Deck 5: Moles, Concentrations, and Dilutions: Making Sense of Chemical Numbers

Question 1

You can have a mole of which of the following? Select any that apply.

A) Atoms
B) Ions
C) Molecules
D) Electrons
E) . Protons

Answer 1

A,B,C,D,E

Question 2

Which of the following numbers represents the Avogadro constant?

A) 6* 10²³
B) 1*10²³
C) 6 *10²
D) 23
E) 6²³

Answer 2

6* 10²³

Question 3

Which of the following is the correct mass of one mole of ¹²C?

A) 1 g
B) 12.5 g
C) 6 * 10²³ g
D) 72 g
E) 12 g

Answer 3

12 g

Question 4

The molar mass of a compound has which of the following units?

A) mol
B) g mol^-1
C) G
D) amu
E) mol g^-1

Question 5

Which of the following has the greatest mass, noting that the molar mass of carbon is 12; the molar mass of oxygen is 16; the molar mass of hydrogen is 1; and the molar mass of nitrogen is 15?

A) 10 mol H₂
B) 2 mol CH₄
C) 5 mol H₂O
D) 3 mol NH₃
E) 5 mol O₂

Question 6

How many moles are there in 30 g of C?

A) 360 mol
B) 30 mol
C) 2.5 mol
D) 0.4 mol
E) 12 mol

Question 7

What is the mass of 1.5 mol CH₃OH?

A) 48 g
B) 21.333 g
C) 32 g
D) 0.05 g
E) 1.5 g

Question 8

2 moles of the amino acid glycine have a mass of 152

A) 152 g mol^-1
B) 0.013 g mol^-1
C) 2 g mol^-1
D) 304 g mol^-1
E) 76 g mol^-1

Question 9

How many moles are there in 121.6 g of glycine?

A) 1.6 mol
B) 0.625 mol
C) 121.6 mol
D) 8.76* 10³ mol
E) 76 mol

Question 10

Which of the following two quantities are identical?

A) 1 dm³
B) 1 m³
C) 1 L
D) 100 mL
E) 1 cm³

Question 11

The concentration of a substance is defined as the number of moles in what volume?

A) 1 mL
B) 1 cm³
C) 1 L
D) 1 m³
E) 1 $\mu$ L

Question 12

What amount of hydrogen chloride is present in 500 mL of a solution with a concentration of 0.5 mol L^-1?

A) 0.5 mol
B) 250 mol
C) 1000 mol
D) 0.001 mol
E) 0.25 mol

Question 13

How many moles are present in 10 mL of a sodium chloride (salt) solution, with a concentration of 2 mol L^-1?

A) 0.02 mol
B) 20 mol
C) 0.2 mol
D) 5 mol
E) 0.1 mol

Question 14

What is the concentration of 100 mL of a solution containing 2.5 moles of glucose?

A) 40 mol L^-1
B) 0.025 mol L^-1
C) 25 mol L^-1
D) 250 mol L^-1
E) 0.25 mol L^-1

Question 15

How many moles of NaOH do we need to prepare 250 mL of a 2M solution?

A) 0.5 mol
B) 500 mol
C) 0.008 mol
D) 8 mol
E) 2 mol

Question 16

How many moles of NH₃ do we need to prepare 100 mL of a 0.5M solution?

A) 0.5 mol
B) 0.2 mol
C) 200 mol
D) 0.05 mol
E) 50 mol

Question 17

We have 100 mL of a solution of NaCl with a concentration of 0.5 mol L^-1 and want to dilute it to a concentration of 0.1 mol L^-1. How much water would we need to add to achieve this?

A) 0.5 L
B) 0.4 L
C) 500 L
D) 0.005 L
E) 0.1 L

Question 18

A sample of a solution with concentration of 0.005 mol L^-1 has a molar absorptivity of 150 L mol^-1 cm^-1 at 350 nm. What absorbance will be measured by a UV-visible spectrophotometer when the sample is measured in a cuvette with a path length of 1 cm at 350 nm?

A) 3.3 *10^-3
B) 0.75
C) 30 000
D) 75
E) 0.075

Question 19

A substance, X, has a molar absorptivity of 1250 L mol^-1 cm^-1 at 325 nm. A sample of X gives an absorbance of 0.8 when measured in a UV-visible spectrophotometer at 325 nm with a path length of 1 cm. What is the concentration of the sample of X?

A) 1000 mol L^-1
B) 1 mol L^-1
C) 1563 mol L^-1
D) 6.4*10^-4 mol L^-1
E) 1.56 mol L^-1

Question 20

Two compounds, A and B, react with the stoichiometry 1:3, i.e. A + 3B. If there are 0.1 moles of A present in a sample initially, how many moles of B must be added for A to be completely consumed?

A) 0.1 mol
B) 0.3 mol
C) 0.0333 mol
D) 3 mol
E) 1 mol

Question 21

A solution containing red blood cells at a concentration of 2000 cells per mL undergoes three serial dilution steps, whereby 1 mL of starting solution is diluted with 9 mL of solvent at each step. What is the concentration of red blood cells after the final dilution step?

A) 666 cells mL^-1
B) 2.47 cells mL^-1
C) 2 cells mL^-1
D) 20 cells mL^-1
E) 74.1 cells mL^-1

Question 22

25 mL of a growth medium containing bacteria at a concentration of 3 * 10⁵ cells per litre is diluted to a volume of 0.05 L. What is the concentration of bacteria after dilution?

A) 1.5 * 10⁶ cells L^-1
B) 1.75 * 10⁸ cells L^-1
C) 6.7 * 10^-6 cells L^-1
D) 6 * 10⁵ cells L^-1
E) 1.5* 10⁵ cells L^-1