Chapter 2

Indicate how many significant figures are in each of the following numbers. a. 903 b. 0.903 c. 1.0903 d. 0.0903 e. 0.09030 f. \(9.03 \times 10^{2}\)

Round each of the following to three significant figures. a. 0.89377 b. 0.89328 c. 0.89350 d. 0.8997 e. 0.08907

Report results for the following calculations to the correct number of significant figures. a. \(4.591+0.2309+67.1=\) b. \(313-273.15=\) c. \(712 \times 8.6=\) d. \(1.43 / 0.026=\) e. \((8.314 \times 298) / 96485=\) f. \(\log \left(6.53 \times 10^{-5}\right)=\) g. \(10^{-7.14}=\) h. \(\left(6.51 \times 10^{-5}\right) \times\left(8.14 \times 10^{-9}\right)=\)

Figure 1.2 shows an analytical method for the analysis of \(\mathrm{Ni}\) in ores based on the precipitation of \(\mathrm{Ni}^{2+}\) using dimethylglyoxime. The formula for the precipitate is \(\mathrm{Ni}\left(\mathrm{C}_{4} \mathrm{H}_{7} \mathrm{~N}_{2} \mathrm{O}_{2}\right)_{2} .\) Calculate the precipitate's formula weight to the correct number of significant figures.

An analyst wishes to add \(256 \mathrm{mg}\) of \(\mathrm{Cl}^{-}\) to a reaction mixture. How many \(\mathrm{mL}\) of \(0.217 \mathrm{M} \mathrm{BaCl}_{2}\) is this?

Commercially available concentrated hydrochloric acid is \(37.0 \% \mathrm{w} / \mathrm{w}\) HCl. Its density is \(1.18 \mathrm{~g} / \mathrm{mL}\). Using this information calculate (a) the molarity of concentrated \(\mathrm{HCl}\), and (b) the mass and volume, in \(\mathrm{mL}\), of a solution that contains 0.315 moles of HCl.

The density of concentrated ammonia, which is \(28.0 \% \mathrm{w} / \mathrm{w} \mathrm{NH}_{3}\), is \(0.899 \mathrm{~g} / \mathrm{mL}\). What volume of this reagent should you dilute to \(1.0 \times 10^{3} \mathrm{~mL}\) to make a solution that is \(0.036 \mathrm{M}\) in \(\mathrm{NH}_{3} ?\)

A \(250.0 \mathrm{~mL}\) aqueous solution contains \(45.1 \mu \mathrm{g}\) of a pesticide. Express the pesticide's concentration in weight-to-volume percent, in parts per million, and in parts per billion.

A city's water supply is fluoridated by adding NaF. The desired concentration of \(\mathrm{F}^{-}\) is 1.6 ppm. How many \(\mathrm{mg}\) of \(\mathrm{NaF}\) should you add per gallon of treated water if the water supply already is 0.2 ppm in \(\mathrm{F}^{-}\) ?

What is the \(\mathrm{pH}\) of a solution for which the concentration of \(\mathrm{H}^{+}\) is \(6.92 \times 10^{-6} \mathrm{M}\) ? What is the \(\left[\mathrm{H}^{+}\right]\) in a solution whose \(\mathrm{pH}\) is 8.923 ?

When using a graduate cylinder, the absolute accuracy with which you can deliver a given volume is \(\pm 1 \%\) of the cylinder's maximum volume. What are the absolute and the relative uncertainties if you deliver 15 \(\mathrm{mL}\) of a reagent using a \(25 \mathrm{~mL}\) graduated cylinder? Repeat for a \(50 \mathrm{~mL}\) graduated cylinder.

Calculate the molarity of a potassium dichromate solution prepared by placing 9.67 grams of \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) in a \(100-\mathrm{mL}\) volumetric flask, dissolving, and diluting to the calibration mark.

For each of the following explain how you would prepare \(1.0 \mathrm{~L}\) of a solution that is \(0.10 \mathrm{M}\) in \(\mathrm{K}^{+}\). Repeat for concentrations of \(1.0 \times 10^{2}\) \(\operatorname{ppm} \mathrm{K}^{+}\) and \(1.0 \% \mathrm{w} / \mathrm{v} \mathrm{K}^{+}\) a. \(\mathrm{KCl}\) b. \(\mathrm{K}_{2} \mathrm{SO}_{4}\) c. \(\mathrm{K}_{3} \mathrm{Fe}(\mathrm{CN})_{6}\)

A series of dilute \(\mathrm{NaCl}\) solutions are prepared starting with an initial stock solution of \(0.100 \mathrm{M} \mathrm{NaCl}\). Solution \(\mathrm{A}\) is prepared by pipeting \(10 \mathrm{~mL}\) of the stock solution into a 250 -mL volumetric flask and diluting to volume. Solution \(\mathrm{B}\) is prepared by pipeting \(25 \mathrm{~mL}\) of solution \(\mathrm{A}\) into a 100 -mL volumetric flask and diluting to volume. Solution \(\mathrm{C}\) is prepared by pipeting \(20 \mathrm{~mL}\) of solution \(\mathrm{B}\) into a 500 -mL volumetric flask and diluting to volume. What is the molar concentration of \(\mathrm{NaCl}\) in solutions \(A, B\) and \(C\) ?

Calculate the molar concentration of \(\mathrm{NaCl}\), to the correct number of significant figures, if \(1.917 \mathrm{~g}\) of \(\mathrm{NaCl}\) is placed in a beaker and dissolved in \(50 \mathrm{~mL}\) of water measured with a graduated cylinder. If this solution is quantitatively transferred to a 250 -mL volumetric flask and diluted to volume, what is its concentration to the correct number of significant figures?

What is the molar concentration of \(\mathrm{NO}_{3}^{-}\) in a solution prepared by mixing \(50.0 \mathrm{~mL}\) of \(0.050 \mathrm{M} \mathrm{KNO}_{3}\) with \(40.0 \mathrm{~mL}\) of \(0.075 \mathrm{M} \mathrm{NaNO}_{3} ?\) What is \(\mathrm{p} \mathrm{NO}_{3}\) for the mixture?

What is the molar concentration of \(\mathrm{Cl}^{-}\) in a solution prepared by mixing \(25.0 \mathrm{~mL}\) of \(0.025 \mathrm{M} \mathrm{NaCl}\) with \(35.0 \mathrm{~mL}\) of \(0.050 \mathrm{M} \mathrm{BaCl}_{2}\) ? What is pCl for the mixture?

To determine the concentration of ethanol in cognac a \(5.00 \mathrm{~mL}\) sample of the cognac is diluted to \(0.500 \mathrm{~L}\). Analysis of the diluted cognac gives an ethanol concentration of \(0.0844 \mathrm{M}\). What is the molar concentration of ethanol in the undiluted cognac?