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CHAPTER 10 Chemical Quantities

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Before We Begin… We need to review some scientific notation.scientific notation Scientific notation is a way of writing very large and very small numbers.

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How to Write Numbers in Scientific Notation Always written as a coefficient multiplied by 10 raised to a power. 3.5 x 10 34 coefficientpower

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How to Multiply in Scientific Notation To multiply numbers written in scientific notation you multiply the coefficients and add the powers. (2.35x10 14 ) x (3.25x10 -23 ) MultiplyAdd Answer = 7.64x10 -9

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How to Divide in Scientific Notation To divide numbers written in scientific notation you divide the coefficients and subtract the powers. (2.35x10 14 ) ÷ (3.25x10 -23 ) DivideSubtract Answer =7.2x10 36

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The Mole: A Measurement of Matter Section 1

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Measuring Matter You often measure the amount of something by one of three different methods – by count, by mass, and by volume.

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What Is a Mole? Mole (mol) – 6.02x10 23 representative particles of that substance (SI unit for measuring the amount of something). Avogadro’s number - 6.02x10 23 named after Amadeo Avogadro di Quarenga (1776-1856) A mole of any substance contains Avogadro’s number of representative particles, or 6.02x10 23 representative particles.

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The Mass of a Mole of an Element The atomic mass of an element expressed in grams is the mass of a mole of the element. Molar mass – the mass of a mole of an element. Find the element on the periodic table and the mass that’s listed is the mass of one mole.

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The Mass of a Mole of a Compound To calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound.

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How Big is a Mole How Big is a Mole

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Mole-Mass and Mole-Volume Relationships Section 2

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The Mole-Mass Relationship Use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance.

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The Mole-Volume Relationship Avogadro’s hypothesis – states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

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Standard temperature and pressure (STP) – means a temperature of 0°C and a pressure of 101.3kPa or 1 atmosphere (atm).

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At STP, 1 mole or 6.02x10 23 representative particles, of any gas occupies a volume of 22.4L Molar volume – the 22.4L of a gas.

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Percent Composition and Chemical Formulas Section 3

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The Percent Composition of a Compound Percent composition – the percent by mass of each element in the compound. The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%

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Percent Composition from Mass Data Can calculate by thinking part over a whole times 100%

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Percent Composition as a Conversion Factor Once you know the percent composition you can say that in a 100g sample you have that percent in grams of that element.

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Example: Propane is 81.8% carbon so in a 100g sample you have how many grams of carbon that you can use this as a conversion factor?

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Empirical Formulas Empirical formula – lowest whole-number ratio of the atoms of the elements in a compound.

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For example HO is an empirical formula for H 2 O 2 (peroxide). Using percent compositions you can determine empirical formulas.

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Molecular Formulas The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula.

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