Percent by Mass & Determining Chemical Formulas

What is the percent by mass of Oxygen in water? H₂O.

• 33 %

• 88.9%

• 11.1%

• 50%

What is the percent by mass of Carbon in sugar C₁₂H₂₂O₁₁ ?

• 144.0

• 42.1

• 12.01

• 342.0

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NGSS.HS-PS1-7

What is the percent by mass of Hydrogen in sugar C₁₂H₂₂O₁₁?

• 42.1

• 22.0

• 342.0

• 6.43

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NGSS.HS-PS1-7

What would the percent by mass be of Oxygen in a compound that has a formula of C₁₀H₁₈O ?

• 154.0

• 77.9

• 10.4

• 11.7

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NGSS.HS-PS1-7

The formula of a compound having the smallest whole-number ratio of atoms in the compound is called ____?

• Chemical Formula

• Empirical Formula

• Mass formula

• Ideal formula

What is the empirical Formula of an unknown compound that is 18.8% sodium, 29.0% chlorine and 52.2% Oxygen?

Hint *(Don't forget to assume a 100 gram sample)

• NaClO

• Na₂Cl₂O₃

• NaClO₄

• NaClO₃

What is the empirical formula for a compound that is 40% Carbon, 6.70% Hydrogen and 53.3% oxygen?

Hint*(remember to assume 100 g sample)

• CHO

• CH₂O

• CH₃O

• CH₂O₂

Indigo the dye used to color blue jeans is prepared using sodium amide. Sodium amid contains the following percentages by mass of the following elements: 5.17% Hydrogen, 35.9% Nitrogen and 58.9% sodium. What is the empirical formula for Sodium amide?

• NaNH

• Na₂NH

• NaNH₂

• NaN₂H₂

The reaction of iron III oxide and aluminum is called the thermite reaction because of intense heat and is used to weld railroad tracks. Below is the balanced equation:

Fe₂O₃ (s) + 2Al (s) --> Al₂O₃ (s) + 2Fe (l)

If 20.0g of each reactant are used, which is the limiting reactant? (runs out first)

Hint(Do molar mass calculation to Fe for Theoretical Yield for both and compare the two.

• Al is limiting

• Fe₂O₃ is limiting

• Both are equal

• Neither is limiting

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NGSS.HS-PS1-7

A manufacturer advertises a new synthesis reaction for methane with a percent yield of 110%. Comment on this claim.

• That is an awesome return as most can not even get 100%

• It is false because you can not get more than 100% it must have contaminants in the product.

• It could be possible if they did not loose any product in the process

• It is unlikely because in the process product is often lost along the way making hitting 110% difficult but not impossible.

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NGSS.HS-PS1-7