Problem Set #2 Flashcards
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?
2.56
- MW = 58.44g for 1M
- We have 500mL or 0.5L of NaCL solution
- In that 500mL, we have 74.7g of NaCl so…
- Well, 74.7/58.4 = 1.27M, but that’s if we had a full liter and we only have 1/2 liter (500mL)
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?
123.67
- Find MW , it’s given, = 36.46g
- We need 5.3M so 36.46*5.3 = 193.24g/L
- We only need 0.64 L or 640 mls
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.
3.51
- Find MW, it’s given = 58.44g
- We need 0.2M so 58.44*0.2 = 11.69g/L
- we only need 0.3 L or 300 ml
If the H+ ion concentration of a household item is 10-3, how many OH- ions does it have?
10^-11
[H+] x [OH-] = 10-14
The pH of an item is 12. Is this acidic or basic and how many H+ ions does it have?
Basic 10^-12
[H+] x [OH-] = 10-14
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?
1.More
2.Less
Enzymes in your stomach are more acidic so then have more H+ (and vice versa).
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
305
Do you have a numerical only answer with NO decimal places (i.e. a whole number)?
(1812) + (271) + (141) + (163)
What type of covalent bonds exist in methane?
Non polar
There is only slight differences in the electronegativity of carbon and hydrogen, so they will share their electrons fairly equally.
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?
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).
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.
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.
How many covalent bonds can a Carbon atom form?
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.
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)
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.
Which functional groups that we talked about are NOT present in nucleotides, like the one depicted below?
Carboxyl groups
Carboxyl is COOH
Phosphate is PO3
Hydroxyl is OH
Amino is NH2
Which of the following is NOT a compound?
O2
A compound is a substance formed from two or more elements chemically united in fixed proportions.
Which of the following is NOT a molecule?
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.
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?
73, 108, 73
Protons = atomic # = electrons
Atomic mass = #protons + #neutrons
Which series of elements below are ordered from high to low electronegativity?
HINT: Remember, Neon is inert. This means it, essentially, has no electronegativity.
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).
Which of these is NOT an essential element that makes up living matter?
All of these are essential elements
Trace elements can be (are) also essential.
Which statement about water’s polarity is TRUE?
All are true
Water is a very unique substance because it can do things unlike any other molecule.
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.
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.
What is the [OH-] in a solution with a pH of 13?
10^-1
[H+] x [OH-] = 10-14
What is the valency of Sulfur?
2
How many electrons does S need to complete it’s outer most shell?
What is the combining power of S?
Which statement about enantiomers is FALSE?
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.
Phosphorus-32 undergoes radioactive decay at a constant rate. Estimate its half-life from the graph below showing its radioactivity measured over time.
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.
An atom with 8 electrons in its outer shell tends to
be chemically inert.
With 8 electrons in its outer shell, an atom isn’t actively seeking bonds, therefore it’s non-reactive, or inert.
