Chapter 4, Problem 4.9QE

Addition of water to concentrated sulfuric acid is dangerous because it generates enough heat to boil the water, causing it to spatter out of the container. For this reason, chemists remember to add acid to water. In a dilution experiment, we calculate the amount of the more concentrated solution that must be measured out. If we place this concentrated solution (Figure 4.7) in the volumetric flask first, then dilute with water, we violate the caution “Add acid to water.” Describe a safer variation on the method shown in Figure 4.7 that allows the quantitative dilution of concentrated sulfuric acid.

Figure 4.7 Preparing a dilute solution from a concentrated solution. (a) Draw the concentrated solution into a pipet to a level just above the calibration mark. (b) Allow the liquid to settle down to the calibration line. Touch the tip of the pipet to the side of the container to remove any extra liquid. (c) Transfer this solution to a volumetric flask. Again touch the pipet to the wall of the flask to ensure complete transfer, but do not blow out the pipet because it is calibrated for a small amount of liquid to remain in the tip. (d) Dilute to the mark with solvent. Frequently, especially with concentrated acids, it is best to have some solvent present in the volumetric flask before you add the concentrated sample.