Question 1

Which of the following statements explains why oxygen is classified asa pure substance and air is classifiedas a mixture?

Accepted Answer

A) Oxygen is more reactive than air. 
B) Oxygen has a higher density than air. 
C) Oxygen undergoes phase changes, whereas air is always a gas. 
D) Oxygen contains only one substance, but air contains several substances.

Question 2

Which of the following occurs in an ionic bond?

Accepted Answer

A) Two ions share protons. 
B) Two ions share electrons. 
C) Similarly charged ions attract. 
D) Oppositely charged ions attract.

Question 3

Which of the following statements explains why the bond in hydrogen chloride (HCl) is polar covalent?

Accepted Answer

A) The atomic mass of chlorine is greater than that of hydrogen. 
B) The electronegativity of chlorine is greater than that of hydrogen. 
C) The diameter of a chlorine atom is greater than that of a hydrogen atom. 
D) The number of valence electrons in a chlorine atom is greater than that in a hydrogen atom.

Question 4

A hospital buys a compound that contains an isotope of barium. Several months later, most of the barium has changed to the element lanthanum. Which of the following is responsible for this change?

Accepted Answer

A) exposure to air 
B) radioactive decay 
C) reactions with the container wall 
D) absorption of moisture from the air

Question 5

Formaldehyde in solution is used as a preservative. It has a melting point of -92°C. When the temperature of a sample of formaldehyde rises from -93°C to -91°C, which of the following occurs?

Accepted Answer

A) The molecules move more freely. 
B) The molecules lose electrical charge. 
C) The molecules break apart into atoms. 
D) The molecules become fixed in a crystal structure.

Question 6

A person left a bottle of distilled water and a bottle of a sugary drink outside overnight. In the morning, one liquid was frozen but the other was not. Which liquid was frozen and why did it freeze?

Accepted Answer

A) The sugary drink froze because solutions are more dense than pure substances. 
B) The distilled water froze because pure substances are more dense than solutions. 
C) The sugary drink froze because solutions have a higher freezing point than pure substances. 
D) The distilled water froze because pure substances have a higher freezing point than solutions.

Question 7

Which of the following is an example of a chemical change?

Accepted Answer

A) burning a scented candle 
B) cutting an apple into slices 
C) freezing liquid water into an ice cube 
D) melting a stick of butter to pour over popcorn

Question 8

Which of the following statements best explains why elements in the same family of the periodic table have similar bonding properties?

Accepted Answer

A) The elements have similar atomic sizes. 
B) The elements have similar atomic masses. 
C) The elements have similar numbers of protons. 
D) The elements have similar valence electron configurations.

Question 9

A leaf gently floats on a pond. Which of the following statements best explains why the leaf stays on top of the water?

Accepted Answer

A) The leaf has nonpolar covalent bonds between its atoms. 
B) The density of the leaf is greater than the density of the water. 
C) The water molecules are held tightly together by hydrogen bonding. 
D) The hydrogen and oxygen atoms in the water are chemically bonded.

Question 10

Which of the following comparisons correctly describes subatomic particles?

Accepted Answer

A) An electron has a negative charge and a mass larger than the mass of a proton. 
B) A neutron has a negative charge and a mass smaller than the mass of a proton. 
C) A neutron has a neutral charge and a mass larger than the mass of an electron. 
D) A proton has a positive charge and a mass smaller than the mass of an electron.

Question 11

Which of the following characteristics of an element can be determined precisely by considering only the element's specificposition on the periodic table?

Accepted Answer

A) radius of each ion 
B) density of the solid 
C) boiling point of the liquid 
D) number of protons in each atom

Question 12

Which of the following statements best explains why atoms bond?

Accepted Answer

A) Atoms bond to make new substances. 
B) Atoms bond to become less chemically stable. 
C) Atoms bond to change from a liquid to a solid. 
D) Atoms bond to become more chemically stable.

Question 13

An insect known as a water strider can walk across the surface of a pond. Which of the following is directly responsible for this insect being able to walk on the surface without sinking?

Accepted Answer

A) ionic bonding 
B) oxygen bonding 
C) hydrogen bonding 
D) nonpolar covalent bonding

Question 14

Gold-198 has a half-life of approximately 3 days. If a 100 g sample of gold-198 decays for 9 days, approximately how much gold-198 remains in the sample?

Accepted Answer

A) 13 g 
B) 25 g 
C) 33 g 
D) 50 g

Question 15

Which of the following statements describes a difference between a mixture and a pure substance?

Accepted Answer

A) A mixture tends to be homogenous, while a pure substance tends to be heterogeneous. 
B) A mixture has a specific melting point, while the melting point of a pure substance can vary. 
C) The density of a mixture can change with temperature, but the density of a pure substance cannot change. 
D) The composition of a mixture can vary from sample to sample, but the composition of a pure substance is always the same.

Question 16

Which of the following statements best explains why ice floats on water?

Accepted Answer

A) Water has a higher specific heat than ice. 
B) Ice has the same molecular mass as water. 
C) Heat is absorbed when water changes from the solid state to the liquid state 
D) Hydrogen bonding causes water to be less dense in the solid state than in the liquid state.

Question 17

As heat is slowly added to a glass of ice water, the temperature remains at 0°C. Which of the following statements explains why the temperature of the mixture of ice and water remains constant as heat is added?

Accepted Answer

A) Heat is stored in the solid ice. 
B) Heat is stored in the liquid water. 
C) Heat is used to turn the solid ice into liquid water. 
D) Heat is absorbed equally by the solid ice and the liquid water.

Question 18

Which of the following statements best explains why water vapor condenses as temperature decreases?

Accepted Answer

A) Collisions between water vapor molecules become elastic. 
B) Water vapor molecules chemically react when they collide. 
C) Water vapor molecules are pulled together by the force of gravity. 
D) Attractive forces between water vapor molecules overcome molecular motion.

Question 19

Which of the following is an example of a physical change?

Accepted Answer

A) Iron exposed to air produces rust. 
B) Hydrogen combined with oxygen forms water. 
C) Sulfur combined with oxygen produces sulfur dioxide. 
D) Liquid nitrogen exposed to air becomes nitrogen gas.

Question 20

In a hydrogen fluoride (HF) molecule, a hydrogen atom and a fluorine atom are held together by a polar covalent bond. Which of the following best explains why this bond is polar?

Accepted Answer

A) the large difference in the atomic radii of hydrogen and fluorine atoms 
B) the large difference in the atomic masses of hydrogen and fluorine atoms 
C) the large difference in theelectronegativities of hydrogen and fluorine atoms 
D) the large difference in the number of electrons of hydrogen andfluorine atoms

Exam 2: Chemistry