Q: Calculate the mass of CuSO4 . 5H2O required to prepare 20 mL of a 1 M solution. (Molar mass = 250 g/mol)

$$\frac{1\ \text{mol}}{1\ \text{L}} \times 0.020\ \text{L} \times 250\ \frac{\text{g}}{\text{mol}} = 5\ \text{g}$$

Q: A student prepares a 0.5 M solution of CuSO4 . 5H2O in 100 mL of water. How many grams of CuSO4 . 5H2O are required? (Molar mass = 250 g/mol)

$$0.5\ \text{mol/L} \times 0.1\ \text{L} \times 250\ \frac{\text{g}}{\text{mol}} = 12.5\ \text{g}$$

Q: If a solution has an absorbance of 0.6 at 635 nm and the standard curve equation is $$A = 1.2c$$, what is the concentration of the solution?

$$c = \frac{A}{1.2} = \frac{0.6}{1.2} = 0.5\ \text{M}$$

Q: Which of the following is the correct calculation for the number of grams of glucose ($$C_6H_{12}O_6$) needed to make 0.3 moles? (Molar mass = 180 g/mol)

$$0.3\ \text{mol} \times 180\ \frac{\text{g}}{\text{mol}} = 54\ \text{g}$$

Question 1

Which of the following best describes the purpose of calibrating a colorimeter with deionized water before measuring sample absorbance?

Accepted Answer

To ensure the colorimeter is set to a baseline of 100% light transmittance, allowing accurate measurement of absorbance for solutions.

Question 2

What is the molecular formula for copper sulfate pentahydrate?

Accepted Answer

CuSO4 . 5H2O

Question 3

Calculate the mass of CuSO4 . 5H2O required to prepare 20 mL of a 1 M solution. (Molar mass = 250 g/mol)

Accepted Answer

$$\frac{1\ 	ext{mol}}{1\ 	ext{L}} 	imes 0.020\ 	ext{L} 	imes 250\ \frac{	ext{g}}{	ext{mol}} = 5\ 	ext{g}$$

Question 4

Which equation correctly represents the relationship between absorbance (A), concentration (c), pathlength (l), and molar extinction coefficient (E) according to Beer-Lambert Law?

Accepted Answer

$$A = Ecl$$

Question 5

Why can’t spectrophotometry be used to determine the concentration of colorless solutes such as salt or sugar?

Accepted Answer

Colorless solutes do not absorb visible light, so no measurable absorbance occurs.

Question 6

A student prepares a 0.5 M solution of CuSO4 . 5H2O in 100 mL of water. How many grams of CuSO4 . 5H2O are required? (Molar mass = 250 g/mol)

Accepted Answer

$$0.5\ 	ext{mol/L} 	imes 0.1\ 	ext{L} 	imes 250\ \frac{	ext{g}}{	ext{mol}} = 12.5\ 	ext{g}$$

Question 7

Which of the following best defines 'molarity'?

Accepted Answer

Moles of solute per liter of solution

Question 8

A standard curve is constructed by plotting which variables on the x- and y-axes, respectively?

Accepted Answer

Concentration (M) on x-axis, Absorbance on y-axis

Question 9

If a solution has an absorbance of 0.6 at 635 nm and the standard curve equation is $$A = 1.2c$$, what is the concentration of the solution?

Accepted Answer

$$c = \frac{A}{1.2} = \frac{0.6}{1.2} = 0.5\ 	ext{M}$$

Question 10

Which safety precaution is most important when handling copper sulfate pentahydrate in the laboratory?

Accepted Answer

Wear safety glasses and gloves to avoid skin and eye contact.

Question 11

Which of the following is the correct calculation for the number of grams of glucose ($$C_6H_{12}O_6$) needed to make 0.3 moles? (Molar mass = 180 g/mol)

Accepted Answer

$$0.3\ 	ext{mol} 	imes 180\ \frac{	ext{g}}{	ext{mol}} = 54\ 	ext{g}$$

Question 12

Which of the following best describes the role of a standard curve in spectrophotometry?

Accepted Answer

It allows determination of unknown concentrations by comparing their absorbance to known standards.

Question 13

A student accidentally uses 25 mL instead of 20 mL to prepare a 1 M solution of CuSO4 . 5H2O. What will be the effect on the final concentration?

Accepted Answer

The final concentration will be lower than 1 M.

Question 14

Which of the following is NOT a correct safety procedure when working with glassware in the lab?

Accepted Answer

Pipetting by mouth.

Question 15

If the absorbance of a solution is measured at 635 nm, what property of the solution is being analyzed?

Accepted Answer

The amount of light absorbed by the solution at a specific wavelength.

Question 16

Which of the following best defines a 'solute'?

Accepted Answer

A substance that is dissolved in a solvent to form a solution.

Question 17

A student needs to prepare 0.2 M solution of CuSO4 . 5H2O in 50 mL. How many grams are required? (Molar mass = 250 g/mol)

Accepted Answer

$$0.2\ 	ext{mol/L} 	imes 0.05\ 	ext{L} 	imes 250\ \frac{	ext{g}}{	ext{mol}} = 2.5\ 	ext{g}$$

Question 18

Which of the following is a correct definition of 'mole' in chemistry?

Accepted Answer

The amount of substance containing Avogadro's number of particles.

Preparation and Analysis of Molar Solutions: Copper Sulfate Pentahydrate and Spectrophotometry

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