Q: What is the percent composition of oxygen in water ($\mathrm{H_2O}$)? (Molar mass of $\mathrm{H_2O}$ is $18.0$ g/mol, oxygen is $16.0$ g/mol)

$\frac{16.0}{18.0} \times 100\% = 88.9\%$

Question 1

Which of the following statements best describes the difference between accuracy and precision in scientific measurements?

Accepted Answer

Accuracy refers to how close a measurement is to the true value, while precision refers to how close repeated measurements are to each other.

Question 2

A student measures the mass of a sample as 12.34 g, 12.35 g, and 12.33 g. The true mass is 13.00 g. Which statement best describes the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which of the following is the correct scientific notation for the number 0.00056?

Accepted Answer

$5.6 	imes 10^{-4}$

Question 4

Which of the following is a physical property?

Accepted Answer

Melting point

Question 5

An atom has 17 protons, 18 neutrons, and 17 electrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: 17, Mass number: 35

Question 6

Which group in the periodic table contains the noble gases?

Accepted Answer

Group 8A (VIIIA)

Question 7

What is the correct formula for magnesium chloride?

Accepted Answer

$\mathrm{MgCl_2}$

Question 8

Which of the following is the correct name for $\mathrm{N_2O_5}$?

Accepted Answer

Dinitrogen pentoxide

Question 9

What is the charge on the iron ion in iron(III) chloride?

Accepted Answer

$+3$

Question 10

Which of the following acids is correctly matched with its formula?

Accepted Answer

Sulfuric acid: $\mathrm{H_2SO_4}$

Question 11

How many moles are in $18.0$ grams of water ($\mathrm{H_2O}$)? (Molar mass of $\mathrm{H_2O}$ is $18.0$ g/mol)

Accepted Answer

$1.0$ mole

Question 12

What is Avogadro's number?

Accepted Answer

$6.02 	imes 10^{23}$

Question 13

Which of the following is the correct balanced equation for the combustion of methane ($\mathrm{CH_4}$)?

Accepted Answer

$\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$

Question 14

A sample contains $3.01 	imes 10^{23}$ molecules of $\mathrm{CO_2}$. How many moles of $\mathrm{CO_2}$ are present?

Accepted Answer

$0.5$ moles

Question 15

Which type of chemical reaction is represented by $\mathrm{2KClO_3 \rightarrow 2KCl + 3O_2}$?

Accepted Answer

Decomposition

Question 16

What is the percent composition of oxygen in water ($\mathrm{H_2O}$)? (Molar mass of $\mathrm{H_2O}$ is $18.0$ g/mol, oxygen is $16.0$ g/mol)

Accepted Answer

$\frac{16.0}{18.0} 	imes 100\% = 88.9\%$

Question 17

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by sharing electrons between two nonmetals.

Question 18

Which of the following is the correct Lewis structure for $\mathrm{CO_2}$?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 19

A reaction has the following stoichiometry: $2A + 3B \rightarrow 4C$. If you start with $4$ moles of $A$ and $9$ moles of $B$, what is the maximum number of moles of $C$ that can be formed?

Accepted Answer

$8$ moles

Exam 1 Review: Measurements, Atoms & Elements, Compounds, and Chemical Reactions

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