Lab Manual- Chapter 28

Procedure

1. Measure copper 2. Add Nitric Acid 3. Add Sodium Hydroxide 4. Centrifuge 5. Heat the Sample 6. Add the Sulfuric Acid 7. Add Magnesium ribbon 8. Measure Recovered copper

At what angle should the test tube circularly in and out of the cool flame?

45⁰

A number of caution chemicals, refer to the procedure and specify what must be handled with care.

A.2 NO2- do not inhale A.2 HNO3- do not touch B.1 NaOH- wash skin if contact D.1 H2SO4- do not touch E.1 H2SO4- do not touch

Step 2: Precipitation of Copper (II) Hydroxide from Solution (NaOH)

Acid-Base Neutralization: Copper Nitrate is treated with Sodium Hydroxide. Cu(NO3)2 + 2NaOH → Cu(OH)2 + 2NaNO3 Products: Copper Hydroxide: a light blue solid Sodium Nitrate: a colorless salt that remains dissolved in solution as Na+ and NO3- ions.

Alloying Element

An element of low percent composition in a mixture of metals, the result of which produces an alloy with unique, desirable properties.

Step 4: Dissolution of Copper (II) Oxide

Copper (II) Oxide reacts readily with sulfuric acid to form Copper sulfate CuO + H2SO4 → CuSO4 + H2O Products: Copper Sulfate: sky-blue water soluble salt H20- supernatant

Patina

Copper that oxidizes with the air

Three of the equations represent oxidation-reduction reactions. Identify the three equations and indicate the oxidizing agent.

Cu + 4 HNO3 → Cu(NO3)2 + 2NO2 + H20 Reducing agent/oxidize/lost electrons: copper Oxidizing agent/reduced/gain electrons: nitric acid CuSO4 + Mg → Cu +MgSO4 Reducing agent/oxidized/ lost electrons: magnesium Oxidizing agent/reduced/ gain electrons: Copper sulfate Mg + H2SO4 → H2 + MgSO4 Reducing agent/oxidized/ lost electrons: magnesium Oxidizing agent/reduced/ gain electrons: H2SO4

One of the equations represents an acid-base reaction. Identify the equation and indicate the base.

Cu(NO3)2 + 2NaOH → Cu(OH)2 + 2NaNO3 Acid: Copper nitrate Base: Sodium Hydroxide

Describe the technique for washing a precipitate

Discard into waste container, use a solution that will remove any lingering ions and than wash with water.

Classify the type of reaction for the conversion of copper (II) oxide to copper (II) sulfate

Double displacement (?) UNSURE

Errors in the experiment technique can lead to the percent recovery being too high. On such error can occur in E.2, and the other in E.3. Cite those two errors and explain what should be done to ensure that these errors do not occur in the recovery.

Failure to centrifuge. Do not let it sit idle, balance properly, avoid contaminants Failure to dry Copper completely. - Follow technique 13 and heat correctly

When the NaOH solution is added, Cu(OH)2 does not precipitate immediately. What else present in the reaction mixture from Part A reacts with the NaOH before the copper (II) ion?

H2O. Cu(No3)2 is aqueous and has Cu(2+) and NO3(-) ions. When NaOH is added, Na+ ions react with the No3- ions to form the NaNo3, and the Cu(2+) ions react with the OH- ions to form Cu(Oh)2 which is light blue precipitate. It is possible that these H+ and OH- ions that form water started to react with NaOH before Cu(No3)2 did. But the reaction, other than that, needed time

Jacob couldn't find the 6 M H2SO4, so instead substituted the 6 M HNO3 that was available. What change was most likely observed as a result of this decision.

HNO3 cannot be use in the redox titration because it oxidizes itself. Unlike HCl, it isn't volatile, and doesn't take part in the reaction

Step 3: Conversion of Copper Hydroxide to a Second Insoluble Salt

Heat will be applied to Copper (II) Hydroxide to form a black, insoluble Copper (II) Oxide. Cu (OH)2 → H20 + CuO Products: H20: gas Copper Oxide: black insoluble solid

Extreme caution must be observed when heating a solution in the test tube. What criterion indicates that you are heating the solution with a cool flame?

If you feel the flame while holding the clamp than it is too hot.

The sample in Part B was not centrifuged. The student had other priorities, the percent recovery of copper in the experiment will decrease. Explain why.

Initially, a blue precipitate is formed. But because it was not centrifuged, the reaction did not fully complete in the tube, and reversed somewhat from sitting still, so some copper will remain within the the Cu (II) hydroxide and not react with the NaOH, lessening the percent recovery of copper from the experiment. Failure to form all of the Cu(Oh)2 will do this if not centrifuged.

Describe the technique for balancing a centrifuge

Insert test tubes opposite one another at an angle. Make sure that the angles are similar.

Sulfuric acid has a dual role in chemistry of this experiment. What are its two roles in the recovery of the copper metal?

It speeds up the reaction in the copper cycle, and also acts as a dehydrating agent. It takes away the water from the Cu (II) hydroxide, allowing you to eventually recover Copper itself

What volume in drops of 16 M HNO3 is required to react with .0214 g Cu? Assume 20 drops per milliliter.

Less than or equal to 10 drops from dropper bottle (?) UNSURE

Identify the oxidizing agent in the conversion of copper (II) ion to copper metal

Magnesium serves as a reducing agent (a substance that donates electrons to another substance). Magnesium reduces copper (II) ion from Copper (II) Sulfate to create copper metal . If magnesium is the reducing agent, than the oxidizing agent is Copper Sulfate.

What is the color and the formula of the gas that is evolved?

NO2, nitric acid, orange-brown color.

A .0194 g sample of copper metal is recycled through the series of reactions in this experiment. If .0169 g of Copper is then recovered after the series of reactions in this experiment, what is the percent recovery of the copper metal?

Percent recovery: (mass recovered)/ (mass original) * 100 (0169/.0194)* 100 = 87.11%

Step 5: Reformation of Copper Metal

Redox Reaction: Magnesium serves as a reducing agent (a substance that donates electrons to another substance). Magnesium is more reactive than copper, reduces copper (II) ion from Copper (II) Sulfate to create copper metal and forms a water soluble magnesium sulfate and thus completing the Copper Cycle. CuSO4 + Mg → Cu + MgSO4 Products: Copper: element that we started with. An orange-brown solid at the bottom of the test tube. Magnesium Sulfate: a clear water soluble aqueous solution. Hydrogen gas: Second reaction occurs where the magnesium metal is added to the acidic copper sulfate. Bubbles of hydrogen gas will be observed where the magnesium metal reacts with the sulfuric acid.

Copper forms many different compounds. Identify the oxidizing agent that converts copper metal into the copper (II) ion

Redox reaction: Copper reacts with nitric acid. Nitric acid oxidizes copper metal to the copper (II) ion. Cu + 4HNO → Cu(NO3)2 + NO2 + 2 H2O Nitric acid

Step 1: Dissolution of Copper (HNO3)

Redox reaction: Copper reacts with nitric acid. Nitric acid oxidizes copper metal to the copper (II) ion. Cu + 4HNO → Cu(NO3)2 + NO2 + 2 H2O Products: Copper Nitrate- water soluble salt that produces blue PPT Nitric Acid- a toxic gas that has a copper color. The solution as whole is slightly acidic

Copper

Soft metal with characteristic bright orange-brown color. Relatively inert chemically, does not readily oxidize and is not attacked by simple inorganic acids such as sulfuric and hydrochloric acids.

What is the consequence of not using this technique properly?

The contents of the test tube can be violently ejected

All of the CuO does not react with the sulfuric acid. Will the percent recovery of copper in the experiment be too high or too low.

The reported recovery will be too low. If 1 mole is present of CuO, and only half of it reacts for example, you only get a part of the Cu that has reacted. 1 mole, .78 moles reacts, then percent collected will be 78%.

Purpose

To observe a series of chemical reactions of redox, precipitation, decomposition, acid-base reactions that produce a number of colorful compounds. 1.Copper 2. Copper Nitrate 3. Copper Hydroxide 4. Copper Oxide 5. Copper Sulfate (back to copper)