Colloid silver is a bright blue-green powder which dissolved in water gives colloid solution of red colour.
Silicon was discovered by Jöns Jacob Berzelius (Sweden) in 1824. The origin of the name comes from the Latin word silicis meaning flint. Amorphous form of silicon is brown powder; crystalline form has grey metallic appearance. Solid form unreactive with oxygen, water and most acids. Dissolves in hot alkali. Silica dust is a moderately toxic acute irritant. Silicon makes up major portion of clay, granite, quartz and sand. Commercial production depends on a reaction between sand (SiO2) and carbon at a temperature of around 2200 °C. Used in glass as silicon dioxide (SiO2). Silicon carbide (SiC) is one of the hardest substances known and used in polishing. Also the crystalline form is used in semiconductors.
Silver has been known since ancient times. The origin of the name comes from the Latin word argentum meaning silver. It is silvery-ductile and malleable metal. Stable in water and oxygen. Reacts with sulfur compounds to form black sulfides. Silver is found in ores called argentite (AgS), light ruby silver (Ag3AsS3), dark ruby silver (Ag3SbS3) and brittle silver. Used in alloys for jewellery and in other compounds for photography. It is also a good conductor, but expensive.
Silver coulometer consists of a platinum vessel which acts as a cathode and contains a solution of pure silver nitrate as an electrolyte (c(AgNO3) = 1 mol/L). A rod of pure silver enclosed in a porous pot acts as the anode. The current density at the anode should not exceed 0.2 Acm-2. After electrolysis, the electrolyte is taken out and the platinum vessel is washed, dried and weighed. The increase in the weight gives the amount of silver deposited (96500 C of electricity deposits 107.88 g of silver). From the mass of the silver deposited, the coulomb involved in the reaction can be calculated.
Silver/silver-chloride electrode is by far the most common reference type used today because it is simple, inexpensive, very stable and non-toxic. It is mainly used with saturated potassium chloride electrolyte, but can be used with lower concentrations such as 3.5 mol dm-3 or 1 mol dm-3 potassium chloride. Silver/silver-chloride electrode is a referent electrode based on the following halfreaction
Potential vs. SHE / V | ||
---|---|---|
t / °C | 3.5 mol dm-3 | sat. solution |
15 | 0.212 | 0.209 |
20 | 0.208 | 0.204 |
25 | 0.205 | 0.199 |
30 | 0.201 | 0.194 |
35 | 0.197 | 0.189 |
Elements in nature are mostly found in different compounds and, rarely, in the free (elementary) state. In Earth’s crust the most abundant of all elements is oxygen (with 49.5 %), then silicon (25 %), aluminium (7.5 %), iron (4.7 %), calcium (3.4 %), sodium (2.6 %), potassium (2.4 %), magnesium (1.9 %) and hydrogen (1.9 %). These nine elements make up almost 99 % of the Earth’s composition.
Generalic, Eni. "Elektromotorna sila." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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