Chem Lab 2 - Chem Lab 2 for Portage PDF

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Chem Lab 2 for Portage...

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Experiment 2: Chemical Reactions Date: 02/10/2020 Title: Chemical Reactions Purpose: To observe the various types of chemical reactions and their results. Procedure:  Examples will be conducted of the different types of chemical reactions  6 types of Simple Chemical Reactions  Reversible Reactions Data, Calculations, Conclusions: Examples of 6 Types of Reactions:  Double Displacement Reaction of two solutions: HCl (aq) and AgNO 3 (aq)  Reaction: white solid formed in tube = silver chloride (AgCl)  two solution that were clear and colorless formed solid  Ag+NO3- (silver nitrate solution) + H+Cl- (hydrochloric acid solution) ---> H+NO3- (nitric acid solution) + AgCl (silver chloride; precipitate)  Double displacement reaction: a reaction in which the positive (+) and negative (-) ions of two reactants are interchanged  Double Displacement Reaction #2: Kl and Pb(NO3)2  Two colorless solutions  forms yellow solid of lead iodine (Pbl2) at the bottom of test tube  solid yellow was used for pigment in yellow paints  led to lead poisoning in babies  Pb+2 (NO3-)2(lead nitrate solution) + 2K+I- (potassium iodine solution) ---> K+NO-3 (potassium nitrate solution; colorless solution) + Pbl2. (lead iodine; yellow precipitate)  Double Displacement Reaction #3 (Acid-Base): NaOH & HCl  Acid-Base Reaction: a reaction in which the positive and negative ions of acid and base reactants are interchanged with the evolution of heat and usually the formation of water  Exothermic (heat given off)  Acid- a reactant containing H+ ion which can be donated  Base- a reactant whose anion (-ion) can accept H+ ion  NaOH and HCl: Starting temperature of 21.5C for both  After the two solutions combined, no solid or gases formed;  Temperature is 30.5C and rising; over 10 degree rise  H+Cl- (hydrogen chloride solution) + Na+OH- (sodium hydroxide solution) ---> Na+Cl(sodium chloride solution) + H2O (water) + heat  Double Displacement Reaction #4 (Acid-Base): HCl & NaHCO3

 Both started off as colorless and clear solutions  bubbles of gas given off  CO2 gas is produced  H+Cl- (hydrochloric acid) + Na+HCO3- (sodium bicarbonate) ---> Na+Cl- (sodium chloride) + H2O + CO2 (carbon dioxide) + heat (All Colorless Solutions)  Similar reaction with vinegar and baking soda which causes foaming  Double Displacement Reaction #5: Ba(OH)2 (s) & NH4NO3 (s)  Endothermic Chemical Reaction  Absorbs heat, unlike most other spontaneous chemical reactions which give off heat  2NH4NO3 (ammonium nitrate) + Ba(OH)2 (Barium hydroxide) + heat ---> Ba(NO3)2 (Barium nitrate) + 2NH3 (Ammonia gas) + 2H2O (water)  Temperature started at around 22C; both solids added to beaker. Because solids do not mix well, small amount of water was added to mix the solids.  Temperature probe readings dropped from 22C  below -5C (endothermic reaction)  Litmus paper turned blue (basic); giving off gas ammonia  We can detect ammonia with litmus paper turning from pink to blue because NH3 is a base  Single Displacement: HCl(aq) & Zn (s)  A reaction in which a reactant element replaces the positive or negative ion of another reactant compound, yielding a new product element and compound  Zn (zinc; gray) + 2H+2Cl- (hydrogen chloride solution; colorless)  Zn+ 2Cl- (zinc chloride solution; colorless)+ H2 (hydrogen gas; colorless) + heat  Bubbling gas, hot; started at room temp (~25-30C); gas and heat given off in this single displacement reaction (~86C)  Single Displacement Reaction #2: Cu (s) & AgNO3 (aq)  Reaction was not immediate. Silver nitrate solution react with copper to become copper nitrate solution  Cu should become black because silver is black in solution  Faint blue color instead of faint or royal blue because of diluted solution  Silver nitrate is dissolved but the copper is not (so reaction was not completed yet)  solution not colorless anymore; blue solution with gray/black silver floating in solution  Once settled, a distinctive blue solution was observed, with gray silver solid precipitated in the bottom of beaker  Cu (copper; brown solid) + 2Ag+2NO3 (silver nitrate solution; colorless) ---> Cu22NO3 (copper nitrate solution; blue) + 2Ag (silver; gray solid)  Combustion (burning) reaction: KClO3 (match head)  A reaction in which O2 gas reacts with another compound to form one or more oxide products, accompanied by the generation of much heat (and often a flame)  2KClO3 (potassium chlorate) ---> 2KCl + 3O2 --(S; sulfer)---> SO3 + heat (causes wood of the match to burn)  Combustion-Reaction #2: candle burning

 The Candle wax melts because it is undergoing combustion  C25H52 (candle wax) + 38O2 (oxygen; air) → 25CO2 (carbon dioxide gas) +26H2O + heat (+ flame)  All gases are colorless  The water produced in these combustion reactions is invisible because it is produced as water vapor (at the high temperature of this reaction).  Decomposition Reaction: H2O2  A reaction which is characterized by a greater number of product substances than the number of reactant substances  2H2O2 (hydrogen peroxide) ---(MnO2)---> 2 H2O (water) + O2 (oxygen gas)  Gas bubbles coming up the sides of test tube (O2 gas); MnO2 will not be consumed in reaction (every milligram will remain because it acts as a catalyst  MnO2 acts as catalyst in this reaction, speeding up the reaction without itself becoming consumed. The same reaction can be catalyzed by the enzyme (biochemical catalyst) called catalase which is present in potatoes or blood. The catalase present in blood is what causes foaming (production of gas) when peroxide is put on a wound to cleanse it.  When hydrogen peroxide is used to treat wounds, as soon as it touches blood, it reacts with iron in blood  Synthesis Reaction- I (aq) & Zn (s)  A reaction is characterized by a lesser number of product substances than the number of reactant substances  Zn (zinc, gray solid) + I2 (Iodine; red-brown solid) ---> ZnI2 (zinc iodide; white solid)  Zinc is added to Iodine (brown) solution; red brown color should diminish when they react.  Zinc is gray powder and iodine is red brown; after reaction ran for 20 mins; final product is zinc iodide (white powder)  color change  Composition (Synthesis) Reaction #2: Cu  Copper heated in flame to react with the oxygen in the air  Shiny color disappeared and became black because oxygen in air reacted with copper metal  2Cu (copper; red-brown) + O2 (oxygen gas; colorless) ---> 2CuO (copper oxide; black solid)

 II- REVERSIBLE REACTIONS  Equilibrium reaction are reversible with the forward reaction (written from left to right) converting reactants to products and the reverse reaction (written from right to left) converting those same products to the same reactants under similar conditions.  Some reversible reactions are not equilibrium reactions, since even though a certain reactant can be converted to the same reactant, the conversion and reconversion require different reagents (reacting substances). This case is demonstrated by the

reversible oxidation-reduction of methylene blue in the classes “blue bottle” reaction. The structures the oxidized (reactant) and reduced forms of methylene blue are shown in model on slide.  Reversible Oxidation Reduction of Methylene Blue (“Blue Bottle” Reaction)  Not true equilibrium because we can reverse but it takes different materials to go back and forth  Methylene blue is colorless in reduced form but blue in oxidized form  Shake flask and it becomes blue because it has become oxidized;  Color faded quickly back to colorless because the sugar in solution quickly reduced the solution back to the reduced, colorless form;  To make it blue again  shake flask so oxygen is pulled into solution  Eventually when all sugar is used up, it wouldn’t be able to be reduced to its unoxidized form  The reversible conversion of methylene blue indicator from the blue oxidized form to the colorless reduced form is accomplished by a slow reaction in a basic (NaOH) solution which also contains a reducing agent (glucose). Periodically, oxygen gas (O2) from the air is added (by shaking the solution) which acts as the oxidizing agent to reconvert colorless reduced methylene blue back to blue oxidized methylene blue in a much faster reaction. This is shown in the following diagram:

 Notes: As a chemical reaction occurs, one of the following often occur:  Heat is given off (an exothermic reaction)  A precipitate (solid product) is formed ( )  A gas is given off ( )  Water (H2O) is formed as a product  A color change...