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- 1. CHEM-111CHEM-111 General ChemistryGeneral Chemistry Unit OneUnit One Scientific MeasurementScientific Measurement Department of ChemistryDepartment of Chemistry February-2007February-2007
- 2. Contents Scientific MeasurementsScientific Measurements • Measurement and Units • System of Measurement • Scientific Notation • Significant figures in measurements • Length and Volume • Converting Units • Unit of Mass • Density and Specific Gravity • Units of Heat and Heat Capacity of Matter
- 3. Metric Units Metric System is used by scientists and health professionals Type Name symbol Mass Gram g Length Meter m Volume Liter L Time Second s Temperatue Celsius 0 C
- 4. Systems of Measurements International System of Units (SI Units) Base Quantity Name Symbol Length Meter m Mass Kilogram kg Time Second s Electric current Ampere A Temperature Kelvin K Luminous intensity Candela cd Amount of substance Mole mol The seven SI base units
- 5. Name Symbol Value in SI units minute (time) min 1 min = 60 s hour h 1 h = 60 min = 3600 s day d 1 d = 24 h = 86 400 s liter L 1 L = 1 dm3 = 10-1 m3 metric ton t 1 t = 1x103 kg unified atomic mass unit u 1 u = 1.66054 x 10-27 kg, approximately 1 meter = 3.3 feet . Units Outside the SI That are Accepted for Use with the SI
- 6. Commonly-used metric prefixes Prefix Name Prefix Symbol Prefix Value giga G 1 billion or 1 000 000 000 109 mega M 1 million or 1 000 000 106 kilo k 1 thousand or 1000 103 deci d 1 tenth or 1/10 or 0.1 10-1 centi c 1 hundredth or 1/100 or 0.01 10-2 milli m 1 thousandth or1/1000 or 0.001 10-3 micro µ 1/1 000 000 or 0.000 001 10-6 nano n 1/1 000 000 000 or 0.000 000 001 10-9 Prefixes that increase the size of the unit Prefixes that decrease the size of the unit
- 7. Prefixes and equalities Measuring length 1 meter 10 dm 100 cm 1000 mm Some Length Equalities 1 m = 100 cm 1 m = 1000 mm 1 cm = 10 mm Measuring Volume 1 L = 10 dL 1 L = 1000 mL 1dL = 100 mL 1cm3 = 1 cc = 1 mL
- 8. Mass and Weight In commercial and everyday use, and especially in common parlance, weight is usually used as a synonym for mass. How are weight and mass differ? 1) Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. 2) Mass is measured by using a balance comparing a known amount of matter to an unknown amount of matter. Weight is measured on a scale. 3) The Mass of an object does not change when an object's location changes. Weight, on the other hand does change with location .
- 9. Measuring mass In metric system, the unit for mass is grams (g) The SI unit of mass, the kilogram (kg), is used for larger masses. 1 kg = 2.20 lb 454 g = 1 lb Some mass equality 1 kg = 1000g 1 g = 1000mg 1 mg = 1000µg
- 10. Scientific Notation Scientists have developed a shorter method to express very large numbers. This method is called scientific notation. Scientific Notation is based on powers of the base number 10. The number 123,000,000,000 in scientific notation is written as 1.23 x 1011 Example 93,000,000 = 9.3 X 107 miles these two digits are retained 93,000,000 miles 7 digits instruction: move decimal point 9.3 x 107 miles seven(7) digits to the right exponent 9.3 x 107
- 11. Scientific Notation for very large Numbers The number 2,398,730,000,000 can be written in scientific notation as: (the starred representation is most common) 0.239873 x 1013 ****2.39873 x 1012 **** 23.9873 x 1011 239.873 x 1010
- 12. A paper clip weighs a bit more than one thousandth of a pound (0.0011 Lb). This would be expressed in scientific notation as 1.1 x 10-3 lb. The negative sign indicates that the decimal point is moved to the left. Scientific notation for very small numbers 0.0011 kg = 1.1 x 10 -3 kg 0.0 0 11 kg 0 1 2 3 4 1.1 x 10 -3 kg these two digits are retained instruction: move decimal point three digits to the left
- 13. The number 0.003,483 can be written in scientific notation as (the starred representation is most common): 0.3483x 10-2 ****3.483 x 10-3 **** 34.83x 10-4 348.3x 10-5 3483.x 10-6 Scientific notation for very small numbers Conventional Notation Scientific Notation 0.012 1.2 x 10-2 0.000541 5.41 x 10-4 0.000007 7 x 10-6 0.0010 1.0 x 10-3
- 14. value significant figures rule 16.74 g 4 sig. figs non zero digits are significant 0.003 m 1 sig. fig a zero at the beginning of a decimal number is not significant 2500 km 2 sig. figs a zero at the end of a large number without a decimal point after is not significant 25.0 ml 50. L 3 sig. figs 2 sig. figs a zero at the end of a decimal number is significant 405 3 sig. figs zeros between non zero digits are significant Number of Significant Figures
- 15. Number of Significant Figures • According to these rules, all of these numbers have three significant digits: 123 123,000 0.000123 • 12.3 1.23 x 106 0.000123 67.2units = three significant figures uncertain digit certain digit
- 16. Remember- Rules for zeros 1. Leading zeros are not significant. 0.523– three significant figuresLeading zeros 2. Captive zeros are significant. 5016 – four significant figures Captive zeros 3.Trailing zeros are significant. 315.60–five significant figures Trailing zeros 4. A zero at the beginning of a decimal number is not significant 0.008 - one significant figure Zero at the beginning of a decimal number
- 17. Scientific notation can be used to clearly express significant figures. A properly written number in scientific notation always has the proper number of significant figures. 0.00524=5.24x 10-3 Three significant figures 378 000 3.78 x 10 5 Three 8931.5 8.9315 x 10 3 Five 0.000 593 5.93 x 10 -4 Three 0.000 000 4 4 x 10 -7 One Conventional Notation Scientific Notation significant figures Scientific notation and significant figures
- 18. Temperature The temperature of an object tells us how hot or cold an object is (intensity of heat). In metric system temperature is measured on the Celsius temperature scale. On Celsius thermometer, freezing point of water is 0 0 C and boiling point of water is 100 0 C. On a Fahrenheit scale, freezing point of water is 320 F and boiling point of water is 212 0 F. • 0 F = 1.8 (0 C) + 32 Kelvin Temperature scale In SI system, temperature is based on Kelvin (K) temperature scale. • K = 0 C + 273
- 19. 180 Fahrenheit degrees 100 Celsius degrees 100 Kelvins degrees FahrenheitCelsiusKelvin Normal body temperature Freezing point of water Boiling water 373 K 100 0 C 212 0 F 310 K 37 0 C 98.6 0 F 273 K 0 0 C 32 0 F Boiling point of water Comparison of the Fahrenheit, Celsius, and Kelvin Temperature
- 20. Accuracy Accuracy indicates how close a measurement is to the accepted value. For example, we'd expect a balance to read 100 grams if we placed a standard 100 g weight on the balance. If it does not, then the balance is inaccurate. Accuracy 100 g 100.00 100 g 98.89 InaccurateAccurate Measurements and Units
- 21. Which Factors effect on Accuracy & Precision Predict the effect on accuracy and precision: 1. Instrument not “zeroed” properly 2. Reagents made at wrong concentration 3. Temperature in room varies “widely” 4. Lab partner is not properly trained
- 22. Precision • Precision indicates how close together or how repeatable the results are. A precise measuring instrument will give very nearly the same result each time it is used. Precision More precise Trial # Mass (g) 1 100.00 2 100.01 3 99.99 4 99.99 Average 100.00 Range 0.01 Std. Dev. 0.05 Less precise Trial # Mass (g) 1 100.10 2 100.00 3 99.88 4 100.02 Average 100.00 Range 0.11 Std. Dev. 0.09
- 23. Measurements and Units Accuracy with PrecisionPrecision with mistake Accuracy with mistake Accuracy and Precision of Measurements
- 24. The box that has more balls has more mass per unit of volume. This property of matter is called density Each box has the same volume If each ball has the same mass, which box would weigh more? Why? What is Density More Dense Less Dense
- 25. Density is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass divided by its total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water). Common units are : g/ mL or g/ cm3 or kg/L (kg/m3 ) ( cm3 = ml) DensityDensity Density = mass volume d = m v or
- 26. Density is a characteristic property of a substance. Air 0.0013 g/L Bone 1.7-2.0 g/ml Water 1.0 g/ml Urine 1.01-1.03 g/ml Gold 19.3 g/ml Gasoline 0.66-0.69 g/ml DensitySubstance Substance Density of some common substance Density
- 27. 1. An Iron ball was weight and found to have a mass of 42.6 g. Its volume was measured to be10.00 mL. What is the density of Fe? SOLUTION: Density is the ratio of mass to volume. Using the symbol d for density, therefore, we obtain d = mass volume 42.6g 10.00mL 4.26g/mL = = Density Calculation Mass Volume =Density 15.69g 1 5mL = 1.046g/mL= 2.What is the density of 15.00 mLof urine if it has a mass of 15.69 grams?
- 28. Density calculation What would be the mass of 3.00 liters of this milk sample? The density was 3.02 g/mL Mass Volume =Density mass = 9.06x 103 g mass = volume x density
- 29. Specific gravity The density of a substance compared to a reference substance is known as specific gravity. Specific Gravity = density of substance density of reference Specific gravity is unit less. Reference material is commonly water at 40 C. At 40 C, density = specific gravity.
- 30. Specific gravity measurement Hydrometer Float height will be based on Specific Gravity. Hydrometer is used to know density of urine by health care workers. The specific gravity of a liquid can be determined with a hydrometer, a hollow, sealed, calibrated glass tube. The depth to which the hydrometer sinks is inversely proportional to the specific gravity of the liquid.
- 31. Units of Heat • Heat is the energy associated with the motion of particles in a substance. • Heat is commonly measured in calories. • A Calorie (cal): is the amount of heat needed to raise the temperature of exactly 1 g of water by exactly 10 C. • 1 Kcal = 1000 calories • 1 cal = 4.18 j ( Joule, pronounced jewel) • 1 kJ = 1000 J
- 32. Specific Heat • All substances absorb energy. • Some need less amount of heat to become hot and others need more. • The amount of heat that raises the temperature of 1 g of a substance by 10 C is known as its specific heat. Specific heat = Amount of heat (Cal) 1 gm x 1 0C
- 33. Specific Heats of some Substances . All substances absorb energy, but some need only small amount of heat to become hot and others need more Substances Specific Heat (cal/g0 C) Water 1.00 Ethanol 0.58 Sand 0.19 Iron 0.11 Copper 0.093 Silver 0.057 Gold 0.031
- 34. Some Relationships to find The Mass Heat Change Temperature Change and Specific Gravity Specific heat Amount of heat ( cal ) = 1 g x 1 0 C Heat gain or loss = (mass) x(temperature change(ΔT) ) X (specific heat) Heat (calories) = g x 0 C x g 0 C cal 1. 2. 3. g 0 C calg 0 C
- 35. Exercise 1. Write the following measurements in scientific notation. a. 350 g b. 0.00016 L c. 5220000 m d. 0.0086 2. What is the name of the unit and the type of measurement ( mass, volume, length, or temperature) indicated for each of the following quantities. a. 4.8 m b. 325 g c. 1.5mL d. 373K 3. How many significant figure are in each of the following numbers a. 4.5 b. 205 c. 5.082 d. 0.0004
- 36. 4. Complete the following metric relationship: a. 1m = cm b. 1 km = m c. 1mm = m d. 1L = mL e. 1 kg = g f. 1mL = L g. 1 g = kg h. 1 g = mg 5. For each of the following pairs, which is the smaller unit a. mg or kg b. mL or µL c. cm or km d. kL or dL 6. Choose the larger unit a. mg or g b. cm or m c. ml or dL d. mm or µm

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