General Chemistry Lab Report 3 PDF

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Abdul Rahim 1

General Chemistry 1 SCC201.641B Afsana Abdul Rahim Lab Partner: Lamia Hauter, Rawan Mohamed Experiment 3: Classification of Chemical Reactions 10/07/2017 Professor Shashikanth Ponnala

Abdul Rahim 2 Objective: 

To observe the evidence for a chemical reaction.

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To classify reactions based on observation and the chemical equations.

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To practice completing and balancing of chemical equations.

Materials Required: 

10 mL graduated cylinder

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Test tubes

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Test tube rack

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Test tube clamps

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Stirring rod

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Tongs

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Spatula

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Wooden splints

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Bunsen burner

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Distilled water (dH2O)

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3M Hydrochloric acid (HCl)

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Sodium carbonate (Na2CO3)

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0.1M Calcium chloride (CaCl2)

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0.1M Sodium phosphate (Na3PO4)

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Copper (II) hydroxide (Cu(OH)2)

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Copper (II) sulfate (CuSO4)

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1M Zinc sulfate (ZnSO4)

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6M Hydrochloric acid (HCl)

Abdul Rahim 3 

3M Sodium hydroxide (NaOH)

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0.1M Iron (III) Chloride (FeCl3)

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0.1M Potassium thiocyanate (KSCN)

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Zn metal

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1-inch piece of Cu wire

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3% Hydrogen peroxide (H2O2)

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Manganese dioxide (MnO2)

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Anhydrous copper sulfate (CuSO4)

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1M Sodium Chloride (NaCl)

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1M Potassium Nitrate (KNO3)

Methods: The following tests were performed and the observations about the chemical reactions were recorded on the lab manual data sheet. 1. 3 mL of 3M HCl was placed in a test tube. A pea-sized amount of solid Na2CO3 was added. A wooden splint was lit by a bunsen burner and allowed to burn for a few seconds. The fire on the splint was blown out until a small ember remained at the tip of the splint. The splint was quickly placed into the mouth of the test tube. 2. 2 mL of 0.1M CaCl2 was mixed with 2 mL of 0.1M Na3PO4 in a test tube. 3. 0.5 g of solid Cu(OH)2 was placed in a test tube. The test tube was placed in a test tube clamped and was heated in a Bunsen burner flame. The test tube was moved back and forth in the flame to keep the test tube moving. 4. 3 mL of 1M CuSO4 was placed in a test tube. Then a piece of Zn metal was added. Observations were recorded after five minutes elapsed.

Abdul Rahim 4 5. 3 mL 1M ZnSO4 was placed in a test tube and a 1-inch piece of Cu wire was added. Observations were recorded after five minutes elapsed. 6. Using tongs, a piece of magnesium ribbon was ignited in a Bunsen burner flame (in a fume hood). As soon as the Mg ribbon ignited, it was removed from the flame. 7. 2 mL of 6M HCl was placed in a test tube. 3 mL of 3M NaOH was added and mixed using a stirring rod. 8. 2 mL of 0.1M FeCl3 was placed in a test tube and 2 mL of 0.1M KSCN was added and mixed. 9. 2 mL of 3M HCl was placed in a test tube and a piece of Zn metal was added carefully. A glowing splint was placed in the mouth of the test tube. 10. 2 mL of 3M HCl was placed in a test tube and a 1-inch piece of Cu wire was carefully added. 11. 2 mL of 3% H2O2 was placed in a test tube and a pinch sized amount of MnO 2 was added to speed up the reaction. A glowing splint was quickly placed in the mouth of the test tube. 12. Half a spatula full of anhydrous CuSO4 was added in a test tube. 3 drops of distilled water was added. 13. 2 mL 1M NaCl was placed in a test tube and 2 mL 1M KNO3 was added and mixed.

Data:

Abdul Rahim 5

Table 1. Chemical reactions, observations, and classifications. #

Reactions and Observations

1. 2HCl(aq) + Na2CO3(s)  2NaCl(aq) + H2O(l) + CO2(g)

Classification Double Replacement

Effervescence was observed. When the wood splint was placed in the mouth of the test tube, the ember from the splint extinguished. 2. 3CaCl2(aq) + 2Na3PO4(aq)  Ca3(PO4)2(s) + 6NaCl(aq)

Double Replacement

The solution turned cloudy white; a white precipitate formed. 3. Cu(OH)2(s)  CuO(s) + H2O(g)

Decomposition

Bright blue solid Cu(OH)2 was turned black when heated and a liquid was present. 4. Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)

Single Replacement

Shiny, bluish-silver Zn metal turned a dull, dark red. 5. Cu(s) + ZnSO4 (aq)  No reaction

No reaction

No change was observed. 6. 2Mg(s) + O2(g)  2MgO

Combination

Shiny Mg produced bright, white light when it was ignited. Then it turned matte and powdery white afterwards. 7. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

Double Replacement

The test tube was warm to touch after the chemicals were mixed. 8. FeCl3(aq) + 3KSCN(aq)  Fe(SCN)3(aq) + 3KCl(aq) The starting product FeC13 was yellow and KSCN was colorless; the product that formed was dark red.

Double Replacement

Abdul Rahim 6 Table 1. Chemical reactions, observations, and classifications (Continued). # 9.

Reactions and Observations Zn(s) + 2HCl  H2(g) + ZnCl2(aq)

Classification Single Replacement

Zn dissolved. Effervescence was observed. The splint glowed when placed in the mouth of test tube. 10 .

Cu(s) + HCl(aq)  No reaction

No reaction

No change was observed. 11. 2H2O2(aq)  2H2O(l) + O2 (g)

Decomposition

Effervescence was observed. The splint glowed when it was placed in the mouth of test tube. 12 .

CuSO4(s) + 5H2O(l)  CuSO4.5H2O(s)

Combination

CuSO4 turned blue after H2O was added. The test tube was warm to touch. 13 .

NaCl(aq) + KNO3(aq)  No reaction

No reaction

No change was observed.

Discussion: A chemical reaction can be described as a process by which two substances interact together to form different substance(s). The substances that interact together are called reactants and the products are the new substances that form in the chemical reaction (Brown, 82). Since the products are different from the reactants, they have different properties and characteristics. Chemical reactions are the basis of everyday phenomena that occur within living organisms and in the environment. A chemical reaction is a process that leads to the formation of a new substance. We can prove the occurrence of a chemical reaction by providing evidence through observation and measurements. Some of the common indicators of a chemical reaction are;

Abdul Rahim 7 effervescence, change in color, change in temperature, catching fire/burning, precipitate formation, sound production and odor production (Miller, 29). Chemists represent reactions by using chemical equations. Chemical equations depict the reactants, products, and the physical states of the chemicals involved in a reaction. In addition to describing the identities of the atoms involved, chemical equations also express the quantity of atoms involved. According to the law of conservation of mass, atoms are neither created nor destroyed (Brown 121). Even though the atoms may be rearranged, the proportion of atoms remains the same before and after a reaction. Therefore, chemical equations should be balanced, meaning that both side of the equations should contain the same proportions of atoms. The chemical reactions are classified into several types. When two or more substances combine to form one product, it is called a combination reaction. When one substance undergoes a reaction and produces two or more products, it is a called a decomposition reaction. Combustion reactions occur when oxygen reacts with a substance and burns the said substance. A common product of this reaction is water which may be in liquid or gaseous form, and it also produces heat. (Brown, 86-89). A single replacement reaction is said to have occurred when one element replaces another in a compound. A double replacement reaction is characterized by the ions of two compounds exchanging partners (Miller, 30). “A chemical reaction is a process that results in formation of a new substance” (Miller, 29). The molecular changes happening in a chemical reaction is represented with equations, as shown below. The formulas of the reactants, separated by addition sign (+), are written on the left side of the equation. The products, if more than one is formed, is also separated by addition sign. An arrow is placed between the reactants and products, pointing from reactants to the products. Five types of reactions, with distinct characteristics, were observed during this experiment.

Abdul Rahim 8 Standard format of a chemical Equation: Reactant A + Reactant B  Product 1 + Product 2 In a combination reaction, two or more substances react to form one product. In test 12, white, anhydrous CuSO4 turned blue after H2O was added. In addition to the color change, a chemical reaction was evident through the emission of heat; the test tube was warm to touch after the chemicals were combined. The reactants combined to form one product, CuSO45H2O (s), which indicated that a combination reaction occurred. In a decomposition reaction, one substance breaks down into two or more substances. When catalyst was added to H2O2 in test 11, effervescence was observed. The glowing splint placed in the mouth of the test tube reignited, indicating the presence of oxygen gas. Based on this observation, the products of the reaction were H2O and O2. Since the starting compound broke down, a decomposition reaction occurred. In combustion reactions, a substance combines with, or reacts with, oxygen gas. In test 6, Mg was burnt in O2. Mg was shiny before the reaction and became a powdery white substance after the reaction, indicating the formation of MgO. In a double replacement reaction, two reacting compounds exchange bonds. In test 2, CaCl2 and Na3PO4 were mixed together in a solution, which resulted in the formation of a precipitate that separated from the solution. PO43- is soluble when combined with alkali metal cations such as Na+, but is insoluble when combined with other cations such as Ca+ (Brown 129). Based on the observation that one of the products was insoluble, it was determined that the products were Ca3(PO4)2 and NaCl. The exchanged bonds indicated that a double replacement reaction occurred. Double replacement reactions do not always result in the formation of an insoluble product, however. In test 7, HCl and NaOH combined in a solution and formed NaCl and H2O. Since NaCl was soluble in water, evidence of a chemical reaction was not visible. Instead, the

Abdul Rahim 9 reaction was evident through the emission of heat; the test tube was warmer to touch after the reactants were combined. In a single replacement reaction, one element replaces another element in a compound. In test 9, solid Zn was placed in HCl. Zn dissolved and bubbles formed in the solution. The formation of bubbles indicated the presence of gas. Based on this observation, the products of the reaction were aqueous ZnCl2 and gaseous H2. Since Zn replaced H after the reaction, a single replacement reaction occurred. Whether an element can replace another element in a compound is determined by the reactivity of the elements involved (Brown 143). One element (A) can only replace element (B) in compound (BC) if (A) is more reactive than (B). In test 5, Cu and ZnSO4 were combined. As expected, there were no observable changes to the substances. According to the reactivity series, Cu is less reactive than Zn. Consequently, Cu did not replace Zn in the compound with SO4 and there was no apparent reaction. Similarly, there was no observable reaction when Cu and HCl were combined in test 10. Cu is also less reactive than H, so Cu did not replace H in the compound with Cl. Precautions: 

Residual substances in test tubes have the potential to contaminate tests, which would skew the results of the tests. All glassware was washed with soap and water and was rinsed off with distilled water before each use. Distilled water was used to remove ions that might have been present in the tap water.

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As a precaution, all chemical labels were read carefully to ensure that the proper chemicals were used.

Conclusion:

Abdul Rahim 10 Chemical reactions result in the formation of new substances. Evidence that a chemical reaction occurred include effervescence, color changes, heat absorption or emission, production of a sound, formation of new odors, and formation of a precipitate. Reactions can be classified based on observations and chemical equations. Based on observations and chemical equations, it was determined that tests 1, 2, 3, and 4 were double replacement reactions, tests 4 and 9 were single replacement reactions, tests 3 and 11 were decomposition reactions, test 6 was a combustion reaction, and test 12 was a combination reaction. There were no observable changes in tests 5, 10, and 13, so there was no evidence of chemical reactions occurring. In the tests where chemical reactions were evident, the chemical equations were completed and balanced (Table 1). Matter cannot be created nor destroyed, so the proportion of reactant atoms should be identical to the proportion of product atoms. Coefficients in equations can be manipulated until the reactant and product sides are proportional; subscripts cannot be altered because then the identity of the substance would be altered. References: Miller, D. Measurement and Significant Figures. In SCC201 General Chemistry Laboratory Manual (pp. 15-19). Dubuque: Kendal Hunt. 2013. Print. Brown, Theodore L., H. LeMay Eugene, and Bruce Bursten Edward. Chemistry: The Central Science. 14th ed. Upper Saddle River, NJ: Prentice Hall. 2014. Print....