Problem Set #2

Question 1

A 0.50 L (500 ml) sample of seawater contains 74.7 g of NaCl, which has a molecular weight of 58.44 g/mol. What is the molar concentration of the NaCl in the seawater?

Answer 1

2.56

1. MW = 58.44g for 1M
2. We have 500mL or 0.5L of NaCL solution
3. In that 500mL, we have 74.7g of NaCl so…
4. Well, 74.7/58.4 = 1.27M, but that’s if we had a full liter and we only have 1/2 liter (500mL)

Question 2

An aqueous 5.3 M solution of hydrochloric acid is prepared with a total volume of 0.64 L (640 ml). The molecular weight of hydrochloric acid is 36.46 g/mol. How much hydrochloric acid (in grams) is needed for the solution?

Answer 2

123.67

1. Find MW , it’s given, = 36.46g
2. We need 5.3M so 36.46*5.3 = 193.24g/L
3. We only need 0.64 L or 640 mls

Question 3

How much NaCl would you need to make a 0.2 L (200 ml) of a 0.3 molar solution? NaCl has a molecular weight of 58.44 g.

Answer 3

3.51

1. Find MW, it’s given = 58.44g
2. We need 0.2M so 58.44*0.2 = 11.69g/L
3. we only need 0.3 L or 300 ml

Question 4

If the H+ ion concentration of a household item is 10-3, how many OH- ions does it have?

Answer 4

10^-11

[H+] x [OH-] = 10-14

Question 5

The pH of an item is 12. Is this acidic or basic and how many H+ ions does it have?

Answer 5

Basic 10^-12

[H+] x [OH-] = 10-14

Question 6

Most of the enzymes in our bodies function at or very close to neutral (pH ~ 7.0). There are a few exceptions. Your stomach is one of these exceptions. The enzymes in your stomach have More H+ ions and Less OH- ions than the enzymes found in your blood?

Answer 6

1.More
2.Less

Enzymes in your stomach are more acidic so then have more H+ (and vice versa).

Question 7

Capsaicin is an active component of chili peppers, which are plants belonging to the genus Capsicum. It is a chemical irritant for mammals, including us, and produces a sensation of burning in any tissue with which it comes into contact. What is the molecular weight of capsicin (g/mol)? Enter a whole number (no decimal places, no units!).

C18H27NO3

Answer 7

305

Do you have a numerical only answer with NO decimal places (i.e. a whole number)?

(1812) + (271) + (141) + (163)

Question 8

What type of covalent bonds exist in methane?

Answer 8

Non polar

There is only slight differences in the electronegativity of carbon and hydrogen, so they will share their electrons fairly equally.

Question 9

Using the pH scale below, compare the can of soda to the glass of milk. What is the difference between these two beverage’s pH readings?

Answer 9

The soda has 1000x more H+ ions than the milk.

pH of soda is 3 and pH of milk is 6. This is three log units of difference (10x10x10).

Question 10

If heavy exercise produces lots of CO2 in the body, will the blood become more acidic or more basic?

*Please make sure you read the comments for this question. This was just to make you think about CO2 and your body. This is far more complicated than explained here and will be investigated deeper in any A&P classes you take.

Answer 10

More acidic

Exercise does initiates chemical changes in the blood (including a drop in pH); however, a biologically significant (dangerous) drop is usually offset by other physiological functions (like proteins/buffers/etc.). This is one reason why we breathe faster when exercising, it actually helps regulate the drop in pH.

Question 11

How many covalent bonds can a Carbon atom form?

Answer 11

4

Carbon contains four electrons in its outer shell. Therefore, it can form four covalent bonds with other atoms or molecules. The simplest organic carbon molecule is methane (CH4), in which four hydrogen atoms bind to a carbon atom.

Question 12

Carbon-14 decays to nitrogen-14 with a half-life of approximately 5700 years. You find and measure a fossil sample composed of 12.5% Carbon-14 and 87.5% Nitrogen-14, approximately how old is your sample?

Hint: At time 0 your organism was 100% Carbon-14 and 0% Nitrogen-14.

Your answer should be numerical only and a whole number (no decimal places)

Answer 12

17,100

I promise you this is a LOT easier than most of you made this.

At time 0 your specimen was 100% C14 and 0% N14

At 1 half-life (or 5700 years) your specimen was 50% C14 and 50% N14

At 2 half-lives (or 11,400 years) your specimen was 25% C14 and 75% N14

At 3 half-lives (or 17,100 years) your specimen was 12.5% C14 and 87.5% N14, so that’s your answer: 17,100 years old.

Question 13

Which functional groups that we talked about are NOT present in nucleotides, like the one depicted below?

Answer 13

Carboxyl groups

Carboxyl is COOH

Phosphate is PO3

Hydroxyl is OH

Amino is NH2

Question 14

Which of the following is NOT a compound?

Answer 14

O2

A compound is a substance formed from two or more elements chemically united in fixed proportions.

Question 15

Which of the following is NOT a molecule?

Answer 15

O

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge.

Question 16

Tantalum is a chemical element with the symbol Ta and atomic number 73 and atomic mass ~181. Its main use today is in tantalum capacitors in electronic equipment such as cell phones, DVD players, video game systems, and computers. How many protons, neutrons, and electrons does it have, respectively, in this most abundant form?

Answer 16

73, 108, 73

Protons = atomic # = electrons
Atomic mass = #protons + #neutrons

Question 17

Which series of elements below are ordered from high to low electronegativity?

HINT: Remember, Neon is inert. This means it, essentially, has no electronegativity.

Answer 17

F, Cl, As, Ba, Ne

Neon is inert, therefore it’s electronegativity is, essentially, zero.

F is the most electronegative element we know of. Start there then use our general trend on the table (top, right are more electronegative).

Question 18

Which of these is NOT an essential element that makes up living matter?

Answer 18

All of these are essential elements

Trace elements can be (are) also essential.

Question 19

Which statement about water’s polarity is TRUE?

Answer 19

All are true

Water is a very unique substance because it can do things unlike any other molecule.

Question 20

Biological fluids regulate pH values using solutions that can resist changes in pH called __________. This is achieved by these solutions accepting _________ when pH is low and donating _________ when pH is high.

*This is not as easy as it seems. You need to think about this, carefully, before answering.

Answer 20

Buffers, H+ ions, H+ ions

Buffers, solutions that can resist changes in pH, are key to maintaining stable H ion concentrations in biological systems. When there are too many H+ ions (pH is lower than it should be), a buffer will absorb some of them, bringing pH back up; and when there are too few H+ ions (pH is higher than it should be), a buffer will donate some of its own H+ ions to reduce the pH.

Question 21

What is the [OH-] in a solution with a pH of 13?

Answer 21

10^-1

[H+] x [OH-] = 10-14

Question 22

What is the valency of Sulfur?

Answer 22

2

How many electrons does S need to complete it’s outer most shell?

What is the combining power of S?

Question 23

Which statement about enantiomers is FALSE?

Answer 23

They differ in the arrangement of their covalent bonds.

Enantiomers are isomers, have the same chemical formula, and are mirror images of one another. They cannot be superimposed. (Like your hands).

Structural isomers differ in their arrangement of covalent bonds.

Question 24

Phosphorus-32 undergoes radioactive decay at a constant rate. Estimate its half-life from the graph below showing its radioactivity measured over time.

Answer 24

2 weeks

If you have 100% P-32 at time 0, follow the curve till you get to 50% remaining. This is at week 2.

Question 25

An atom with 8 electrons in its outer shell tends to

Answer 25

be chemically inert.

With 8 electrons in its outer shell, an atom isn’t actively seeking bonds, therefore it’s non-reactive, or inert.