students? 10 rooms25 students = 250 Students 1 room

An example of this would be the conversion of speed in miles per hour to meters per second. An object was traveling at 400. m/min. What was its speed in cm/s? 400. m 100 cm 1 min = 667 cm/sec 1 min 1 m 60sec Convert 423 m/sec to km/min. 423 m 1 km 60sec = 25.4 km/min 1 sec 1000 m 1 min

The density of manganese is 7.21 g/cm 3. What is the density of manganese expressed in units of kg/m 3 ? 7.21 g 1 kg cm 3 = 7210 kg/m 3 1 cm g 1 3 m 3