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Chem101 Chapter 01. Chemical Foundations. What is chemistry?. The science that explains:. the properties of materials. how new materials may be made. the relationship between energy and chemical reactions. how materials may be analyzed at the atomic and molecular
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Chem101Chapter 01 Chemical Foundations
What is chemistry? The science that explains: the properties of materials how new materials may be made the relationship between energy and chemical reactions how materials may be analyzedat the atomic and molecular level (Macroscopic & Microscopic. A key concept is that chemists look for explanations
1.1Chemistry: An overview • Chemistry is fundamentally concerned with: "How one substance changes to another" • How plants grow by absorbing water and Carbon dioxide? • How humans manufacture the proteins from the food we consume? • ….. and on and on • A substance is composed of atoms, all universe is made of only 110 {different types of atoms}
1.2 The Scientific Method It is a systematic approach to research that includes: • Making Observation • Making a Prediction "Hypothesis" • Doing Experiment to test the Hypothesis Law: summary of observed behavior Theory: model attempt to explain
1.3 Units of Measurement Quantitative Measurement, consists of two parts: a number and a scale (unit) • In 1960, an international agreement get up a system of units called International System (SI- system) based on metric system.
1.3 Units of Measurement Prefixes:are used to change the size of the unit
1.3 Units of Measurement • Volume is not fundamental SI – unit, but very commonly used in chemistry, {SI derived unit for volume is cubic meter (m3)} • 1 m3 = (10 dm)3 = 1000 dm3 = 1000 L • Used unit in liter = 1dm3 • 1 L = 1dm3 = (10 cm)3 = 1000 cm3 (ml)
1.4 Uncertainty in measurement Any measurement always has some degree of uncertainty. Uncertainty depends on the precision of measuring device. e.g., measurement of volume of a liquid using a buret: • the used liquid is about ………………….mL If 4 different people read the same volume we might get:
1.4 Uncertainty in measurement • You have to record the certain digits and the first uncertain digit only. • All digits together [ certain + first uncertain] are called " Significant Figures" • The uncertainty in the last number must be assumed to be # 1 Volume = 22.2 ± 0.1 ml Example 1.1: What is the difference between the measurements 25.00mL and 25mL?
1.4 Uncertainty in measurement Precision and Accuracy Not Accurate Not precise • Accuracy: it is the agreement of a particular value with the true value. • Precision: it is the agreement among several measurements of the same quantity. Not Accurate But precise Accurate and precise
1.4 Uncertainty in measurement Errors Large Random Error • Random error: it means that a measurement has an equal probability of being high or low. • Systematic error: error accurse in the same direction each item. Small Random and Large Systematic Error Small Random And NO Systematic Error
1.5 Significant Figures (SF) and Calculations Rules for Counting Significant Figures: It is important to be applied to get the uncertainty in the final results out of adding, subtracting multiplying ..etc. • Nonzero integers, count as SF. • Zeros: - "Leading zeros” are not significant. e.g. 0.0025 (2 SF) - "Captive zeros” Count as s.f. e.g.: 1.008 (4 SF) - "Trailing zeros” count as s.f. eg. : 100 = 1.00 X 102 (3 SF) • Exact numbers have an infinite number of SF e.g. 10 experiment, 5 apples, 8 books … so on. .. • Exponential notation: it is used to unite large or small numbers in the correct sig.fig. e.g. 0.000060 convenient 6.0 x 10-5
1.5 Significant Figures (SF) and Calculations Rules for SF in Mathematical Operations: • Multiplication / Division: Final results have the same SF in the least precise measurement used in calculation. e.g. 4.56 x 1.4 = 6.38 = (………………?) • Addition / Subtraction: Final results have the same number of decimal places as the least precise numbers e.g. 12.11 + 18.0 + 1.013 = 31.123 = (…………?)
1.5 Significant Figures (SF) and Calculations Note: To get the correct total SF in the final results you may round off the results. Rules for rounding: if the number to be removed is < 5, the preceding digit stays the same. e.g., round 1.33 to 2 S.F. (…………?) Exercise 1.4: a) 1.05 x 10-3 ÷ 6.135 = (………….?) b) 21 – 13.8 = (……………?)
1.6 Dimensional Analysis conversion of a given results from one system unit to an other using "Unit Factor Method" or dimensional analysis. Means Multiply any expression by "1" will not change its value. • Exercise 1.5: A pencil is 7.00 in long, What is its length in centimeter? • Solution: • what is the in/cm relation: 2.54cm = 1 in • which unit is needed: cm • unit factor must has cm unit as nominator. i.e. 2.54 cm / 1 in = 1 [unit factor] Multiply the length by the unit factor gives: 7.00 in x 2.54 cm /1 in = 17.8 cm 7.00 in = 17.8 cm
1.6 Dimensional Analysis Note: Sometime you have to do multi-step conversion to get correct answer. Exercise 1.7: A student has entered a 10.0 km race. How long is the run in miles? • Solution: km m yd mi [1 km = 1000m, 1 m = 1.09yd, 1760yd = 1 mi] • Results:10.0 km = 6.22 mi
1.7 Temperature Engineering Science Difference Is complicated Difference Is in their zero • Conversion • Adjustment in the degree step • Adjustment in the zero Conversion Adjust the zero difference Tc = (TF-32oF) x 5oF/ 9oC TF = (T0C x 9oF/5oC) + 32oF T(Kelvin) = T(oC) + 273.15
1.8 Density It is the mass per unit volume of the substance. A property of matter that is often used by chemists. Density = Exercise 1.13: A chemist finds that 25.00cm3 of a CD- cleaner has a mass of 19.625g at 20oC. The following are the names and densities of the compounds that might be the main component: Which of them is the most likely to be the main component of the CD-cleaner? Solution:
1.9 Classification of matter Read (pp. 26-30) and Report (HW#2): • Define : "Matter, Mixtures, Physical changes, Compound, and Element" • Define: "Distillation, Filtration, and Chromatography.
