Unit 6 Re-assessment Assignment

What percentage of the total atomic mass of carbon monoxide (CO) is composed of carbon?

• 29%

• 43%

• 57%

• 73%

Answer explanation

43% of the total atomic mass of carbon monoxide is composed of carbon, making it the correct choice.

What is the molar mass of NaOH?

• 40 g/mol

• 38.989 g/mol

• 23.998 g/mol

• 57.004 g/mol

Answer explanation

The molar mass of NaOH is calculated by adding the atomic masses of sodium (Na), oxygen (O), and hydrogen (H), which gives a total of 40 g/mol. Therefore, the correct answer is 40 g/mol.

In which compound is the percent composition by mass of Cl equal to 42%?

• HClO (gram formula mass = 52 g/mol)

• HClO₂ (gram formula mass = 68 g/mol)

• HClO₃ (gram formula mass = 84 g/mol)

• HClO₄ (gram formula mass = 100 g/mol)

Answer explanation

The compound with a percent composition by mass of Cl equal to 42% is HClO3, with a gram formula mass of 84 g/mol.

Find the percent composition of Cu₂S?

• %Cu= 67.987 %S= 32.013

• %Cu= 79.854   %S= 20.145

• %Cu= 35.946   %S= 64.054

Answer explanation

The correct choice is %Cu= 79.854 %S= 20.145 as it represents the percent composition of Cu2S.

• Total Molar Mass of Element in Compound

• Total Molar Mass of Compound

• Molar Mass of a Single Element

• 100

Answer explanation

To calculate the percent composition by mass of an element in a compound, you divide the total molar mass of the element in the compound by the total molar mass of the compound and then multiply by 100.

How many grams are in 1.2 x 10²⁴ atoms of C?

• 29.34 grams

• 23.94 grams

• 6.02 grams

• 1.21 grams

Answer explanation

To calculate the grams in 1.2 x 10^24 atoms of C, use the molar mass of carbon (12.01 g/mol) and Avogadro's number. 1.2 x 10^24 atoms x (12.01 g/mol / 6.022 x 10^23 atoms) = 23.94 grams.

How many moles are in 3.01 x 10²² atoms of magnesium?

• 0.05 moles

• 1.81 x 10⁴⁶ moles

• 5.00 x 10²¹ moles

• 5.00 moles

Answer explanation

To find the number of moles, divide the number of atoms by Avogadro's number (6.022 x 10^23). 3.01 x 10^22 / 6.022 x 10^23 = 0.05 moles, so the correct answer is 0.05 moles.

How many moles are in 19.82 g Mg?

• 1.23 mol Mg

• 481.70 mol Mg

• 1.00 mol Mg

• 0.82 mol Mg

Answer explanation

To find the number of moles, divide the given mass by the molar mass of Mg (24.305 g/mol). 19.82 g / 24.305 g/mol = 0.82 mol Mg.

The mass of 1 mole is known as

• A mole

• Molar mass

• Percent Composition

• Grams

Answer explanation

The mass of 1 mole is known as Molar mass.

If a dozen = 12, how much does a mole equal?

• 18 g

• 184 g

Answer explanation

A mole is equivalent to Avogadro's number, which is approximately 6.02x10^23. Therefore, the correct answer is 6.02x10^23.