Med Tech Exam Review - Clinical Chemistry | Actual Exam Questions | 100% Correct Answers | Verified 2024 Version

In the analytic technique of potentiometry, a comparison is made between the voltage of one half-cell connected to another half-cell. It is customary that all half-cell potentials be compared to the potential generated by a standard electrode. This standard electrode is: a. A hydrogen electrode b. a calcium electrode c. a potassium electrode d. a copper electrode e. an iron electrode - A. a half-cell, also called an electrode, is composed of a single metallic conductor surrounded by a solution of electrolyte. An electrochemical cell consists of two half-cells. If two different kinds of half-cells are connected in such a way as to make a complete circuit, a current will flow because of the potential difference between the two electrodes. The connection must be between the two electrolyte solutions, usually by means of a salt bridge. The universally accepted standard halfcell with which all other half-cells are compared is the hydrogen electrode, arbitrarily assigned a potential E of 0.000 volt in an electrolytic cell, the half-cell where reduction takes place is known as the a. anode b. cathode c. inidcating electrode d. reference electrode e. standard electrode - B. oxidation involves the loss of electrons, and reduction the gain of electrons. In an electolytic cell composed of two different half-cells - for example, zinc in zinc sulfate and copper in copper sulfate - electrons will flow from the anode to the cathode. thus reduction takes place at the cathode mercury covered by a layer of mercurous chloride in contact with satruated potassium chloride solution is a description of which of the following types of electrodes? a. antimonyb. calomel c. hydrogen d. quinhydrone e. silver/silver chloride - B. In practical applications of potentiometry, it is desirable to use one halfcell with a known and constant potential that is not sensitive to the composition of th ematerial to be analyzed. This is called the reference electrode. One common reference electrode is the calomel electrode, which consists of mercury covered by a layer of mercurous chloride in contact with a saturated solution of potassium chloride. The other half-cell, called the indicator electrode, is selected on the basis of the change in its potential with change in the concentration of the analyte of interest when the pH-sensitive glass electrode is not actively in use, it should be kept in a. distilled or deionized water b. physiologic saline solution c. the medium recommended by the manufacturer d. a buffer solution with a pH near the pH of the internal solution in the electrode e. a buffer solution with a pH near the pH at which the electrode is to be used - C. for optimum performance, pH-sensitive glass electrodes that are not actively in use should be kep timmersed in an aqueous medium. Since the exact composition of the pH-sensitive glass varies from one manufacturer to another, the glass electrode should be maintained in the medium recommended by the manufacturer. Usual media are water, dilute HCl, and buffer with a pH near the pH of the solution to be measured. The functioning of a glass electrode depends on the properties of the pH-sensitive glass. A typical glass electrode is made by sealing a thin piece of pH-sensitive glass at the end of a piece of glass tubing and filling the tube with a solution of hydrochloric acid saturated with silver chloride. A silver wire is immersed in the solution in the tube with one end extending outside the tube for external connection. This is essentially a silver/silver chloride reference