9.5 The Laws Governing Formulas andnkscience.weebly.com/uploads/8/7/1/4/8714635/chapter09_section05_edit.pdfProportions The Laws of Definite and Multiple Proportions What are the two

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chemistry

© Copyright Pearson Prentice Hall

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The Laws Governing Formulas and Names

A birthday cake for a four-year-old has four candles. The ratio of candles to birthday cake is 4:1. In chemistry, similar relationships exist among the masses of elements as they combine in compounds.

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> The Laws of Definite and Multiple Proportions

The Laws of Definite and Multiple Proportions

What are the two laws that describe how compounds form?

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The rules for naming and writing formulas for compounds are possible only because compounds form from the elements in predictable ways.

These ways are summed up in two laws: the law of definite proportions and the law of multiple proportions.


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The Law of Definite Proportions

The law of definite proportions states that in samples of any chemical compound, the masses of the elements are always in the same proportions.


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Water obeys the law of definite proportions. In every sample of water, the mass ratio of oxygen to hydrogen is always 8:1.


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Hydrogen peroxide obeys the law of definite proportions. The mass ratio of oxygen to hydrogen is always 16:1.


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The Law of Multiple Proportions

The law of multiple proportions: Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.


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A Diagram of the Law of Multiple Proportions


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SAMPLE PROBLEM

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SAMPLE PROBLEM

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Practice Problems for Sample Problem 9.1

Problem Solving 9.34 Solve Problem 34 with the help of an interactive guided tutorial.

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Practicing Skills: Naming Chemical Compounds

How do you use a flowchart to write the name of a chemical compound?


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Follow the arrows and answer the questions on the flowchart to write the correct name for a compound.


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> Practicing Skills: Naming Chemical Compounds

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CuSO4 is an example from the flowchart. The compound will end in -ite or -ate. Cu is not part of Group A, so you must name the ions and use a Roman numeral to identify the charge of the transition metal. The name is copper(II) sulfate.


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Practicing Skills: Writing Chemical Formulas

What four guidelines should you follow to write the formula of a chemical compound?

9.4 Practicing Skills: Naming Chemical Compounds

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In writing a chemical formula from a chemical name, it is helpful to remember the following guidelines.

An -ide ending generally indicates a binary compound.

An -ite or -ate ending means a polyatomic ion that includes oxygen is in the formula.


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Prefixes in a name generally indicate that the compound is molecular.

A Roman numeral after the name of a cation shows the ionic charge of the cation.


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> Practicing Skills: Naming Chemical Compounds

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9.5 The Laws Governing Formulas andnkscience.weebly.com/uploads/8/7/1/4/8714635/chapter09_section05_edit.pdfProportions The Laws of Definite and Multiple Proportions What are the two