Q: How many molecules are present in 2.50 moles of water ($H_2O$)?

$1.51 \times 10^{24}$ molecules

Q: Which of the following is the correct formula to determine the molecular formula from the empirical formula?

$\text{Molecular formula} = n \times (\text{Empirical formula})$

Question 1

Which statement best describes a mole in chemistry?

Accepted Answer

A mole is the amount of a substance that contains exactly $6.022 	imes 10^{23}$ particles.

Question 2

How many molecules are present in 2.50 moles of water ($H_2O$)?

Accepted Answer

$1.51 	imes 10^{24}$ molecules

Question 3

A sample contains $1.20 	imes 10^{24}$ formula units of NaCl. How many moles of NaCl does this sample contain?

Accepted Answer

$0.199$ moles

Question 4

What is the molar mass of $Ca(NO_3)_2$?

Accepted Answer

$164.10$ g/mol

Question 5

If you have 6.25 g of sodium (Na), how many moles of sodium atoms do you have? (Atomic mass of Na = 22.99 g/mol)

Accepted Answer

$0.272$ moles

Question 6

A compound has the empirical formula $CH_2O$ and a molar mass of $180.16$ g/mol. What is its molecular formula?

Accepted Answer

$C_6H_{12}O_6$

Question 7

Calculate the percent composition by mass of oxygen in $H_2O$ (Molar mass $= 18.02$ g/mol).

Accepted Answer

$55.49\%$

Question 8

A laboratory analysis of a compound yields $30.4\%$ nitrogen and $69.6\%$ oxygen by mass. If the molar mass is $92.0$ g/mol, what is the molecular formula?

Accepted Answer

$N_2O_4$

Question 9

How many atoms are present in $105$ g of carbon? (Atomic mass of C = $12.01$ g/mol)

Accepted Answer

$5.26 	imes 10^{24}$ atoms

Question 10

Which of the following best explains why the mole concept is useful in chemistry?

Accepted Answer

It allows chemists to count large numbers of particles by weighing.

Question 11

You need $0.713$ moles of cobalt for an experiment. What mass of cobalt should you weigh out? (Atomic mass of Co = $58.93$ g/mol)

Accepted Answer

$42.03$ g

Question 12

Which of the following is the correct sequence of steps to determine the empirical formula from percent composition?

Accepted Answer

Convert percent to grams, convert grams to moles, divide by smallest number of moles, multiply to get whole numbers, write formula.

Question 13

A sample contains $8.40 	imes 10^{24}$ molecules of $CH_3OH$. How many moles of $CH_3OH$ are present?

Accepted Answer

$13.9$ moles

Question 14

What is the mass in grams of $1.95$ moles of sodium sulfate ($Na_2SO_4$, molar mass $= 142.04$ g/mol)?

Accepted Answer

$277.98$ g

Question 15

Which of the following is NOT a correct use of Avogadro’s number?

Accepted Answer

To measure the mass of a substance directly.

Question 16

A compound contains $7.00$ g nitrogen and $16.0$ g oxygen. What is the empirical formula of the compound?

Accepted Answer

$N_2O$

Question 17

Which of the following best describes the relationship between atomic mass and molar mass?

Accepted Answer

Atomic mass in amu is numerically equal to molar mass in g/mol.

Question 18

If you have $9.00$ moles of NaCl, what is the mass in grams needed? (Molar mass of NaCl = $58.44$ g/mol)

Accepted Answer

$526$ g

Question 19

Which of the following is the correct formula to determine the molecular formula from the empirical formula?

Accepted Answer

$	ext{Molecular formula} = n 	imes (	ext{Empirical formula})$

Question 20

A student weighs out $3.16$ lbs of nails, knowing that $316$ nails weigh $1$ lb. Approximately how many nails does the student have?

Accepted Answer

$999$ nails

Chemical Quantities and the Mole: Chapter 7 Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards