Determination of the formula unit of a compound

  1. The crucible is weighed and the exact mass is recorded.
  2. Approximately 0.2g of zinc is placed into the crucible and the crucible with its contain is weighed. The exact mass of zinc is determined.3)10 ml of 6M HCl solution is poured into a measuring cylinder.
  3. The 10 ml of 6M HCl solution is carefully added into the crucible containing zinc powder and the contents is stirred gently using a glass rod. A vigorous chemical reaction occurred and hydrogen gas is released. (This step is carried out in a fume cupboard.


  4. If the zinc powder has not dissolved completely, acid was added, 5 ml at a time, until the zinc is completely dissolved. The amount of acid used did not exceed 20 ml.
  5. The crucible is placed on a hot plate in the fume cupboard and the contents are heated slowly so that the compound does not splatter during the heating process.
  6. The compound is heated gently until it is completely dry. The compound is made sure not to melt.
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  7. The crucible is allowed to cool to room temperature. Then, it is weighed.
  8. The crucible is reheated. It is let to cool to room temperature and then is weighed again. The procedure is repeated until the difference in mass does not exceed 0.02g.
  9. The mass of zinc chloride is determined from the final weight of the sample. The mass of chloride in the zinc chloride is calculated.
  10. The formula unit of zinc chloride is calculated.


Chemical compound is a pure chemical substance consisting of two or more different chemical elements which can be separated into simpler substances by chemical reaction chemical compound has a unique chemical structure and defined.

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They consist of the fixed ratio of atoms are held together in a room setting is defined by chemical bonds. Chemical compound molecule compounds that can be held together by covalent bonds, salt is held together by ionic bonds, intermetallic compounds are held together by metal ties, or a complex held together by a coordinate covalent bond. Another main property of a compound is its chemical composition, which identified only by determining the elements present in the compound. The molecular weight of the empirical formula weight divided by the number of atoms of each element to produce a percentage of each element. This is done for each element in the empirical formula and tabulated as chemical composition. Please note the order is based on electro-negative elements.

When zinc metal is reacted with hydrochloric acid, hydrogen gas is released and an aqueous solution of zinc chloride is produced. The zinc chloride solution when evaporated to dryness leaves a pure salt product. In order to calculate the simplest whole number ratio of chlorine to zinc or empirical formula for zinc chloride, we need to use the initial mass of zinc and the solid product formed. It is important that all of the zinc used be reacted and that large excess amounts of hydrochloric acid not be used. Then, from the mass of zinc consumed and the total mass of product formed, the masses of both zinc and chlorine may be determined. Converting these to number of moles and then calculating the simplest whole number ratio, by dividing by both by the smaller of the two numbers, gives the empirical formula. If either of the numbers is non-integral, then multiply by the smallest number required to give two whole numbers as subscripts in the formula unit: ZnxCly.

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Determination of the formula unit of a compound. (2016, Apr 08). Retrieved from

Determination of the formula unit of a compound
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