Lab 14: Titration Lab


In this lab, we wanted to find the percent ionization of acetic acid in vinegar. To do this, we titrated a weak acid (acetic acid) with a strong base (sodium hydroxide). We began by filling up a burette to the zero point with 0.25 M NaOH and then we used a graduated cylinder to measure out 7.6mL of vinegar (CH3COOH) into a flask. Next, we added 20 mL of distilled water and a few drops of phenolphthalein (acid-base indicator) to the flask. We used a hot plate and magnetic stirring bar to stir our solution as we added  drops of NaOH to the base-filled flask. We began by slowly adding in drops of acid, but as the pink color remained longer, we dropped the rate of drops even lower. Finally, we added NaOH drop by drop until we reached a very light pink solution.

The setup

Our analyte at the equivalence point

 

Our final percent ionization of vinegar was 0.46%. This percentage is a low number because acetic acid is a weak acid, therefore the reaction between the acid and the base doesn't result in 100% complete ionization and not many hydronium atoms are present in the solution.



Lab 13: Solubility: A Guided Inquiry Lab

Introduction:
In this lab, we identified an unknown salt using the solubility curves of known solids (NaNO3, KNO3, and NaCl). Solubility can be defined as the ability for a substance to dissolve and solubility often increases as temperature increases (which creates the solubility curve). In a solution, there is always a solvent and solute. A solvent can be defined as a substance that dissolves another while a solute is defined as the minor component dissolved in a solution. My lab partners and I created a procedure involving the heating of water to dissolve certain amounts of the mystery substance. By finding the solubility of the substance, we were able to use the given solubility curves to identify the substance.

Procedure:

1. First, we measured out 10 mL of distilled water in a small graduated cylinder and poured it into a small beaker.
2. We began heating our hot water bath (the distilled water beaker in a larger beaker filled with regular water) to our chosen temperature of 45°C using a thermometer and a hot plate. We chose 45°C because that temperature had a large variation in solubility between the three solubility curves, therefore it would be more easy to distinguish between the different substances after finding the solubility of the mystery salt.
3. While the hot bath heated up, we measured out 4.8 g of the mystery salt using a scale. We wanted to use 4.8g of solute at first because it clearly lies over the NaCl curve, but under the KNO3 curve.
4. We poured the 4.8g of solute into the small beaker with distilled water and mixed the solution with a stirring rod. After a few minutes we found the solution remained unsaturated since all the solute dissolved in the solvent. This means the substance is not NaCl.
5. We continued to mass and add 3.5 g more of solute because a total of 8.3g of solute lies over the KNO3 curve while definitely lying under the NaNO3 curve. After a few minutes, all the added solute dissolved in the solution and the solution still remained unsaturated. This means the substance is also not KNO3.
6. By now, we knew the substance must've been NaNO3, but we continued our third test for confirmation. We massed and added 3.4g to our previous solution and later found our solution was finally saturated. This meant our substance was for sure NaNO3.

Data:
Trial 1 (NaCl testing)- Dissolved solute (unsaturated solution)
Mass of solute: 4.8g
Mass of solvent: 10g
Temp: 45°C

Trial 2 (KNO3 testing)- Dissolved solute (unsaturated solution)
Mass of solute: 8.3g
Mass of solvent: 10g
Temp: 45°C

Trial 3 (NaNO3 testing)- Undissolved solute (saturated solution)
Mass of solute: 11.7g
Mass of solvent: 10g
Temp: 45°C

Concluding Summary:
The mystery solute we had was NaNO3. Our claim was justified when we found that 4.8g of solute (above the NaCl solubility curve) and 8.3g of solute (above the KNO3 solubility curve) both fully dissolved and produced unsaturated solutions. Our third test for NaNO3 produced a saturated solution, meaning NaNO3 was certainly our substance. The relationship between the solubility and temperature is that as the temperature of a substance increases, the solubility of the substance also increases. This relationship in the solubility curves is what overall helped us identify the mystery salt.

Lab 12: Alka Seltzer and the Ideal Gas Law

 In this lab, solid sodium bicarbonate (NaHCO3) and citric acid (C6H8O7) reacted with water (H2O) to produce CO2. We collected the CO2 that was given off and used it in the ideal gas law to determine the amount of gas produced. By using a balloon filled with Alka Seltzer powder and a test tube full of water, the powder reacted with the water to produce CO2 that inflated the balloon. Once the reaction ended, we measured the circumference of the inflated balloon and filled the balloon up with water until the water balloon had the same circumference as the gas balloon. We used the water volume in the ideal gas law to finally calculate the amount of CO2 in the balloon.

My Data Table

My Calculations

CO2 inflating the balloon

Analysis Questions:
1. There are multiple areas experimental error may have occurred. For example, we could have inaccurately measured the circumference of the CO2-filled balloon or we could have dropped some powder while transitioning it from the mortar to the balloon. I also know that some water escaped the balloon as we were trying take it off the sink head and pour it into the graduated cylinder.

2. If water leaked out from the balloon, the recorded volume of the balloon would be smaller than the actual volume of the balloon. Since volume has a direct relationship with mass according to Avogadro's law, the number of moles ("n") of CO2 would be too small.

3.  38.00cm= 2πr --> r=6.05cm; V=4/3π (6.05cm)^3= 926.6cm^3= 926.6mL

4. The two volumes (experimental and calculated) of the balloon appear close. I feel that the experimental volume of the balloon is more accurate than the calculated volume because the shape of the balloon is not a perfect sphere. Although some human error may have effected the final numbers of the experimental volume, it is still more accurate than the calculated volume of the balloon.

5. Real gas molecules have interactive forces such as repulsion and attraction while ideal gases aren't supposed to have any interactive forces according to the kinetic molecular theory of gases. This theory also states how ideal gases should not lose energy from collisions with objects or other gas particles, but real gases do not have elastic collisions and tend to lose energy in any collision.

6. The CO2 in this lab would not be considered an ideal gas because ideal gases don't exist and it takes up mass and volume.

Advanced Questions:
1. Each tablet had 1000 mg of citric acid (C6H8O7) and 1916 mg of baking soda (NaHCO3). Using three Alka Seltzer tablets, we found that 3g of citric acid produced 2.062 g of CO2 while 5.74g of baking soda produced 3.011 g of CO2. Since citric acid was the limiting reactant, the theoretical yield is 2.062 g CO2.

2. 1.86g CO2/ 2.062g CO2= 90.2%

3. Some of the CO2 may have been dissolved in the water and therefore was not measured in the balloon as part of the gas volume. This explains how out calculated amount of CO2 appeared higher than our actual amount of CO2 obtained.

Lab 11B: Calories in Food Lab



In this lab we found the number of Calories per gram of different food items using a calorimeter. Each piece of food (a cashew, pecan or cheese puff) was lit on fire and covered with a tin can. The tin can "stove" heated up a flask of water and a change in water temperature was recorded using a thermometer. By using the mass of the food burned, the change in water temperature, and the specific heat of water, we were able to calculate the Calories per gram of each food type.

 

 

Questions #1-#4
1. Since it isn't possible to directly measure the temperature change of a food item, we measured the temperature change of the water. The amount of heat absorbed by the water in the flask is equivalent to the amount of heat given off by the burning food, therefore we know the temperature change of the water would be equivalent to the temperature change of the burning food sample.

2. The energy released by the food sample was gained by the water, therefore we measured the same amount of energy for both the food and the water.

3. The small amount of energy that was not absorbed by the water escaped into its surroundings. The glass flask or tin can may have absorbed some energy, while some energy may have also escaped through the holes of the tin can into the air.

4. I was surprised that the nuts contained more Calories than the cheese puffs because I have always been told that "unhealthy foods" contain more Calories than "healthy foods", but this lab challenged my knowledge of Calories in comparison to healthiness. I also was surprised that cheese puffs had a higher Calories/gram compared to the nuts because I didn't process how the mass of large cheese puffs are still light compared to a small nuts.

Lab 10: Evaporation and Intermolecular Attractions

Pre-Lab Table

My Data Table

Questions #2-#4
2. There was a wide range of temperature differences as shown in my data table above. Even though all of the substances had the same intermolecular attractive force, some substances had stronger forces than others. A substance with weaker hydrogen bonds (even though it is not an actual bond) will evaporate faster, which leads to a larger temperature difference and higher vapor pressure. Evaporation is a process that involves the use of energy which is why the temperature of the substance often decreases as it loses energy. The more a substance evaporates, the more energy it used and the lower the minimum temperature will be.

3. In this particular lab, Ethanol (molar mass= 46.068) and Methanol (molar mass= 32.0416) were the two compounds with similar molar masses. After experimentation, we found Methanol had the quicker evaporation rate and the larger temperature difference. This result was expected because Ethanol does have a slightly larger molar mass than Methanol. A larger molar mass indicates a substance contains more electrons and a greater number of electrons increases the strength of a substances intermolecular forces. A compound with stronger forces needs more energy to evaporate and therefore it is took less energy for Methanol to evaporate compared to Ethanol.

4. Hydrogen bonds are the strongest type of covalent bonds. The more hydrogen bonds a substance contains, the more energy it needs to break and change in the form of evaporation. In this lab, Glycerin contained the most amount of OH- groups and therefore it needed the most energy to evaporate. Our data shows how Glycerin actually increased in temperature because it was absorbing heat from the room rather than evaporating.