Wire dips

A length of 6-7 mm of platinum wire of 0.5 mm diameter sealed into a glass tube is satisfactory electrical connection is made by means of a copper wire dipping into a little mercury in contact with the platinum wire. 

Any inert metallic component of an electrode is written as the outermost component of that electrode in the cell diagram. For example, a hydrogen electrode constructed with platinum is denoted H+(aq) H2(g) Pt(s) when it is the right-hand electrode in a cell diagram and Pt(s) H2(g) H+(aq) when it is the left-hand electrode. An electrode consisting of a platinum wire dipping into a solution of iron(II) and iron(III) ions is denoted either Fe3+(aq),Fe2 (aq) Pt(s) or Pt(s) Fe3+(aq),Fe2+(aq). In this case, the oxidized and reduced species are both in the same phase, and so a comma rather than a line is used to separate them. Pairs of ions in solution are normally written in the order Ox,Red. 

Self-Tfst 4B Write the diagram for a cell that has an electrode consisting of a manganese wire dipping into a solution of manganese(II) ions on the left, a salt bridge, and a coppcr(II)/copper(I) electrode on the right with a platinum wire. 

Oxidation- reduction An inert metal dips into a solution containing ions in two different oxidation states. An example consists of a platinum wire dipping into a solution containing ferrous and ferric ions. Such a cell is described by Pt Fe2 (c,). Fe3 (c2). The comma is used to separate the two chemical species which are in the same solution. These electrodes are similar to the gas electrodes, except that the two species involved in the electrode reaction are ions. The electrode reaction in the example is Fe3 + e Fe2, and there is the possibility of the electrode either donating or accepting electrons. 

Wrap the copper wire around a pencil to make a closely spaced coil. Leave 10 cm of the wire unwrapped. Measure and record the mass of the wire. Dip the coil in the nitric acid, and rinse the coil with water. Use the 10 cm of uncoiled wire to secure the coil on the opposite side of the beaker from the anode, as shown in the diagram. This copper wire will serve as the cathode. 

The electrodes usually are rotated at about 600 rpm. Contact to the platinum wire is made internally by filling the electrode with mercury. A stationary wire dips into the mercury pool at the top to make external contact to the potential-control circuitry. The platinum-glass seals are prone to crack, which causes erratic currents that are associated with the leaking of mercury to the electrode surface. Once cracked, the electrodes are not easily repaired and should be discarded. Table S.9 indicates the dependence of the current on the rotational speed of the electrode. 

Place in separate clean, dry test tubes (100 x 13 mm) 2 mL of distilled water and 2 mL of the residue liquid from the boiling flask. Obtain a clean nickel wire from your instructor. In the hood, dip the wire into concentrated nitric acid and hold the wire in a Bunsen burner flame until the yellow color in the flame disappears. Dip the wire into the distilled water sample. Put the wire into the Bunsen burner flame. Record the color of the flame. Repeat the above procedure, cleaning the wire, dipping the wire into the liquid from the boiling flask, and observing the color of the Bunsen burner flame. Record your observations. Sodium ions produce a bright yellow flame with a Bunsen burner. 

Kappes et al. evaluated the potentiometric detection of acetylcholine and other neurotransmitters through capillary electrophoresis [209]. Experiments were performed on an in-house capillary electrophoresis instrument that made use of detection at a platinum wire, dip-coated in 3.4% potassium tetrakis (4-chlorophenyl) borate/64.4% o-nitrohenyl octyl ether/32.2% PVC in THF. The results were compared to those obtained using capillary electrophoresis with amperometric detection at a graphite electrode. Samples prepared in the capillary electrophoresis buffer were electrokinetically injected (7 s at 5 kV) into an untreated fused silica capillary (88 cm x 25 pm i.d.) and separated with 20mM tartaric acid adjusted to pH 3 with MgO as the running buffer. The system used an applied potential of 30 kV, and detection versus the capillary electrophoresis ground electrode. 

The electrode assembly has been described (see synthesis of dimethyl decanedioate, p. 1, Note 1 and Figure 1). In this case the electrodes have the same polarity and are electrically connected with a platinum wire dipping into the mercury contacts. 

Wire Dips and Colored Fire Sticks These devices are made in the same way as sparklers, by dipping wires or twisted narrow strips of iron or thin sticks of wood, and generally bum with a tranquil flame except for the sparks that come from the burning of the iron wire or strip. Several typical compositions are listed. Alcohol is used for applying the compositions which contain shellac water, for applying the others which contain dextrin. 

To avoid artifacts in impedance measurements when modulating the input voltage of the potentiostat at high frequencies (>10 kHz), the reference electrode should be short-circuited via a capacitance of 10 nF and a Pt wire dipped into the solution in the main part of the cell (Fig. 4.2). The surface of the counter electrode should be sufficiently large so that its interface with the electrolyte does not influence the current-potential curve. Usually a platinized Pt sheet is used as a counter electrode. The electrolyte is made conductive by adding an inert salt of a concentration in the range of 10-3-10- M. 

Discuss the processes occurring in the following electrochemical set up. A Daniell cell is being used to generate an electric current which causes electrolysis in a solution of AgNOsCaq). The electrodes are Ag(s) wires dipping into the AgN03(aq) solution. It is observed that electrons flow from the Zn(s) electrode of the Daniell cell to the electrolytic cell, and from the electrolytic cell back to the Cu(s) electrode of the Daniell cell. 

This electrode is made up of a platinum wire dipping into an aqueous solution of ions of a metal in two oxidation states. Alternatively the solution could be that of a complex of a metal in two oxidation states. The electrode is reversible to the oxidised and reduced forms of the species in solution which appear in the electrode reactions. 

A second or reference electrode is necessary to complete the electrical circuit. The reference electrode is sometimes welded to the pH electrode so that the pair look like a single electrode. Reference electrodes are too often taken for granted their spurious potentials are a common source of error in soil pH measurements. A typical reference electrode is also sketched in Fig. 10.5. The wire dipping into the liquid mercury makes electrical contact with the pH meter, and current flows from the electrode to the solution phase through the reversible reaction ( ° = 0.268 V at 25° C) ... 

A second widely used reference electrode is the saturated calomel electrode (SCE), which consists of a pool of mercury in contact with a solution that is saturated with mercury(I) chloride (calomel) as well as potassium chloride. Platinum wire dipping in the mercury provides electrical contact to the other conductor, and a salt bridge to the second electrolyte completes the circuit. The potential of this reference is about 0,24 V positive. The electrode reaction is... 

Calculate the theoretical potential of a halfcell composed of a silver wire dipped into a solution of 10" A/ AgNOa versus the standard hydrogen electrode (SHE) and versus the saturated calomel electrode (SCE). Assume activity coefficients are unity and the temperature is 25°C. 

To capitalize upon the very rapid heating rates possible using the Curie-point technique, the sample and wire should be kept to a low mass. The technique is best suited to the analysis of samples that may be coated onto the filament as a very thin layer. Soluble materials may be dissolved in an appropriate solvent and the wire dipped into the solution. As the solvent dries, it leaves a thin deposit of the sample material, which will then heat rapidly and uniformly to pyrolysis temperature when the wire is heated. Paints, varnishes, and soluble polymers may be analyzed in this way quite easily. 

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