Complete the following passage with the best answers. Some…
Complete the following passage with the best answers. Some answers may be used more than once, some may not be used. The strength and concentration of acids and bases can be measured in multiple ways. Perhaps the simplest, oldest, and most common methods involve the use of pH 1)____________________, which change color in the presence of acid or base. One type is called 2)____________________ paper, which generally changes to blue in the presence of base, and pink (or red) in the presence of acid. Another type, which goes by the generic name of 3)_________________________ uses several different compounds which change color at different pH values, generating a spectrum of different colors and allowing a more accurate estimate of the pH of the solution. For even more precise results, a digital 4)________________________ can be used, which is an electronic instrument with an electrode that is immersed in the solution to give a digital readout of pH. Such instruments do require frequent calibration, however. A different sort of measure involves an actual stoichometric experiment — in a 5)_______________________, a solution with a very precisely known concentration is reacted with the unknown acid or base until the exact point of complete reaction is reached, at which point the volume and concentration are used to calculate the concentration of the unknown. In such an experiment, a common visual indicator known as 6)________________________ can be used, which changes color from clear to a purple-pink color very close to neutral pH, with the pink color seen in the basic pH range and clear when the solution is acidic.