Abstract
Crucibles, Bunsen burners, a hot plate, and an evaporating dish were used to examine the reactions of magnesium and oxygen, zinc and hydrochloric acid, and the dehydration of Copper (II) sulfate. The results were MgO, ZnCl2, and CuSo4 + 5H2O.
Introduction
Individual elements are chemically combined to form new, complex compounds through synthesis reactions. Synthesis reactions follow the pattern of simple to complex; which means that simple elements are combined in order to create complex compounds. Reactants get manipulated in a variety of ways in order to yield specific results; the type of factors manipulated can influence how two chemicals combine. Because new bonds are being formed between elements, energy is released, which makes synthesis an exothermic reaction. The energy in synthesis is released in forms such as light or heat.
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Compounds containing precisely two elements are considered binary compounds. The pre-fix bi means “two”, detailing that the compound is composed of two elements. More specific, there are binary ionic compounds and binary covalent compounds. With binary covalent compounds, two nonmetals are combined. Pre-fixes are used to name them, and they indicate how many of each atom is present. The two non-metals are held together through covalent bonds; therefore, they share electrons. Binary ionic compounds involve two metals and a non-metal, which are attracted by their opposite charges. These compounds are named based on the cation (if it is a transition metal, it will have a roman numeral present to indicate the charge) and the anion plus the suffix “ide”.
Molecular formulas tell how many atoms of each element are in a compound, whereas empirical formulas give the simplest ratio of elements in a compound. Molecular formulas imply that the number of atoms given in the formula is the number of atoms present in that compound. Empirical formulas present a ratio of elements; however, they do not indicate the exact number present in a compound. Empirical formulas are used to examine how much of one element must be present relative to another element. Compounds are represented by molecular formulas since they tell precisely how many atoms of an element are needed to make that specific compound. Multiple compounds may have the same empirical formula; however, they vary in molecular formulas.
Conservation of mass discusses the principle that mass cannot be created, nor destroyed. Thus, during chemical reactions, the quantity of elements cannot be destroyed, only transferred. Because mass cannot be created/destroyed in a reaction, the quantity of reactants provided must equal the quantity of the products. During reactions, the reactants may be lost in the form of gas, however, they are not destroyed.
Atomic theory is composed of the concepts that all matter is composed of small units called atoms and that atoms combine in ratios to form compounds. Atoms can differ in protons, which creates different atoms, but if atoms are the same element, they will have the same number of protons. Atoms combine in whole number ratios when they form compounds since you cannot have part of an atom make something up, you have to have the whole unit present. Atoms are composed of subatomic particles, which include electrons, protons, and neutrons. The protons determine the type of atom, and the electron configurations generally determine the behavior of the atoms.
The electron bonding and structures within molecules or compounds is explained by the molecular orbital theory. When atoms are combined, the atomic orbitals of the atoms can overlap to form the molecular orbital. Within this orbital, the electrons are found orbiting multiple nuclei, rather than being limited to one. When atoms have extensively different electronegativities, they do not apply to the molecular orbital theory. Geometry of molecules, as well as the bonding order and other properties can be determined/influenced by this theory.
The law of definite proportions states that a compound will always have the same ratio of elements, despite any other factors. No matter how many grams of a compound is given, there will always be the same ratio of elements. The law of definite proportions pertains to stoichiometry, providing a basis of studying the ratios of elements in compounds. The proportions of elements are constant, even though the quantity may differ. A compounds composition is definite within this law, meaning that the ratio of elements within it is always the same.
Dehydration of compounds involves the removal of water. When a dehydration reaction takes place, two molecules join together, and a water molecule is lost in the process. Often, dehydration reactions take place over heat. When this reaction takes place, it means that there is water within a molecule’s structure, and that during the formation of a new compound, that water is released as a byproduct. The hydration, or addition of water, back into the compound is the reverse of this type of reaction.
By reacting multiple sets of elements, new compounds were produced. Using the mass values from before the reactions and after the reactions, the empirical formulas were able to be determined. In this lab, different sets of elements were reacted in order to determine the lowest ratio of elements in each compound. The reactions between magnesium and oxygen, and zinc and hydrochloric acid were synthesis reactions, seeing as individual elements combined to form larger, more complex compounds. These compounds consisted of two types of atoms, which made them binary compounds.
The chemical equations and the math steps for the synthesis reactions are:
2Mg + O2 => 2MgO
Zn + 2HCl => ZnCl2 + H2
Mg mass= 23.9984-23.5780=.4202g
Mg moles = .4202/24.31=.01728507 mol
O mass= .4202-.001=.4192
O moles= .4192/15.9999= .026214 mol
Molar ratio= 1:1
Empirical formula- MgO
Zn mass= 53.3136-52.8442= .4717 g
Zn moles= .4717/63.37= .0072158482 mol
Cl mass= .6186-.4717= .1472 g
Cl moles= .1472/ 35.5= .004146789 mol
Molar ratio=1:2
Empirical formula=ZnCl2
In each of the above reactions, elements combined to form a larger, more complex compound. Each series of reactions above contains 2 elements, making it binary. The empirical formula was found through a series of calculations that started when the elements were put on the scale prior to the reaction, where the mass was collected. By comparing the mass of before and after of specific elements, the moles of each element in the compound were found. Molar ratios were converted into empirical formulas, which resulted in the above equations. In each case, the same amount of matter was in the reactants as the products. The amount of matter didn’t change during the reaction, which is why the equation must be balanced.
By knowing the mass of each element in the compound, the law of definite proportions can be used to work backwards and determine the ratios of each element. Figuring out the mass leads to the moles of each element, which can be used to calculate molar ratios, which can find the empirical formulas.
The way that the atoms interacted was in part because of the atomic theory. The composition of each atom influenced how it bonded with the other element. The reactivity each element had together was based on the concepts of electrons influencing reactivity introduced in the atomic theory.
The reaction of Copper (II) sulfate and H2O results in the loss of a water molecule, making it a dehydration reaction. Using this information, the mass of individual compounds was calculated. Using the mass calculations, moles of the water and CuSO4 were found. The moles were used to figure out the ratios between the elements.
The chemical equation and math for the hydration reaction is:
CuSO4 + H2O => CuSO4 + 5H2O
Mass CuSO4=19.9919-19.50256= .48934g
Mol CuSO4=.48934/(63.54+32.06+4(15.l999))= .0030677
Mass H2O= 19.9919-19.7727=.2192, .4893-.2192=.2696g
Mol H2O= .2701/18=.015005 mol
Molar ratio= .0030677/.00306777= 1, .015005/.0030677= 4.89= 1:5
Empirical formula= CuSO4 + 5H2O
When the hydrous Copper (II) sulfate was heated, the compound lost its water molecule, resulting in an anhydrous solution. In this lab, the dehydration allowed the number of water molecules in the Copper (II) sulfate to be seen. The water molecules that were found to be in the copper (II) come in a fixed ratio, meaning for every 1 CuSO4, there are 5 water molecules. The fixed proportion of this is found by the mass of the sample and the water that was calculated During this reaction, the mass was not destroyed or created, it only transferred forms. The water was released in the product; however, it was still within the hydrous CuSO4 found in the reactant side of the equation.
Purpose
The purpose is to determine the empirical formulas of Magnesium oxide, Zinc Chloride, and the number of waters of hydration in Copper (II) sulfate.
Procedure
Using the analytical balance, an evaporating dish’s mass was measured. After the mass of the dish was recorded, .5 grams of zinc was measured and placed in the evaporating dish. The dish was placed on the hotplate, where 15 mL of hydrochloric acid was added. The zinc and HCl was stirred until all of it reacted, then it was left on the hot plate to dry. After the zinc and HCl was dried and cooled, the mass was taken again.
The mass of a crucible and the lid was taken on the analytical balance. .5 g of magnesium was measured, then placed into the crucible. The crucible with magnesium was placed over the Bunsen burner flame using the wire triangle. The lid of the crucible was positioned so that there was an opening It was heated until the reaction finished and the magnesium glowed. The crucible’s mass was taken again, after it cooled down. Then, 1 mL of water was added to the crucible with magnesium, and the crucible was heated again. After that, the mass of the final product was taken.
A crucible and lid’s mass were taken on the analytical balance. .5 grams of hydrated copper (II) sulfate was measured out on the analytical balance, then added to the crucible. Using the wire triangle, the crucible was placed over the Bunsen burner flame. It was heated for 15 minutes, then it was left to cool down. The mass of the crucible and final product was taken again.
Data and Results
Discussion
The empirical formula for magnesium oxide was found to be MgO. The results aligned with what they should have. The law of definite proportions states that elements in a compound will always have the same ratio no matter how much of the substance is given. Even though a small quantity of the substance was given, the ratio of each element was still the same, which allowed the ratio to be found. Because the ratio does not change, the amount of the substance that was being worked with did not affect the formula. Knowing that the ratio of Mg and O in magnesium oxide is one to one, the same can be expected regardless of how much of the compound is tested. In the lab, using mass and molecular weight, the ratio was found to. The lowest ratio at which the charges may be balanced is seen with these numbers as well. The atomic theory discusses valence electrons, which determine the charge of an atom. In the compound, the charges on each atom must cancel out and equal zero. Mg has a charge of negative 2, and oxygen does as well, so have one of each will allow the charges to cancel and equal zero. The lowest number of atoms required to create a charge of zero in the compound also influences if the ratio is acceptable.
With the Zinc and hydrochloric acid reaction, the law of definite proportions applies as well. The results obtained in the lab aligned with the results that the law of definite proportions says should be present regardless of the content. The ratios that were found were supposed to be the same numbers because the lowest whole number ratio between Zn and Cl in the reaction had to be one: two. The atomic theory discusses electrons, which contribute to the charge of an atom. With these ratios, the charges are balanced, which means that the charge of Zn is the opposite, but the same magnitude as the Cl, so they cancel out and the compound has a charge of zero. The ratios require the compounds to have a balanced charge, which influences the lowest ratio of each atom that must be present to create that balanced charge. With Zn (II), the charge is +2, and in Cl, the charge is -1, which means there must be at minimum, 2Cl and 1Zn to create a net charge of zero, which also is the same ratio found through the empirical formula.
With the Copper (II) sulfate reaction, the empirical formula was found to be CuSO4+5H2O. This agrees with the empirical formula that is expected. The ratios of copper (II) sulfate and water were found as a result of the law of definite proportions, which allows the ratio to be found regardless of the amount given. The proportions in this reaction state that for every one molecule of CuSO4, there will be 5 water molecules. In hydration reactions, there is water trapped inside of the compound; the compound with the water was the CuSO4. When it was heated, it released the water and was left in anhydrous form. The water content was found this way, and since the amount of the compound was known before it was heated, the mass of it after determined the amount of water released.
Conclusion
The empirical formulas for magnesium oxide, zinc and hydrochloric acid, and copper (II) sulfate and water were found through reactions involving evaporating dishes and crucibles. The magnesium was placed in a crucible, then heated to the point of reaction. It was weighed, then water was added. The magnesium and water were heated, then the mass was taken again. The zinc was measured out then placed in an evaporating dish. The dish was taken to the hot plate where 15 mL of HCl was added. After the HCl was added, it was mixed, then left to sit until in dried, after which the mass was taken again. The copper (II) sulfate was measured out, placed in a crucible, then heater for 15 minutes. It was weighed again after the 15 minutes, where the mass of the anhydrous CuSO4 and water was found.
The magnesium oxide was found to form the empirical formula MgO. For every one magnesium, there must be one oxygen. This is the minimum ratio of each element that must be present to create magnesium oxide. With the zinc and hydrochloric acid reaction, the ratio was found to be one Zn for every 2 Cl. The empirical formula was ZnCl2, which means that the lowest ratio of Zn to Cl in a compound of Zinc (II) chloride must be 1:2. The copper (II) sulfate had an empirical formula of CuSO4 5H2O. The results state that in ever CuSO4 compound, there must be at least 5 water molecules.
While there were relatively few errors, there was one in particular that could have affected the experiments. In the magnesium and oxygen reaction, there was error when heating the magnesium. The crucible was not situated close enough to the hottest section of the flame, so it took longer to react that normal. This aspect was fixed; however, it would have been ideal to redo the test.
Bibliography
- Wozniewski, Linda, Indiana University Northwest C125 Laboratory Manual, 2013. Pearson Custom Library
- Tro, Nivaldo J., Chemistry Structure and Properties, 2015, Pearson Education, p 263-264
- Chemistry Libretexts, 16 Oct. 2019, chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK12)/07%3A_Chemical_Nomenclature/7.11%3A_Naming_Binary_Molecular_Compounds.
- Key, Jesse A. Introductory Chemistry: 1st Canadian Edition, Pressbooks, opentextbc.ca/introductorychemistry/chapter/atomic-theory-2/#navigation.
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