14. Solutions

Fluoride ion is added to drinking water at low concentra- tions to prevent tooth decay. What mass of sodium fluoride (NaF) should be added to 750 L of water to make a solution that is 1.5 ppm in fluoride ion? (LO 13.5) (a) 1.1 g (b) 2.5 g (c) 0.51 g (d) 3.1 g

Phosphorus is present in seawater to the extent of 0.07 ppm by mass. Assuming that the phosphorus is present as dihydrogenphosphate, H2PO4-, calculate the correspond-ing molar concentration of H2PO4- in seawater.

How would you prepare each of the following solutions? (a) 100 mL of a 155 ppm solution of urea, CH4N2O, in water

Which of the following solutions has the higher molarity? (a) 10 ppm KI in water or 10,000 ppb KBr in water

The ozone layer in the Earth's stratosphere has an average total pressure of 10 mm Hg 11.3 * 10-2 atm2. The partial pressure of ozone in the layer is about 1.2 * 10-6 mm Hg 11.6 * 10-9 atm2. What is the concentration of ozone in parts per million, assuming that the average molar mass of air is 29 g/mol?

(b) Concentrations of lead in the bloodstream are often quoted in units of μg/dL. Averaged over the entire country, the mean concentration of lead in the blood was measured to be 1.6 μg/dL in 2008. Express this concentration in ppb.

An impurity in water has an extinction coefficient of 3.45 * 103 M-1 cm-1 at 280 nm, its absorption maximum (A Closer Look, p. 576). Below 50 ppb, the impurity is not a problem for human health. Given that most spectrome- ters cannot detect absorbances less than 0.0001 with good reliability, is measuring the absorbance of a water sample at 280 nm a good way to detect concentrations of the impu- rity above the 50-ppb threshold?

Most fish need at least 4 ppm dissolved O2 in water for survival. (a) What is this concentration in mol>L?

The maximum allowable concentration of lead in drinking water is 9.0 ppb. (b) How many grams of lead are in a swimming pool containing 9.0 ppb lead in 60 m3 of water?

The Safe Drinking Water Act (SDWA) sets a limit for mercury—a toxin to the central nervous system—at 0.0020 ppm by mass. Water suppliers must periodically test their water to ensure that mercury levels do not exceed this limit. Suppose water becomes contaminated with mercury at twice the legal limit (0.0040 ppm). How much of this water would a person have to consume to ingest 50.0 mg of mercury?

Federal regulations set an upper limit of 50 parts per million (ppm) of NH3 in the air in a work environment [that is, 50 molecules of NH31g2 for every million molecules in the air]. Air from a manufacturing operation was drawn through a solution containing 1.00 * 102 mL of 0.0105 M HCl. The NH3 reacts with HCl according to: NH31aq2 + HCl1aq2¡NH4Cl1aq2 After drawing air through the acid solution for 10.0 min at a rate of 10.0 L/min, the acid was titrated. The remaining acid needed 13.1 mL of 0.0588 M NaOH to reach the equivalence point. (b) How many ppm of NH3 were in the air? (Air has a density of 1.20 g/L and an average molar mass of 29.0 g>mol under the conditions of the experiment.)

Federal regulations set an upper limit of 50 parts per million (ppm) of NH3 in the air in a work environment [that is, 50 molecules of NH31g2 for every million molecules in the air]. Air from a manufacturing operation was drawn through a solution containing 1.00 * 102 mL of 0.0105 M HCl. The NH3 reacts with HCl according to: NH31aq2 + HCl1aq2¡NH4Cl1aq2 After drawing air through the acid solution for 10.0 min at a rate of 10.0 L/min, the acid was titrated. The remaining acid needed 13.1 mL of 0.0588 M NaOH to reach the equivalence point. (a) How many grams of NH3 were drawn into the acid solution?