Water

Question 1

1. In each of the pairs of statements that follow, place an X next to or highlight the one that correctly describes how hydrogen bonding affects the properties of water. Hydrogen bonding causes water…
   a.
   to boil at a lower temperature than expected.
   to boil at a higher temperature than expected.

Answer 1

to boil at a higher temperature than expected.

Question 2

1. In each of the pairs of statements that follow, place an X next to or highlight the one that correctly describes how hydrogen bonding affects the properties of water. Hydrogen bonding causes water…
   To be more dense as ice, then as liquid water
   To be less dense as ice than as liquid water

Answer 2

To be less dense as ice, then as liquid water

Question 3

1. In each of the pairs of statements that follow, place an X next to or highlight the one that correctly describes how hydrogen bonding affects the properties of water. Hydrogen bonding causes water…
   To absorb heat with a minimal charge in temperature
   To absorb heat with a maximum charge in temperature

Answer 3

To absorb heat with a minimal charge in temperature

Question 4

1. In each of the pairs of statements that follow, place an X next to or highlight the one that correctly describes how hydrogen bonding affects the properties of water. Hydrogen bonding causes water…
   To be cohesive the water molecules cling to each other
   Molecules to shun one another

Answer 4

To be cohesive, the water molecules cling to each other

Question 5

How will two water molecules bond to each other? Explain what type of bond this is, and how it forms.

Answer 5

Hydrogen bonding. The slightly positive Hydrogen atom of one water molecule is attracted to the slightly negative Oxygen atom of a different water molecule.

Question 6

In the properties of water lab, you caused a paperclip to “float” on a surface of water in a petri dish. Explain how this was possible using appropriate vocabulary terms.

Answer 6

This was due to surface tension caused by high cohesion. The clustering of water molecules at the surface of the water creates surface tension, where the tightly packed molecules will actually give the surface some “strength”. The paper clip was supported by the tight clustering of water molecules, which could be seen as the water was bending around the paper clip (the paper clip did not truly float, it was just sitting on the surface tension of the water).

Question 7

5. Water sticks to the side of a glass when condensation occurs, explain how this is possible using appropriate vocabulary terms.

Answer 7

This is due to adhesion. Water’s adhesion attracts water molecules to other substances that are also polar or charged. Glass is a substance that water is attracted to through adhesion, so the water can “stick” to the side of a glass when condensation occurs.

Question 8

Water is an amazing solvent because it is a polar molecule
A. What types of molecules are able to be dissolved by water?

Answer 8

Polar and a hydrophilic

Question 9

What types of molecules are not able to be dissolved by water?

Answer 9

Nonpolar and hydrophobic

Question 10

Sweating is a homeostatic mechanism to regulate body temperature. Explain how this homeostatic mechanism is effective using the information that you’ve learned about water.

Answer 10

Sweating uses water’s high heat of vaporization to act as a cooling mechanism for some organisms. Water requires a lot of heat & energy to convert from a liquid to a gas and evaporate. When sweat evaporates from your skin, it is taking some of that heat from your body and creates a cooling effect when evaporated. This helps to cool down your body, regulating your internal temperature.

Question 11

8. Coastal climates are much more moderate year-round than inland climates are. How does water explain the differences in these two climates through the seasons?

Answer 11

Water’s high heat capacity and high heat of vaporization both contribute to moderating coastal climates. Locations along the coast have close proximity to an ocean, a large body of water. This water absorbs a lot of heat with minimal change in temperature, so during hot summer months, the ocean stays cooler, keeping the surrounding area cooler also. In the winter, the ocean slowly releases this stored heat as the surrounding air becomes colder, keeping winter months more mild. Inland locations do not have a nearby ocean, so the air will heat up and cool down quickly and more drastically.

Question 12

After you get your car waxed, rainwater will just run off the car in large beads. Using the properties of water and correct vocabulary, explain why this happens.

Answer 12

The wax is a hydrophobic product, so it creates a hydrophobic coat on your car.
Water is repelled by hydrophobic molecules and does not have any adhesion to the car when covered in wax. This causes the rain to run right off the car. Water’s cohesion, attraction of water to other water molecules, is still happening, so large water beads are made as the rain runs off the waxed car.

Question 13

11. Explain why the pH scale is a logarithmic scale.

Answer 13

The pH scale is a negative log scale. Every change in a pH number is a 10x change in the H* ion concentration. By decreasing the pH, the H* ion concentration will increase. Ex: pH 7 to pH 6 means a 10x increase in H* ion concentration

Question 14

12. What characteristic of a solution determines its pH?

Answer 14

The concentration of H* ions. The greater the concentration = the lower the ph. The
lower the concentration = the higher the ph

Question 15

If water has a pH of 7 and Windex has a pH of 9, what is the difference in hydrogen ion concentration between these two substances?

Answer 15

PH 7 to pH 9 is a 100x decrease in H° concentration, so Windex is 100x less acidic/more basic than pure water.

Question 16

Explain why a certain substance would be classified as an acid.

Answer 16

An acid will have a greater H* ion concentration than pure water. The higher the H* concentration, the stronger the acid, and the lower the pH value.

Question 17

Explain why a certain substance would be classified as a base/alkaline.

Answer 17

A base will have a lower H* ion concentration (or greater OH ion concentration) than pure water. The lower the H* concentration or the higher the OH concentration, the stronger the base, and the higher the pH value.

Question 18

16. For water to “dissociate”, it will split into an equal amount of H+ ions and OH- ions. Why is water classified as neutral, given the way it dissociates?

Answer 18

Since the H* and OH are present in equal amounts, there is no greater or lesser concentration of H* to make it acidic or basic. The equal parts of the two ions makes pure water neutral.

Question 19

18. When you have stomach acid or heartburn issues, you may take Tums (an antacid) as a remedy. Tums, or calcium carbonate, has a basic/alkaline pH. Why do Tums provide relief when taking for stomach acid or heartburn issues?

Answer 19

When Tums (base) react with your stomach acid (acid), a neutralization reaction occurs. The higher pH of the Tums decreases the H° concentration, raising the stomach acid’s pH closer to neutral, which provides relief to the person with heartburn.

Question 20

Indicate whether the following statements are true (T) or false (F):

If the pH of blood changes from 7.4 to 7.6 it becomes more acidic.

Answer 20

F

Question 21

Indicate whether the following statements are true (T) or false (F):
When an acid is added to a solution, the pH decreases

Answer 21

T

Question 22

Indicate whether the following statements are true (T) or false (F):
A basic pH indicates that OH- ions outnumber H+ ions

Answer 22

T

Question 23

Indicate whether the following statements are true (T) or false (F):
An acidic pH indicates that H+ ions out number 0H-

Answer 23

T

Question 24

Chemical reactions in the human body produce many acid end products. Yet, the pH of the blood remains remarkably constant. Why?

Answer 24

Buffers! Buffers help an organism maintain pH homeostasis

Question 25

What purpose does a buffer serve for an organisms homeostasis?

Answer 25

A buffer’s function is to prevent drastic changes in pH. By maintaining a relatively constant pH in the various environments of an organism’s body, they can maintain homeostasis.

Question 26

How is a buffer able to maintain an organism’s pH homeostasis?

Answer 26

A buffer is a weak acid or a weak base that is able to donate or remove H* ions to or from a solution. A buffer releases or donates H* to a solution if the solution’s pH is increasing too much and needs to come back down. A buffer removes or “absorbs” H* from a solution if the solution’s pH is decreasing too much and needs to go back up.
This two way reaction allows buffers to regulate an environment’s/solution’s pH.

Question 27

The blood buffer system is shown below:
H2CO3 ↔️ H+ + HCO3-
What does the double arrow indicate about this buffer system?

Answer 27

The reaction can go in either direction

Question 28

The blood buffer system is shown below:
H2CO3 ↔️ H+ + HCO3-
If the pH of your blood begins increase in which way will this reaction occur?

Answer 28

If the blood pH is increasing, it is becoming too basic. The reaction will go to the right so that the buffer releases H* then lower the pH.

Question 29

The blood buffer system is shown below:
H2CO3 ↔️ H+ + HCO3-
If the pH of your blood begins to decrease in which way will the reaction occur?

Answer 29

If the blood pH is decreasing, it is becoming too acidic. The reaction will go to the left so that the buffer removes (takes in) H+ two then raise the pH

Question 30

24. Each of the following is a property of water EXCEpT
    a. easily changed from liquid to gas
    b. good solvent
    c. maximum density at 4°C
    d. molecules are cohesive

Answer 30

A

Question 31

Select the correct statement about acids.
a. They cannot be buffered in a solution.
b. They donate hydroxide ions in solution.
c. HCI is an example.
d. They tend to raise the pH.

Answer 31

C

Question 32

Select the most basic pH of the given hydrogen ion concentrations.
a. 1 × 10-3
b. 1 × 104
c. 1 x 10-9
d. 1 x 10-12

Answer 32

D

Question 33

Select the incorrect statement about bases.
a. They can be buffered in solution.
b. They release hydroxide ions in solution.
c. NaOH is an example.
d. They tend to lower the pH.

Answer 33

D

Question 34

Acid

Answer 34

A substance that increases the H+ when added to H2O

Question 35

Base

Answer 35

A substance that decreases the H+ when added to H2O

Question 36

Buffer (3)

Answer 36

Weak acids/bases that prevent sudden changes in pH/A chemical that keeps pH within normal limits
Can either accept hydrogen ions when there’s too many or donate when there’s not enough

Question 37

Polar covalent bond

Answer 37

A bond formed when there’s unequal sharing of electrons

Question 38

Hydrogen bond

Answer 38

When the H of one H2O molecule is attracted to the O of another H2O molecule

Question 39

Cohesion

Answer 39

The attraction of H2O molecules to other water kolefules

Question 40

Adhesion

Answer 40

When water is attracted to substances other than itself