Johns Hopkins University Mixtures Solution Concentrations and Dialysis Questions

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Johns Hopkins University

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Please answer/solve all of the attached questions in the word document. They are focused on Mixtures, Solution Concentrations, and Dialysis.

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1. Complete this equation for the dissociation of CdCl2(aq). Omit water from the equation because it is understood to be present. CdCl2(aq)--> 2. How many grams of CaCl2 are needed to make 965.1 g of a solution that is 31.5% (m/m) calcium chloride in water? Note that mass is not technically the same thing as weight, but (m/m) has the same meaning as (w/w). mass: g CaCl2 How many grams of water are needed to make this solution? mass: g H2O 3. What is the volume percent, % (v/v), of an alcohol solution made by dissolving 125 mL of isopropyl alcohol in 765 mL of water? Assume that volumes are additive. volume percent: % (v/v) The mass of solute per 100 mL of solution is abbreviated as % (m/v). The abbreviation % (w/v) is also common. How many grams of sucrose are needed to make 920 mL of a 34.0% (w/v) sucrose solution? mass: g sucrose 4. A fictional cubed-shaped bacterium, Bacterius cubis, occupies a volume of 1.0 femtoliters. This particular type of bacteria is known to communicate with its own species by secreting a small molecule called bactoX ( MW=112.0 g/mol ). A. Each bacterium contains 4820 bactoX molecules that can be secreted. How many moles of bactoX are present in a 1.6 μL sample volume that contains 7.664×106 bacterial cells? moles: mol B. Calculate the molarity (mol/L) of bactoX in the 1.6 μL sample volume if all of the bacteria were to simultaneously secrete all of the bactoX molecules contained within their cell bodies into the vial. concentration: M C. Scientists discovered that bactoX will induce a luminescence response in B. cubis when the concentration in a sample reaches 9.40×10−12 M. How many molecules of bactoX must be present in solution to initiate luminescence in a 1.8 μL sample? How many individual bacteria cells does this represent? The number of bactoX molecules per cell is given in part A. molecules: molecules cells: cells D. What volume, in nanoliters, would the bacteria cells in part C occupy if tightly packed? Assume that there is no space between the cells. volume: nL 5. Suppose a group of volunteers is planning to build a park near a local lake. The lake is known to contain low levels of arsenic (As). Therefore, prior to starting construction, the group decides to measure the current level of arsenic in the lake. If a 13.9 cm3 sample of lake water is found to have 170.3 ng As, what is the concentration of arsenic in the sample in parts per billion (ppb), assuming that the density of the lake water is 1.00 g/cm3? concentration: ppb One of the volunteers suggests hiring an on‑site water treatment company to remove the arsenic from the lake. The company claims their process takes 2.23 days to remove 32.30 kg of arsenic from a water source. Calculate the total mass, in kilograms, of arsenic in the lake that the company will have to remove if the total volume of water in the lake is 0.510 km3. total mass: kg 6. Based on the company's claim and the concentration of arsenic in the lake, how many years will it take to remove all of the arsenic from the lake, assuming that there are always 365 days in a year? number of years: years The adult dosage of diphenhydramine, an antihistamine, is 50.0 mg. A 24 lb child should only receive 20.0% of the adult dose. Calculate this dose in milligrams. dose: mg Liquid diphenhydramine comes in a concentration of 12.5 mg per 5 ml . Using the dosage calculated, how many milliliters of diphenhydramine should be administered to the child? volume: mL 7. A 89.2 lb child has a Streptococcus infection. Amoxicillin is prescribed at a dosage of 45 mg per kg of body weight b.i.d. How many milligrams of amoxicillin should be given at each administration? mass of amoxicillin: mg 8. The recommended single dose for acetaminophen is 10.0 to 15.0 mg/kg of body weight for adults. Using this guideline, calculate the maximum single dosage for a person who weighs 209 lb . maximum dosage: mg 9. A 5.19 g sample of a solid containing Ni is dissolved in 20.0 mL water. A 5.00 mL aliquot of this solution is diluted to 100.0 mL and analyzed in the lab. The analyzed solution was determined to contain 5.73 ppm Ni . Determine the molar concentration of Ni in the 20.0 mL solution. concentration: M Determine the mass, in grams, of Ni in the original sample. mass: g Determine the weight percent of Ni in the sample. weight percent: % 10. A 75.0 mL aliquot of a 1.30 M solution is diluted to a total volume of 208 mL. A 104 mL portion of that solution is diluted by adding 165 mL of water. What is the final concentration? Assume the volumes are additive. concentration: M 11. How many milliliters of 10.5 M HCl(aq) are needed to prepare 465.0 mL of 1.00 M HCl(aq)? 𝑉= mL
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Explanation & Answer

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1. Complete this equation for the dissociation of CdCl2(aq). Omit water from the equation because
it is understood to be present.
CdCl2(aq)--> Cd2+ + 2Cl-

2. How many grams of CaCl2 are needed to make 965.1 g of a solution that is 31.5% (m/m)
calcium chloride in water? Note that mass is not technically the same thing as weight, but (m/m)
has the same meaning as (w/w).
mass:

304.007 g CaCl2

How many grams of water are needed to make this solution?
mass:

661.09 g H2O

3. What is the volume percent, % (v/v), of an alcohol solution made by dissolving 125 mL of
isopropyl alcohol in 765 mL of water? Assume that volumes are additive.
volume percent: 14.045

% (v/v)

The mass of solute per 100 mL of solution is abbreviated as % (m/v). The abbreviation % (w/v) is
also common. How many grams of sucrose are needed to make 920 mL of a 34.0% (w/v)
sucrose solution?
mass:

312.8

g sucrose

4. A fictional cubed-shaped bacterium, Bacterius cubis, occupies a volume of 1.0 femtoliters. This
particular type of bacteria is known to communicate with its own species by secreting a small molecule
called bactoX ( MW=112.0 g/mol ).
A. Each bacterium contains 4820 bactoX molecules that can be secreted. How many moles of bactoX
are present in a 1.6 μL sample volume that contains 7.664×106 bacterial cells?
moles:

6.133 x 10-14

mol

B. Calculate the molarity (mol/L) of bactoX in the 1.6 μL sample volume if all of the bacteria were to
simultaneously secrete all of the bactoX molecules contained within their cell bodies into the vial.
concentration: 3.833 x 10-8

M

C. Scientists discovered that bactoX will induce a luminescence response in B. cubis when the
concentration in a sample reaches 9.40×10−12 M. How many molecules of bactoX must be present in
solution to initiate luminescence in a 1.8 μL sample? How many individual bacteria cells does this
represent? The number of bactoX molecules per cell...


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