Measuring Matter Chemistry is the study of matter and all its changes

SI System of Units What does SI stand for? Système Internationale d’Unités It’s a standard of measurements used by all nations so that scientific results mean the same here or in Timbuktu

Prefixes to use with Base Units

What is Density? Density measures how much mass is packed into a certain space

Density is a ratio of mass over volume

Density Problem: 1. A piece of metal with a mass of 147 g is placed in a 50-mL graduated cylinder. The water level rises from 20 mL to 41 mL. What is the densityof the metal?

2. What is the volume of a sample that has a mass of 20 g and a densityof 4 g/mL?

3. A metal cube has a mass of 20 g and a volume of 5 cm3 3. A metal cube has a mass of 20 g and a volume of 5 cm3. Is the cube made of pure aluminum?

What is Temperature? Temperature measures the movement of particles We use 3 scales to measure temp: Kelvin, Celsius and Fahrenheit

Review Questions What is the difference between a base unit and a derived unit? How does adding the prefix mega- to a unit affect the quantity being described? How many milliseconds are in a second? How many centigrams are in a gram? Why does oil float on water?

Scientific Notation Negative exponents mean that in standard form the number is less than 1

Examples of Scientific Notation

Let’s Practice! Express the following quantities in scientific notation on your white boards a. 360 000 s b. 0.000 054 s c. 5060 s d. 89 000 000 000 s

Now you Try: Solve the following addition and subtraction problems Now you Try: Solve the following addition and subtraction problems. Express your answers in scientific notation. a. 5 x10–5 m + 2 x10–5 m e.1.26 x104 kg + 2.5x103 kg b. 7 x108 m – 4 x108 m f. 7.06 x10–3 kg + 1.2 x10–4 kg c. 9 x 102 m – 7 x 102 m g. 4.39 x 105 kg – 2.8 x 104 kg d. 4 x 10–12 m + 1 x10–12 m h. 5.36 x 10–1 kg – 7.40 x 10–2 kg

Answers A. 7.0 X 10-5 B. 3.0 x 108 C. 2.0 x 102 D. 5 x 10-12 E. 1.51 x 104 F. 7.18 x 10-3 G. 4.11 x 105 H. 4.62 x 10-1

a. (4 x 102 cm) (1 x 108 cm) b. (2 x 10–4 cm) (3 x 102 cm) Now you Try: Find the area (cm2). Express your answers in scientific notation. a. (4 x 102 cm) (1 x 108 cm) b. (2 x 10–4 cm) (3 x 102 cm) c. (3 x 101 cm) (3 x 10–2 cm) d. (1 x 103 cm) (5 x 10–1 cm)

Answers 4 x 1010 6 x 10-2 9 x 10-1 5 x 102

Calculate the following densities. Report the answers in g/cm3 a. (6 x 102 g) ÷ (2 x 101 cm3) b. (8 x 104 g) ÷ (4 x 101 cm3) c. (9 x 105 g) ÷ (3 x 10–1 cm3) d. (4 x 10–3 g) ÷ (2 x 10–2 cm3)

What is Dimensional Analysis? It is a method chemists use to convert measurements from one unit to another Example: I bought 3 dozen donuts for class; each dozen costs $2.79. How much money did I pay in all?

When using D.A. You always want to cancel what you have to get what you want

D.A. Steps: Start with what you have Figure out what you want Set up your Conversion Factor Cancel the units Calculate the answer

How many seconds in a day? What I know: 1 day = 24 hours 1 hour = 60 minutes 1 min = 60 seconds Mrs. Chaves will solve on dry erase board.

Now you try: Refer to Table 2-2 (pg26 in your text) to figure out the relationship between units. 17. a. Convert 360 s to ms. 18. a. Convert 245 ms to s. b. Convert 4800 g to kg. b. Convert 5 m to cm. c. Convert 5600 dm to m. c. Convert 6800 cm to m. d. Convert 72 g to mg. d. Convert 25 kg to Mg.

Answers 17. a. 360,000 ms. 18. a. .245 s b. 4.8 kg. b. 500 cm. c. 560.0 m. c. 68.00 m. d. 72,000 mg. d. .025 Mg.

Warm up: Use dimensional analysis to convert the following: 7 mi. to yards (1 mile = 1760yards) 2) 234 oz. to tons (1lbs = 16 oz.) (1 ton = 2000 lbs.) 3) 1.35 km to centimeters (1km = 1000m) (100cm = 1m)

Example: Sometimes both the top and bottom need to be converted 3.5 mph (miles per hour) to feet per second *Mrs. Chaves will solve on the board.

Now you try 153 ft/s (feet per second) to miles per hour ( 5,280 ft = 1 mile) 248 mph to meters per second (1,609 meters = 1 mile) (1hr = 3600 s)

Use dimensional analysis to solve the following: On a recent trip, Jan traveled 260 miles using 8 gallons of gas. How many miles per 1-gallon did she travel? How many yards per 1-ounce?

Reliability of Measurements Accuracy = how close your measurements are to the “right” answer Precision = being consistently right or consistently wrong all the time.

I will calculate percent error for student B on the board. Errors for Data Student A Student B Student C Trial 1 (g/cm3) -.05 -.19 +.11 Trial 2 +.01 +.09 +.10 Trial 3 -.02 -.14 +.12 I will calculate percent error for student B on the board. You need to find Student C’s errors in your notes.

Sig Figs Measurements can only be as precise as the quality of the instrument that they were taken with. Example: Measuring mass with a scale that has 3 numbers after the decimal is more precise than a scale with 2 numbers after the decimal.

Rules for Significant Figures 1. Non-zero numbers are always significant. 72.3 g has three 2. Zeros between non-zero numbers are always significant ex: 60.5 g has three sig figs 3. All final zeros to the right of the decimal place are significant ex: 6.20 g has three sig figs 4. Zeros that act as placeholders are not significant. ex: 0.0253 g and 4320 g both have 3 sig figs

Applying Significant Figure Rules Determine the number of significant figures in the following masses. a. 0.000 402 30 g b. 405 000 kg