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Introduction
In this lab we will use Alka Seltzer to learn about solubility and temperature.

Alka Seltzer was first produced in 1931by Pharmascist Mikey Wiseman, (1)

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Alka Seltzer is composed of the chemicals sodium bicarbonate, salicylic acid(aspirin) and citric acid.(1) Sodium bicarbonate is baking soda. The reaction is NaHCO3 + Citric acid ---> CO2 + H2O + Sodium Citrate. (2) The aspirin is not involved in the reaction. (1)

When carbon dioxide dissolves in water it makes an acidic solution because it produces carbonic acid. H2CO3.This is why sodas are acidic.

My Hypothesis:
When we dissolve the tablet in cold water it should dissolve slower. When we dissolve the tablet in hot water it should dissolve much faster. This is because in hot water the molecules are moving much faster and can bump into the alka seltzer faster and more times helping it to dissolve. The simulation below shows this. (I recorded this using Jing and a gizmo from [|exploraelearning].)

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From our text book we know that the solubility of gasses decreases when the temperature goes up so when we dissolve the table in hot water, not as much CO2 will dissolve and not as much acid (H2CO3) will form so the solution will be less acidic.

Procedure:
First we boiled red cabbage to make an indicator. We heated water on the stove until it was around 80 degrees and poured it into a glass. We put water in a glass into the freezer and left it until it was about 20 degrees We used water at room temperature as a control. We put a couple of drops of indicator in each container. We dropped an alka seltzer into the hot and the cold water glasses. We noted the color changes and the rate of bubblling. We added Ammonia as a substitute for NaOH since ammonia is a household base.

Data
Solutions after adding indicator. Hot/Room Temp/Cold Hot water fizzed much faster. Hot and Cold Solutions turned pinkish. After a minute, the hot water was dissolve but the cold water still had some of the tablet left. Bubbled were still noticeable in the cold water.
 * || Cold || Neutral || Hot ||
 * color to start (1) || light green || light green || light green ||
 * time to dissolve (2) || 1min 48 sec || not added || 24sec ||
 * color after dissolving (3) || pink || light green || pink ||
 * drops of Ammonia to return to light green(4) || 84 || 0 || 22 ||



Cold Water - In cold water, the tablet dissolved much slower and it required more ammonia to get the color to match the color of the control glass.

Hot Water In hot water, the tablet dissolved really fast.It took fewer drops to get the color to match the pure water.

Room Temperature Water

Questions
I used ammonia instead of NaOH but answered the questions the same.

1. Why was it necessary to be accurate in measuring the two Alka Seltzer portions, the water, and the BTB? You need to measure all substances to make sure that everything is the same. You want to know that the reaction and the conditions produced the results. You want to know that the water is acidic because of the reaction and temperature not because there was more of one chemical.

2. What is the dependent variable in the lab? The independent variable? The dependent variable is acidity and solubility. The independent variable is temperature.

3. What was the function of the control? THe control let us see how far from neutral the hot and cold solution were.

4. In which beaker did the tablet dissolve faster? Why did it do that? The tablet dissolved faster in the hot beaker because the molecules move faster. 5. To which test tube was more NaOH added ? What do the number of drops of sodium hydroxide indicate? The NaOH needed to be added to the cold beaker because the CO2 did not escape but dissolved in the water making it an acidic solution. The more drops of NaOH, the more acidic the solution was.

6. What can you conclude about the water temperature and the solubility of carbon dioxide gas? Carbon Dioxide dissolves more in colder water.

7. On the basis of what you have learned during this experiment answer the following: If Earth’s climate warms because of additional carbon dioxide in the atmosphere, and then the oceans of the world warm, what will happen to the ocean’s ability to absorb carbon dioxide? Will it increase, decrease, or stay the same? Explain. The oceans will not be able to dissolve as much CO2 since warm water dissolves less gas than cold water. If even less CO2 is dissolved then the amount of CO2 in the air will increase even more and the climate will warm even more. It is a bad cycle.

Conclusion
Solids dissolve faster in hot water than cold. Gases do not dissolve as well in hot. In hot water the CO2 gas just bubbled away but in cold water it dissolved and made the water turn to acid. Indicators change colors if they are in an acid or a base or a neutral solution.