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CHEM 1127Q (29)
Chapter 1-2

CHEM 1127Q Chapter 1-2: Pre-lecture 1: Sections 1.5-1.6, 2.1-2.3

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CHEM 1127Q
Joseph De Pasquale

1.5 Measurement Uncertainty, Accuracy, and Precision ● Exact number - number derived by counting or by definition Significant Figures in Measurement ● Read at the bottom of the meniscus in the graduated cylinder ● Uncertainty - estimate of amount by which measurements differs from the true value Significant Figures/digits ● Leading zeros are not significant ● Digits 1-9 are always significant ● Addition/subtraction of numbers - add/subtract then round to the same number of decimal places ● Multiplication/division of numbers - multiply/divide then round to same number of significant figures ● Rouding ○ # > 5 round up ○ # < 5 round down ○ # = 5 ■ Round so that the digit is an even number Accuracy and Precision ● Accuracy - a measurement is considered accurate if it yields a result that is very close to the accepted value, accurate values agree with a true value ● Precision - Measurements are said to be precise if they yield very similar results when repeated in the same manner 1.6 Mathematical Treatment of Measurement Results ● Dimensional analysis - the units of quantities must be subjected to the same mathematical operations as their associated numbers ● Unit conversion factor - ratio of two equivalent quantities expressed with different measurement units Conversion of Temperature Units ● T°F = 9/5 × T°C + 32 ● T°C = 5/9 (T°F − 32) ● TK = T°C + 273.15 ● T°C = TK − 273.15 Chapter 2: Atoms, Molecules, and Ions 2.1 Early Ideas in Atomic Theory ● Greek beliefs ○ Atomos ■ Means “invisible” ■ Moving particles that differ in shapes and sizes and could join together that made everything in the universe ○ Four elements - fire, earth, air, water ● Dalton’s atomic theory ● He actually tested his theories and did experiments 1. Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change. 2. An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element. A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties. 3. Atoms of one element differ in properties from atoms of all other elements. 4. A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the numbers of atoms of each of its elements are always present in the same ratio. 5. Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change. ● Law of definite proportions/constant composition - all samples of a pure compound contain the same element in the same proportion by mass ● Law of multiple proportions - when two elements react to form more than one compound, a fixed mass of one ele
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