Q: A sample contains 3.0 moles of oxygen gas ($$O_2). $$How many molecules of $$O_2$$ are present in the sample? $$\text{Number of molecules} = \text{moles} \times 6.022 \times 10$$^{23}$$

$$1.81 \times 10$$^{24}$$ molecules

Question 1

Which of the following best describes the difference between an element and a compound?

Accepted Answer

An element consists of only one type of atom, while a compound consists of two or more types of atoms chemically bonded together.

Question 2

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

$$	ext{Moles} = \frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Accepted Answer

$$0.0005$$ moles

Question 3

Which statement about isotopes is correct?

Accepted Answer

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

Question 4

A solution is prepared by dissolving 5.0 g of NaCl in enough water to make 250 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

$$	ext{Molarity} = \frac{	ext{moles of solute}}{	ext{liters of solution}}$$

Accepted Answer

$$0.34 M$$

Question 5

Which of the following is a chemical change?

Accepted Answer

Burning wood

Question 6

A sample contains 3.0 moles of oxygen gas ($$O_2). $$How many molecules of $$O_2$$ are present in the sample?

$$	ext{Number of molecules} = 	ext{moles} 	imes 6.022 	imes 10$$^{23}$$

Accepted Answer

$$1.81 	imes 10$$^{24}$$ molecules

Question 7

Which of the following best explains why water is considered a polar molecule?

Accepted Answer

The oxygen atom attracts electrons more strongly than the hydrogen atoms, creating a partial negative charge on oxygen.

Question 8

A nurse needs to prepare 500 mL of a 0.9% (w/v) saline solution. How many grams of NaCl are required?

$$	ext{mass (g)} = 	ext{volume (mL)} 	imes \frac{	ext{percent (w/v)}}{100}$$

Accepted Answer

$$4.5 g$$

Question 9

Which of the following is the correct electron configuration for a neutral sodium atom ($$Na$$, atomic number 11)?

Accepted Answer

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

Question 10

A chemical reaction releases 150 kJ of energy. Which statement best describes this reaction?

Accepted Answer

The reaction is exothermic because energy is released.

Question 11

Which of the following is the correct formula for calcium phosphate?

Accepted Answer

$$Ca_3$$($$PO_4)_2$

Question 12

A patient’s blood sample has a pH of 7.2. Which statement is correct?

Accepted Answer

The blood is slightly acidic.

Question 13

Which of the following is a correct statement about ionic bonds?

Accepted Answer

Ionic bonds form between metals and nonmetals through the transfer of electrons.

Question 14

A solution contains 0.25 mol of glucose ($$C_6H_{12}O_6$) in 500 mL of water. What is the molarity of the solution?

$$	ext{Molarity} = \frac{	ext{moles of solute}}{	ext{liters of solution}}$$

Accepted Answer

$$0.50 M$$

Question 15

Which of the following is the best example of a heterogeneous mixture?

Accepted Answer

Blood

Question 16

A student mixes 100 mL of 1.0 M HCl with 100 mL of 1.0 M NaOH. What is the final concentration of NaCl in the resulting solution?

$$	ext{HCl} + 	ext{NaOH} ightarrow 	ext{NaCl} + 	ext{H}_2O$$

Accepted Answer

$$0.5 M$$

Question 17

Which of the following statements about covalent bonds is correct?

Accepted Answer

Covalent bonds involve the sharing of electrons between atoms.

Question 18

A sample of gas occupies 2.0 L at 1.0 atm. If the pressure is increased to 2.0 atm at constant temperature, what is the new volume?

$$P_1V_1 = P_2V_2$$

Accepted Answer

$$1.0 L$$

Question 19

Which of the following is the correct name for $$K_2SO_4$$?

Accepted Answer

Potassium sulfate

Question 20

A patient receives 100 mL of a 5% (w/v) glucose solution. How many grams of glucose did the patient receive?

$$	ext{mass (g)} = 	ext{volume (mL)} 	imes \frac{	ext{percent (w/v)}}{100}$$

Accepted Answer

$$5 g$$

Study Guide for Exam 1 (Chapters 1, 2, 3, 4, 6, 7): GOB Chemistry

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