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In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative amounts of each element in a chemical compound.
For example, the chemical compound n-hexane has the structural formula CH|3|CH|2|CH|2|CH|2|CH|2|CH|3, which shows that it has 6 carbon atoms arranged in a straight chain, and 14 hydrogen atoms. Hexane's molecular formula is C|6|H|14, and its empirical formula is C|3|H|7, showing a C:H ratio of 3:7. Different compounds can have the same empirical formula. For example, formaldehyde, acetic acid and glucose have the same empirical formula, CH|2|O. This is the actual chemical formula for formaldehyde, but acetic acid has double the number of atoms and glucose has six times the number of atoms.
Examples of common substances
Use in physics
An example was the Rydberg formula to predict the wavelengths of hydrogen spectral lines. Proposed in 1888, it perfectly predicted the wavelengths of the Lyman series, but lacked a theoretical basis until Niels Bohr produced his Bohr model of the atom in 1913.
Zinc oxide is an inorganic compound with the formula ZnO. It usually appears as a white powder, nearly insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g., car tires), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient), batteries, ferrites, fire retardants, first aid tapes, etc. ZnO is present in the Earth's crust as the mineral zincite; however, most ZnO used commercially is produced synthetically.
In materials science, ZnO is often called a II-VI semiconductor because zinc and oxygen belong to the 2nd and 6th groups of the periodic table, respectively. This semiconductor has several favorable properties: good transparency, high electron mobility, wide bandgap, strong room-temperature luminescence, etc. Those properties are already used in emerging applications for transparent electrodes in liquid crystal displays and in energy-saving or heat-protecting windows, and electronic applications of ZnO as thin-film transistors and light-emitting diodes are forthcoming as of 2009.
ZnO occurs as white powder known as zinc white or as the mineral zincite. The mineral usually contains a certain amount of manganese and other elements and is of yellow to red color. Crystalline zinc oxide is thermochromic, changing from white to yellow when heated and in air reverting to white on cooling. This color change is caused by a very small loss of oxygen at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 Â°C, x = 0.00007.
- ZnO + 2 HCl â†’ ZnCl2 + H2O
Bases also degrade the solid to give soluble zincates:
- ZnO + 2 NaOH + H2O â†’ Na2(Zn(OH)4)
ZnO reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate. ZnO forms cement-like products when mixed with a strong aqueous solution of zinc chloride and these are best described as zinc hydroxy chlorides. This cement was used in dentistry.
ZnO also forms cement-like products when treated with phosphoric acid; related materials are used in dentistry. A major component of zinc phosphate cement produced by this reaction is hopeite, Zn3(PO4)2Â·4H2O.
ZnO decomposes into zinc vapor and oxygen only at around 1975 Â°C, reflecting its considerable stability. Heating with carbon converts the oxide into the metal, which is more volatile than the oxide.
- ZnO + C â†’ Zn + CO
It reacts with hydrogen sulfide to give the sulfide: this reaction is used commercially in removing H2S using ZnO powder (e.g., as deodorant).
- ZnO + H2S â†’ ZnS + H2O
Zinc oxide crystallizes in three forms: hexagonal wurtzite, cubic zincblende, and the rarely observed cubic rocksalt). The wurtzite structure is most stable at ambient conditions and thus most common. The zincblende form can be stabilized by growing ZnO on substrates with cubic lattice structure. In both cases, the zinc and oxide centers are tetrahedral. The rocksalt (NaCl-type) structure is only observed at relatively high pressures about 10 GPa.
Hexagonal and zincblende polymorphs have no inversion symmetry (reflection of a crystal relatively any given point does not transform it into itself). This and other lattice symmetry properties result in piezoelectricity of the hexagonal and zincblende ZnO, and in pyroelectricity of hexagonal ZnO.
The hexagonal structure has a point group 6 mm (Hermann-Mauguin notation) or C6v (Schoenflies notation), and the space group is P63mc or C6v4. The lattice constants are a = 3.25 Ã… and c = 5.2 Ã…; their ratio c/a ~ 1.60 is close to the ideal value for hexagonal cell c/a = 1.633. As in most From Yahoo Answers
Answers:This is taught in our high schools under the section: catalysts: Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogem The copper sulphate acts as a catalyst and does not take part in the reaction. Zn + 2HCl (CuSO4) ZnCl2 + H2. I have used the sign (CuSO4) to indicate that CuSO4 is a catalyst. If you do follow the above link - do not worry too much about the colour change - only take note of the increased generation of H2 when the CuSO4 has been added.
Answers:using these: MW Zn = 65.4 g/mol Mw O = 16 g/mol Mw Cl = 35.5 g/mol we get: Molar mass of ZnCl2 is 136.4 g/mol Molar mass of ZnO is 81.4 g/mol in the past 10 grams of ZnO was desired, because of the substitution , we need to modify that 10. grams ZnO @ (136.4 g/mol ZnCl2) / (81.4 g/mole ZnO) = 16.757 g ZnCl2 is needed because of its purity problem , we need a slight excess: 16.757 g ZnCl2 is needed @ 100% / 98% = 17.1 grams your answer is you need to add 17.1 g of ZnCl2 for every 100 grams of mix to be equivalent to 10% ZnO ========================================= p.s. in the past , a slight excess was needed of ZnO to get 10% 1O @ 100 % / 99% = 10.1 grams of Zn O was needed for every 100 grams of mix to be equivalent to 10% ZnO ======================================== p.p.s. this means that now 17.1 / 10.1 = 1.69 you now are adding 16.9 times as many grams of ZnCl2 , as you add ed grams of ZnO in the past when you add that 17.1 g of ZnCl2 for every 100 grams of mix, in order to be equivalent to 10% ZnO
Answers:find the mass of copper in each trial and convert it to mass per liter A) 1.694 - 0.908 g Cu / 0.0496 L = 15.847 g Cu / L repeat for B and C compare your three results if they are fairly close, average them if one is pretty far off the others you probably should discard that value however, a glance tells me that your results should be tight subtract the value for Cu from the value for the compound (42.62) that gives the amount of chlorine then do a simple empirical formula calculation I ran the numbers and got CuCl3 which surprised me because copper usually exhibits +1 or +2 oxidation state, but a quick check gave the possibility of +3 and +4 also guess you learn something everyday
Answers:MgCl2 is very hygroscopic (attracts and binds to atmospheric water)