BIO 221 Human Anatomy & Physiology I

Fall 2014

Homework - Chemistry

Making solutions is an important part of doing scientific research or caring for patients. There are two methods for measuring solution concentrations: percent solutions, and molarity.

Percent solutions:

“Percent” is defined as the number of grams of a substance dissolved in 100 mL of solution. For example, a 2% solution equals 2 g of a substance in 100 mL of water.

1) Determine the number of grams of NaCl needed to make 100 mL of a 0.09% NaCl solution.

2) Determine the number of grams of dextrose needed to make 200 mL of a 5% dextrose solution.

3) Determine the number of grams of protein needed to make 750 mL of a 14% protein solution.

Molarity:

“Molar” (M) is a unit of concentration defined as the number of moles of a substance per 1 liter (L) of solution. In other words, M = mol/L. A “mole” (abbreviated “mol”) is a particular (very large) number of particles of a substance; it is similar to the concept that a dozen equals 12. A mole equals 6.02 x 1023, but this number is irrelevant for our calculations. Keep in mind that 1000 mL = 1 L.

4) Calculate the number of moles of NaCl you need to make 500 mL of a 0.1 M solution.

5) Calculate the number of moles of sucrose needed to make 75 mL of a 2M solution.

6) a) Calculate the number of moles of NaHCO3 (sodium bicarbonate) needed to make 100 mL of a 0.3M solution.

b) NaHCO3 has a formula weight of approximately 84 g / mol. How many grams of NaHCO3 do you need to equal the number of moles you calculated in part (a)?

c) Using your answer from part (b), describe in sentence form how you would make the solution described in this problem.

7) a) How many moles of Enalapril (a common blood pressure-reducing drug) do you need to make 10 mL of a 20mM solution (1000mM = 1M)?

b) How many grams of Enalapril do you need to make the solution in part (a) if the formula weight of the drug is 4952.53 g / mol?

A second important numerical concept in biology is that of pH.The pH of a solution measure of the concentration of H+ ions in that solution. Because the H+ concentration can vary widely – by up to 14 factors of 10 in everyday solutions – a logarithmic scale is used to describe the H+ concentration. The pH of a solution equals the negative log of the H+ concentration. As a mathematical formula: pH = –log [H+]. Because we are dealing with many zeros behind a decimal point, it is helpful to become comfortable with scientific notation. In scientific notation, 3000 is written as 3 x 103. 5,000,000 is written as 5 x 106. Numbers less than 1 use negative exponents: 0.003 is written as 3 x 10-3; whereas 0.00000006 is written as 6 x 10-8.

8) If the pH of a solution is 8, what is the H+ concentration of that solution? Write your answer first in decimal form, then write it in scientific notation.

9) If the pH of a solution is 2, what is the H+ of that solution? Again, write your answer in decimal form, then in scientific notation.

10) a) Using your answers from problems 8 and 9, is a solution of pH 8 more concentrated or less concentrated than a solution with a pH of 2?

11) Gastric (stomach) “juice” has a pH ~2. Food taken into the stomach is likely to be digested by (select one): a) H+ being added to food particles; or b) H+ being stripped off of food particles? Defend your answer.