Q: How many molecules are present in $0.50$ moles of $\mathrm{H}_2\mathrm{O}$? ($N_A = 6.022 \times 10^{23}$ molecules/mol)

$3.01 \times 10^{23}$ molecules

Question 1

Which of the following correctly defines the term 'molar mass'?

Accepted Answer

The mass of one mole of a substance, expressed in grams per mole ($\mathrm{g/mol}$).

Question 2

Given the atomic masses: C = $12.01\ \mathrm{g/mol}$, H = $1.008\ \mathrm{g/mol}$, N = $14.01\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$, what is the molar mass of caffeine ($\mathrm{C}_8\mathrm{H}_{10}\mathrm{N}_4\mathrm{O}_2$)?

Accepted Answer

$210.14\ \mathrm{g/mol}$

Question 3

A sample contains $3.50$ moles of $\mathrm{N}_2$. What is the mass of this sample? (N = $14.01\ \mathrm{g/mol}$)

Accepted Answer

$98.07\ \mathrm{g}$

Question 4

How many moles of hydrogen atoms are present in $0.20$ moles of $\mathrm{C}_7\mathrm{H}_8\mathrm{N}_2\mathrm{O}$?

Question 5

If you have $16$ grams of $\mathrm{NaOH}$ (Na = $22.99\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$, H = $1.008\ \mathrm{g/mol}$), how many moles of $\mathrm{NaOH}$ do you have?

Question 6

Which of the following best describes the difference between a molecular formula and an empirical formula?

Accepted Answer

The molecular formula shows the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest whole-number ratio of the elements.

Question 7

A compound contains $40.0\%$ carbon, $6.7\%$ hydrogen, and $53.3\%$ oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$\mathrm{CH}_2\mathrm{O}$

Question 8

How many molecules are present in $0.50$ moles of $\mathrm{H}_2\mathrm{O}$? ($N_A = 6.022 	imes 10^{23}$ molecules/mol)

Accepted Answer

$3.01 	imes 10^{23}$ molecules

Question 9

A patient receives $0.25$ moles of $\mathrm{NaCl}$ intravenously. What is the mass of $\mathrm{NaCl}$ administered? (Na = $22.99\ \mathrm{g/mol}$, Cl = $35.45\ \mathrm{g/mol}$)

Question 10

Which of the following statements about formula mass is correct?

Accepted Answer

Formula mass is the sum of the atomic masses of all atoms in a chemical formula.

Question 11

A chemist needs $0.75$ moles of $\mathrm{KBr}$ for a reaction. What mass of $\mathrm{KBr}$ should be weighed out? (K = $39.10\ \mathrm{g/mol}$, Br = $79.90\ \mathrm{g/mol}$)

Question 12

How many moles of oxygen atoms are present in $2.00$ moles of $\mathrm{H}_2\mathrm{SO}_4$?

Accepted Answer

$8.00$ moles

Question 13

A student dissolves $5.00$ grams of $\mathrm{NaCl}$ in water. How many moles of $\mathrm{NaCl}$ is this? (Na = $22.99\ \mathrm{g/mol}$, Cl = $35.45\ \mathrm{g/mol}$)

Accepted Answer

$0.086$ moles

Question 14

Which of the following is the correct formula for a compound containing barium and chloride ions?

Accepted Answer

$\mathrm{BaCl}_2$

Question 15

A medication contains $0.10$ moles of $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$. How many grams of glucose does this represent? (C = $12.01\ \mathrm{g/mol}$, H = $1.008\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$)

Question 16

Which of the following best explains why ionic compounds are represented by formula units rather than molecular formulas?

Accepted Answer

Ionic compounds do not exist as discrete molecules, but as extended lattices.

Question 17

A sample of $\mathrm{CaCO}_3$ contains $0.50$ moles. What is the mass of the sample? (Ca = $40.08\ \mathrm{g/mol}$, C = $12.01\ \mathrm{g/mol}$, O = $16.00\ \mathrm{g/mol}$)

Accepted Answer

$50.05$ g

Question 18

How many moles of hydrogen atoms are present in $1.00$ mole of $\mathrm{C}_2\mathrm{H}_6$?

Accepted Answer

$6.00$ moles

Question 19

A chemist has $0.25$ moles of $\mathrm{Al}_2\mathrm{O}_3$. How many moles of aluminum atoms are present?

Accepted Answer

$0.50$ moles

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