SLG-11.1 Laws of Chemical Combination PDF

INTERACTION BETWEEN SUBSTANCES LAWS OF CHEMICAL COMBINATION At the end of this module, you should be able to: 1. Explain the Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions. (C9.A.1)...

INTERACTION BETWEEN SUBSTANCES LAWS OF CHEMICAL COMBINATION At the end of this module, you should be able to: 1. Explain the Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions. (C9.A.1) 2. Use of triple beam balance or top balance. (C9.A.2) Time Allotted: 1 min Actual Time: __________ In the previous quarter, we learned that matter’s fundamental building blocks are ​atoms​. But were there chemical indications for such existence and the scale of relative atomic masses and how did we obtain them? We know that the most fundamental substances are elements, which when chemically combined form compounds. But on a nanoscopic scale, no information or evidence on the structure of matter is provided, as well as how chemical reactions produced such structures. Thus, the fascinating question was dealt through the assumptions and postulates on the structure of matter proposed by ancient philosophers. It started when Democritus, a Greek philosopher, suggested the existence of indivisible atoms which basically make up all things ​(as discussed in LG 5.1 – History of the Development of the Atoms) ​and many other theories followed, but is still lacking with experimental capabilities and the modern scientific view from testing and refinement by experiment. Nonetheless, an overwhelming, if indirect, evidence on the existence of atoms and molecules was provided when a convenient method for counting the number of atoms of each element in a reaction was suggested based on the definite mass ratios involved in reactions. As a result, it summarized the ​laws of chemical combination​, the basic principles obeyed in the interaction of atoms and molecules. Time Allotted: 3 min Actual Time: __________ In science, the transformation of matter from one form to the other is the focus of the study in chemistry. The said transformation is a result when two different types of matter combine (such as combination of different elements to form a compound). This is governed by certain basic rules we referred to as the ​laws of chemical combination. ​In this module, we will discuss the three basic laws of chemical combination: the (1) Law of Conservation of Mass, (2) Law of Definite Proportions, and (3) Law of Multiple Proportions. ​Learning Guide 11. 1 | ​page 1 of 7 During the 18​th century, the studies about heat and combustion started the first steps in formulating the laws of chemical combination. It was observed when an organic material was burned, a solid residue was left such as ash in wood. The formation of “calx”, which we now call oxide, was also seen when metal was heated in air. At that time, there was no established or recognized principle of conservation of mass, but they realized that there is no reason why the mass of the material would change during heating. In 1789, French chemist ​Antoine Lavoisier demonstrated that in a chemical reaction, the sum of the masses of both the products and the reactants are equal. He used an analytical balance because of the high accuracy provided by the instrument which, during his time, was accurate to perhaps 1 part in 10,000. In his experiment, mercury was heated in a sealed flask with air and was left several days. Thereafter, he noticed a red substance that was produced, an oxide of mercury. He then took an amount of the red oxide of mercury which was carefully weighed and heated to a very high temperature. Subsequently, the products after heating, both the mercury and the gas produced showed the same amount of the combined mass when he started. Figure 2. Visualization of the original experiment (heating of mercury oxide) conducted by Lavoisier Retrieved from ​https://www.youtube.com/watch?v=1q_8i_4tzgk After further experiments, Lavoisier was able to state the ​law of conservation of mass: From the experiment, we can write the reaction as ​Learning Guide 11. 1 | ​page 2 of 7 Although the identity of the gas produced ​(now known as oxygen) was not yet known during his lifetime. In 1794, another French chemist, ​Joseph Proust published the fundamental ​law of definite proportions: Figure 3. Portrait of Joseph Proust Retrieved from ​https://commons.wikimedia.org/wiki/File:Proust_joseph.jpg His idea started when he was battling with another French chemist, Claude Berthollet. It was during his time when determination of the mass of the reactants and products in a more accurate way began. Proust disagreed with the belief of Berthollet that there are no fixed proportions (by mass) of the elements in a compound. He argued that impurities and experimental errors may cause any apparent variation. Thus, he also stressed the difference between chemical compounds and a homogeneous mixture. For example, wherever the source is, 60.66% chlorine by mass is contained in a pure sodium chloride (NaCl) whether it was obtained in salt mines, crystallized from the waters of ocean or inland salt seas, or synthesized from the elements sodium and chlorine. The law of definite proportions was widely accepted and supported by the measurements of the composition of a large number of compounds. It is also said that development of this law provided an excellent example of how science progresses. But later, establishment of more precise measurements uncovered exceptions to the general principle of the law. Thereafter, an English scientist, ​John Dalton proposed the existence of atoms ​(as discussed in LG 5.1 – History of the Development of the Atoms)​. He postulated that atoms of various elements existed using the mass relationships findings of Lavoisier and Proust. In 1808, ​A New System of Chemical Philosophy ​was published wherein the ​atomic theory of matter ​was stated comprising five postulates. The fourth and fifth postulates are ​Learning Guide 11. 1 | ​page 3 of 7 related and aim to explain the law of conservation of mass and law of definite proportions, respectively. Figure 4. ​Frontispiece of ​John Dalton and the Rise of Modern Chemistry​ by Henry Roscoe Retrieved from ​https://commons.wikimedia.org/wiki/File:Dalton_John_desk.jpg In the 19​th century, considered as a major accomplishment was building on the atomic hypothesis of Dalton and the determination of chemical formulas, where composition of a compound is shown. For example, water has a chemical formula of H​2​O, it means that in one unit of water there are two atoms of hydrogen for each atom of oxygen. As we know, the unit for the strong bond that exists between them is a molecule. Nevertheless, many solid substances do not exist as molecules but are called ionic or covalent solids wherein their chemical formula gives the relative ratio of the numbers of their constituent atoms. It was also this time that chemists knew, however, that there are different proportions when two elements combine. For instance, given a carbon (C) and oxygen (O) they may form into two different compounds, ​A and ​B​, when combined under different conditions. At this point, the chemical formula of the compounds is still unknown but, when given the analysis: Compound Mass of oxygen in grams (g) per 1.000 g of carbon A 1.333 B 2.667 From the given data, we can infer that ​A contains half as many oxygen atoms per carbon atom as to ​B​. The conclusion was derived from the ratio of the masses of oxygen in ​A and B​, 1.333:2.667, or simply 1:2. If the formula of compound ​A is CO, the formula of ​B would be CO​2​ (or its other multiple). ​Learning Guide 11. 1 | ​page 4 of 7 The example given explains the ​law of multiple proportions: In the example, 1:2 is the ratio of the masses of oxygen of the two compounds for the given mass of carbon. At present, the carbon oxides are known as CO (carbon monoxide) and CO​2​ (carbon dioxide). To illustrate: Figure 5. Carbon atom can form two different compounds with oxygen Retrieved from: ​https://courses.lumenlearning.com/cheminter/chapter/law-of-multiple-proportions/ Time Allotted: 15 min Actual Time: __________ Tutorial: Triple Beam Balance. ​This online video tutorial on can be used as a supplementary material to learn how to use a triple beam balance or top balance. Access via: ​https://www.youtube.com/watch?v=BAf6HoVK6JI ​Learning Guide 11. 1 | ​page 5 of 7 GRADED FORMATIVE ASSESSMENT Choose the letter that best completes the statements or answer the questions about the different Laws of Chemical Combination. _____ 1. The following is the best example of law of conservation of mass: a. 12 g of carbon is heated in vacuum, there is no change in mass. b. The weight of wire of platinum is the same before and after heating c. A sample of air increases in volume when heated at constant pressure but remains unchanged d. 12 g of carbon combines with 32 g of oxygen to give 44 g of carbon dioxide _____ 2. If water samples are taken from sea, rivers, clouds, lakes, or snow, they will be found to contain hydrogen and oxygen in the approximate ratio of 1:8. This indicate the law of: a. Multiple Proportions b. Definite Proportions c. Conservation of Mass d. None of These _____ 3. He claimed that oxygen is the key substance involved in combustion (burning). He demonstrated that when it is carried out in a closed container, the final product of combustion exactly equals the mass of the starting reactants. a. John Dalton b. Joseph Proust c. Joseph Priestley d. Antoine Lavoisier _____ 4. Phosphorus forms three oxides containing 39.22, 49.22 and 56.40 percent phosphorus. This example illustrates the law of: a. Constant Composition b. Multiple Proportions c. Definite Proportions d. Conservation of Mass _____ 5. 143 g AgNO​3 reacts with NaCl solution and gave 143.5 g AgCl and 85 g NaNO​3​. If the law of conservation of mass holds, the weight of NaCl will be: a. 117.0 g b. 5.85 g c. 85.5 g d. 11.70 g _____ 6. Which compounds do not demonstrate the law of multiple proportions? a. Na​2​S, NaF b. H​2​O, H​2​O​2 c. NO, NO​2 d. CO, CO​2 Time Allotted: 9 min Actual Time: __________ ​Learning Guide 11. 1 | ​page 6 of 7  Time Allotted: 2 min Actual Time: __________ Cracolice, M. S. and Peters, E. I. (2013). Introductory Chemistry: An Active Learning Approach. [5th ed]. Brooks/Cole Cengage Learning Bergstresser, M. Laws of Chemical Combination: Overview & Explanation. Retrieved on December 27, 2020 from https://study.com/academy/lesson/laws-of-chemical-combination-overview-explana tion.html Ferrer, K. (2010). Laws of Chemical Combination. Retrieved on August 28, 2020 from http://camia2013.weebly.com/uploads/4/6/6/7/4667073/handout.chem1_lt3.pdf Kart, X. (2016). Apparatus Used by Antoine Lavoisier. Retrieved on December 26, 2020 from ​https://www.youtube.com/watch?v=1q_8i_4tzgk Sravanth, C. et. al. Laws of Chemical Combination. Retrieved on December 26, 2020 from https://brilliant.org/wiki/laws-of-chemical-combination/ Prepared by: Reviewed by: Approved by: JUNLEE M. VARGAS MERRIAM DANIELLE G. TARRE REX S. FORTEZA Special Science Teacher I Special Science Teacher Special Science Teacher IV Bicol Region Campus Caraga Region Campus Central Luzon Campus ​Learning Guide 11. 1 | ​page 7 of 7