Experiment #3 Classification OF Chemical Reactions PDF

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General Chemistry I, SCC 201 Section: 629A

Experiment #3 CLASSIFICATION OF CHEMICAL REACTIONS October 11, 2020

TYNESIA SMITH

MA AMELITA DAYAO, PHD

Objectives: • •

To observe and classify chemical reactions To practice the completion and balancing of chemical reactions

Data & Calculations: # 1.

2. 3.

4. 5. 6. 7. 8.

9.

10. 11.

12.

13.

Reaction and Observations

Classification

2HCl(aq) + Na2CO3(s) à 2NaCl(aq) + H2O(l) + CO2(g) Effervescence was observed. When the wood splint was placed in the mouth of the test tube, the ember from the splint extinguished CaCl2 (aq) + Na3PO4 (aq) à NAR

DR

Cu(OH)2(s) -à CuO(s) + H2O(g) Bright blue solid Cu(OH)2 was turned black when heated and a liquid was present Zn(s) + CuSO4(aq) à Cu(s) + ZnSO4(aq) Shiny, bluish-silver Zn metal turned a dull, dark red Cu(s) + ZnSO(4) -à No Reaction

D

2Mg(s) + O2(g) -à 2MgO(g) Shiny Mg produced bright, white light when it was ignited HCl(aq) + NaOH(aq) -à NaCl(aq) + H2O(l) The test tube was warm to touch after the chemicals were mixed FeCl3(aq) + 3KSCN(aq) à Fe(SCN)3(aq) + 3KCl(aq) The starting product FeC13 was yellow and KSCN was colorless; the product that formed was dark red Zn(s) + 2HCl à H2(g) + ZnCl2(aq) Zn dissolved. Effervescence was observed. The splint glowed when placed in the mouth of test tube Cu(s) + HCl(aq) à No reaction No reaction observed 2H2O2(aq)à 2H2O(l) + O2(g) Effervescence was observed. The splint glowed when it was placed in the mouth of test tube CuSO4(s) + 5H2O(l) à CuSO(l) + 5H2O(s) CuSO4 turned blue after H2O was added. The test tube was warm to touch. NaCl(aq) + KNO(aq) à No Reaction No Reaction Observed

CU

NAR

SR NAR

DR DR

SR

NAR D

C

NAR

Discussion: A chemical reaction can be described as a process by which two substances interact together to form different substances. The substances that interact together are called reactants and the products are the new substances that form in the chemical reaction. Since the products are different from the reactants, they have different properties and characteristics. 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; effervescence, change in color, change in temperature, catching fire/burning, precipitate formation, sound production and odor production (Miller, 29). According to the law of conservation of mass, atoms are neither created nor destroyed. 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 sides of the equations should contain the same proportions of atoms. The reactants of a formula are separated by addition sign (+), are written on the left side of the equation. Addition sign, if more than one is formed, also separates the products. An arrow (à) is placed between the reactants and products, pointing from reactants to the products. Five types of reactions were observed during this experiment. When two or more substances combine to form one product, it is called a combination reaction. In test 12, white, anhydrous CuSO4 turned blue after H2O was added. The reactants combined to form one product, CuSO45H2O(s), which indicated that a combination reaction occurred. When one substance undergoes a reaction and produces two or more products, it is a called a decomposition reaction. When catalyst was added to H2O2 in test 11,

effervescence was observed. The glowing splint placed in the test tube reignited, indicating the presence of oxygen gas. The products of the reaction were H2O and O2. Because the starting compound broke down, a decomposition reaction occurred. Combustion reactions occur when oxygen reacts with a substance and burns the said substance. In test 6, Mg was burnt in O2 to form 2MgO. This reaction resulted in a extremely bright glowing light. A single replacement reaction is said to have occurred when one element replaces another 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. A double replacement reaction is characterized by the ions of two compounds exchanging partners (Miller, 30). 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 reaction was evident through the emission of heat; the test tube was warmer to touch after the reactants were combined modeling a double replacement reaction. Error: Estimating measurements when mixing chemicals and the measuring devices involved possibly could have affected the reactants ratio. For example, in experiment #11, the ‘pinch-sized’ amount of MnO2 added to a test tube with 2mL of 3% H2O2 could have been inaccurate because a “pinch” is not a definitive unit of measurement. Also, contamination of equipment could have affected the reactions occurring and produced a slightly different color solution or precipitate.

Precautions: When instructed, using the correct measuring tools ensured the precise measurements of each substance.

References: Miller, D. (2013). Measurements and Significant Figures. In General chemistry I, SCC201, lab manual (pp. 23-28). Dubuque, IA: Kendall Hunt....