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CHEM 1127Q Lecture Notes - Lecture 6: Chemical Reaction, Strong Electrolyte, Chemical Equation

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coppersnake702
11 Oct 2018
School
UConn
Department
Chemistry
Course
CHEM 1127Q
Professor
Dr. Cady

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CHEM 1127Q Full Course Notes
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CHEM 1127Q Full Course Notes
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Document Summary

When two or more substances interact with each other to form something new. There are dozens of different classifications of chemical reactions. Rather then classify them by how the reaction happens we sometimes classify them by what happens. Precipitation - solid formed from a clear solution. Color change - if you observe a color change something probably happened. Heat emitted or absorbed - hear is often given off or absorbed in chemical reactions. We now have a bunch of ways to observe that a chemical reaction has happened. Next step is to learn how to write out what happened. C3h8 + o2 = co2 + h2o. 3 carbons on the left only one on the right. 2 oxygen on the left and 3 on the right. 8 hydrogen on the left and 2 on the right. This is a very unbalanced chemical equation. C3h8 + 5o2 = 3co2 + 4h2o. Many ionic compounds dissolve in water but some don"t.

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Related Questions

I need help doing my lab homework, I missed lab that day because, I was sick and it's due.

1. (1 point) What are transferred in an oxidation-reduction reaction? *

• atoms

• electrons

• ions

• protons

2. (1 point) In the reaction of beryllium with fluorine, which atom is oxidized? *

• fluorine

• beryllium

• neither of them

• both of them

3. (1 point) Ag - - > Ag ^+ +1 e^- This equation represents the type of reaction called _____. *

• hydrolysis

• oxidation

• redox

• reduction

4. (1 point) What is the reducing agent in the following reaction? 2K + S - - > K2S *

• K

• S

• K2S

• None of the above

5. (1 point) The oxidation number of oxygen when it is in a compound other than a peroxide is ____. *

• -2

• -1

• 0

• +2

6. (1 point) What is the oxidation number for each atom in NH4F? *

• N=+3, H=-4, F=+1

• N=-3, H=+1, F=-1

• N=+3, H+1, F=-1

• N=-3, H=-1, F=+1

7. (1 point) Which atom has a change in oxidation number of +4 in the following redox reaction?K2Cr2O7 + H2O + S - - > KOH + Cr2O3 + SO2 *

• K

• Cr

• O

• S

Metal activity series for question 8

8. (1 point) Of the following metals, which ions are most easily reduced? Use the above table to answer the question. *

• magnesium

• lead

• copper

• sodium

9. (1 point) In a zinc-copper cell, Zn(s) | Zn^+2(1M) || Cu^+2(1M) | Cu(s), which electrode is positive? *

• Cu^+2

• Cu(s)

• Zn(s)

• Zn^+2

10. (1 point) How must a redox reaction that is to be used as a source of electrical energy be set up? *

• One half reaction must involve two metals.

• Two half reactions must use a metal wire electrodes.

• One half reactions must involve more than one electron.

• Two half reactions must be physically separated.

11. (1 point) In a voltaic cell at which electrode does reduction occur? *

• anode only

• cathode only

• both anode and cathode

• Either anode or cathode , depending on the metal

12. (1 point) What assures that there is no charge build up in a voltaic cell as oxidation and reduction occur? *

• one of the half cells

• the electrolyte solutions

• the moving electrons

• the salt bridge

13. (1 point) In the most common dry cell what material is the electrode that is the center rod made of? *

• copper

• graphite

• lead

• zinc

14. (1 point) To charge a lead storage battery you must ________. *

• apply a direct current to it.

• hold a magnet close to it.

• Use alternating current through it.

• increase the oxygen in it.

15. (1 point) In a hydrogen- oxygen fuel cell ______________. *

• hydrogen diffuses through the cathode.

• hydrogen and oxygen are mixed before entering the anode.

• oxygen diffuses through the anode.

• oxygen diffuses through the cathode.

16. (1 point) When electrical energy is used to cause a chemical reaction we call this process _____. *

• electronation

• electrolysis

• hydration

• reduction

17. (1 point) Which of the following is true about an electrolytic cell? *

• It changes chemical energy into electrical energy.

• It is the type of cell used in electrocution

• It uses an electric current to make a nonspontaneous reaction go.

• All of the above

18. (1 point) The products formed in the net reaction of the electrolysis of water are ____. *

• aqueous hydrogen ion and hydroxyl ion

• hydrogen gas and oxygen gas

• hydrogen gas and liquid oxygen

• water vapor

19. (1 point) What occurs in electroplating? *

• decomposition of an ionic compound

• decomposition of a salt layer

• deposition of a metal layer on a material

• deposition of a salt layer on a metal

Open response Questions : Answer questions 20 through 22 in complete sentences

20. ( 5 points) Write the equation for the reaction of calcium and oxygen ( 1 point). Write the oxidation numbers for both the reactants and the products ( 2 points) What is the reducing agent and why? ( 2 points)

21. ( 5 points) Tell how a voltaic cell works. Be sure to mention the various parts of the voltaic cell and what they have to do with how it works.

22. (4 points) What are the signs given to the electrodes in both the voltaic and electrolytic cells? What reaction (oxidation or reduction) is occurring at each?

In this experiment you will construct a smal electrolytic cell. Then using indicators you will determine the products fromed at the anode and the cathode druing several different electrolysis experiments.

About the experiment: in the first part of this experiment you will construct a small scale chlorine production plant. it is a miniature of the real, large scale process used for production of chlorine by the electrolysis of sodium chloride or brine (procedure written by Dr. Stephen thompson, CSU, CO) You will then investigate the electrolysis of several other aqueous solutions. You will perform the electrolysis in a solution containing an idicator to help you identify the reaction products. Because chlorine gas is toxic, do not extend the time of the electrolysis unnecessarily, keep the electrodes in the solution only as long as you need to see the results and then remove them.

Prodedure: Part 1

1. Place a drop of dilute mineral acid on the lid of a 24-well tray. Add a drop of bromocresol green

2. Place a drop of dilute strong base on thelid of a 24 well tray. Add a drop of bromocresol gree.

Production of Chlorine:

1. Fill one well of a 24 well tray about 3/4 full with brine (saturation NaCl solution). Add 3 drops of bromocresol green to the brine solution in the well. Record the color of the solution in the well.

2. Place the electrolytic set up (straws and electrodes) in the well. Make sure that the electrodes are inserted deep into the solution

3. Attach the alligator clips to the electrodes but not attach the battery yet.

4. Place a small drop of strch/KI solution on the upper part of the inside wall of each straw.

5. Place a cap on the straw containing the lead (anode)

6. Attache the battery to the set up. Keep the battery on for about 3-5 seconds, long enough to observe the changes. Record you observations. If bubbles appear of solution colors change make sure that you record that. It is important to record the initial and final colors of the soltuion. Also note any change in the starch/KI solution in the straw at the anode.

7. Detacht he alligator clips and clean

part 2: investigating the electrolysis process of water and aqueous salt solutions

For part two of the experiment, use the lid of the 24 well tray to hold your solutions. Make sure that it is clean and dry. Use the same pin as in part 1 for one electrode and a second pin for the other electrode (no graphite used). To perform the electrolysis, attach the alligator clips to the pins and then connect the leads to the battery . Hold the alligator clips by their plastic insulation and insert them into the solution in such a way that they are as par apart as possible, yet immersed fully in the solution. Make careful observasion and redord what happens in hte solution around each electrode for every investigation carried out.

1. H2O

a. Place 4 drops of distilled water in one of the circles on the lid. Perform electrolysis for about 3 seconds.

b. Repeat step one but use tap water

2. Na2SO4 or K2SO4

a. perform electrolysis on 4 drops of 0.1 M Na2SO4 solution for about 3 seconds

b. Place 4 drops of 0.1 M Na2SO4 solution in another circle, add one drop of bromothymol blue, and electrolize for about 3 seconds.

3. KI or NaI

a. perform electrolysis on four drops of 0.1 M KI solution for about 3 seconds

b. Place 4 drop of 0.1 M KI solution in another circle , add 1 drop of starch solution , and perform electrolysis for about 3 seconds.

KI or NaI

A. Can you easily determine the identities of the products formed on the electrodes based on the first part of this experiment? explain

B. In the second part, why does the starch added to the solution change color?

C. How does the starch help in identifying the products of the oxidation reaction and the chemical species being oxidized?

D. write the equation for the redox reaction taking place at the anode

E. write the equation for the redox reaction taking place at the cathode