empirical and molecular
TRANSCRIPT
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Chapter EightChapter Eight
Part II
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Obtain one piece of gum, and find its mass in the wrapper.
Keep the wrapper for later and start chewing. We are experimenting.
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Percents
If you have 7 green cars, 8 blue cars, and 4 red cars, what percentage is green?
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Percents
% = part
wholex 100
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Percents
The mass of a mini Hershey Bar is 6.5 grams and the mass of a mini Mr. Goodbar is 8.3 grams. If you have a basket with 5 Hershey bars and 3 Mr. Goodbars, what is the percent BY MASS of each?
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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
What is the percent by mass of each element in FeSO4?
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Percentage Composition
What is the percent by mass of each element in Mg3(PO4)2?
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Percentage Composition
What is the percent by mass of carbon in sucrose, C12H22O11?
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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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Review
Find the percent of oxygen in each of the following:
Rb2O
Al(NO3)3
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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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You try
How many grams of oxygen are in 56.0 grams of each of the following:
Rb2O
Al(NO3)3
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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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We Try
Calculate the empirical formula of a compound that is 62.0 % C, 13.9 % H, and 24.1 % N.
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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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You Try
Benzoic Acid is used as a preservative, A 15.0 gram sample contains 10.32 grams of C, 0.743 grams of H, and 3.93 grams of O. Find the empirical formula.
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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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Molecular Formula
Example:C2H6 is ethane. What is
ethane’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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The Math
What is the same compound’s molecular formula if its molar mass = 90.18 g/mol?
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Molecular formula
What is the molecular formula of dichloroacetic acid, if the empirical formula is CHOCl, and its molar mass is 129 g/mol.
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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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Molecular formula
Find its empirical and molecular formulae, if a compound contains 40.0 % carbon, 6.73 % hydrogen, and 53.3 % oxygen with a mass of 240 g/mol.
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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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Hydrates
Example:Li2SO4 * 2 H2O
This formula tells you that 1 mole of lithium sulfate is bonded to 2 moles of water.
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Hydrates
Example:MgCO3 * 7 H2O
This formula tells you that 1 mole of magnesium carbonate is bonded to 7 moles of water.
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Hydrates
Example:MgSO3 * 6 H2O
This formula tells you that 1 mole of magnesium sulfite is bonded to 6 moles of water.
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Hydrates
Notice the mole ratio is shown as a coefficient and the compound gets the 1.
General form: any compound * __ H2O
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We try
0.391 grams of Li2SiF6 is found to contain 0.0903 grams of water.
Find the formula for the hydrate
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We try
A compound is analyzed and found to contain 86.7 % Mo2S5 and 13.3 % water.
Find the formula for the hydrate
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You try
A particular hydrate contains 89.2 % BaBr2.
Find the formula for the hydrate.
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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?