Q: Which of the following best describes a mole?

A mole is a specific number of particles, equal to $$6.022 \times 10$$^{23}$$.

Q: Which of the following is the correct formula for calculating the number of moles from mass and molar mass?

$$\text{Number of moles} = \dfrac{\text{mass}}{M_r}$$

Q: Which of the following is the correct equation for calculating the final concentration after dilution?

$$V_1$$ \times $$C_1$$ = $$V_2$$ \times $$C_2$$

Q: Which of the following is a correct expression for molarity (M)?

$$M = \dfrac{\text{number of moles}}{\text{volume (l)}}$$

Question 1

Which statement best describes the Law of Conservation of Mass as it applies to chemical equations?

Accepted Answer

The total mass of the products must be equal to the total mass of the reactants.

Question 2

What is the balanced chemical equation for the reaction between aluminum and oxygen?

Accepted Answer

$$4Al + 3O_2 \rightarrow 2Al_2O_3$$

Question 3

A solution is prepared by dissolving 20 g of NaOH (molar mass = 40 g/mol) in 500 ml of water. What is the molar concentration of NaOH in the solution?

Accepted Answer

$$1\,M$$

Question 4

How many moles are present in 0.09 g of water? (Relative molecular mass of water = 18)

Accepted Answer

$$0.005$$ mol

Question 5

Which of the following best describes a mole?

Accepted Answer

A mole is a specific number of particles, equal to $$6.022 	imes 10$$^{23}$$.

Question 6

A 1M NaCl solution contains 58.5 g of NaCl in 1 liter. What is the percentage concentration (% m/v) of this solution?

Accepted Answer

$$5.85\%$$

Question 7

If 1.2 g of carbon reacts completely with oxygen to form carbon dioxide, what mass of $$O_2 is $$required? ($$M_r of$$ $$O_2 = 32$; M_r$ of C = 12)

Accepted Answer

$$3.2 g$$

Question 8

Which of the following is the correct formula for calculating the number of moles from mass and molar mass?

Accepted Answer

$$	ext{Number of moles} = \dfrac{	ext{mass}}{M_r}$$

Question 9

A scientist needs to prepare 50 ml of a 10 mM solution from a 1 M stock solution. What volume of the stock solution should be used?

Accepted Answer

$$0.5 ml$$

Question 10

Which of the following best describes Le Chatelier's Principle?

Accepted Answer

If a dynamic equilibrium is disturbed, the system will move to partially reverse the change.

Question 11

What is the molar concentration of a solution containing 2 g of $$NaH_2PO_4$$ ($$M_r = 120) in 1 $$liter?

Accepted Answer

$$0.0167 M$$

Question 12

A normal saline solution used in medicine is closest to which concentration of NaCl?

Accepted Answer

$$0.9\% w/v$

Question 13

Which of the following is the correct equation for calculating the final concentration after dilution?

Accepted Answer

$$V_1$$ 	imes $$C_1$$ = $$V_2$$ 	imes $$C_2$$

Question 14

A serial dilution is performed by adding 1 ml of sample to 9 ml of diluent in each tube. What is the total dilution factor after two tubes?

Accepted Answer

$$10^2$$

Question 15

Which of the following is NOT a correct definition?

Accepted Answer

Solute: The component of a solution present in the greatest amount.

Question 16

How much NaOH is required to make 10 ml of a 1M solution? ($$M_r of $$NaOH = 40)

Accepted Answer

$$0.4 g$$

Question 17

Which of the following is a correct expression for molarity (M)?

Accepted Answer

$$M = \dfrac{	ext{number of moles}}{	ext{volume (l)}}$$

Question 18

Which of the following is a real-world application of serial dilution?

Accepted Answer

Estimating the number of colonies in a microbiology sample.

Question 19

A solution contains 3 g of NaCl in 100 ml. What is the % mass/volume (% m/v) concentration?

Accepted Answer

$$3\%$$

Question 20

Which SI prefix corresponds to $$10^{-6}$$?

Accepted Answer

Micro

Chemical Calculations: Moles, Molarity, and Dilutions

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