Empirical Formulas: Synthesis, Decomposition, and Single-Replacement Reactions

Categories: ChemistryScience

Abstract

A crucible, an evaporation dish, and Bunsen Burner flame tests were used to determine the empirical formulas of the products of the synthesis of magnesium oxide from magnesium and oxygen, zinc chloride from zinc and hydrochloric acid and the decomposition of the hydrate of copper (II) sulfate. The results showed that zinc chloride’s empirical formula is ZnCl2 and magnesium oxide has an empirical formula of MgO. The results showed that hydrated copper (II) sulfate has an empirical formula of CuSO4 + 4H2O.

Introduction

Synthesis reactions obtain chemical reactions that happen when two (or more) atoms or molecules come together to create a single product. These are the most basic reactions to think of when it comes to any type of solution or reaction. When synthesis occurs, energy is usually let out in the form of heat and (or) light. This is what makes the reaction exothermic. Exothermic reactions let out energy, while endothermic reactions take up heat (energy). A way to remember this is to think of when sodium (Na) and chlorine (Cl) come together to make sodium chloride (NaCl).

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The chemical equation for this reaction is 2Na + Cl2 → 2NaCl. Essentially, synthesis is the reversal of a decomposition reaction.

A decomposition (dehydration) reaction is when a compound separates into two or more simpler products. Dehydration reactions are usually known to be endothermic. This is because heat (energy) is necessary to break the chemical bonds in the compound that is going through decomposition. An easy way to remember a decomposition reaction is by the general equation: BC→B + C.

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Another way to visualize a decomposition reaction is the breakdown of water. It separates into hydrogen and oxygen.

When one element occupies the place of another in a compound, the result is what is known as a single-replacement reaction. The general equation: X+YZ→ Y+ XZ. For instance, when potassium (K) reacts with water (H2O). The result that is formed is potassium hydroxide (KOH) and hydrogen gas (H2) is released. To find out whether a single replacement reaction will occur, an activity series must be used.

The principle that claims that mass isn’t created or destroyed is referred to as the conservation of mass. This means that the mass of the reactants in a chemical reaction will be the same as the mass of the products. One element’s mass in the beginning of a reaction will be the same as the same element’s mass at the end of the reaction. This law was discovered in 1789 when Antoine Lavoisier placed some mercury in a jar, recorded the total mass, and concluded that the mass of both the reactants and the products were the same. Each conservation law has the same concept: the total amount is the same before and after something occurs.

The theory that all matter is composed of tiny (indivisible) particles called atoms is known as the atomic theory. John Dalton is the scientist who was credited for this theory. The atomic theory is traced back to an ancient philosophical tradition known as atomism. This natural philosophy proposed that the world was composed of fundamental, indivisible, components. The mole, which is a unit of measurement for an amount of substance in the International system of units (SI), is also known as 6.022 x 1023, which may be the number of electrons, ions, molecules, or atoms. This number (6.022 x 1023) is also known as Avogadro’s number. The name of the mole is in honor of the Italian scientist, Ameo Avogadro.

The law that states that a chemical compound will be constant in the amount of each element no matter the weight is known as the law of definite proportions. This states that all samples of a given chemical equation have the same elemental composition by mass. A given chemical compound will forever contain its elements in a fixed ratio and won’t rely on the source or method of preparation. It was proposed by French chemist Joseph Proust. In 1806, the law of definite proportions became known as Proust’s law.

A compound’s molecular formula is the total number of atoms of each element in that specific compound. The empirical formula simplifies the molecular formula to the most reduced ratio of elements even possible. In some cases, the empirical formula is the same as the molecular formula. This means that the simplest ratio of the number of elements is the same (equal) as the molecular formula. The molecular formulas are what is most commonly found in nature. An example is the molecular formula C6H12O6 (Glucose), which is most commonly found the nature, however the empirical formula of this is CH2O.

Hydrates are typically crystalline compounds in which water molecules are chemically bound to another compound or an element. Compounds that absorb water molecules and incorporate them into their structures are known as hydrates. An example is sodium carbonate (Na2CO3). To form larger crystals, sodium carbonate builds in ten molecules of water into its crystal grid. This is now: Na2CO3 x 10 H2O. This is called the hydrate.

A substance composed of two different elements is known as a binary compound. These substances cannot be simplified further by any chemical means. Binary ionic compounds have a certain naming style and formula. The metal cation’s name is placed before the base name of the nonmetal’s anion + the ending ide. Examples of binary compounds include H2O, H2S, and NH3.

The theories are used in this experiment when the reactions are formed: synthesis occurs, and binary compounds are produced. n this lab, the first reaction that was performed was the synthesis of Magnesium Oxide (MgO). Magnesium Oxide is a binary compound. The second reaction was the synthesis reaction of Zinc Chloride. The product of this is the binary compound ZnCl2. H2 gas was produced as well. The third (last) reaction performed involved the dehydration of hydrated Copper (II) Sulfate. The reactions performed are shown in the following equations:

Mg (metal solid) + O2 (gas) = Magnesium Oxide

Zn + HCl = Zn (s) + HCl (aqueous) = Zinc Chloride (aqueous) + H2 (gas)

Zinc Chloride (aqueous) + Heat= Zinc Chloride (solid) + H2O (gas)

CuSO4 • XH2O + Heat = CuSO4 + XH2O

The purpose of this lab was to determine the empirical formulas of the reactions.

Procedure

Three separate experiments were conducted to determine the chemical equations of three different compounds. The synthesis of magnesium oxide was achieved by heating half a gram of magnesium over a Bunsen burner flame. To get the most heat out of the flame, the magnesium was placed directly on top of the inner most cone of the flame. The heating continued until the glowing of the magnesium went away. The cooling process took a while. To speed up the cooling process, the crucible was moved to different parts of the countertop of the lab table. This helped cool it down faster, which made finding the mass of it easier to do. For the reaction with water and the crucible, it was measured in terms of its scent and the bubbles that were formed. The product and the water added were then reheated and then dried.

These measurements before and after adding the water were used to find the chemical equation of magnesium oxide. For the second reaction, it involved the synthesis of zinc chloride. Half a gram of zinc was placed in an evaporating dish on a hotplate with hydrochloric acid. After the reaction occurred, the product and dish were recorded. The third and final reaction involved the hydrated copper (II) sulfate. It was heated under the Bunsen burner flame. After this cooled, the mass of the product was found. This mass includes the mass of the crucible, lid and the anhydrous copper (II) sulfate. The chemical equations of each of the compounds were found using the data from each reaction.

Discussion

The results of the calculations of the synthesis of magnesium oxide resulted in the formula MgO. 0.4146g of magnesium was heated and it resulted in 0.6725g of the final product. By subtracting the mass of magnesium from the final product (0.6725-0.4146), the mass of oxygen was found. The individual masses of both magnesium and oxygen were converted into moles and then divided by the smallest number of moles to determine the empirical formula. The mole to mole ratio was found after this, resulting in a ratio of 1:1. The empirical formula calculated for the synthesis of magnesium oxide was MgO. Therefore, this empirical formula is correct.

The synthesis of zinc chloride was determined to be ZnCl2. 0.4885g of zinc reacted with 6M HCL. This created 1.0812g of product. To find the mass of chloride, the mass of zinc was subtracted from the mass of product (1.0812-0.4885). The mass of chloride was found to be 0.5927g. The masses of both chloride and zinc were then converted to moles, and by dividing by the smallest number of moles, the mole to mole ratio was able to be found. The mole to mole ratio was 1:2, which resulted in the empirical formula of zinc chloride to be ZnCl2. The result of this reaction is correct, as zinc chloride’s empirical formula is ZnCl2.

The empirical formula that was determined for hydrated copper (II) sulfate was CuSO4 + 4H2O. 3.6076g was hydrated copper (II) sulfate was reacted and 2.4266g of anhydrous copper (II) sulfate was produced. To find the mass of water, the mass of anhydrous copper (II) sulfate was subtracted from the mass of hydrated copper (II) sulfate (3.6076-2.4266). The mass of water and the mass of anhydrous copper (II) sulfate were then used to find the empirical formula of the reaction, which was CuSO4 + 4H2O. The expected formula for this reaction was CuSO4 + 5H2O. Therefore, the empirical formula calculated is incorrect. There might have been an error in the completion of the dehydrated reaction, which resulted in the difference in the calculated empirical formula.

Conclusion

Three individual reactions were each performed to find the chemical equations of compounds. The masses calculated of both reactants and products helped in find the number of moles of each element in each compound. The number of moles were then used to calculate and determine the mole to mole ratio. This then helped to find the empirical formulas for each reaction.

The initial reaction was the magnesium oxide’s synthesis. The empirical formula was determined to be MgO. The next reaction, the synthesis of zinc chloride, was found to be ZnCl2. The third and final reaction involved the dehydration of copper (II) sulfate. The empirical formula found for this reaction was CuSO4 + 4H2O. By finding the masses of the reactants and the products, these empirical formulas were found.

The empirical formula for magnesium oxide was correct. Zinc chloride’s empirical formula was also determined to be correct. However, the empirical formula found for the results of the dehydrated copper (II) sulfate were incorrect. The empirical formula for copper (II) sulfate is CuSO4 + 5H2O. The results from the lab found the empirical formula to be CuSO4 + 4H2O. A factor that could have contributed to the calculation of this empirical formula is that there could have been an error in the completion of the dehydrated reaction. The final reaction of dehydrated copper (II) sulfate had a higher error than the other two reactions.

Bibliography:

  1. Wozniewski, L, Indiana University Northwest C125 Laboratory Manual, The Determination of Chemical Equations, August 2020
  2. Tro, Nivaldo J., Chemistry: Structures and Properties. 2nd ed., Pearson, Upper Saddle River, NJ. 2018, 41-171.
  3. Orenstein, K. (2019). Synthesis Reactions - Concept - Chemistry Video by Brightstorm. Retrieved September 26, 2020, from https://www.brightstorm.com /math/chemistry/chemical-reactions/synthesis-reactions/
  4. Chemistry Libretexts, I. (2020, August 10). Single Replacement Reactions.
Updated: Feb 22, 2024
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Empirical Formulas: Synthesis, Decomposition, and Single-Replacement Reactions. (2024, Feb 22). Retrieved from https://studymoose.com/document/empirical-formulas-synthesis-decomposition-and-single-replacement-reactions

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