# Water Water Everywhere Water as Liquid Rainwater Water

- Slides: 86

Water, Water Everywhere

Water as Liquid - Rainwater

Water Vapor (Steam)

Snow and Snow Flakes

Water as Solid - Iceberg

The Three States of Water Macroscopic and Microscopic Views

Water Cycle

Colors in Nature

Chemical Reaction

Where does Chemistry fit in? • Chemistry provides the links between the macroscopic world that we experience and the microscopic world of atoms and molecules. • It is relevant to all form of scientific studies.

Roles of Chemistry

The Central Science • Chemistry is the study of matter and the changes/reactions they undergo. • Chemistry is a central science. • It is essential in understanding both biological and non-biological worlds;

What is Matter? • The materials of the universe anything that has mass and occupies space

What Type of Change? • Physical and Chemical; • Physical Changes: Processes that alter the states of substances, but not their fundamental compositions. • Chemical Changees: Processes that alter the fundamental compositions of substances and their identity.

Study of Matter & Changes In chemistry you will study: • the existence of matter at macroscopic and microscopic levels; • the different states they can exist, • factors that determine their stability, and • their physical and chemical properties.

Atoms vs. Molecules • Matter is composed of tiny particles called atoms. • Atom: smallest part of an element that is still that element. • Molecule: Two or more atoms joined and acting as a unit.

Chemical Reaction • One substance becomes another substance(s), such that the fundamental compositions of products are different from those of reactants.

Roles of Science • Science is not a just list of facts or knowledge; • Science is a framework for gaining and organizing knowledge/fact about matter, including changes they undergo;

Roles of Scientists • Scientists continuously challenge our current beliefs about nature, and always: • asking questions about what we have already known; • Testing the fact/knowledge to confirm it or to gain new insight.

The Process: Scientific Method

The Scientific Method

Fundamental Steps in Scientific Method 1. Identify the problems and collect information/data; 2. Develop a hypothesis based on available data; 3. Test the hypothesis (Design & perform experiments) 4. Collect and analyze more data to support hypothesis 5. Make a Conclusion: • Observations may become Law; • Hypotheses may become Theory.

Terms in the Scientific Method 1. Hypothesis: a possible explanation for an observation. 2. Theory: a set of (tested) hypotheses that gives an overall explanation of certain natural phenomenon. 3. Scientific Law: a concise statement that summarizes repeatable observed (measurable) behavior.

Units and Measurements Measurement • Quantitative observations consist of: § Number & Units (without unit, the value becomes meaningless. • Examples: § 65 kg (kg = kilogram; unit for mass) § 4800 km (km = kilometer; unit for distance) § 3. 00 x 108 m/s (m/s = meter per second; unit for speed)

Units and Measurements The Number System • Decimal Numbers: 384, 400 0. 08206 • Scientific Notations: 3. 844 x 105 8. 206 x 10 -2 (but 384. 4 x 103 is not)

Meaning of 10 n and 10 -n • The exponent 10 n : § if n = 0, 100 = 1; § if n > 0, 10 n > 1; § Examples: 101 = 10; 102 = 100; 103 = 1, 000; • The exponent 10 -n : § if n > 1, 10 -n < 1; § Examples: 10 -1 = 0. 1; 10 -2 = 0. 01; 10 -3 = 0. 001

Units of Measurements • Units give meaning to numbers. Without Unit 384, 400 ? With Units 384, 400 km (implies very far) 384, 400 cm (not very far) 144 ? 0. 08206 ? (No meaning) 144 eggs (implies quantity) 0. 08206 L. atm/(K. mol)

English Units Mass: ounce (oz. ), pound (lb. ), ton; Length: inches (in), feet (ft), yd, mi. , etc; Volume: pt, qt, gall. , in 3, ft 3, etc. ; Area: acre, hectare, in 2, ft 2, yd 2, mi 2.

Metric Units Mass: gram (g); kg, mg, ng; Length: meter (m), cm, mm, km, mm, nm, pm; Area: cm 2, km 2 Volume: L, m. L, d. L, cm 3, m 3; (cm 3 = m. L)

Fundamental SI Units Physical Quantity Name of Unit Abbreviation Mass kilogram kg Length meter m Time second s Temperature Kelvin K Amount of substance mol Energy Joule J Electrical charge Coulomb C Electric current ampere A

Prefixes in the Metric System • Prefix Giga Mega kilo deci centi milli micro nano pico Symbol G M k d c m m n p 10 n 109 106 103 10 -1 10 -2 10 -3 10 -6 10 -9 10 -12 Decimal Forms 1, 000, 000 1, 000 0. 1 0. 001 0. 000, 000, 001

Mass and Weight • Mass is a measure of quantity of substance; • Mass does not vary with condition or location. • Weight is a measure of the gravitational force exerted on an object; • Weight varies with location if the gravitational force changes.

Errors in Measurements • Random errors 1. values have equal chances of being high or low; 2. magnitude of error varies from one measurement to another; 3. error may be minimize by taking the average of several measurements of the same kind;

Errors in Measurements • Systematic errors 1. Errors due to faulty instruments; 2. reading is either higher or lower than the correct value by a fixed amount; 3. the magnitude of systematic error is the same, regardless of quantity measured; 4. For balances with systematic errors, weighing by difference can eliminate systematic errors.

Accuracy and Precision in Measurements • Accuracy The agreement of an experimental value with the “true” or accepted value; • Precision Degree of agreement among values of same measurements; (degree of repeatability)

Accuracy and Precision

Accuracy and Precision • Accuracy and degree of precision in a measurement is defined by the type of instrument used.

Balances with Different Precisions Centigram Balance (precision: ± 0. 01 g) Milligram Balance (precision: ± 0. 001 g)

Analytical Balance (precision: ± 0. 0001 g)

Significant Figures • Way of expressing measured values with degree of certainty; • For examples: • Mass of an object on a centigram balance = 2. 51 g • Mass of same object on analytical balance = 2. 5089 g Absolute error for centigram balance = 0. 4%; Absolute error for analytical balance = 0. 004%; Analytical balance gives mass with more significant figures (5) and more precise (a greater degree of certainty), compared with a centigram balance that gives 3 significant digits for the same mass.

How many significant figures are in the following measurements?

What is the Buret Reading shown in the Diagram? • Reading liquid volume in a buret; • Read at the bottom of meniscus; • Suppose meniscus is read as 20. 15 m. L: – Certain digits: 20. 15 – Uncertain digit: 20. 15

What is the volume of liquid in the graduated cylinder?

Rules for Counting Significant Figures 1. All nonzero integers are counted as significant figures Examples: 453. 6 has 4 significant figures; 4. 48 x 105 has 3 significant figures;

Rules for Counting Significant Figures 2. Leading zeroes – zeroes that precede all nonzero digits are NOT counted as significant figures. Examples: 0. 0821 has 3 significant figures 0. 00055 has 2 significant figures

Rules for Counting Significant Figures 3. Captive zeros – these are zeros between nonzero digits; they are always counted as significant figures. Examples: 1. 079 has 4 significant figures 0. 08206 has 4 significant figures

Rules for Counting Significant Figures 4. Trailing zeroes – these are zeroes at the right end of the number. They are counted as significant figures if the number contains a decimal point, otherwise it is not counted. Examples: 208. 0 has 4 significant figures; 2080. also has 4 significant figures, but 2080 has 3 significant figures;

Rules for Counting Significant Figures 5. Exact numbers – these are numbers given by definition or obtained by counting. They have infinite number of significant figures; the value has no error. Examples: 1 yard = 36 inches; 1 inch = 2. 54 cm (exactly); there are 24 eggs in the basket; this class has 60 students enrolled; (There are 35, 600 spectators watching the A’s game at the Coliseum is not an exact number, because it is an estimate. )

How many significant figures? (a) (b) (c) (d) (e) (f) (g) (h) 0. 00239 0. 01950 1. 00 x 10 -3 100. 40 168, 000 0. 082060 One dime equals to 10 pennies Express 1000 as a value with two significant figures.

Rounding off Values in Calculations • In Multiplications and/or Divisions Round off the final answer so that it has the same number of significant figures as the value with the least significant figures. Examples: (a) 9. 546 x 3. 12 = 29. 8 (round off from 29. 78352) (b) 9. 546/2. 5 = 3. 8 (round off from 3. 8184) (c) (9. 546 x 3. 12)/2. 5 = 12 (round off from 11. 913408)

Rounding off Calculated values • In Additions and/or Subtractions Round off the final answer so that it has the same number of digits after the decimal point as the data value with the least number of such digits. Examples: (a) 53. 6 + 7. 265 = 60. 9 (round off from 60. 865) (b) 53. 6 – 7. 265 = 46. 3 (round off from 46. 335) (c) 41 + 7. 265 – 5. 5 = 43 (round off from 42. 765)

Mean, Median & Standard Deviation • Mean = average Example: • Consider the following temperature values: 20. 4 o. C, 20. 6 o. C, 20. 3 o. C, 20. 5 o. C, 20. 4 o. C, and 20. 2 o. C; (Is there any outlying value that we can throw away? ) • No outlying value, the mean temperature is: (20. 4 + 20. 6 + 20. 3 + 20. 5 + 20. 4 + 20. 2) ÷ 6 = 122. 4/6 = 20. 40 o. C

Mean, Median & Standard Deviation Median: 1. the middle value (for odd number samples) or 2. average of two middle values (for even number) 3. when values are arranged in ascending or descending order. Arranging the temperatures from lowest to highest: 20. 2 o. C, 20. 3 o. C, 20. 4 o. C, 20. 5 o. C, and 20. 6 o. C, the median = (20. 4 o. C + 20. 4 o. C)/2 = 20. 4 o. C

Mean, Median & Standard Deviation • Standard Deviation, S = (for n < 10, Xi = sample value; = mean value) [Note: calculated value for std. deviation should have one significant figure only. ] For above temperatures, S = 0. 1; Mean = 20. 4 ± 0. 1 o. C

Calculating Mean Value • Consider the following masses of pennies (in grams): 2. 48, 2. 50, 2. 52, 2. 49, 2. 50, 3. 02, 2. 49, and 2. 51; • Is there outlying value? Yes; 3. 02 does not belong in the group – can be discarded • Outlying values should not be included when calculating the mean, median, or standard deviation. • Average (mean) mass of pennies is, (2. 48 + 2. 50 + 2. 52 + 2. 49 + 2. 50 + 2. 49 + 2. 51) ÷ 7 = 2. 50 g;

Calculating Standard Deviation _____________ -0. 02 0. 0004 -0. 0000 0. 02 0. 0004 -0. 01 0. 0000 -0. 01 0. 0001___ Sum: 0. 0011 ---------------------

Mean and Standard Deviation • The correct mean value that is consistent with the precision is expressed as follows: 2. 50 ± 0. 01

Using Q-test to retain or reject questionable values • Calculate Qcalc. as follows: • Qcalc. = • Compare Qcalc with Qtab from Table-2 at the chosen confidence level for the matching sample size; • If Qcalc < Qtab, the questionable value is retained; • If Qcalc > Qtab, the questionable value is can rejected.

Rejection Quotient • Rejection quotient, Qtab, at 90% confidence level • —————————— • Sample size Qtab ___ • 4 0. 76 • 5 0. 64 • 6 0. 56 • 7 0. 51 • 8 0. 47 • 9 0. 44 • 10 0. 41 —————

Performing Q-test on Sample Data • Consider the following set of data values: 0. 5230, 0. 5325, 0. 5560, 0. 5250, 0. 5180, and 0. 5270; • Two questionable values are: 0. 5180 & 0. 5560 (the lowest and highest values in the group) • Perform Q-test at 90% confidence level on 0. 5180: • Qcalc. = 0. 13 < 0. 56 • (limit at 90% confidence level for sample size of 6) • We keep 0. 5180.

Performing Q-test on questionable value • Calculate rejection quotient for 0. 5560: • Qcalc. = 0. 618 > 0. 56 • (limit at 90% confidence level for a sample of 6 is 0. 56) • We reject 0. 5560.

Calculate the mean using acceptable values • Re-write the mean value to be consistent with the precision: • Mean = 0. 526 ± 0. 005

Calculating Standard Deviation • • • 0. 5230 0. 5325 0. 5250 0. 5180 0. 7270 -0. 0028 0. 0067 -0. 0008 -0. 0078 0. 0012 7. 8 x 10 -6 4. 5 x 10 -5 6. 4 x 10 -7 6. 1 x 10 -5 1. 4 x 10 -6 S = 1. 16 x 10 -4

Mean value must be consistent with the precision Standard deviation: 1. 2. 3. 4. should have one significant digit only; It shows where the uncertainty appears in mean value; That is, which digit on the mean contains error; The mean value should be rounded off at the digit where it becomes uncertain. Thus, the mean consistent with the precision will be: 0. 526 ± 0. 005 (the mean value is precise up to the third decimal place)

Problem Solving by Dimensional Analysis • Value sought = value given x conversion factor(s) Example: How many kilometers is 25 miles? (1 mi. = 1. 609 km) Value sought: ? km; value given = 25 miles; conversion factor: 1 mi. = 1. 609 km ? km = 25 mi. x (1. 609 km/1 mi. ) = 40. km

Unit Conversions (1) Express 26 miles per gallon (mpg) to kilometers per liter (kmp. L). (1 mile = 1. 609 km and 1 gallon = 3. 7854 L) (Answer: 11 kmp. L) (2) If the speed of light is 3. 00 x 108 m/s, what is the speed in miles per hour (mph)? (1 km = 1000 m and 1 hour = 3600 s) (Answer: 6. 71 x 108)

Temperature • Temperature scales: 1. Celsius (o. C) 2. Fahrenheit (o. F) 3. Kelvin (K) Reference temperatures: freezing and boiling point of water: Tf = 0 o. C = 32 o. F = 273. 15 K Tb = 100 o. C = 212 o. F = 373. 15 K

Temperature Prentice-Hall © 2002 General Chemistry: Chapter 1 Slide 68 of 19

Relative Temperatures Prentice-Hall © 2002 General Chemistry: Chapter 1 Slide 69 of 19

Temperature Conversion • Fahrenheit to Celsius: Example: convert 98. 6 o. F to o. C;

Temperature Conversion • Celsius to Fahrenheit: Example: convert 25. 0 o. C to o. F;

Temperature Conversion • Celsius to Kelvin: T o. C + 273. 15 = T K • Kelvin to Celsius: T K – 273. 15 = T o. C Examples: convert: 25. 0 o. C to Kelvin = 25. 0 + 273. 15 = 298. 2 K 310. K to o. C = 310. – 273. 15 = 27 o. C

Temperature Conversion 1) What is the temperature of 65. 0 o. F expressed in degrees Celsius and in Kelvin? (Answer: 18. 3 o. C; 291. 5 K)

Temperature Conversion 2) A newly invented thermometer has a T-scale that ranges from -50 T to 300 T. On this thermometer, the freezing point of water is -20 T and its boiling point is 230 T. (a) What is the temperature of 92. 5 T in degrees Celsius? (b) Derive a formula that would enable you to convert a T-scale temperature to degrees Celsius. Answer: (a) 45. 0 o. C (b)

Density (Mass = volume x density; Volume = mass/density) Units: g/m. L or g/cm 3 (for liquids or solids) g/L (for gases) SI unit: kg/m 3

Determining Volumes • Rectangular objects: V = length x width x thickness; • Cylindrical objects: V = pr 2 l (or pr 2 h); • Spherical objects: V = (4/3)pr 3 • Liquid displacement method: the volume of object submerged in a liquid is equal to the volume of liquid displaced by the object.

Density Determination Example-1: A cylindrical metal rod that is 1. 00 m long and a diameter of 1. 50 cm weighs 477. 0 grams. What is the density of metal? Volume = p(1. 50 cm)2 x 100. cm = 177 cm 3 Density = 477. 0 g/177 cm 3 = 2. 70 g/cm 3

Density Determination Example-2: A 100 -m. L graduated cylinder is filled with 35. 0 m. L of water. When a 45. 0 -g sample of zinc pellets is poured into the graduate, the water level rises to 41. 3 m. L. Calculate the density of zinc. Volume of zinc pellets = 41. 3 m. L – 35. 0 m. L = 6. 3 m. L Density of zinc = 45. 0 g/6. 3 m. L = 7. 1 g/m. L (7. 1 g/cm 3)

Density Calculation #1 • The mass of an empty flask is 64. 25 g. When filled with water, the combined mass of flask and water is 91. 75 g. However, when the flask is filled with an alcohol sample the combined mass is found to be 85. 90 g. (a) If we assume that the density of water is 1. 00 g/m. L, what is the density of the alcohol sample? (b) What is the density of alcohol in SI unit? (Answer: (a) 0. 787 g/m. L; (b) 787 kg/m 3)

Density Calculation #2 A 50 -m. L graduated cylinder weighs 41. 30 g when empty. When filled with 30. 0 m. L of water, the combined mass is 71. 25 g. A piece of metal is dropped into the water in the graduate, which causes the water level rises to 36. 9 m. L. The combined mass of graduate, water and metal is 132. 65 g. Calculate the densities of water and metal. (Answer: 0. 998 g/m. L and 8. 9 g/m. L, respectively)

Classification of Matter

Classification of Matter • Mixture: matter with variable composition • Homogeneous mixture: One that has a uniform appearance and composition throughout the mixture; • Heterogeneous mixture: One that has neither uniform appearance or composition – the appearance and composition in one part of the mixture may differ from the other part; • Pure Substance: matter with a fixed composition

Pure Substances • Element: Composed of only one type of atoms – it cannot be further reduced to simpler forms of matter. • Compound: Composed of at least two different types of atoms combined chemically in a fixed ratio – it may be broken down into simpler forms (or reduced to the elements)

Physical Changes Examples: 1. Melting: solid becomes liquid; 2. Freezing: liquid becomes solid; 3. Evaporation: liquid becomes vapor; 4. Condensation: vapor becomes liquid; 5. Sublimation: solid becomes vapor; 6. Dissolution: solute dissolves.

Chemical Changes Examples: 1. 2. 3. 4. 5. 6. 7. Combustion (burning), Decomposition, Rotting, Fermentation, Rancidity, Corrosion/rusting, Any type of chemical reactions

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