Systems: Open and Closed

• Open System:–A system in which both matter and

energy can be exchanged with its surroundings

• Closed System:–A system in which only energy, but not

matter, can be exchanged with its surroundings

Mass Changes in Closed Systems

Beginning Question• Is there a change in mass in a

closed system when a physical or chemical change occurs?

Explanation of Lab

• You will be conducting 4 different experiments. Two of the experiments, dissolving salt and melting ice, involve physical changes only. The other two experiments, Alka seltzer in water, and heating copper and sulfur, involve chemical changes. In each lab the initial and final volumes of the mixtures will change. Your job is to determine whether the mass also changes.

Predictions

• For each experiment you will predict whether the mass of the system will increase, decrease or stay the same.

• Experiments:1. Dissolving salt

2. Melting ice

3. Alka Seltzer and water reaction

4. Copper and sulfur reaction

Safety Considerations

• These will be discussed for each lab before we begin.

Procedures

• Lab 1: Dissolving Salt1. Obtain a small vial and a sample cup of salt. Fill

the vial about ½-full with water.2. Mass the vial + water + sample cup of salt.

Record this as your initial mass.3. Add the salt to the vial and allow it to dissolve. 4. Mass the vial + water + salt + empty sample cup.

Record this as your final mass.5. Calculate the change in mass.

Procedures

Lab 2: Melting Ice1. After cleaning out the salt water, add a small

piece of ice to the vial. 2. Immediately mass the vial + ice before it melts.

Record this as your initial mass.3. Allow the ice to melt completely.4. Mass the vial + melted ice. Record this as your

final mass.5. Calculate the change in mass.

Procedures

Lab 3: Alka Seltzer1. Add 50 mL of water to the plastic water bottle.

Obtain ½-Alka seltzer tablet.2. Mass the water bottle + water + cap + Alka

seltzer. Record this as your initial mass.3. Add the Alka seltzer to the water bottle and

immediately cap the bottle. Allow the Alka seltzer to dissolve completely.

4. Mass the water bottle and contents. Record this as your final mass.

5. Calculate the change in mass.

ProceduresLab 4: Copper/Sulfur1. Add a small amount of copper/sulfur mixture to the

test tube. Cover the end of the test tube with the finger from a rubber glove and rubber band securely in place.

2. Mass the test tube and contents. Record this as your initial mass.

3. Gently heat the test tube and contents until a reaction occurs. Extinguish the burner and allow the test tube to cool.

4. Mass the test tube and new contents. Record this as your final mass.

5. Calculate the change in mass.

Data, Observations, Calculations and Graphs:

Lab Initial Mass (g)

Final Mass (g)

Change in Mass (g)

Dissolving Salt

Melting Ice

Alka Seltzer

Copper and Sulfur

Calculating the Change in Mass

Change in Mass = Final Mass – Initial Mass

• Change in mass can be positive or negative.

• Positive change in mass indicates your system gained mass.

• Negative change in mass indicates your system lost mass.

Ladies’ Bowling ScoresNew Car Gas Mileage

The Conservation of MassWhat have the last four experiments shown? If you worked carefully, you would have found that in all four cases, the change in mass that you measured was within the experimental uncertainty of your equipment.

If the change in mass was significantly more than this experimental margin of error, it could be explained by human error, such as spilling salt when transferring the sample to the water; condensation on the outside of the vial; or gas escaping from the plastic bottle or the sealed test tube.

When looking at the histograms showing the change in mass data for several classes, our results agree with the conclusion that there was no change in mass that we could measure.

What we have done is collect evidence to support the law of conservation of mass. This law states that in a closed system, where no matter is added (like condensation) and no matter escapes (like gas or spilled salt), the total mass stays exactly the same, regardless of the changes that take place within the system. In other words, matter cannot be created or destroyed, it can only change form.

The atoms that make up matter can be rearranged to make thousands of different compounds, but the same atoms get recycled over and over. This law has been tested with hundreds of different chemical reactions and has been checked to one part in a billion, and it still holds.

Law of Conservation of Mass

In a closed system, where no matter is added and no matter escapes, the total mass stays exactly the same, regardless of the changes that take place within the system.

In other words, matter cannot be created or destroyed, it can only change form.