chapter2 - Chapter 1 highlights Scientific method, theory...

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1 Chapter 1 highlights z Scientific method, theory vs law z Significant figures, dimensional analysis z Precision accuracy relative range %erro Precision, accuracy, relative range, %error z Lots of definitions: Homogeneous, heterogenious, elements, compounds, mixtures,…. . Chapter 2 Atoms, Molecules and Ions…. And lots of moles Dalton’s Atomic Theory 1. All matter consists of atoms. 2. Atoms of one element cannot be converted into atoms of another element. The Postulates 3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element. 4. Compounds result from the chemical combination of a specific ratio of atoms of different elements. Dalton’s Atomic Theory explains the mass laws Mass conservation Atoms cannot be created or destroyed or converted into other types of atoms. postulate 1 postulate 2 Since every atom has a fixed mass, during a chemical reaction atoms are combined differently and therefore there is no mass change overall. postulate 3 Dalton’s Atomic Theory explains the mass laws Definite composition Atoms are combined in compounds in specific ratios and each atom has a specific mass. postulate 3 postulate 4 So each element has a fixed fraction of the total mass in a compound. Dalton’s Atomic Theory explains the mass laws Multiple proportions Atoms of an element have the same mass and atoms are indivisible. postulate 3 postulate 1 So when different numbers of atoms of elements combine, they must do so in ratios of small, whole numbers.
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2 The total mass of substances does not change during a chemical reaction. reactant 1 + reactant 2 product Law of Mass Conservation: total mass total mass = calcium oxide + carbon dioxide calcium carbonate CaO + CO 2 CaCO 3 56.08g + 44.00g 100.08g Figure 2.2 The law of mass conservation: mass remains constant during a chemical reaction. No matter the source, a particular compound is composed of the same elements in the same parts (fractions) by mass. Calcium carbonate Law of Definite (or Constant) Composition: Figure 2.3 Analysis by Mass (grams/20.0g) Mass Fraction (parts/1.00 part) Percent by Mass (parts/100 parts) 8.0 g calcium 2.4 g carbon 9.6 g oxygen 20.0 g 40% calcium 12% carbon 48% oxygen 100% by mass 0.40 calcium 0.12 carbon 0.48 oxygen 1.00 part by mass Sample Problem 2.1 Calculating the Mass of an Element in a Compound PROBLEM: Pitchblende is the most commercially important compound of uranium. Analysis shows that 84.2 g of pitchblende contains 71.4 g of uranium, with oxygen as the only other element. How many grams of uranium can be obtained from 102 kg of pitchblende? PLAN: The mass ratio of uranium/pitchblende is the same no matter the source. We can use the ratio to find the answer. mass(kg) of pitchblende SOLUTION: mass(kg) of uranium mass(g) of uranium = 86.5 kg uranium = 102 kg pitchblende x mass(kg) pitchblende x mass(kg) uranium in pitchblende mass(kg) pitchblende 71.4kg uranium 84.2kg pitchblende mass (kg) of uranium = 86.5 kg uranium x 1000g kg = 8.65 x 10 4 g uranium If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers.
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This note was uploaded on 03/18/2010 for the course CHEM 210 taught by Professor Mcomber during the Spring '10 term at Skyline College.

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chapter2 - Chapter 1 highlights Scientific method, theory...

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