Cu-S-H

First, free energy data

The free energy data of Cu-S-H ₂ O system at 423 K is shown in Table 1.

Free energy data of Cu-S-H2O system at 423K

Second, the equilibrium equation

As mentioned earlier, a full cell reaction should be used at higher temperatures to get the correct results.

Third, the analysis of the advantage zone map

Sulfur-containing ionic activity ^10-1 containing copper ion activity 10 ^-3 mol / L drawn Cu-S-H ₂ O system at 423K predominance area shown in Figure 1, in this figure HCuO ₂ ^- is pH 12.91 is in equilibrium with CuO, but CuO ₂ ^{2 -} does not appear.

Figure 1 Cu-S-H ₂ O dominant area map

(423K, S and H ₂ S activity is 10 ^-1 , Cu ion activity is 10 ^-3 )

Advantages of the system of FIG region 423K and 298K in the most important difference is that, at lower temperatures, | Cu ⁺ | lower = 10 ^-6 mol / L Cu ⁺ appears still to see, while in the 423K | Cu ⁺ | = When 10 ^-3 mol ∕ L, there is a dominant zone of Cu ⁺ . Cu ⁺ advantages region surrounded by four line _{^{balance: Cu 2 +, Cu 2 O}} , Cu metal and Cu ₂ S. After an equilibrium line is HSO ₄ ^- ion reduced to produce Cu ₂ S. If the activity of the sulfur-containing ions in the system is very low, or its reduction is very slow, the upper and lower boundaries of the Cu ⁺ dominant region are Cu ^{2 +} ions and Cu metal regions, respectively, and the right side is determined by the solubility product of Cu ₂ O. The limiting pH for Cu ⁺ activities of 10 ^-2 , 10 ^-1 and 1 mol ∕ L was 2.15, 1.15 and 0.15, respectively. Whether or not the dominant region of Cu ⁺ appears on the graph depends entirely on Cu ^{2 +} or Cu ⁺ formation when Cu metal is oxidized with increasing oxidation-reduction potential at a specific activity. At 298K, when Cu ⁺ |=|Cu ⁺ |=10 ^-6 mol∕L, Cu ^{2 +} is formed at a lower E value, and when the activity is 10 ^-3 mol ∕L at 423 K, it is a Cu ⁺ .

It is customary to draw the dominant area maps to set the activity of all ions containing a particular element to be the same, but in reality this is not common. Take a look at the limit activity of Cu ⁺ at a given Cu ^{2 +} activity for 423K. This can be calculated by setting the E values ​​of the reaction formulas (h) and (i) to be equal. then

0.340+0.0420lg|Cu ^{2 +} |=0.406+0.0839lg|Cu ⁺ |

Lg|Cu ^{2 +} |-2lg|Cu ⁺ |=1.57

From this

Using lg|Cu ^{2 +} | to plot lg|Cu ⁺ | to obtain a straight line with a slope of 0.5 intercept 1.57.

Similar calculations at 298K

Lg|Cu ^{2 +} |-2lg|Cu ⁺ |=6.04

From this

These calculations show that in a solution that is not strongly coordinated with cuprous ions, such as sulfuric acid solution, the maximum Cu ⁺ activity is only about 10 ^-3 when the copper sulfate activity reaches 1 mol ∕L. Since the activity coefficient γ _{± of} CuSO ₄ is 0.062 in a 0.5 mol solution and 0.15 in a 0.1 mol solution, the Cu ⁺ activity achievable in the solution is actually much lower than this value. At 423 K, cuprous ions can be considered as a possible reactant.

The main difference between copper sulfides in the dominant regions of 298K and 423K is that CuS is stable only in solutions with a pH below 8 at 423 K, while the stable region of CuS extends to pH = 11 at 298 K. It is worth noting that at these two temperatures, Cu ₂ S is formed by reduction of HSO ₄ ^- , SO ₄ ^{2 -} or CuS. CuS is formed by the reduction of Cu ₂ S from SO ₄ ^{2 -} or HSO ₄ ^- to provide additional sulfide ions. However, it is well known that, like many other elements, the addition of sulfides, usually in the form of NaHS, precipitates out of solution. This reaction is reflected in this advantage map, where the sulfides are stable in the dominant regions of H ₂ S(aq) and HS ^− . CuS can coexist with elemental sulfur and Cu ₂ S cannot coexist with sulfur.

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