CR Chapter 9 Mole & Stoich Test Review

How many Carbon atoms are in one mole of Carbon?

• 6.022 x 10²³

• 1

• 12.01

• not enough information

Answer explanation

One mole of Carbon contains Avogadro's number of atoms, which is 6.022 x 10^23. Therefore, there are 6.022 x 10^23 Carbon atoms in one mole of Carbon.

How many water molecules are in 5.2 moles of water?

• 94

• 5.2

• 3.1 x 10²⁴

• 8.6 x 10^-24

Answer explanation

5.2 moles of water contain 3.1 x 10²⁴ water molecules, calculated by multiplying Avogadro's number (6.022 x 10²³) by the number of moles.

What is the molar mass of aluminum nitrate?

• 40.99 g/mol

• 213.01 g/mol

• 88.99 g/mol

• 184.99 g/mol

Answer explanation

The molar mass of aluminum nitrate Al(NO₃)₃ is calculated by adding the atomic masses of aluminum and three nitrogen and nine oxygen, resulting in a molar mass of 213.01 g/mol.

Don't forget to balance charges Al is +3 and (NO₃) is -1 so you need three (NO₃) to balance with aluminum.

How many moles are in 16.94g of water?

• 16.94

• 0.9403

• 305.2

• 1.063

Answer explanation

To find the number of moles, divide the given mass of water by its molar mass (18.02 g/mol). 16.94g x (1 mol / 18.02 g) = 0.9403 mol. Therefore, there are 0.9403 moles in 16.94g of water.

Which of the following dimensional analysis setups will correctly convert 27.76g of Li to atoms of Li?

• A

• B

• C

• D

Answer explanation

Choice D is correct because it correctly converts grams to atoms using Avogadro's number and the molar mass of Li and shows the given unit being cancelled.

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

• 28 grams

• 24 grams

• 6.02 grams

• 1.2 grams

Answer explanation

To calculate the grams in 1.2 x 10²⁴ atoms of C, we use the molar mass of carbon (12.01 g/mol). 1.2 x 10²⁴ atoms x (1 mol / 6.022 x 10²³ atoms) x (12.01 g/1 mol) = 24 grams.

How many grams are in 3.33 mol of potassium sulfide?

• 367 g

• 454 g

• 238 g

• 132 g

Answer explanation

Balance K's +1 charge with S's -2 charge, two K's are needed for every 1 sulfur: K₂S

Find the molar mass of K₂S by adding K's atomic mass x 2 and sulfur to get 110.26 g/mol.

3.33 mol x ( 110.26 g / 1 mol) = 367 g.

Which has more molecules?

• 1 mole H₂O

• 1 mole CH₄

• 1 mole Cl₂

• They're are all the same.

Answer explanation

All choices represent 1 mole of each substance, which contains Avogadro's number of molecules (6.022 x 10^23). Therefore, they all have the same number of molecules.

How many molecules are in 32.4 grams of phosphorus pentoxide?

• 1.76 x 10²³ molecules

• 0.29 moles

• 1.76 x 10²² molecules

• 0.29 molecules

Answer explanation

32.4 grams of phosphorus pentoxide is equivalent to 1.76 x 10²³ molecules based on Avogadro's number and the molar mass of phosphorus pentoxide.

32.4 g x ( 1 mol / 110.97 g) x (6.022x10²³ molecules / 1 mol) = 1.76 x 10²³ molecules

Determine the mass of calcium hydroxide produced from 0.64 g of water.

__CaC₂ + __H₂O → __Ca(OH)₂ + __C₂H₂

• 10 g Ca(OH)₂

• 41 g Ca(OH)₂

• 1.3 g Ca(OH)₂

• 31 g Ca(OH)₂

Answer explanation

Using stoichiometry,

0.64 g H₂O x (1 mol H₂O / 18.02 g H₂O) x (1 mol Ca(OH)₂/ 2 mol H₂O) x (74.1 g Ca(OH)₂/ 1 molCa(OH)₂) = 1.3 g of Ca(OH)₂.

The first & third conversion are molar masses from periodic table.

The second step is mole ratio from the balanced chemical equation.