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From Wikipedia

Empirical formula

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.

In contrast, the molecular formula identifies the number of each type of atom in a molecule, and the structural formula also shows the structure of the molecule.

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

In physics, an empirical formula is a mathematical equation that predicts observed results, but is derived from experiment or conjecture and not directly from first principles.

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

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.

Chemical properties

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 °C, x = 0.00007.

Zinc oxide is an amphoteric oxide. It is nearly insoluble in water and alcohol, but it is soluble in (degraded by) most acids, such as hydrochloric acid:

ZnO + 2 HCl → ZnCl2 + H2O

Bases also degrade the solid to give soluble zincates:

ZnO + 2 NaOH + H2O → 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)2·4H2O.

ZnO decomposes into zinc vapor and oxygen only at around 1975 °C, reflecting its considerable stability. Heating with carbon converts the oxide into the metal, which is more volatile than the oxide.

ZnO + C → Zn + CO

Zinc oxide can react violently with aluminium and magnesium powders, with chlorinated rubber and linseed oil on heating causing fire and explosion hazard.

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 → ZnS + H2O

When ointments containing ZnO and water are melted and exposed to ultraviolet light, hydrogen peroxide is produced.

Physical properties

Crystal structure

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

Question:I am a chemistry student and i need the chemical equation for the following and i cant find the answer anywhere on the web... Zn + HCl + CuSO4 --> WHAT!! ..... please help me

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.

Question:2. Product A consists of 10% zinc oxide, 10% nitric acid and 5% hydrochloric acid (all wt%). The zinc oxide is 99% purity powder. It has been decided that future batches of product A would be made using Zinc Chloride (ZnCl2) instead of Zinc Oxide (ZnO). The zinc chloride available is a 98% purity product. How much zinc chloride do we need to substitute for zinc oxide in order to maintain the same active percentage of Zn2+ in the formula? MW Zn = 65.4 g/mol Mw O = 16 g/mol Mw Cl = 35.5 g/mol

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

Question:This is due today! Please help! In a student experiment, the empirical formula of a copper halide was found by adding aluminum metal to an aqueous solution of the halide, displacing copper metal. The copper metal was filtered, washed with distilled water, dried, and weighed; three separate determinations were performed. The copper halide solution contained 42.62 g of copper chloride per liter. The student recorded the following experimental data. In trial A, the volume of the copper chloride solution was 49.6 mL, the mass of the filter paper was 0.908 g, and the mass of filter paper with copper was 1.694 g. In trial B,the volume of the copper chloride solution was 48.3 mL, the mass of the filter paper was 0.922 g, and the mass of filter paper with copper was 1.693 g. In trial C, the volume of the copper chloride solution was 42.2 mL, the mass of the filter paper was 0.919 g, and the mass of filter paper with copper was 1.588 g. Write the empirical formula of copper chloride based on the experimental data. Help please!

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

Question:When conducting a lab in which you are trying to find the empirical formula of Magnesium Chloride, the directions instruct us to leave product of magnesium chloride (after the reaction takes place), inside of a drying oven overnight. Why is this process necessary? And why would it be important to mass the dry magnesium chloride right away after it is taken out of the oven the next day?

Answers:MgCl2 is very hygroscopic (attracts and binds to atmospheric water)

From Youtube

SPM Chemistry Empirical Formula Worksheet 4 Solution #3 :7. Zinc phosphide is made by heating zinc and phosphorous together. It is found that 8.4 g of zinc combines with 3.1 g of phosphorous. Find the empirical formula for the compound. 8.Indigo is a dye used to colour sweets and cakes. Indigo contains 73.3 % carbon, 3.81 % hydrogen, 10.69 % nitrogen and 12.2 % oxygen according to mass. Determine the empirical formula of indigo. 9. Nicotine is a compound found in tobacco. It contains 74.10 % carbon, 8.64% hydrogen and 17.26% nitrogen. Determine the empirical formula of nicotine.

SPM Chemistry Empirical Formula Worksheet 4 Solution #2 :3. An experiment shows that 32 g of sulphur combine with 32 g of oxygen to form the compound sulphur dioxide. What is its empirical formula? 4. In a reaction to make manganese from manganese oxide, the following results were obtained: 174 g of manganese oxide produced 110 g of manganese. Find its empirical formula. 5. 27 g of aluminium burns in a stream of chlorine to form 133.5 g of aluminium chloride. Find its empirical formula. 6. Hydrocarbon A and B both contain 85.7 % carbon. The molar masses of A and B are 42 g mol-1 and 84 g mol-1. (a) What are the two elements are present in a hydrocarbon? (b) Determine the empirical formula of A and B. (c) Determine the molecular formula of A and B.