Copper standard reduction potentials

Copper compounds, which represent only a small percentage of ah copper production, play key roles ia both iadustry and the biosphere. Copper [7440-50.8] mol wt = 63.546, [Ar]3/°4.t is a member of the first transition series and much of its chemistry is associated with the copper(II) ion [15158-11-9] [Ar]3i5. Copper forms compounds of commercial iaterest ia the +1 and +2 oxidation states. The standard reduction potentials, for the reasonably attainable valence states of copper are... 

The table of standard reduction potentials assists in the determination as to whether species can react with each other, or not. This can be substantiated by considering the reaction of hydrogen with two metals, copper and zinc. In order to determine whether or not a reaction takes place spontaneously under standard conditions, one calculates the standard potential using hydrogen ions and the metal as reactants. 

When water is electrolyzed with copper electrodes or using other common metals, the amount of 02(g) is less than when Pt electrodes are used, but the amount of H2(g) produced is independent of electrode material. Why does this happen In electrolysis, the most easily oxidized species is oxidized and the most easily reduced species is reduced. If we compare Cu and H20 by looking on the standard reduction potentials chart (data given below), we see that Cu is a stronger reducing agent than H20, because 0.337 V is less than 0.828 V. This means that Cu is more easily oxidized than water. 

Reduction always occurs at the cathode. Note that H°ed for silver is +0.7991 volt, according to the Table of Standard Reduction Potentials. E°ed for copper is +0.337. This means that the copper metal is higher in the activity series than the silver metal, so copper metal will reduce the silver ion. The equation that describes reduction (or the cathode reaction) is therefore... 

For a Daniell cell, you know that copper is the cathode and zinc is the anode. The relevant half-reactions and standard reduction potentials from Table 11.1 are as follows. 

One more example demonstrates how to use standard reduction potentials to determine the standard potential of a cell. Let s say you wanted to construct a cell using silver and zinc. This cell resembles the Daniell cell of the previous example except that a silver electrode is substituted for the copper electrode and a silver nitrate solution is used in place of copper sulfate. From Table 14.2, it is determined that when silver and copper interact silver is reduced and copper oxidized. The two relevant reactions are... 

Notice, however, that if the reaction at the Zn/Zn2+ interface is reversed and written as an electronation (reduction) rather than a deelectronation, then this electronation does not proceed spontaneously and its free-energy change is positive. This positive value of AG° = -nFE0 implies that E° must be negative. The standard reduction potentials for the zinc and copper systems are, therefore, -0.76 and +0.34 V, in contrast to the standard oxidation potentials, which are +0.76 and -0.34 V, respectively. 

Table 20.2 lists standard potentials E° for oxidation of first-series transition metals. Note that these potentials are the negative of the corresponding standard reduction potentials (Table 18.1, page 775). Except for copper, all the E° values are positive, which means that the solid metal is oxidized to its aqueous cation more readily than H2 gas is oxidized to H+(aq). 

TABLE 10.6 Standard Reduction Potentials of Copper Complexes in H20... 

You have probably worked with tables of standard reduction potentials before. These tables provide the reduction potentials of various substances. It describes an oxidized species s ability to gain electrons in a reduction half-reaction (like copper in the voltaic cell example). According to this definition, we can use a value from the table to represent the E°red in the expression above, but how do you find the E°ox ... 

The correct answer is (C). You can answer this by looking at the table of standard reduction potentials. Silver is the only substance that is below copper. 

Thus, the standard reduction potential of copper u2, Cu is 0.34 V. Hence, the standard... 

TTHE COPPER(II) AND COPPER(I) IONS undergo facile redox interconversions for which the standard reduction potential is highly dependent on the nature of the ligands and coordination geometries observed (1). Thus, copper ion is a useful electron transfer or oxidation catalyst in the presence of dioxygen (02) (2-4). These properties have been put to advantage by nature, where copper-containing proteins (5-11) exist as electron... 

The corrosion products of noble metals such as copper and silver are complex and affect the use of these metals as decorative materials. Under normal atmospheric conditions copper forms an external layer of greenish copper carbonate called patina. Silver tarnish is silver sulfide (Ag2S), which in thin layers gives the silver surface a richer appearance. Gold, with a positive standard reduction potential (1.50 volts), significantly larger than that for oxygen (1.23 volts), shows no appreciable corrosion in air. 

For solutions with unit activities of ions, the standard reduction potentials for these reactions are 0.337 Vsh and -1.630 Vsh. respectively The reduction potentials in our case are shifted in the active direction however because the activities of the metal ions in solution are less than unity. Because the reduction potential of titanium is more active (more negative) than that of copper, the reduction of copper ions by the titanium metal and the concurrent oxidation of titanium metal by the copper ions will be thermodynamically favored. 

What would the potential of the hydrogen electrode be if the copper electrode were the standard How would the relationships among the standard reduction potentials change ... 

TABLE 13.2 Standard Reduction Potentials for a Series of Elements of Importance to Electrolytic Purification of Copper"... 

A voltaic cell is designed with a copper electrode immersed in 1.0 M copper (II) sulfate solution, CuSO j(aq), and a lead electrode immersed in 1.0 M lead (II) nitrate solution, Pb(NO3)2(aq) at 25 °C. Given the standard reduction potentials shown below, determine the potential of the cell in volts. 

The standard electrode potentials might well be called standard reduction potentials because they measure the tendency of the electrode material to be reduced by the gain of electrons. They naturally determine many of the properties of a substance. Because zinc has a more negative standard electrode potential than copper, elemental zinc will tend to reduce copper salts ... 

Althongh the transition metals are less electropositive (or more electronegative) than the alkali and alkaline earth metals, their standard reduction potentials suggest that all of them except copper should react with strong acids such as hydrochloric acid to produce hydrogen gas. Flowever, most transition metals are inert toward acids or react slowly with them becanse of a protective layer of oxide. A case in point is chromium ... 

For example, the potential of a cell consisting of a copper electrode immersed in 1.000 M Cu2+ solution suitably connected to a standard hydrogen electrode just described has a potential of 0.34 V, with the copper ions being reduced. We assign the standard reduction potential of the Cu +/Cu half-cell to be 0.34 V. The potential... 

The reaction of a metal with an aqueous acid to yield hydrogen, a severe form of corrosion, involves oxidation of the metal and reduction of hydrogen ions in solution, H (aq), to H2 gas, and so can be thought of in terms of an electrochemical cell. The tendency for a reaction to occur follows the order of the electrochemical series (Table 9.1). Metals below H2 in the electrochemical series-those with a negative standard reduction potential-will react with aqueous acids to release hydrogen gas. Those above it will not react with acid. Thus, zinc will dissolve in acid to give hydrogen, whereas copper will not. 

Copper salts are available in the -i-l or -i-2 oxidation state, while the stable In and Ga oxidation states are -i-3. The relevant standard reduction potentials are given below. 

---