Chapter 1. Introduction: Matter and Measurement. Chemistry. In this science we study matter, its properties, and its behavior. Matter And Measurement

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1 Chapter 1 Introduction: and Chemistry 2 In this science we study matter, its properties, and its behavior.

2 We define matter as anything that has mass and takes up space. 3 4 Atoms are the building blocks of matter. Each element is made of the same kind of atom. A compound is made of two or more different kinds of elements.

3 5 Three States of Water Liquid solid 6 gas

4 Classification of 7 salt in sand sucrose soln Properties and Changes of 8 Types of Properties Physical Properties Can be observed without changing a substance into another substance. Boiling point, density, mass, volume, etc. Chemical Properties Can only be observed when a substance is changed into another substance. Flammability, corrosiveness, reactivity with acid, etc.

5 9 Types of Properties Intensive Properties Are independent of the amount of the substance that is present. Density, boiling point, color, etc. Extensive Properties Depend upon the amount of the substance present. Mass, volume, energy, etc. Types of Changes 10 Physical Changes These are changes in matter that do not change the composition of a substance. Changes of state, temperature, volume, etc. Chemical Changes Chemical changes result in new substances. Combustion, oxidation, decomposition, etc.

6 Chemical Reactions 11 In the course of a chemical reaction, the reacting substances are converted to new substances. 12 Separation of Mixtures

7 Filtration 13 In filtration, solid substances are separated from liquids and solutions. Distillation 14 Distillation uses differences in the boiling points of substances to separate a homogeneous mixture into its components.

8 Chromatography 15 This technique separates substances on the basis of differences in solubility in a solvent. The Scientific Method 16 Process of Science : asking questions and making careful observations. science as a means of knowing; raising questions, designing experiments, gathering data, interpreting the data, drawing conclusions, raising more questions : the structured way of knowing

9 17 Units of 18 SI Units Système International d Unités A different base unit is used for each quantity.

10 19 Metric System Prefixes convert the base units into units that are appropriate for the item being measured. Mass vs. weight 20 Mass: a measure of the amount of matter Weight: a measure of downward force given by g.

11 21 Volume The most commonly used metric units for volume are the liter (L) and the milliliter (ml). A liter is a cube 1 decimeter (dm) long on each side. A milliliter is a cube 1 centimeter (cm) long on each side. Temperature 22 By definition temperature is a measure of the average kinetic energy of the particles in a sample.

12 Temperature Conversions 23 Kelvin T K = T C Celsius T C = (T F 32)/1.8 Fahrenheit T F = 1.8(T C ) Derived Units Density is a physical property of a substance. It has units (g/ml, for example) that are derived from the units for mass and volume. d = m V

13 25 Uncertainty in Accuracy versus Precision 26 All measurements are made with some degree of uncertainty. To express uncertainty: 151±1 g. Exact numbers: Defined quantities such as a 1meter = 100 centimeters and items that are counted. Precision: Indicator of how close repeated measurements are to each other Accuracy: Indicator of how close a measurement is to its true value

14 Accuracy and Precision 27 Accuracy: How close we are to the true value. Precision: How close our measurements are to each other; how consistent (or reproducible) our measurements are. Uncertainty in s 28 Different measuring devices have different uses and different degrees of accuracy.

15 29 Significant Figures The term significant figures refers to digits that were measured. When rounding calculated numbers, we pay attention to significant figures so we do not overstate the accuracy of our answers. 30 Significant Figures 1. All nonzero digits are significant. 2. Zeroes between two significant figures are themselves significant. 3. Zeroes at the beginning of a number are never significant. 4. Zeroes at the end of a number are significant if a decimal point is written in the number.

16 Significant Figures 31 : specific numbers in a measurement whose values we can trust 325K / 3 = Are the endless decimal digits significant? Significant Figures 32 When addition or subtraction is performed, answers are rounded to the least significant decimal place. When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.

17 Sample Exercise 1.5 Relating Significant Figures to the Uncertainty of a What difference exists between the measured values 4.0 g and 4.00 g? Solution The value 4.0 has two significant figures, whereas 4.00 has three. This difference implies that the 4.0 has more uncertainty. A mass reported as 4.0 g indicates that the uncertainty is in the first decimal place. Thus, the mass might be anything between 3.9 and 4.1 g, which we can represent as 4.0 ± 0.1 g. A mass reported as 4.00 g indicates that the uncertainty is in the second decimal place. Thus, the mass might be anything between 3.99 and 4.01 g, which we can represent as 4.00 ± 0.01 g. (Without further information, we cannot be sure whether the difference in uncertainties of the two measurements reflects the precision or the accuracy of the measurement.) Practice Exercise A sample that has a mass of about 25 g is placed on a balance that has a precision of ± g. How many significant figures should be reported for this measurement? 33 Answer: five, as in the measurement g, the uncertainty being in the third decimal place Significant Figures in Calculations 34

18 Sample Problem 35 Report the answer to the correct number of significant figures. a = 10.5 b. (16)(0.0159) = 0.25 c /( ) = Dimensional Analysis 36 We use dimensional analysis to convert one quantity to another. Most commonly, dimensional analysis utilizes conversion factors (e.g., 1 in. = 2.54 cm) 1 in cm or 2.54 cm 1 in.

19 37 Dimensional Analysis Use the form of the conversion factor that puts the sought-for unit in the numerator: Given unit desired unit given unit desired unit Conversion factor 38 Dimensional Analysis For example, to convert 8.00 m to inches, convert m to cm convert cm to in m 100 cm 1 m 1 in cm 315 in.

20 Sample Exercise 1.10 Converting Units Using Two or More Conversion Factors 39 The average speed of a nitrogen molecule in air at 25 C is 515 m/s. Convert this speed to miles per hour. Homework 40 필수숙제 : 22, 30, 40, 52, 76, 81, 82 추가연습 14, 18, 26, 28, 36, 46, 64, 67, 70