Chapter 2 SCIENTIFIC MEASUREMENT Types of Measurement
1. Quantitative: Use numbers to describe. -Examples: 4 feet, 10 inches
2. Qualitative: Description without numbers -Examples: extra large, hot
Accuracy: How close the measurement is to the actual value
Precision: How well can the measurement be repeated
Percent Error
Error: Accepted Value – Experimental Value
Error can be positive or negative
Percent Error = (Error ÷ Accepted Value) x 100
Significant Figures
A measurement consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated.
All digits including the uncertain one are significant.
Usually, the final digit is uncertain but significant.
Significant Figures Rules
Rule #1 All non zero digits are always significant. How many significant figures in each? 274 (3) 26.632 (5) 8.987 (4) Rule # 2 All zeros between significant digits are always significant
How many significant figures in the following? 504 (3) 60002 (5) 9.077 (4)
Rule # 3 All final zeros to the right of the decimal are significant.
How many significant figures in the following: 32.0 (3) 19.000 (5) 105.0020 (7)
Rule # 4 Zeros acting as place holders are not significant.
How many significant figures in the following? 0.0002 (1) 6.02 x 10 23 (3) 800 (1)
Rule # 5 All counting numbers and constants have an infinite number of significant figures.
How many significant figures in the following
458g (3) 4085g (4) 4850g (3) 0.0485g (3) 0.004085 g (4) 40.004085 g (8)
Adding and Subtracting When you add or subtract measurements, your answers must have the same number of decimal places as the one with the fewest.
Example: 27.93 + 6.4 Calculator Answer: 34.33 Final Answer: 34.3 Practice: 12.52 + 349.0 + 8.25 = 369.76 Final answer: 369.8
74.626 – 28.34 = 46.286 final answer: 46.29
Multiplication & Division Look at the total number of significant figures.
Your answer must have the same number of significant figures as the one with the fewest.
Example: 3.6 x 653 Calculator Answer: 2350.8 Final Answer: 2400 (2 significant figures)
Practice: 3.6 x 653 = 2350.8 Final answer: 2400 (2 significant figures)
2.10 x 0.70 = 1.47 Final answer: 1.5
2.4526 / 8.4 = 0.291976 Final answer: 0.29
Metric System
A decimal system
Based on units of 10
A metric unit has two parts a prefix & base
Prefix tells you how many times to divide or multiply by 10.
Base Units Length: meter (m) Mass: grams (g) Time: seconds (s) Temperature: Kelvin or °Celsius Volume: Liter (L) Energy: Joule (J) Amount of substance: mole (mol)
Volume Base unit is liters (L) Calculated by Length x Width x Height 1 L = 1000 cm3 1000 cm3= 1000 mL
Solving Problems Analyze the problem. Determine the known and unknown.
Calculate the unknown
Solve for the unknown using a conversion factor.
Conversion Factors 1. Allow you to convert units. 2. Are defined quantities so they have unlimited significant figures
Convert 25 mg to g Identify the known and unknown Known: 25 mg Unknown: ? g
Identify the conversion factor: 1g = 1000 mg Solving Problems Set up youryour problemproblem usingusing the conversion factor.
25 mg × 1 g = 0.025 g 1000 mg
Conversion Factor
Convert the 0.45 km to mm Identify the known and unknown Known: 0.45 km Unknown: ? mm
Identify the conversion factor 1 km = 1,000,000 mm Solving Problems Set up youryour problemproblem usingusing the conversion factor.
0.45 km × 1000,000 mm = 450mm 1 km Conversion Factor Convert 35 mL to L Identify the known and unknown Known: 35 mL Unknown: ? L
Identify the conversion factor 1 L = 1,000 mL Solving Problems Set up youryour problemproblem usingusing the conversion factor.
35 mL × 1 L = 0.035 L 1,000 mL Conversion Factor
Convert 12.0 in to cm Identify the known and unknown Known: 12.0 in Unknown: ? cm
Identify the conversion factor 1 in = 2.54 cm Solving Problems Set up youryour problemproblem usingusing the conversion factor.
12.0 in × 2.54 cm = 30.5 cm 1 in Conversion Factor
Convert 65.0 mi/h to m/s Identify known & unknown Known: 65.0 mi/h Unknown: ? m/s
Identify the conversion factor.
1 hr = 3600 s 1000 m = 0.6214 mi
65 mi × 1000 m × 1 hr hr 0.6214 mi 3600 s
= 29 m/s
Density How heavy something is for its size
The ratio of mass to volume for a substance It is independent of how much you have The units are usually g/L or g/ mL or g/cm3
Density Density Formula D = M V Density Triangle M D V
When you use the circle cover up the variable you are trying to find.
Horizontal line: divide Vertical line: multiply Calculating Density 1. A piece of wood has a mass of 11.2 g and a volume of 23 mL. What is the density?
D = M ÷ V
= 11.2 g / 23 mL
= 0.48869 g/mL Using the correct number of significant figures the final answer is 0.49 g/mL 2. A piece of wood has a density of 0.93 g/mL and a volume of 23 mL. What is its mass? M = D x V = 0.93 g/mL x 23 mL = 21.39 g Using the correct number of significant figures the final answer is 21 g
Temperature
Temperature: Which way heat will flow (from hot to cold).
Heat: Energy, ability to do work.
Scientists use the Kelvin scale to measure temperature.
Kelvin: °C + 273
The Kelvin scale starts at absolute zero (- 273 °C)