Zinc replacement

In this reaction, the more active zinc replaces the less active copper from solution. The reaction is evident because the blue color of the copper sulfate solution slowly turns colorless and a deposit of copper can be seen to form on the strip of zinc. 

The Leclanche dry cell with zinc replaced by magnesium offers considerable advantages. In the electromotive series, magnesium occupies a more basic position as compared to zinc ( n = -0.76 V / g = -2.38 V), and this means that the voltage of a magnesium cell is greater than that of a similar zinc cell. 

C ZDDP + polyisobutylene succinimide dispersant + calcium carbonate-phenate [Ca] = 4220 ppm Low-molecular weight phosphates, short chain ortho- and pyro-phosphates ( 50% of zinc replaced by calcium in phosphate film some carbonates detected in tribofilm)... 

Equation (46) shows that under standard conditions, this cell, with a positive SrxnG, is not spontaneous. Copper does not spontaneously replace zinc ions in solution. With the zinc electrode as anode (i.e., with zinc replacing copper ions in solution), the cell... 

Zinc oxide is a very old technological material. Already in the Bronze Age it was produced as a byproduct of copper ore smelting and used for healing of wounds. Early in history it was also used for the production of brass (Cu-Zn alloy). This was the major application of ZnO for many centuries before metallic zinc replaced the oxide [149]. With the start of the industrial age in the middle of the nineteenth century, ZnO was used in white paints (chinese white), in rubber for the activation of the vulcanization process and in porcelain enamels. In the following a number of existing and emerging electronic applications of ZnO are briefly described. 

The reaction is known as the Simmons-Smith reaction, after the two chemists at the DuPont chemical factory who discovered it in 1958. Even after several decades, it is the most important way of making cyclopropane compounds, though nowadays a variant that uses more easily handled starting materials is often used. Diethyl zinc replaces the Zn/Cu couple of the traditional Simmons-Smitji reaction. In this example, a double cyclopropanation on a C2 symmetric diene derived from tartaric acid gives very good stereoselectivity for reasons we will soon discuss. 

In many reactions, one atom or group of atoms replaces another. For example, zinc replaces copper from a solution of copper sulfate ... 

Therefore, K = e856 = 1.50 x 1037, indicating that the equilibrium in the reaction for zinc replacing copper lies far to the right. The reactions... 

These are the first studies of zinc absorption reported In a large group of normal subjects. Results of these studies are Important as a basis for comparison with data from patients with various diseases who may exhibit abnormalities of zinc absorption. Zinc absorption has been shown to decrease with age In normal humans, but whether this Is related to decreased anabolism with reduced demand for zinc or to some physiological or pathological process associated with aging Is unclear. The decreased absorption of zinc taken with food Is Important with respect to the design of studies of zinc metabolism. In the determination of zinc bloavallablllty and nutritional requirements of the trace metal and In treatment of subjects who may require zinc replacement. 

The -solution of zinc in acid can be accelerated by adding a small amount of cupric ion to the acid. The probable mechanism of this effect is that zinc replaces cupric ion from the solution, depositing small particles of metallic copper on the surface of the zinc, and these small particles then act in the way described above. 

Zinc deficiency is common in patients with cirrhosis and has been reported to cause overt HE. Zinc is a required cofactor for ammonia metabohsm two of the five metabolic pathways are zinc dependent. Both supportive and nonsupportive studies evaluating the efficacy of zinc replacement have been published. In a controlled trial in cirrhotic patients with mild HE, the administration of zinc sulfate 600 mg/day for 3 months resulted in increased urea formation and lower ammonia levels, along with improvement in psychological test scores. Zinc supplementation is recommended for long-term management in patients with cirrhosis who are zinc deficient. ... 

The mainstay of therapy of HE involves measures to lower blood ammonia concentrations, and inclndes diet therapy, lactnlose, and antibiotics, alone or in combination with lactnlose. Other adjnnc-tive therapies include zinc replacement. 

Simple stereoselective aldol reactions (chapter 3) can also be controlled by tandem conjugate addition. Addition of Me2CuLi to the simple unsaturated ketone 27 gives the lithium enolate 28. It would be very difficult to produce this enolate from the parent ketone MhiCO.Me with regio- or stereoselectivity. The cyclic transition state 29 with zinc replacing lithium then shows the way to the anti-aldol7 30. 

Single-replacement reaction zinc replaces Pb in Pb(N03)2, forming Zn(N03)2 and lead metal. 

Metal Displacement. A metal in a compound can be displaced by another metal in the elemental state. We have already seen examples of zinc replacing copper ions and copper replacing silver ions (see p. 121). Reversing the roles of the metals would result in no reaction. Thus copper metal wiU not displace zinc ions from zinc sulfate, and silver metal will not displace copper ions from copper nitrate. 

Slip into the test tube two strips of zinc, replace the stopper... 

Zinc plating Tools made of steel are often covered with a layer of zinc to prevent corrosion. Zinc is more reactive than the lead in steel. During zinc plating, the zinc replaces some of the surface lead, coating the steel. 

If the sample solution contains any ions of magnesium and alkaline-earth metals, they will replace zinc and form EDTA complexes since their apparent stability constants are much larger than zinc. The zinc set free will form a complex with the indicator changing the color to violet. The amount of zinc replaced is equivalent to the amoimt of magnesium, and alkaline-earth metals in the sample solution is determined in the second titration. 

Lie Ken Jie, M.S.F., and Lam, WI. K. (1987) Ultrasound in Lipids. Furan Formation Under Ultrasonic Assisted Simmons-Smith Reaction and the Effect of Cadmium and Copper as Zinc Replacers,/. Chem. Soc. Chem. Commun., 1460-1461. 

The notation (aq) indicates that the compound is dissolved in water — in an a<7ueous solution. Because zinc replaces copper in this case, it s said to be more active. If you place a piece of copper in a zinc sulfate solution, nothing will happen. Table 8-1 shows the activity series of some common metals. Notice that because zinc is more active in the table, it will replace copper, just as the preceding equation shows. 

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