Question 1

Numbers 1 through 4 are used to identify four different elements.Based on periodic table trends,which number identifies the element that is expected to have the greatest tendency to attract a shared pair of electrons?

Accepted Answer

The element that is expected to have the greatest tendency to attract a shared pair of electrons is the one with the highest electronegativity. Based on periodic table trends, electronegativity increases from left to right across a period. Therefore, element 3 would be expected to have the highest electronegativity and the greatest tendency to attract a shared pair of electrons.

Question 2

How many moles of sodium chloride are there in 250 mL of a 1.20 M sodium chloride solution?

Accepted Answer

The number of moles of sodium chloride can be calculated using the formula: moles = molarity × volume (in liters). Here, 1.20 M means 1.20 moles per liter, and 250 mL is 0.250 liters. So, moles = 1.20 moles/L × 0.250 L = 0.30 moles.

Question 3

The recommended daily requirement of calcium is 1,000 mg.Tap water in a Midwestern city contains approximately 150 mg Ca/L.A person living in the city who drinks two liters of water in one day would receive ________ percent of his/her RDA of calcium.

Accepted Answer

D

Question 4

What is the molarity of sodium chloride in a solution containing 0.50 mol of sodium chloride in 500 mL of water?

Accepted Answer

Molarity is calculated as moles of solute divided by liters of solution. Here, 0.50 mol NaCl / 0.5 L = 1.0 M.

Question 5

Which shows the Lewis structure of water with the correct partial charges and nonbonding electrons?

Accepted Answer

The answer of Which shows the Lewis structure of water...

Question 6

In general,hydrogen bonds are

Accepted Answer

Hydrogen bonds are weaker than typical covalent bonds, with only about 1/10th of the strength. This is because they are based on the attraction between a partially positive hydrogen atom and a partially negative atom of another molecule, rather than the sharing of electrons in a covalent bond. Hydrogen bonds are not found in every molecule containing more than one hydrogen atom, and they can also occur between H atoms and other atoms such as nitrogen or oxygen, not just in molecules like H₂.

Question 7

Which molecule(s) contain(s) polar covalent bonds,but is(are) nonpolar?

Accepted Answer

Molecule I (CO2) contains polar covalent bonds, but is nonpolar because the dipole moments of the polar bonds cancel each other out in the linear molecule. Molecule III (CCl4) also contains polar covalent bonds, but is nonpolar because the molecule is tetrahedral and the bond polarity is evenly distributed around the central carbon atom. Molecule II (H2O) and IV (NH3) both contain polar covalent bonds and are polar molecules due to their molecular geometry. Therefore, choices B and C can be eliminated, leaving D as the correct answer.

Question 8

Which best symbolizes the hydrogen bonding between two water molecules?

Accepted Answer

The answer of Which best symbolizes the hydrogen bonding between...

Question 9

If the lead concentration in water is 1 ppm,then we should be able to recover 1 mg of lead from _____ L of water.

Accepted Answer

1 ppm means there is 1 mg of lead per 1 L of water. So, to recover 1 mg of lead, we need to process 1 L of water. Therefore, the answer is C.

Question 10

Which is the best definition of specific heat?

Accepted Answer

Specific heat is defined as the amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius. Choice A describes the heat of vaporization, choice C describes boiling point, and choice D describes the temperature range of a substance.

Question 11

What percentage of Earth's water is in the oceans?

Accepted Answer

About 97 percent of Earth's water is in the oceans. This means only 3 percent is fresh water, with about 2 percent of that locked up in glaciers and ice caps, leaving just 1 percent as usable freshwater in lakes, rivers, and underground.

Question 12

Which correctly describes groundwater?

Accepted Answer

Groundwater refers to water found in natural aquifers or underground reservoirs, and is typically accessed by drilling wells or pumping stations.

Question 13

Hard water in parts of the Midwest may have a calcium ion concentration as high as 400 ppm.What is this calcium ion concentration when expressed as a percentage?

Accepted Answer

To convert ppm to a percentage, divide by 10,000. So, 400 ppm is 400/10,000 = 0.04 percent.

Question 14

The drawing shows two water molecules.Which statement is correct?

Accepted Answer

The bond between the two hydrogen atoms and the oxygen atom within each water molecule is a covalent bond. The bond between the hydrogen atom of one water molecule and the oxygen atom of another water molecule is a hydrogen bond. While hydrogen bonds are important to the structure of water and many biological molecules, they are weaker than covalent bonds. Therefore, choice C is the correct option.

Question 15

Electronegativity

Accepted Answer

Electronegativity is defined as the ability of an atom to attract a shared pair of electrons towards itself in a chemical bond. It is determined by several factors such as nuclear charge, atomic radius, and electron shielding. It is measured on a scale from 0 to 4, with fluorine having the highest electronegativity of 4.0. Therefore, option A is the correct choice. Options B and C are incorrect. Option D is partially correct but not the best choice, as electronegativity actually increases from left to right across a period.

Question 16

A student wants to prepare exactly 250 mL of a 0.500 M aqueous potassium hydroxide solution.What mass of potassium hydroxide (molar mass = 56.10 g/mol) must the student dissolve in the 250 mL of solution?

Accepted Answer

To prepare a 0.500 M solution in 250 mL (0.250 L), use the formula: Molarity (M) = moles of solute / liters of solution. Rearranging to find moles: moles = Molarity × liters = 0.500 M × 0.250 L = 0.125 moles. The mass of KOH needed = moles × molar mass = 0.125 moles × 56.10 g/mol = 7.0125 g, which rounds to 7.01 g.

Question 17

The fact that carbon (C) is less electronegative than nitrogen (N) means that in a C - N bond,the

Accepted Answer

The fact that carbon is less electronegative than nitrogen means that the shared electrons in a C-N bond are closer to the nitrogen atom than to the carbon atom. Electronegativity is a measure of the attraction that an atom has for electrons in a chemical bond. Nitrogen is more electronegative than carbon, which means that it has a greater attraction for electrons. This results in the electrons being pulled closer to the nitrogen atom in a C-N bond.

Question 18

A 4-L sample of water contains 80 µg of lead.What is this lead concentration,in parts per billion (ppb)?

Accepted Answer

The concentration of lead in the water sample is calculated as micrograms of lead per liter of water. Since there are 4 liters of water containing 80 µg of lead, the concentration is $ \frac{80 \mu g}{4 L} = 20 \mu g/L $. Since 1 ppb is equivalent to 1 µg/L, the concentration is 20 ppb.

Question 19

A polar covalent bond is created when

Accepted Answer

Polar covalent bond is created when two atoms share their bonding electrons unequally. This happens when one of the atoms has a higher electronegativity than the other, resulting in an uneven distribution of electrons in the bond.

Question 20

Which covalent bond is the most polar?

Accepted Answer

The electronegativity difference between hydrogen and oxygen (3.44-2.20=1.24) is greater than the electronegativity differences between hydrogen and nitrogen (3.04-2.20=0.84) and hydrogen and sulfur (2.58-2.20=0.38). Therefore, the H-O bond is the most polar.

Quiz 8: Water Everywhere: A Most Precious Resource