2 Scientific Measurement Distinguish between quantitative and qualitative measurements.List SI units of measurement and common SI prefixes.Distinguish between the mass and weight of an object.Convert measurement to scientific notation.Distinguish among the accuracy, precision, and error of measurement.Identify the number of significant figures in a measurement and in the result of calculation.Identify and calculate derived units.Calculate the density of an object from experiment data.TEKS: 2A, 2B, 2C, 2D, 2E, 3C, 3D, 3E, 4B, 4C
3 Branches of chemistryorganic chemistry—the study of carbon-containing compounds inorganic chemistry—the study of non-organic substances physical chemistry—the study of properties of matter, changes that occur in matter, and the relationships between matter and energy analytical chemistry—the identification of the composition of materials biochemistry—the study of the chemistry of living things theoretical chemistry—the use of mathematics and computers to design and predict the properties of new compounds
4 Quantitative vs. Qualitative Observations Qualitative – observations made with adjectives“The water is clear and cool.”Quantitative – observations that include a measurement or other numeric data“There are 40mL of water.”
6 Two parts of measurements Quantity – indicates size or magnitude (how much?)Unit – tells us what is to be measured and compares it to a previously defined size (of what?)Measurements must have both a quantity and a unit to be valid.
7 International System of Units Length – meterMass – kilogramTemperature – KelvinEnergy – jouleAmount of a substance – moleElectric current - ampereVolume – m3Density – g/cm3Weight - NewtonSI units are defined by a system of objects or natural phenomena that are of constant value and are easy to reproduce used as a standard of measurement.
8 Commonly Used Prefixes in the Metric System MeaningExponentmega (M)106kilo (k)1000103hecto (h)100102deka (da)10101deci (d)1/1010-1centi (c)1/10010-2milli (m)1/100010-3micro (µ)1/10-6nano (n)1/10-9pico (p)1/10-12
9 Conversion FactorsConversion factors are equalities written in ratio form:1 km = 1000m km = m1000 m kmChoose the format that allows you to cancel the original units and leave the new units.Ex km = ________ mYou would choose 1000 mkm
10 FoldableCan use this to simply move your decimal in order to convert between unitsEx. 1 mg = ? g
11 Conversion FactorsMake sure that you have a valid equality before writing your conversion factor.Which of these equalities are correct?1 m = 1 x 10-6 µm1 m = 1 x 106 µm1 x 10-6 m = 1µm
13 Conversion Practice Problem List in order – largest to smallest a. 1 dm3b. 1 µLc. 1 mLd. 1 Le. 1 cLf. 1 dL
14 Largest to smallestA. dm3D. 1 LF. dLE. cLC. mLB. μL
15 Derived UnitsDerived units are formed from a combination of other units.Examples include:m/s & km/hr (speed), cm3 & dm3(volume), J/g·°C (specific heat), g/mol (molar mass), g/cm3 & kg/m3 (density)
16 Density Density is the ratio between the mass and volume of an object. Density = Mass or D = mVolume VDensity is an intensive physical property.
17 Density (Math Triangle) D = M / VM = D X VV = M / D
18 Density ProblemsA student finds a shiny piece of metal that she thinks is aluminum. She determined that the metal has a volume of 245 cm3 and a mass of 612 g. Calculate the density. Is the metal aluminum?The density of silver at 20ºC is 10.5 g/cm3. What is the volume of a 68 g bar of silver?
19 Density Problems Continued A weather balloon is inflated to a volume of 2.2 x 103 L with 37.4 g of helium. What is the density of helium, in grams per liter.A plastic ball with a volume of 19.7 cm3 has a mass of 15.8 g. What is its density? Would the ball sink or float in a container of water?
20 Specific Gravity Density water (g/cm3) Specific Gravity = Density substance (g/cm3)Density water (g/cm3)
22 Review Scientific Notation rule: move decimal to a number between 1-10 600,000 ==2.3 X =5.5 X =
23 Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value.(how close)Precision refers to the degree of agreement among several elements of the same quantity. (how repeatable)
24 Target (a) shows neither accuracy or precision. Target (b) shows precision, but not accuracy.Target (c) shows both accuracy and precision.
25 Uncertainty in Measurement A digit that must be estimated is called uncertain.The last digit in a measurement always shows uncertainty.
26 Significant DigitsSignificant Digits show the degree of certainty in a measurement.Not all digits in a number show certainty, therefore, all digits are not significant.
27 Counting Significant Digits Rule 1:Nonzero integers always count as significant digits.3456 has 4 “sig digs”
28 Counting Significant Digits Rule 2:Leading zeros do not count as significant figures.has 3 “sig figs”
29 Counting Significant Digits Rule 3:Captive zeros always count as significant figures.16.07 has 4 “sig digs”
30 Counting Significant Digits Rule 4:Trailing zeros are significant only if the number contains a decimal point.9.300 has 4 “sig figs”
31 Counting Significant Digits Exact numbers have an infinite number of significant figures.Exact numbers include counting numbers and conversion factors.Examples:12 students1m = 100 cm
32 Practice Problems Determine the number of significant figures. a. 12 kilometersb m2c thumbtacksd me mf m3.g x 103 cmh x 1023 atoms
33 Rules for Significant Figures in Mathematical Operations Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation.6.38 cm 2.0 cm = cm213 (2 sig figs)
34 Multiplication and Division Your answer can only have the least number of significant figures in your data.a.2.0 mLx 3.00 mLb.8432 m =12.5 m
35 Rules for Significant Figures in Mathematical Operations Addition and Subtraction: # sig figs in the result equals the number of decimal places in the least precise measurement.6.8 cm cm cm = cm22.5 cm (1 digit after decimal - 3 sig figs)
36 Addition and Subtraction Count the decimal places. You can only have in your answer the least number of decimal places that is seen in your data.
37 Rounding RulesIf the digit following the last digit to be retained is:Then the last digit should:Example (rounded to 3 sig dig’s)greater than 5be increased by 138.68 g to gless than 5stay the same12.51 m to m5, followed by nonzero digit(s)cm to cm5, not followed by nonzero digit(s), and preceded by an odd digit2.975 kg to kg(because 7 is odd)5, not followed by nonzero digit(s), and the preceding significant digit is evenStay the same2.985 kg to kg(because 8 is even)
39 Measurement Tools Distance = Meter Sticks & Metric Tapes Volume = Graduated CylinderTime= StopwatchMass= BalanceWeight= Spring Scale
40 Mass vs. WeightMass is the amount of matter in an object; weight is the effect of gravity on a mass.Mass is measured on a balance; weight is measured with a scale.Mass remains constant at all locations; weight varies with change in gravitational pull.
41 Volume Never measure in a beaker. They are for estimation only! 2. Place the graduated cylinder on a level surface and read the bottom of the meniscus.3. Check the scale of the graduated cylinder Different scales for different sizes!Use displacement to find the volume of irregular solids.
42 Mass Make sure the balance is on a level surface. Use the same balance in the same place for all parts of a procedure.3. DO NOT MOVE A BALANCE ONCE IT IS ZEROED!
43 LengthRulers & meter sticks wear on the ends – start at a point other than zero.Choose the unit most reasonable for the item you are measuring – make sure you convert your number accordingly.
44 SymbolsΔ “Delta” means “change in”Σ “Sigma” means “sum of”
45 Graphing Relationships Direct Relationship-Variables do the sameStraight LineInverse (Indirect) Relationship-Variables do the oppositeParabola
46 ModelsWhy do scientists use models in their research???