Q: If the wavelength of purple light used in a spectrophotometer is $$400 \\ \mathrm{nm}$$, what is its frequency? (Speed of light $$c = 3.00 \times 10^8$ \\ \mathrm{m/s})$$

$$7.5 \times 10$$^{14}$$ \\ \mathrm{Hz}$$

Question 1

A student measures the mass of a penny as 2.50 g and its volume as 0.35 cm$$^3. $$What is the density of the penny, reported to the correct number of significant figures?

Accepted Answer

$$7.1 \ \mathrm{g/cm}^3$$

Question 2

Which of the following best describes the independent and dependent variables when graphing the relationship between the concentration of a solution and its absorbance in a spectrophotometry experiment?

Accepted Answer

Concentration is the independent variable; absorbance is the dependent variable.

Question 3

A student is asked to dilute a 1.0 M solution to make 100 mL of a 0.25 M solution. What volume of the original 1.0 M solution should be used?

Accepted Answer

$$25 \ \mathrm{mL}$$

Question 4

When constructing a graph of mass versus volume to determine the density of a substance, what does the slope of the best-fit line represent?

Accepted Answer

The density of the substance

Question 5

A student records the following measurements for the mass of a sample: 2.1 g, 2.13 g, and 2.134 g. If the balance is accurate to the hundredths place, how should the student report the average mass?

Accepted Answer

$$2.12 \ \mathrm{g}$$

Question 6

In a chemical reaction, a gas is evolved and a precipitate forms. Which of the following best describes the type of reaction?

Accepted Answer

Double replacement

Question 7

Which of the following statements about anthocyanin as a pH indicator is correct?

Accepted Answer

Anthocyanin changes color depending on the acidity or basicity of the solution.

Question 8

A student is asked to categorize ammonia and vinegar using the pH scale. Which is correct?

Accepted Answer

Ammonia is a base; vinegar is an acid.

Question 9

Why does a boiled potato show less enzymatic activity than a raw potato in a chemical reaction experiment?

Accepted Answer

Boiling denatures the enzyme, making it inactive.

Question 10

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

It speeds up the reaction without being consumed.

Question 11

A student is preparing a graph of absorbance versus concentration for a set of solutions. If the equation of the best-fit line is $$y = 0.45x + 0.02$$, where $$y is $$absorbance and $$x is $$concentration in mol/L, what is the absorbance of a solution with a concentration of $$0.30 \ \mathrm{mol/L}$$?

Accepted Answer

$$0.155$$

Question 12

Which of the following is the correct formula to calculate the concentration of a diluted solution?

Accepted Answer

$$M_1$$ $$V_1$$ = $$M_2$$ $$V_2$$

Question 13

If a student adds 10.0 mL of water to 40.0 mL of a 0.50 M NaCl solution, what is the new concentration of NaCl?

Accepted Answer

$$0.40 \ \mathrm{M}$$

Question 14

Which of the following best explains why it is important to use the correct number of significant figures when reporting measurements in chemistry?

Accepted Answer

It reflects the precision of the measuring instrument.

Question 15

During a double replacement reaction, which of the following is a possible visual sign that a chemical change has occurred?

Accepted Answer

Formation of a precipitate

Question 16

A student is asked to balance the following chemical equation: $$\mathrm{NaOH} + \mathrm{HCl} \rightarrow \mathrm{NaCl} + \mathrm{H}_2\mathrm{O}. $$What are the correct coefficients?

Accepted Answer

1, 1, 1, 1

Question 17

Which of the following best describes the difference between a physical and a chemical change?

Accepted Answer

A chemical change results in the formation of new substances, while a physical change does not.

Question 18

If the wavelength of purple light used in a spectrophotometer is $$400 \ \mathrm{nm}$$, what is its frequency? (Speed of light $$c = 3.00 	imes 10^8$ \ \mathrm{m/s})$$

Accepted Answer

$$7.5 	imes 10$$^{14}$$ \ \mathrm{Hz}$$

Question 19

A student is asked to determine the density of an irregularly shaped object. They measure its mass as 15.0 g and find its volume by water displacement to be 6.0 mL. What is the density?

Accepted Answer

$$2.5 \ \mathrm{g/mL}$$

Introduction to Chemistry: Lab Concepts and Skills Study Guide

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