Molecular formula

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Empirical and Empirical and Molecular Molecular Formula and Formula and Percentage Percentage Composition Composition Stoichiometry Math of Chemistry

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Transcript of Molecular formula

Page 1: Molecular formula

Empirical and Empirical and Molecular Formula Molecular Formula

and Percentage and Percentage CompositionComposition

Stoichiometry Math of

Chemistry

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Percents

% = part

wholex 100

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Percentage Composition

Percent Composition is finding the percent by mass of each element in a compound using the periodic table.

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Percentage Composition

An 8.20 gram piece of magnesium combines with 5.40 grams of oxygen to form a compound.

What is the percent composition of this compound?

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Percentage Composition

How many grams of Ca are in 64.3 grams CaCl2?

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You Try

How many grams of Oxygen are in 19.2 grams Na3PO4?

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Finding a ratio

If a school has 30 boys and 60 girls, what is the ratio of boys to girls?

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Finding a whole number ratio in its lowest terms

If a school has 27 boys and 18 girls, what is the ratio of boys to girls?

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Finding a whole number ratio in its lowest terms

If a school has 75 boys and 60 girls, what is the ratio of boys to girls?

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Finding a whole number ratio in its lowest terms

A certain compound contains 4.14 moles of Mg and 2.76 moles of P.

Find the mole ratio between Mg and P.

Write the formula.

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Empirical Formula

An Empirical formula gives the lowest whole number MOLE ratio between the atoms in a compound.

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The Math

A compound contains 0.900 grams of calcium and 1.60 grams of chlorine.

Find its empirical formula.

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The Math

A compound is analyzed and found to consist of 36.0 % aluminum and 64.2 % sulfur.

Find its empirical formula.

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You Try

What is the empirical formula of a compound that is 66.0 % Ca and 34.0 % P?

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Molecular Formula

A Molecular formula gives the actual ratio between the atoms in a compound.

For Ionic compounds, the empirical and molecular formulas are the same.

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Molecular Formula

For molecular compounds, the molecular formula is a multiple of the empirical.

Example:C6H6 is benzene. What is

benzene’s empirical formula?

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The Math

A compound contains 31.10 grams of carbon and 7.872 grams of hydrogen.

Find its empirical formula.

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Molecular formula

Vitamin C is ascorbic acid. It has a percentage composition of 40.9 % carbon, 4.58 % hydrogen, and 54.5 % oxygen with a molecular mass of 176.1 u.

Find its empirical and molecular formulae.

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Review Molecular formula

Aspirin, acetylsalicylic acid, contains 60.0 % carbon, 4.48 % hydrogen, and 35.5 % oxygen with a molecular mass of 180 u.

Find its empirical and molecular formulae.

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Hydrates

Hydrates are compounds with water molecules trapped in their crystal structure.

The water is weakly bonded and can be removed by heating the substance.

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Quiz Review

A particular hydrate of MgSO4 contains 51.14 % water.

Find the formula for the hydrate.

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Quiz Review

Find the percentage of water in the hydrate, Na2CO3 * 10 H2O.

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Quiz Review

Find the percentage of oxygen in P2O5.

How many grams of oxygen are in 25.5 grams of P2O5?