The Copper Cycle Most of the background material for this laboratory will be covered in greater detail in the lecture course later in the semester. Here is some background information so you will understand the chemistry behind the reactions you will perform. Many aspects of our lives involve chemical reactions-?from the batteries that power our cars and cell phones to the thousands of processes occurring within our bodies. Most of these reactions can be classified into one of three main types of chemical reactions: precipitation reactions, acid-base naturalization reactions, and oxidation- deduction (also called “redo”) reactions.
Aqueous Solutions(as) Many reactions occur in an aqueous environment (I. E. , in a solution where ions and compounds are dissolved in water). When we indicate that a reactant or product has the physical state (as), we mean the substance is dissolved in water. When an ionic compound is in aqueous solution, the individual ions are present in solution; for example, NCAA(as) exists as An+ and CLC- ions moving around in water. Solubility Rules Many ionic compounds are soluble-?I. E. , they dissolve in water.
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Others generally do not dissolve in water and are considered insoluble. To determine if an ionic compound is soluble-?I. E. , will dissolve-?in water, we use the Solubility Rules: Solubility Rules for Ionic Compounds in Water The compound is SOLUBLE if it has: An+, NH 4+ ton (ALWAYS! ) 2. CHICHI-, NON-, CHIC- 3. CLC-, BRB-, or 1-, except compounds with Gag+, BP+2, and Hag+2 are insoluble 4. SASS- except compounds with Saga’s, cases, scars, Bases, PBS, and Haggis are insoluble The compound is INSOLUBLE if it has: 5.
CHIC-, crack-, IPPP-, except compounds with Lie+, An+, K+, NH+ are soluble 6. SO-, except compounds with Lie+, An+, K+, NH+, ca+2, sir+2, AAA+2 are soluble . Hydroxide ion, OH-, except compounds The Solubility Rules indicate which compounds are soluble, and thus are represented as aqueous: e. G. , Kill(as), Abaca(as), Noah(as), etc. The Solubility Rules also indicate which compounds are insoluble-?I. E. , do not dissolve in water and remain as solids: e. G. Basso+), Call(s), cacao(s), etc.
Double Replacement/Precipitation Reaction For example, consider the reaction between aqueous lead(al) nitrate with aqueous potassium bromide, as shown below: KGB(as) Puff KNEE Note that the chemical formulas for the products formed are based on their charges, to how they appear on the reactant side of the chemical equation. ICC CHEM. 151 AL: The copper cycle O ICC, 2013 page 1 of 12 Based on Solubility Rules #4 and #1, we find that BRB is insoluble and KNEE is soluble.
Thus, the complete, balanced equation is: + 2 KGB(as) Pacific) + 2 KNEE(as) We can cancel the spectator ions from the ionic equation and write the net ionic equation: Pub+(as) + 2 BRB -(as) 0 BRB(s) This reaction produces a cloudy mixture with small particles of the solid suspended in the solution. When enough solid has formed, it will begin to settle at the bottom of the beaker. Thus, a clear solution becoming cloudy when another solution is added is often taken as experimental evidence of a solid or precipitate forming.
Acids and Bases Acids can be defined as substances that produce hydroxide ions (HUH+) when they are dissolved in water. A hydroxide ion is the product of a hydrogen ion that reacts with a water molecule: H+(as) + H2O(l) 0 HUH+(as). A hydrated hydrogen ion (H+(as)) is equivalent to an aqueous hydroxide ion. The two equations below both represent the unionization of hydrochloric acid, HCI(as), but the second one shows a particular water molecule explicitly. HCI(as) O H+(as) + CLC-(as)
HCI(as) + H2O(l) O HUH+(as) + CLC-(as) Acids are usually easy to recognize since their formulas start with H and contains nonmetal elements other than H-?e. G. HCI(as), HON.(as), and HASPS(as) are all acids. Note that the physical state aqueous, (as), must be included to distinguish a compound that is acting like an acid from other forms of a substance. For example, the formula “HCI” can also be used for hydrogen chloride gas, HCI(g), so to indicate aqueous hydrochloric acid, one must specify HCI(as). One useful definition of bases is that bases are compounds that produce hydroxide ions (OH-) when dissolved in water.
The dissociation of sodium hydroxide, Noah, is shown below. : Noah(s) Noah(as) which is equivalent to An+(as) + OH-(as) Acid-Base Naturalization Reactions In an acid-base naturalization reaction, a hydrogen ion-containing acid reacts with a hydromechanics’s base to produce water and a salt (an ionic compound): HCI(as) + Noah(as) O acid base H2O(l) + Niacin(as) water salt Acids can react with bases, regardless of whether the salt is soluble or insoluble. There are other types of acids and bases that can react without forming water.
If the reactants and products of an acid/base reaction are colorless and soluble, it is impossible to monitor the progress of an acid-base reaction based solely on the appearance of the solutions. To help us monitor acid-base reactions, we use litmus paper to determine if a solution is acidic or basic. Litmus paper changes color depending on the presence of H+ or OH- ions in the substance being tested. Blue litmus paper turns red in acidic solutions containing H+ ions, and red litmus paper turns blue in basic solutions containing OH- ions. Age 2 of 12 Oxidation/Reduction Reactions In an oxidation/reduction reaction, electrons are transferred from one reactant to the other. In the simplest form of these reactions, single-displacement reactions (also called single-replacement reactions), metal ions react with pure metals. If the reaction proceeds, the pure metal gives electrons to the metal action. This causes the pure metal to become a action and the action to become a pure metal. The action must always have an anion partner which is present either in an ionic solid or in a solution.
For example: MGM(s) + 2 Gag+(as) 0 2 Gag(s) + MGM+(as) metal action If the charge of an element is changing, that is a good indication that an oxidation/ reduction reaction is taking place. Later in the semester you will learn about oxidation numbers which are used to keep track of more complicated oxidation/ reduction reactions. Step l: Chemistry The different copper species obtained in each part is shown in Equation 1 below: cue(S) Part I cue+(as) Part II part Ill cue(S) part Part V blue l.
Oxidation Copper Metal with Concentrated Nitric Acid, HON.(as) The first step involves transforming Cue metal to copper(al) ions, Cue+, using concentrated nitric acid, HON.(as). At the same time, the nitrate ions (NON-) undergo a series of reactions to form nitrogen monoxide, NO. This product rapidly reacts with oxygen in the air to form NON, a brown gas. The presence of Cue+(as) makes the solution blue. When the reaction mixture is diluted with water, the Cue+ ions are hydrated (surrounded by water) to form the octahedral complex ion, [Cue(H2O)6]2+, as shown below.
Six water molecules (shown as red O and white H atoms) are bonded to a Cue+ ion (shown in gray as the central atom). Cue+(as) + 6 H2O(l) 0 [Cue(H2O)6]2+(as) Figure 1 page 3 of 12 Step II: Chemistry II. Precipitating Cue(OH)2(s) with Noah(as) In Part II, two reactions are carried out by adding Noah(as). In the first reaction, the hydroxide ions (OH-) from the Noah(as) neutralize the excess hydroxide ions (HUH+) feet over from the previous part: HUH+(as) + OH-(as) 2 H2O(l) Once all the HUH+ ions are neutralized, additional OH- ions react with the Cue+ ion to form Cue(OH)2 precipitate. Once all the Cue+ ions have reacted, no more precipitate forms.
Adding more OH- ions makes the solution basic, so it can turn red litmus paper blue. Figure 2 on the next page shows the step-wise reaction of Cue+ with Noah. Figure 2: Step-wise Illustration of the Precipitation of Cue(OH)2 in Part II – Remember: [Cue(H2O)]2+ indicates the same substance as Cue+. 1st Beaker: At the end of Part I, hydrated copper complex, Cue+ are present, making he solution blue, and excess hydroxide ions (HUH+) remain from the nitric acid used. 2nd Beaker: Adding Noah(as) to the blue solution results in the OH- ions neutralizing the HUH+ ions to form water: HUH+(as) + OH-(as) 0 2 H2O(l).
The An+ ions and resulting water molecules are not shown. 3rd and 4th Beakers: Once all the HUH+ are neutralized, adding more Noah(as) results in the OH- ions reacting with the Cue+ to form the blue Cue(OH)2(s) precipitate shown at the bottom of the beaker. Water molecules released from the complex ion are not shown. 5th Beaker: When all of the Cue+ ions have been converted to Cue(OH)2(s) precipitate, adding more Noah(as) results in unrelated OH- ions in solution, which makes the solution basic. Red litmus paper can be used to confirm the solution is basic.
Note that the solution is no longer blue since no Cue+ ions are present in the solution. Step Ill: Chemistry Ill. Converting solid Cue(OH)2 to solid Cue In Part Ill of the sequence, the reaction mixture is heated. This transforms the Cue(OH)2 precipitate to Cue precipitate. Page 4 of 12 The Cue precipitate is separated from the solution, called the supernatant liquid, using a method called gravity filtration. The mixture is filtered using a filter funnel, ND the solid is collected on filter paper. The supernatant liquid runs through the filter paper and collects in a beaker.
This resulting filtered solution is called the filtrate. Step IV: Chemistry ‘V. Dissolving Cue(s) with sulfuric acid, HASPS(as) In Part ‘V, the Cue precipitate is dissolved using sulfuric acid, HASPS(as). This redo reaction returns copper to its aqueous phase. Step V: Chemistry V. Reducing Cue+ ions with Zinc Metal In Part V, zinc metal (Zen) is added to the copper solution to convert the copper ions back to copper metal, Cue(s). The resulting solution will contain colorless zinc ions, Zen+(as) and copper solid. Visible evidence of this reaction is observed as bubbles of gas being released from the solution. Since the HUH+ ions do not dissolve the Cue metal, the amount of copper yielded is not affected by excess acid. ) Identify the gas displaced from the acid in this reaction. When the solution becomes colorless, all of the Cue+ ions have been converted to Cue metal. All of the excess Zen metal is also converted to Zen+ ion by the excess HUH+ ions from the sulfuric acid, HASPS(subdued to dissolve the Cue precipitate in Part IV. Once all the Zen metal is dissolved, the Cue metal can be isolated by decanting, or pouring off, the supernatant liquid. The Cue will then be rinsed, dried, and weighed as described in the procedure. Age 5 of 12 In this experiment, you will carry out a series of reactions starting with copper metal. This will give you practice handling chemical reagents and making observations. It is typical for scientists to observe materials before they react, what happens during a reaction and how it looks when the reaction has come to completion. The product of the final reaction will be copper metal and the percent copper that is recovered will be calculated. **Lab Notebook** You should include one table that contains the mass of copper at the beginning and ND of the experiment along with % of copper recovered.
This table should include: Mass of copper at the start of experiment (in Part l) Mass of copper + evaporating dish (from Part V) Mass of empty evaporating dish (from Part V) Mass of copper recovered (from Part V) Percent of copper recovered Record observations for each of the steps (I-V) of the copper cycle in your lab book. Be sure to label each step (I-V). The observations for each step should include: the appearance of the reactants before the reaction the appearance of the reactants during the reaction (for example, bubbles, flames, etc. The appearance of the products after the reaction.
Your observations should include state(s) of matter, color, texture, smell, etc. Where applicable. If your observations are not detailed, you may not receive full credit. One step also requires a specific chemical test using litmus paper to check for acidity. Be sure to also record the results of these tests in your lab notebook. **You will turn in worksheet pages 11-12 along with the duplicate pages from your lab notebook. Step l: Procedure – Oxidation Cue with concentrated nitric acid, HON.(as) 1 . Place a sample of weighing paper in the balance. Tare the balance, so it reads 0. 0000 g. Use forceps to transfer about 0. 5-0. 40 g of Cue strips onto the weighing paper. Record the mass of the Cue strips. Transfer the Cue strips into a clean 250-ml beaker labeled with one of your group member’s initials. Record the appearance of the copper metal in your lab report. CAUTION: Concentrated nitric acid is highly corrosive, so it can cause severe chemical burns and damage clothing. Handle with care and avoid breathing the fumes. Any nitric acid spilled on skin must be rinsed immediately with water for 15 minutes. Any acid spilled on your work area must be neutralized then the entire rear should be washed and dried.
CAUTION: Concentrated nitric acid reacts with copper metal to form brown toxic NON gas. Leave the reaction beaker in the fume hood until all of the brown gas is vented in the hood. ICC CHEM. 151 AL: The Copper Cycle page 6 of 12 2. In a fume hood, use a 10-ml graduated cylinder to carefully measure about 3 ml of concentrated nitric acid, HON.(as). Slowly pour the nitric acid onto the Cue strips in the beaker, swirling the beaker to maximize contact between the Cue and nitric acid until all of the solid Cue has dissolved and the NON gas has escaped.
Keep the action beaker in the hood until all the toxic brown NON gas is gone, and keep your face away from the hood to avoid inhaling nitric acid fumes and NON gas. Describe the reaction between HON. and the Cue metal in your lab report. 3. Dilute the resulting solution with about 10 ml of denizen water. Describe the appearance of the resulting solution containing Cue+ in your data table. Step II: Chemistry – Precipitating Cue(OH)2(s) with Noah(as) left over from the previous part. Once all the HUH+ ions are neutralized, additional OH- ions react with the Cue+ complex ion to form a gelatinous blue Cue(OH)2 precipitate.
Once all the Cue+ ions have reacted, no more precipitate forms. Adding more OH- ions makes the solution basic, so it can turn red litmus paper blue. The picture sequence on the next page outlines the step-by-step process that occurs during this step. Step II: Procedure – Precipitating Cue(OH)2 with Noah solution CAUTION: Sodium hydroxide (Noah) can easily damage eyes. It is corrosive and can cause chemical burns and damage clothing. Any Noah splashed into eyes or spilled on skin must be rinsed immediately with water for 15 minutes. Any base spilled on your work area must be neutralized then the entire area should be washed and dried. While constantly stirring the Cue solution, slowly add MM Noah(as) from the dropper bottles. First, the OH- from the Noah added will neutralize the excess acid left over from Part l. 2. Once all the acid is neutralized, additional OH- ions react with the Cue+ to form Cue(OH)2(s), a blue precipitate. Record what you observe in your lab report. When adding more Noah does not produce more precipitate, the solution can be tested to determine if all the Cue+ has been precipitated and additional OH- has made the solution basic. Use red litmus paper to test if the solution is basic as follows.
Without stubbing any precipitate, use a glass stir rod to place a drop of solution (NOT the precipitate) on a piece of red litmus paper. If it turns blue, the solution is basic. Stop adding Noah when the solution turns red litmus paper blue. Describe your litmus test in your lab report. Page 7 of 12 Step-wise Illustration of the Precipitation of part II 1st Beaker: Check solution using red litmus paper (refer to background handout). Continue adding base until solution is basic. At the end of Part I Cue+ ions are present, making the solution blue, and excess hydroxide ions (HUH+) remain from the nitric acid used. D Beaker: Adding Noah(as) to the blue solution results in the OH- ions ions are not shown. 3rd and 4th Beakers: 5th Beaker: Once all the HUH+ are neutralized, adding more Noah(as) results in the OH- ions reacting with the Cue+ to form the blue Cue(OH)2(s) precipitate shown at the bottom of the beaker. When all of the Cue+ ions have been converted to Cue(OH)2(s) precipitate, adding more Noah(as) results in unrelated OH- ions in solution, which makes the solution basic. Red litmus paper can be used to confirm the solution is basic. Note that the solution is no longer blue since no Cue+ ions are present in the solution.
In reality, your solution may still appear blue because of the dispersion of the Cue(OH)2 in the solution by mixing. Step Ill: Procedure – Converting Cue(OH)2(s) to Cue(s) 1. Set up a ring stand as shown in the figure at the right. Set up a ring clamp, and put a wire gauze on top of it. Above it, attach another ring clamp with a diameter large enough to go around a 250-ml beaker. You are going to set your 250 ml beaker on the lower ring and gauze. The upper clamp will hold the beaker in place so it does not fall. 2. Add about 30-40 ml of denizen water to your reaction beaker from Part II.
Carefully place the beaker on the ring stand inside the upper ring. CAUTION: Gently heat the beaker over a medium flame. (Set the inner cone of the Bunsen burner flame to a height of about 1. 5 inch and the lower ring stand about 4 inches above the top of the Bunsen burner). Constantly stir the solution with the glass end of the stirring rod until all the blue precipitate turns black, and the solution is clear. If the solution starts to bump or boil, immediately remove the beaker from the heat and let the solution cool slightly. Describe what happens to the Cue(OH)2 precipitate upon heating in your lab port. Age 8 of 12 3. Allow the beaker and contents to cool. While they are cooling, set up the gravity filtration apparatus. Obtain a second ring stand, and attach a ring clamp that is small enough to hold the plastic funnel. Prepare the filter paper as shown below: Finally, place the plastic funnel in the small ring clamp, and place a 400-ml beaker beneath it to collect the filtrate (the liquid that goes through the filter paper). The funnel’s stem should be Just inside the beaker to prevent splashing. 4. Use the markings on a clean 150-ml beaker to measure out about 25 ml of denizen water.
Boil the water on a hotplate to wash the precipitate in step 6. 5. When the 250-ml reaction beaker has cooled to room temperature, pour the Cue precipitate into the funnel to filter the contents. Transfer the last traces of the solid from the reaction beaker into the funnel, using a stream of denizen water. 6. Use a disposable pipette to wash the precipitate on the filter paper using the hot denizen water heated in the 150-ml beaker. Allow each portion of hot water to drain through the filter paper into the beaker below before adding the next portion. Use 15 ml of the hot denizen water to thoroughly wash the Cue precipitate.