Q: A sample contains 3.0 moles of sodium chloride ($$NaCl). $$How many formula units are present in the sample? (Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$1.81 \times 10$$^{24}$$ formula units

Q: Which of the following is the correct formula for calculating the percent composition by mass of an element in a compound?

$$\text{Percent composition} = \frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \times 100\%$$

Question 1

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

Accepted Answer

A chemical change results in the formation of new substances with different properties, while a physical change does not alter the chemical identity of the substance.

Question 2

Which statement correctly distinguishes between an element and a compound?

Accepted Answer

Elements consist of only one kind of atom, while compounds consist of two or more elements chemically combined.

Question 3

A student mixes two clear solutions and observes the formation of a white precipitate. Which type of change has occurred?

Accepted Answer

Chemical change, because a new substance (precipitate) has formed.

Question 4

Which of the following is the correct electron configuration for a neutral atom of oxygen ($$Z = 8$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^4$$

Question 5

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

Ionic compounds consist of ions held together by strong electrostatic forces in a lattice structure.

Question 6

A sample contains 3.0 moles of sodium chloride ($$NaCl). $$How many formula units are present in the sample? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.81 	imes 10$$^{24}$$ formula units

Question 7

Which of the following is a correct balanced chemical equation for the reaction of hydrogen gas with oxygen gas to form water?

Accepted Answer

$$2H_2 + O_2$ \rightarrow 2H_2O$$

Question 8

A student is given a mixture of sand and salt. Which method would best separate the two substances?

Accepted Answer

Dissolve the mixture in water, filter to remove the sand, then evaporate the water to recover the salt.

Question 9

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 10

Which of the following best describes the process of distillation?

Accepted Answer

Separating a mixture based on differences in boiling points.

Question 11

A chemical reaction is carried out in a closed container. The mass of the reactants is measured as 50.0 g, and the mass of the products is measured as 50.0 g. Which law does this observation support?

Accepted Answer

Law of Conservation of Mass

Question 12

Which of the following is the correct formula for calculating the percent composition by mass of an element in a compound?

Accepted Answer

$$	ext{Percent composition} = \frac{	ext{mass of element in 1 mole of compound}}{	ext{molar mass of compound}} 	imes 100\%$$

Question 13

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

Accepted Answer

Water has a bent molecular geometry and the oxygen atom is more electronegative than hydrogen.

Question 14

A patient is given a saline solution intravenously. Which property of the solution is most important to ensure safety?

Accepted Answer

The solution must be isotonic compared to blood.

Question 15

Which of the following is the correct formula for calculating the molarity ($$M) of a $$solution?

Accepted Answer

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

Question 16

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electrons between two atoms.

Question 17

A chemical reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is obtained. What is the percent yield?

Accepted Answer

$$75\%$$

Question 18

Which of the following is a correct statement about the atomic number of an element?

Accepted Answer

The atomic number is equal to the number of protons in the nucleus.

Question 19

Which of the following best describes the difference between a homogeneous mixture and a heterogeneous mixture?

Accepted Answer

A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture does not.

Question 20

Which of the following is the correct formula for calculating the density ($$d) of a $$substance?

Accepted Answer

$$d = \frac{	ext{mass}}{	ext{volume}}$$

General Chemistry I: Module Objectives Overview

Guida di studio - Domande di pratica

Study guide - Flashcard