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Ch 1. Matter, Measurement, and Problem Solving

What is chemistry?

Matter and Mind

a specific matter — substance

Chemistry is the science of substances ― their structure, their properties, and the reactions that change them into other substances. Linus Pauling

Substances are composed of extremely small particles called atoms. If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. Richard Feynman

Substances are composed of extremely small particles called atoms. Atoms combine together and form a particle called molecule. More details later. hydrogen atomoxygen atom hydrogen molecule oxygen moleculewater molecule

Chemistry is the science of substances ― their structure, their properties, and the reactions that change them into other substances. Linus Pauling

Mercury and Iodine Combine to Form Mercury (II) Iodide Chemical Change = Chemical Reaction new substances produced

Chemistry is the science of substances ― their structure, their properties, and the reactions that change them into other substances. Linus Pauling

Chemistry is a discipline of science that strongly depends on experiments. Experiments  Measurements Every physical quantity consists of a number AND a unit. Results of measurements: physical quantities e.g.: length, temperature, voltage …

Two Systems for Units English System Metric SystemSI System

We use SI System for measurements

My height: 1.74 m San Francisco to Barnesville: m Thickness of paper: m

Try to remember them.

My height: 1.74 m San Francisco to Barnesville: m Thickness of paper: m = 4100 km = 0.2 mm

Scientific Notation a x 10 n 1 ≤ |a| < 10, n is an integer Negative exponent:

Express the following numbers in scientific notation 25− − Read Appendix I: A a x 10 n 1 ≤ |a| < 10, n is an integer

Units are involved in calculations just as numbers. Your calculator does not deal with units. You must work on it! Unit Calculations Never drop units!

A physical quantity can be viewed as a product of a number and its unit. a x numberunit 5 m

AB AB = 15 m C AC = 10 m CB = ? CB = AB − AC = 15 m − 10 m = (15 − 10) m = 5 m a x − b x = (a − b) x

H = 3 cm W = 6 cm Area = W x H = 6 cm x 3 cm = 18 cm 2 a x b x = ab x 2

V = L 3 = (5 cm) 3 = 5 3 (cm) 3 = 125 cm 3 (a x) 3 = a 3 x 3 What is the volume of a cube with edge length 5 cm? L = 5 cm

How many times is AB compared to CD in length? AB 15 m C 10 m D

AB 15 m Time consumed to move from A to B is 5 s. What is the average speed? meters per second

We use SI System for measurements

Mass is a measure of the quantity of material in an object. Weight is the force that gravity exerts on an object. F = ma G = mg Unit: kg Unit: N Mass ≠ Weight

Chemistry is a discipline of science that strongly depends on experiments. Experiments  Measurements Some basic concepts related to measurements

Reliability of Measurements Accuracy refers to the agreement of a particular measurement with the true value.

absolute error = experimental value − true value To quantify accuracy, define: experimental value (m)absolute error (m) −2 True value = 50 m sign of absolute error: direction |error|: size

relative error = absolute error / true value = absolute error / theoretical relative error is often given in percentage: | |: to make % error a positive number unknown theoretical: from calculation or provided by experts

experimental value (m)absolute error (m) −2 True or theoretical value = 50 m What are the percent errors for the measurements listed in the table?

1.Random Error: from imperfection of measurements. random, cannot avoid. can take average of multiple measurements to reduce it to certain degree. Types of error based on sources

true value

2. Systematic Error: usually from the measuring tool same direction could fix Types of error based on sources

true value Random error and systematic error.

Reliability of Measurements Accuracy refers to the agreement of a particular measurement with the true value. Precision is the degree of agreement among several measurements. Accuracy ≠ Precision

The Results of Several Dart Throws Show the Difference Between Precise and Accurate

No class on Wednesday Lecture tomorrow Meet in classroom IC 420 Section E: 10:00 am Section F: 1:00 pm

How to report a measurement?

mL

We report a measurement by recording ALL the certain digits + ONE uncertain digit Significant Figures (except leading zeros. more details in a minute.) Sig figs carry the information you know about a physical quantity from your measurement.

Rules for counting sig figs 1. Nonzero digits always count. 2. Zeros a) Leading zeros do not count. b) Zeros between nonzero digits always count. c) Zeros at the end count only if the number contains a decimal point. Special case: Exact numbers have infinite number of sig figs. Determined by counting, theory, or conversion.

Or conversions involving prefixes:

Rules for counting sig figs 1. Nonzero digits always count. 2. Zeros a) Leading zeros do not count. b) Zeros between nonzero digits always count. c) Zeros at the end count only if the number contains a decimal point. Special case: Exact numbers have infinite number of sig figs. Determined by counting, theory, or conversion. Examples: questions 77 and 78 on p 40

Note: Scientific expression does not change the number of sig figs. a x 10 n 1 ≤ |a| < 10, n is an integer Only need to count sig figs in “a”

Rules for sig figs in calculations 1.For multiplication and division, the result has the same number of sig figs as the measurement with the fewest sig figs.(e.g. Q 83, practice on Q 84) 2.For addition and subtraction, the result has the same number of decimal places as the measurement with the fewest decimal places. (e.g. Q 85, practice on Q 86) Round properly 3.For calculations including two types, follow the two rules in each step but round off at the end. (e.g. Q 87, practice on Q 88) (made to preserve the information carried by the sig figs)

Or conversions involving prefixes:

Conversion factor #: copy from the relation between two units. = 1

Physical quantity with given unit x Conversion factor = Physical quantity with desired unit 5.0 in = ? cm in = ? cm cm = ? in 6.81 cm 2 = ? in 2 66 km/h = ? m/s in = ? m 3.2 m = ? mm 3.2 cm = ? mm 7.8 g/cm 3 = ? kg/m 3

Three Basic Physical Quantities Volume Density Temperature

1 m = 10 dm = 100 cm (1 m) 3 = (10 dm) 3 = (100 cm) 3 1 m 3 = 10 3 dm 3 = 10 6 cm 3 For liquid or gas, define : 1 L = 1 dm 3 Then: 1 mL = 1 cm 3 Volume and its units How much room an object occupies in space.

Density: mass of a substance per unit volume of the substance. Unit: kg/m 3, g/cm 3, g/mL Density is a property of substances. It is determined by the substance’s identity and external conditions, not by the substance’s mass or volume.

A metal has a mass of 35.5 g and volume 4.55 cm 3. a) What is the density of this metal? b) What is the volume of the same kind of metal with mass 101 g? c) What is this metal likely to be?

How to find density? How to find mass?balance

How to find volume? Liquid: graduated cylinder, beaker, buret, pipet… Solid Regular shape: Measure dimensions, then calculate Irregular shape: water displacement First lab, Experiment 2 Gas: Chapter 5 Second lab, Experiment 3

Temperature scales T C, Celsius scale, °C T F, Fahrenheit scale, °F T K, Kelvin scale, K (not °K) Temperature: a measure of hotness or coldness of an object.

Temperature conversions Normal body temperature is 98.6 °F. Convert this temperature to the Celsius and Kelvin scales.

Problem Set 1