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**Scientific Measurement**

Chemistry Chapter 3 Scientific Measurement

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**Scientific Notation Convert to or from Scientific Notation:**

2.41 x 102 B) 6015 6.015 x 103 C) 1.62 x 10-2 D) 0.512 5.12 x 10-1 E) 6.62 x 102 662 F) 3.4 x 10 -3 0.0034

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**Accuracy -how close measurements are to the correct or accepted value.**

Precision - closeness of a set of measurements.

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Figure UNEOC Title: Visualizing Concepts 1.5 Caption: The dartboards illustrate the types of errors often seen when one measurement is repeated several times. The bull’s-eye represents the “true value,” and the darts represent the experimental measurements. Which board best represents each of the following scenarios: (a) measurements both accurate and precise, (b) measurements precise but inaccurate, (c) measurements imprecise but yield an accurate average? [Section 1.5] Notes: Keywords:

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Percent error – compares the accuracy of an individual value or average values to the correct or accepted value.

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**% error = Accepted value – Experimental value x 100% Accepted value**

STAAR CHART FORMAT

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**Example: What is the percent error for a mass measurement of 17**

Example: What is the percent error for a mass measurement of 17.7g, given that the correct value is 21.2g? % error = 21.2g – 17.7g x 100% = 21.2g 16.5%

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**Significant Figures Rules**

1. Nonzero Digits – every nonzero digit is significant. Ex: a) 32.8 m has three sig figs b) km has five sig figs

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**2. Sandwich zeros – zeros appearing between nonzero digits are significant.**

Ex: c) g has four sig figs d) 50.1 L has three sig figs

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**3. Placeholder – leftmost zeros appearing in front of nonzero digits are not significant.**

Ex: e) has one sig fig f) has four sig figs

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**Ex: g) 2000. m has four sig figs h) 34.0 mL has three sig figs**

4. Trailer zeros – zeros at the end of a number and to the right of the decimal point are significant. Ex: g) m has four sig figs h) 34.0 mL has three sig figs Uncertainty in Measurement

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**STAAR CHART FORMAT FOR SIG. FIGS.**

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Rounding *The calculated value cannot be more precise than the measured values used to obtain it.

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**Example: Round each measurement to the three sig. figs.**

b) 3004 m 3.00 x 103m c) cm 17.3 cm d) L 2.00x104 L

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**Rounding – Addition and Subtraction**

Round the answer to the same number of decimal places (not digits) as the measurement with the least number of decimal places.

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**Example: Subtract 2.6103m from 5.44m.**

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**Rounding – Multiplication and Division**

Round the answer to the same number of sig. figs as the measurement with the least number of sig. figs.

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**Example: Multiply 2.4 m2 and 15.82m.**

2.4 m2 x m = m3 38 m3 Extra Practice

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**SI Measurement – Le Systeme International d’Unites**

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**7 SI Base Units l meter m kilogram kg t second s T Kelvin K n mole mol**

Quantity Symbol Unit Name Unit Abbreviation Length l meter m Mass kilogram kg Time t second s Temperature T Kelvin K Amount of Substance n mole mol Electric Current I ampere A Luminous Intensity Iv candela cd

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**SI Prefixes kilo k 103 100 deci d 10-1 centi c 10-2 milli m 10-3 micro**

Unit abbreviation Exponential factor Example kilo k 103 1 kilometer(km)= 1000 m 100 1 meter (m) deci d 10-1 10 decimeter(dm) = 1 m centi c 10-2 100 centimeter (cm) = 1m milli m 10-3 1000 millimeter (mm) = 1m micro u 10-6 micrometer (um) =1m nano n 10-9 nanometer (nm) = 1m

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**Mass – measure of the quantity of matter (SI unit is kg).**

The gram, g, is ideal for expressing masses of small objects such as a beaker. For even smaller masses like weighing out chemicals the milligram is used.

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Mass vs Weight Mass is the measure of the amount of matter, whereas weight is the measure of the gravitational pull on matter.

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**Derived units are a combination of SI base units.**

*Volume is the amount of space occupied by an object. The derived unit for volume is cubic meters, m3. (Volume = l x w x h)

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Figure UNEOC Title: Visualizing Concepts 1.8 Caption: (a) How many significant figures should be reported for the volume of the metal bar shown below? (b) If the mass of the bar is g, how many significant figures should be reported when its density is calculated using the calculated volume? [Section 1.5] Notes: Keywords:

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**Figure 01.20 Figure 01-20 Title: Common volumetric glassware. Caption:**

The graduated cylinder, syringe, and buret are used in laboratories to deliver variable volumes of liquid. The pipet is used to deliver a specific volume of liquid. The volumetric flask contains a specific volume of liquid when filled to the mark. Notes: Keywords:

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**Density is a derived unit. It is mass divided by volume.**

density = mass or D = m volume V The SI units are kg/m3

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**Density…: is a physical property of a substance.**

does not depend on the size of the sample. As the mass of the sample increases so does the volume.

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Figure 01-T06 Title: Table 1.6 Caption: Densities of Some Selected Substances at 25 °C Notes: Keywords:

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**Density of a substance determines whether it floats or sinks in a liquid.**

For instance, ice has a density of 0.92 g/mL, which is less than that of water (0.998 g/mL). Since ice is less dense, it will float on water.

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**The copper would sink as its density is higher than that of water.**

Example: The density of water is g/mL. If copper pellets were placed in the water would it sink or float? (Density of copper is 8.92g/mL) The copper would sink as its density is higher than that of water.

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**Examples:A sample of aluminum metal has a mass of 8. 40g**

Examples:A sample of aluminum metal has a mass of 8.40g. The volume of the sample is 3.1cm3. Calculate the density of aluminum. D = m = 8.40g = 2.7g/cm3 V cm3

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**D = m/V m = D x V m = 620 g m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm)**

A sheet of metal has a length of 32.0cm, a width of 2.00cm, and a height of 1.000cm. The density of the metal is 9.7g/cm3. Calculate the mass of the metal. D = m/V m = D x V m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm) m = 620 g

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Specific Gravity Comparison of the density of a substance with the density of a reference substance. A hydrometer is used to measure the specific gravity of a liquid.

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Temperature Determines the direction of heat transfer.

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Temperature Scales Celsius scale: Uses water as the reference (i.e. 0oC and 100oC)

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**Temperature Scales (cont.)**

Kelvin scale: Freezing point of water is K and its boiling point is K. Absolute Zero – all motion ceases

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**Converting between Celsius and Kelvin**

K = oC oC = K – 273

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**Liquid nitrogen boils at 77. 2 K**

Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius? oC = K – 273 oC = 77.2 – 273 -195.8oC

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