ISBN-13: 9780321596949 978-0321596949
Chapter 3: Mass and Volume Measurements
- (A) Accurate mass measurements are critically important to many analytical chemistry applications. Knowing the properties of the analytical balance used for those determinations is part of those determinations. Suppose a balance has a capacity of XXX and a readability of YYYY . What is the resolution of the balance?
(B) For detailed mass determinations on a balance, the buoyancy factor may need to be considered before reporting the mass of a sample. Some studies show that taking a small daily dose of aspirin (acetylsalicylic acid; ASA) offers protection from heart attacks. (This is somewhat controversial and should only be done under a doctor’s care.) If you massed 1.0810g of ASA (density of 1.40 g/cm3) what would you report as the corrected mass?
(Assume the density of air is 0.0012 g/cm3; and the density of the counterweights = 8.00g/cm3.)
2.(A) Even though we know that buoyancy effects can cause slight errors when determining masses, we often ignore the slight error. When you examine the buoyancy correction equation would the error be less or more when the density of the material being massed is closer to the assumed 8 g/mL for the calibration weights?
(B) Sometimes we calibrate the volume delivered in analytical glassware by determining the mass of water delivered by a predicted volume. Suppose the water delivered by a 25.0 mL pipet had an apparent mass (uncorrected) of 25.05 grams. If the density of air at the temperature was 0.001 2 g/mL, the density of the calibration weights was 8.0 g/mL and the density of water at the temperature was 0.9950 g/mL what would you report as the corrected mass of the sample? (report to four significant digits)
(C) Using the actual mass of water delivered by the pipette, what is the volume of water delivered by the “25 mL” pipette?
- (A) The primary standard acid potassium hydrogen phthalate (KHP) is often used to help determine the concentration of a basic solution of sodium hydroxide. If 4.826 2 grams of KHP were massed on a balance when the air had a density of 0.001 2 g/mL and the counterweights used had a density of 8.00 g/mL, what would be the true mass, accounting for possible buoyancy affects, of the KHP? The density of KHP is 1.636 g/mL.
(B) Without detailed calculations, which one of the following when measured would have the greatest difference between its displayed mass (in air) and its true mass?
(i) acetic acid (d = 1.05 g/mL) (ii) CCl4 (d = 1.59 g/mL) (iii) Sulfur (d = 2.07 g/mL) (iv) PbO2 (d = 9.4 g/mL)
- Suppose a biochemist is using bovine serum albumin (BSA) in an assay. The solution on hand has a concentration of 425 mg/mL. Describe how that solution could be used to prepare 100.0 mL of a 125 mg/mL solution to use in the assay.
- The amount of glucose in a person’s blood right now would depend on if food was eaten before working this problem or after working the problem. If the level of glucose in a blood sample (C6H12O6 molar mass = 181 g/mol) was 95 mg/100mL, what would be the Molarity of glucose in the blood?
- During cold winters a solution of antifreeze in car cooling systems will often keep the coolant solution from freezing. If a 50.00% (by mass) solution of environmentally friendly propylene glycol, with a density of 1.04 g/mL is used, what would be the molality (m) of the solution? (molar mass of propylene glycol = 76.09 g/mol)
- (A) Concentrated hydrochloric acid (HCl; molar mass = 36.46g/mol) is commonly found in analytical labs (of course, kept under the exhaust hood). The density of this dangerous solution is 1.18 g/mL. The solution is known to be 37.1%, by mass HCl. What is the molarity (M) and molality (m) of this solution?
(B) The density reported in part (A) was taken at 25oC. If the lab temperature dropped to 15oC would that make the density of the solution increase or decrease ?
(C) Which of the following best describes the effect on concentration when the temperature in the lab dropped?
(i) Neither the M nor m would be affected.
(ii) M would be greater; m would be unaffected.
(iii) M would be smaller; m would be unaffected.
(iv) M would be unaffected; m would be greater
(v) M would be unaffected; m would be smaller
- (A) Silver nitrate is often used to precipitate chloride ions in water analysis. How many grams of silver nitrate would be needed to prepare 100.0 mL of 0.100 M silver nitrate (AgNO3) solution? (1 mol = 169.9 g/mL)
(B) Suppose the lab already has a solution that is 0.250 M AgNO3. Calculate and describe how to prepare, using a volumetric flask, 100.0 mL of 0.100 M AgNO3 from a stock 0.250 M AgNO3 solution. (Report the amount and brief directions for preparation.)
(C) It is a little known fact that in the USA drinking water contains, on the average, approximately 28 ppb Ag. Consuming about one liter of water in a day (recall that the density of water is 1.0g/mL) would result in ingesting how many grams of silver?
- (A) Lactic acid can be produced by bacteria and fungi through fermentation. Lactic acid can help produce a sour taste in yogurt and sourdough bread. Suppose you are going to analyze a solution of lactic acid that is known to have a density of 1.15 g/mL and is also known to be 4.88% w/w lactic acid (C3H6O3; molar mass = 90.08 g/mol) What would you report as the molarity of the solution?
(B) Convert 4.88% w/w to ppm.
- (A) High fructose corn syrup is made by using an enzyme reaction to convert some glucose in corn to fructose (which has a sweeter taste and is cheaper than sucrose). HFCS is a mass mixture of approximately 55.0% fructose and 45.0% glucose. What is the molarity (M) of fructose in a soft drink containing 42.0 grams of HFCS in a volume of 355 mL? (molar mass of fructose = 180.2 g/mol)
(B) Molarity (M) is a very common way to express solution concentration. However, analytical concentration (C) may also be used. Which of the following is the accurate statement?
(i) Analytical concentration (C ) calculations are based only on molar masses of the ions rather than the entire formula unit.
(ii) C calculations express a concentration with more significant digits than M.
(iii) C communicates that strong electrolyte substances are converted to other ionic species in solution.
(iv) An analytical concentration of 0.44 M MgCl2 (a strong electrolyte) implies that there are 0.44 moles/L of MgCl2 in the solution.
(v) C concentrations are not temperature dependent.