Lab 20: Solubility Inquiry Lab

Lab 20

Solubility Inquiry Lab

Shiva Senthil

8/2/17

Introduction

The purpose of this lab was to create a procedure to identify an unknown solid using given solubility data. The lab consisted of adding solute to the solvent, water, at certain temperatures and using the solubility data given to identify it. Important terms in this lab are solute, solvent, and solubility. The solute is the substance that is dissolved. The solvent is the substance that dissolves the solute. Solubility is the measurement of how much solute will dissolve in water, and is usually defined in grams dissolved per 100 grams of water. The solubility for solid solutes generally increases with increasing temperature.

Procedure

The first step in the procedure was to measure about 6 grams of the unknown solid and place it into 10 grams of water. The water was at room temperature (about 21.5°C). The reason we chose room temperature is because the two of the possible solids (KNO3 and NaCl) had similar solubilities at that temperature and the other solid (NaNO3) had a much higher solubility. The solubility of KNO3 and NaCl is about 37 grams per 100 grams of water. Scaling it down to per 10 grams of water, the solubility is 3.7g/10gH2O. The solubility of NaNO3 at room temperature is about 8.7g/10gH2O. A value in between those two (~6) was chosen as the amount of solute to put into 10 grams of 21.5°C water. If the solid was NaNO3, the solute would completely dissolve, and the solid would be identified. If the solid was KNO3 or NaCl, some of the solute would not dissolve and would settle at the bottom. Then, to distinguish between KNO3 and NaCl, 10 grams of water would be heated to about 60°C and again about 6 grams of the solid would be added. At 60°C, the solubility of KNO3 is about 11g/100gH2O and the solubility of NaCl is about 3.8g/100gH2O. If the 6 grams dissolved, the solid would be KNO3, and if it didn't dissolve completely it would be NaCl.

Data

The procedure needed either one or two trials depending on the results of the first trial. In this case, the second trial was not necessary as the first trial delivered the results needed to identify the solid.

Conclusion

The solid was identified as NaNO3. Because of the planned procedure, only one trial was necessary to prove that the solid was indeed NaNO3. At 21.5°C, NaNO3 was the only one of the three solids that was soluble enough for 10mL of water to dissolve 6.04 grams.
When the 6.04 grams were placed into the 10mL of water, all of the solute was dissolved. Thus NaNO3 was a viable option as its solubility allows for more than 6.04 grams to be dissolved.

Had the solute been NaCl or KNO3, some of the solute would not have dissolved as they are not soluble enough. If that occurred, a second trial would have been necessary to distinguish between NaCl and KNO3.
This second trial would increase the temperature. In solids, as temperature increases, solubility increases. KNO3's solubility increases much more than NaCl's, so another test at a higher temperature with the same 6 grams of solute would have identified the solid.

Set up with 10mL water and 6.04g solute.

Lab 19: Concentration and Molarity Lab

Lab 19

Concentration and Molarity

Shiva Senthil

8/2/17

Done on paper.

Lab 18: Alka Seltzer and the Ideal Gas Law Lab

Lab 18

Alka Seltzer and the Ideal Gas Law

Shiva Senthil

8/1/17

Introduction

The purpose of this lab was to calculate how much gas was produced in a chemical reaction. Alka seltzer powder was mixed with water to produce carbon dioxide, which was collected in a balloon.

Data

Calculations

Questions
1. Discuss an area in this lab where experimental error may have occurred.
Errors could have occurred in measuring the alka seltzer's mass, the measuring of the circumference of the balloon, and filling the balloon to the same circumference with water.

2. Choose one error from above and discuss if it would make "n" the number of moles of CO2 too big or too small.
While measuring the mass of the alka seltzer, the whole alka seltzer powder was measured. It was nearly impossible to scoop all of the alka seltzer into the balloon. Since there would be less alka seltzer than you would expect, the moles of CO2 would be too small.

3. Using the value for the circumference of the balloon in cm, calculate the volume of the balloon mathematically.
Using 2πr for circumference and 4/3πr^3 for volume of the sphere, we can solve for the volume using the measured circumference of 31.5cm. 31.5 = 2πr → r = 5.01cm. V = 4/3πr^3 → V = 527cm^3

4. Compare your answer to #3 to the volume obtained by filling the balloon with water. Is it close? Which is more accurate and why?
The mathematically calculated value is much lower. Filling the balloon with water is probably more accurate because the shape of the balloon is not exactly a sphere. The circumference measured was shorter than it would have been if the balloon had been a perfect sphere (the measurement was made where the balloon was thinner). Thus, a mathematical calculation would be smaller than the actual value, and filling the balloon up with water until it is about the same size is a more accurate representation.

5. The ideal gas law technically applies to ideal gases. Give two differences between a real gas and an ideal gas.
Real gases actually have a volume, while ideal gases are assumed to have particles infinitesimally small. Real gases also do not have elastic collisions like ideal gases do.

6. Would the CO2 you collected in this lab be considered ideal? Why or why not?
The CO2 would not be ideal because gases will behave ideally only when the temperature is very high and the pressure is very low (this allows the particles to move without being restricted and are less likely to be affected by intermolecular forces, which can cause collisions to transfer energy).


Advanced Questions
1. Using info from the label, calculate the mass of CO2 that should be collected per tablet.

2. What is the percent yield?

3. CO2 is water soluble. The solubility around room temperature is around 90mL/100mL of water. What effect does this have on your calculated n value?
This means that not all of the CO2 went in to the balloon as some was dissolved in water. Thus the n value was smaller than expected.

Balloon with CO2 inside.

Lab 17: Calories in Food Lab

Lab 17

Calories in Food

Shiva Senthil

8/1/17

Didn't get to do this lab

:(