Q: A sample contains $$0.250\ \mathrm{mol} of$$ $$\mathrm{CO}_2. $$How many molecules of $$\mathrm{CO}_2$$ are present in the sample?

$$1.51 \times 10$$^{23}$$ molecules

Question 1

Which of the following statements correctly describes the difference between an atom and an ion?

Accepted Answer

An atom is always neutral, while an ion has a net electrical charge due to the loss or gain of electrons.

Question 2

A certain element has two naturally occurring isotopes: $$^{35}\mathrm{Cl} ($$mass = 34.97 u, abundance = 75.77%) and $$^{37}\mathrm{Cl} ($$mass = 36.97 u, abundance = 24.23%). What is the atomic mass of chlorine?

Accepted Answer

$$35.45\ \mathrm{u}$$

Question 3

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 4

What is the charge of the ion typically formed by an atom of magnesium ($$\mathrm{Mg}$$)?

Accepted Answer

$$+2$$

Question 5

Which group on the periodic table contains the halogens?

Accepted Answer

Group 17

Question 6

How many protons, neutrons, and electrons are present in the isotope $$^{23}_{11}\mathrm{Na}^+$$?

Accepted Answer

11 protons, 12 neutrons, 10 electrons

Question 7

A sample contains $$0.250\ \mathrm{mol} of$$ $$\mathrm{CO}_2. $$How many molecules of $$\mathrm{CO}_2$$ are present in the sample?

Accepted Answer

$$1.51 	imes 10$$^{23}$$ molecules

Question 8

Which of the following compounds is ionic?

Accepted Answer

$$\mathrm{NaCl}$$

Question 9

What is the empirical formula of a compound that contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 10

Which of the following is the correct balanced chemical equation for the combustion of methane ($$\mathrm{CH}_4) in $$oxygen?

Accepted Answer

$$\mathrm{CH}_4 + 2\ \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2\ \mathrm{H}_2\mathrm{O}$$

Question 11

Calculate the mass percent of oxygen in $$\mathrm{H}_2\mathrm{O}_2 ($$hydrogen peroxide).

Accepted Answer

$$47.1\%$$

Question 12

How many grams of $$\mathrm{Na}_2\mathrm{SO}_4$$ are required to prepare $$0.500\ \mathrm{mol} of $$the compound? (Molar mass of $$\mathrm{Na}_2\mathrm{SO}_4 = 142.04\ \mathrm{g/mol})$$

Accepted Answer

$$71.0\ \mathrm{g}$$

Question 13

A 10.0 g sample of a compound containing only carbon and hydrogen produces 33.0 g of $$\mathrm{CO}_2$$ and 13.5 g of $$\mathrm{H}_2\mathrm{O}$$ upon complete combustion. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_8$$

Question 14

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

Accepted Answer

The molecular formula shows the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest whole-number ratio of the elements.

Question 15

How many moles of $$\mathrm{O}_2$$ are required to completely react with 4.00 moles of $$\mathrm{C}_2\mathrm{H}_6 in $$the following reaction?

$$2\ \mathrm{C}_2\mathrm{H}_6 + 7\ \mathrm{O}_2 \rightarrow 4\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O}$$

Accepted Answer

$$14.0$$ moles

Question 16

Which of the following is a transition element?

Accepted Answer

Copper ($$\mathrm{Cu})$$

Question 17

A patient is given a 250 mg dose of a medication. If the molar mass of the medication is $$500\ \mathrm{g/mol}$$, how many moles of the medication did the patient receive?

Accepted Answer

$$5.0 	imes 10$$^{-4}$$ moles

Question 18

Which of the following best describes the arrangement of elements in the periodic table?

Accepted Answer

Elements are arranged in order of increasing atomic number in rows (periods) and columns (groups) with similar properties.

Question 19

Which of the following formulas represents a molecular compound?

Accepted Answer

$$\mathrm{SO}_2$$

Question 20

If $$3.00\ \mathrm{g} of$$ $$\mathrm{Al}$$ reacts with excess $$\mathrm{O}_2 to $$form $$\mathrm{Al}_2\mathrm{O}_3$$ according to the equation $$4\ \mathrm{Al} + 3\ \mathrm{O}_2 \rightarrow 2\ \mathrm{Al}_2\mathrm{O}_3$$, what mass of $$\mathrm{Al}_2\mathrm{O}_3 is $$produced? (Molar mass: $$\mathrm{Al} = 26.98\ \mathrm{g/mol}$$, $$\mathrm{Al}_2\mathrm{O}_3 = 101.96\ \mathrm{g/mol})$$

Accepted Answer

$$5.67\ \mathrm{g}$$

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