Electricity is defined as a flow of electrons. Ionic substances and things like metals are good conductors of electricity since they either have valence.

DOUBLE TUBE APPARATUSLabs 17/18

Electricity

Electricity is defined as a flow of electrons. Ionic substances and things like metals are good conductors of electricity since they either have valence electrons that move, or like metal, have a “sea of valence electrons” that it would like to get rid of. Surprisingly, things like pure water DO NOT CONDUCT ELECTRICTY. Solutions that conduct electricity are called electrolytic and they contain electrolytes.

Electrolytes are needed

In the first part of the experiment you used a setup that had NO electrolytic solution.

Since no electrolytes are present, no current flows.

NO ELECTROLYTIC SOLUTION

Electrolytes STILL needed

Next you added DISTILLED water and noticed that the light did not light. The reason for this is that distilled water is pure water. It contains no ions or electrolytes, so it does not conduct electricity. Distilled, so NO IONS

Electrolytes

You should have noticed that even when you began to add the copper sulfate compound to the water, the light bulb did not light. This is because even though you now have SOME electrolytes, you need a minimum amount in order to have electricity flow.

Adding Electrolytes

Once CuSO4 is added, in a sufficient amount, you are adding ions. This means that the substance dissociates, or forms ions in the solution. It now conducts electricity.

While you stir the solution, the light should flicker due to the ions concentration changing in solution while you stir.

Now we run electricity

What will happen to the setup if we check it after a period of time?

Answer to Question

Cu will form on the negative terminal (Cathode).

The solution will become less blue as Cu is removed from the solution and forms on the carbon rod.

The bulb will burn less brightly as more ions are removed from the solution.

Although you can’t see this, sulfate ions will gather at the positive terminal (Anode).

IONS IONS IONS

A key thing here that is easily overlooked is the fact that as you stirred the liquid, more ions went into the solution. With more ions, you have more electricity flowing so a brighter bulb.

Dissolving substances

Dissolving

The previous slide does a good job illustrating what we talked about with compounds dissolving and DISSOCIATING. Dissociating means that it forms ions. Notice that the DIPOLAR water surrounds the ions to keep them from recombining.It is important to remember that things like SUGAR will dissolve, but not dissociate.

Sugar, continued

This is because sugar is COVALENTLY BONDED and the bonds are too strong for it to dissociate in water. However, since the molecule of sugar is DIPOLAR, the individual sugar molecules attract with a weak, dipolar bond. This bond is easily separated by water, so sugar dissolves.Not all organic substances will dissolve in water.

Dissociating-note ions forming

IONS IONS IONS

Another point of note is this. If you think back to the lab you did earlier in the year with KI and Pb(NO3)2 you should have noted that the different compounds did NOT dissolve equally. This is due to a difference in the strength of the bonds and is the reason that COVALENT substances do not conduct. Their bonds are too strong to separate.

Reverse the Current

What do you think will happen if the current on the test leads is reversed after a period of time?

Why?

Answers

Copper will leave the rod that it is on for two reasons:

Like charges repel (it is positive and the rod is now positive).

The other rod is negative and opposite charges attract.

Answers Continued

Copper will form on the other carbon rod since it is now the negatively charged rod.

The solution, which faded somewhat, will become bluer for a bit, then fade again. The bulb should brighten and then dim as the concentration of ions change.

Lab Part II, Double Tube Apparatus

There are many objectives for this part of the lab.1. To show that copper in solution is

BLUE.2. To show that it is an electrical

charge that attracts ions.3. That sulfate ions are negative.4. To prove that it was NOT the carbon

rod that attracted the ion, but the electrical current.

Second Part of the Lab

This was an important set up for a number of reasons.

Look at it and see if you can determine what will happen if a current is run. Ammonium nitrate is in the tubes.

Answers to Previous Slide

The tube with no current has NR. It is a control proving that you need electricity for ions to move in solution.

The negatively charged tube will attract Cu atoms and the carbon rod will turn pink.

The same tube will have a blue color as Cu in solution is blue.

The solution in the beaker below the double tube apparatus will remain blue (in the beaker). As Cu is moving into the double tube, Cu from the copper strip goes into the solution replacing the missing ions, since like charges repel.

Part III, Proving SO4 is Neg.

To show that Sulfate is negative, you need an indicator as the ion is not visible. In order to do this you have added BaCl2 to two different copper compounds. Both made double replacement reactions. The difference in them is that one made a white solid. The white solid contained the sulfate ion.

Test for SO4

BaCl2 is added to CuSO4 and to Cu(NO3)2.

The reactions are shown on the next slide.

Reactions of BaCl2 and Cu

BaCl2 + CuSO4 CuCl2 + BaSO4

The reaction makes a blue liquid and a white solid.

BaCl2 + Cu(NO3)2 CuCl2 + Ba(NO3)2

There is no SOLID and the liquid remains a blue color. In fact, it looks as if no reaction has occurred.

Reactions of BaCl2 and Cu

BaCl2 + CuSO4 CuCl2 + BaSO4

BaCl2 + Cu(NO3)2 CuCl2 + Ba(NO3)2

Since both beakers are blue and both contain CuCl2, it must be responsible for the blue color. BaSO4 must be responsible for the white solid as it is the only remaining product.

Copper THE COMPOUND is blue in solution. Cobalt THE COMPOUND is a shade of red in solution. Notice the handsome guys in the background photo?

Notice that the Cobalt Sulfate is red in solution. Copper Sulfate is blue in solution. The nitrates are clear.

BaSO4 Barium Sulfate

You did exactly the same thing with the cobalt compound. The compound containing the NITRATE had no reaction to the barium chloride. This means that the white solid had to be formed by the reaction with the barium and the sulfate.

Notice that the two test tubes that this handsome gentleman is holding are very different. The tubes on the left are showing a positive reaction to the barium chloride. Note the white precipitate. These tubes both contained Sulfate as the Anion. The fact that all four tubes have color let you know that COBALT compounds are RED in solution while COPPER compounds remain BLUE in solution.

Test for Sulfate Ion

So your test for the sulfate ion is to do this:

Add the Barium Ion-if a white solid forms, then you have sulfate ions present.

Ba + SO4 BaSO4 a white solid

Ions move toward electrical charge

This setup proved that an electrical charge is needed for ions to flow. The tube that had no electricity was a control.

Results continued

The tube that was hooked to the negative terminal did TWO things. The liquid turned BLUE and you had copper metal form on the rod.

Results after 15 Minutes

Copper will formon the Cathode, ornegative rod. Thisproves that Cu isPOSITIVE. Cu

is a CATION. TheSolution turns BLUE.Cu reacts with Nitrate

To make Cu(NO3)2

Copper Compound is Blue in Solution

You used ammonium nitrate as an electrolyte since it is colorless. That way, if copper were to move into the tube containing the cathode, you would be able to see a color change. After running a current through the set-up for 10 minutes, you should have noticed that the tube became BLUE.

What does that mean?

That means that Copper is Positive since it formed on the negative rod.

It also means that copper in solution is BLUE.

Results after 15 Minutes

When you do the sameReaction using COBALT

The tube turns a pinkColor. Cobalt

is a CATION. TheSolution turns PINK And cobalt metal is

Either a Blue or Pink.

What does that mean?

It means that COBALT is positive since it goes to the negative terminal (cathode).

It also means that cobalt in solution is PINK.

What is the point of the Cu strip?

The purpose of the copper strip was to add COPPER IONS to the solution of copper sulfate. If you did not do this then the concentration of Cu ions would drop and the flow of electricity would drop. COPPER STRIP

Notice the following. The tube that had the negatively charged rod is now BLUE. The control tube is colorless. There is a copper strip to add ions to the solution.

Control Rod.

The control rod proves several things:1. Copper does not form on a carbon rod without a current. Therefore, electrical forces must be responsible for holding atoms together since it is responsible for their movement in solution.

OD-IONS MOVE TOWARD A CHARGED

ROD IN SOLUTION.

Operational Definition IONS move towards a charged

rod in solution.

2. The copper did not form from the uncharged carbon rod, the ammonium nitrate, or the set-up, as they were all present.3. Copper must be positive since it formed on the negatively charged carbon rod.4. The tube remained colorless, so the copper must have been responsible for the tube with the cathode becoming blue in color. Copper in solution is blue.

Concentration affects electrical flow.

When electricity is added to the system, Cu ions are removed from the system and form on the carbon rod. To keep the concentration of ions constant, a copper strip is hooked to the ANODE, or positive lead. Since like charges repel, this will put copper ions in solution to replace the copper that is being removed from the solution.

Keeping Cu constant

By using the copper strip on the positive terminal copper ions are constantly added to the solution. Since like charges repel, they move from the strip into the water. These ions replace the lost copper that move from the solution into the double tube apparatus and onto the carbon rod.

Eventually, if you let the system run long enough the copper strip would disappear.

Double Tube test for Cu and SO4

You next hooked up your double tube apparatus as shown. You connected the carbon rod to the negative terminal (cathode). The aluminum rod was connected to the positive terminal (anode).

Results Continued

In the tube with the aluminum rod, sulfate forms. When you add barium chloride to this, a white solid forms.

Since you have copper sulfate the other tube would turn blue.

SHOW ME THE COBALT!!!!

Remember cobalt sulfate is a pink/red color. In the tube with the aluminum rod, sulfate forms, AGAIN. When you add barium chloride to this, a white solid forms. A pink/red color should have formed in the Negative tube.

Notice that the tube with the POSITIVE ROD has turned a cloudy color when the Barium Chloride has been added. This is a POSITIVE TEST FOR SULFATE ION.

You should also see that the tube containing the copper ion has NO REACTION.

Summary

Electrolytes are IONIC substances that dissociate (forms ions) in liquids and allow electricity to flow.

If electrolytes are not present, electricity cannot flow. The more electrolytes, the more electricity flows, the brighter the bulb.

Copper is positive, it formed on the Cathode. This means it is a CATION.

Copper compounds in solution are BLUE.

Summary Continued

Sulfate ions are negative as they attract to the positive rod. Sulfate ions are ANIONS. You proved this TWICE. Once with

copper sulfate and once with cobalt sulfate.

A positive test for Sulfate is to add Ba ions. If sulfate is present a WHITE SOLID will form.

Ba + SO4 BaSO4 a white solid It is an electrical charge that holds

ions together as it is an electrical charge that attracts them.

Summary

Cobalt compounds are red/pink in solution. Cobalt IONS are positive, cations, as they

collected on the CATHODE.Our experiments suggest that it is an

ELECTRICAL FORCE that holds ions together. The logic is that since they are charged, and are attracted to charged rods in solution, that it must be a charge that holds them together.

Summary

This makes a lot of sense if you think about different electrical charges and strength of bond. Some ionic bonds are stronger than others and therefore need more energy to separate in a liquid. Warm liquids have more energy. A cold liquid does not separate and dissolve ions as well since it is lacking energy.

Summary

If Energy is the ability to do work, and work is exerting a force through a distance, then dissolving is WORK.

The warmer the liquid the more heat energy is available and therefore the more WORK, dissolving, that can be done.