Q: Which of the following is the correct formula for calculating the percentage yield of a chemical reaction?

$\text{Percentage yield} = \dfrac{\text{actual yield}}{\text{theoretical yield}} \times 100$

Question 1

Which of the following statements best describes the difference between atomic number ($Z$) and mass number ($A$) for an atom?

Accepted Answer

Atomic number ($Z$) is the number of protons, while mass number ($A$) is the sum of protons and neutrons.

Question 2

A sample contains $3.01 	imes 10^{23}$ atoms of magnesium. What is the number of moles of magnesium in the sample?

Accepted Answer

$0.50$ mol

Question 3

Which equation correctly relates the number of particles ($N$), the number of moles ($n$), and Avogadro's constant ($N_A$)?

Accepted Answer

$n = \dfrac{N}{N_A}$

Question 4

Which of the following best explains why ionization energy generally increases across a period in the periodic table?

Accepted Answer

Nuclear charge increases while shielding remains relatively constant, increasing attraction between nucleus and valence electrons.

Question 5

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

$\mathrm{CH_2O}$

Question 6

Which of the following is the correct electron configuration for a neutral atom of phosphorus ($Z = 15$)?

Accepted Answer

$1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^3$

Question 7

A student uses mass spectrometry to analyze a sample of chlorine and finds two peaks at $m/z = 35$ and $m/z = 37$ with relative abundances of $75\%$ and $25\%$, respectively. What is the relative atomic mass of chlorine?

Accepted Answer

$35.5$

Question 8

Which of the following best describes the trend in ionization energy down Group 2 of the periodic table?

Accepted Answer

Ionization energy decreases due to increased atomic radius and electron shielding.

Question 9

Which of the following is the correct formula for calculating the percentage yield of a chemical reaction?

Accepted Answer

$	ext{Percentage yield} = \dfrac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100$

Question 10

A solution contains $0.25$ mol of sodium chloride in $500$ mL of water. What is the concentration of sodium chloride in $\mathrm{mol\,dm^{-3}}$?

Accepted Answer

$0.50\ \mathrm{mol\,dm^{-3}}$

Question 11

Which of the following best explains the concept of atom economy in a chemical reaction?

Accepted Answer

It is the percentage of reactant atoms that end up in the desired product.

Question 12

Which of the following is the correct balanced equation for the reaction of sodium with water?

Accepted Answer

$2\mathrm{Na} + 2\mathrm{H_2O} \rightarrow 2\mathrm{NaOH} + \mathrm{H_2}$

Question 13

A gas occupies $2.50$ L at $300$ K and $1.00$ atm. What is the number of moles of gas present? (Use $R = 0.0821\ \mathrm{L\,atm\,mol^{-1}\,K^{-1}}$)

Accepted Answer

$0.102$ mol

Question 14

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

Accepted Answer

Empirical formula shows the simplest whole-number ratio of atoms, while molecular formula shows the actual number of atoms in a molecule.

Question 15

Which of the following factors does NOT affect the first ionization energy of an element?

Accepted Answer

The number of neutrons in the nucleus

Question 16

A student needs to prepare $250$ mL of $0.20\ \mathrm{mol\,dm^{-3}}$ sodium sulfate solution. What mass of sodium sulfate ($\mathrm{Na_2SO_4}$, molar mass $= 142\ \mathrm{g\,mol^{-1}}$) is required?

Accepted Answer

$7.10$ g

Question 17

Which of the following best explains why the second ionization energy of sodium is much higher than the first?

Accepted Answer

The second electron is removed from a new shell closer to the nucleus, which is more strongly attracted.

Question 18

Which of the following is the correct formula for the ideal gas law?

Accepted Answer

$PV = nRT$

Question 19

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

General Chemistry Exam 1 Study Guide: Atomic Structure and Amount of Substance

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