- The amount of reactants needed (7.1 grams of diluted HCl and 11.7 grams of diluted KOH) and the amount of water needed to dilute them into their solutions were the independent variables.
Dependent
- The changes in temperatures needed to find the actual enthalpies to compare to our theoretical values.
- The actual enthalpies of our reactions were also dependent variables.
Control
- The beakers, graduated cylinder, gloves, stopwatch, water, goggles, and the time recorded.
Part 3
Independent
- The 1.5 grams of both reactants that we needed to manipulate in order to create a constant for the our reaction temperatures.
Dependent
- The changes in temperatures needed to find the actual enthalpies to compare to our theoretical values.
- The actual enthalpies of our reactions were also dependent variables.
Control
- The beakers, gloves, mortar and pestle, bowl, fume hood, stopwatch, goggles, and the time recorded were the controls.
Materials
- 50 mL Beaker and Graduated Cylinder
- 10 mL Graduated Cylinders
- 100 mL Graduated Cylinder
- 250 Beakers
- Gloves
- Stopwatch
- Goggles
- Stirring Rod
- Sodium Hydroxide (Part 1)
- Hydrochloric Acid (Part 1 and 2)
- Potassium Hydroxide (Part 2)
- Barium Hydroxide (Part 3)
- Mortar and Pestle (Part 3)
- Fume Hood (Part 3)
- Ammonium Chloride (Part 3)
Procedure
Part 1
- First we got all the necessary equipment and tools to perform the lab.
- We then measured the amounts of Hydrochloric Acid and Sodium Hydroxide.
- We then placed the reactants in their separate 50mL beakers.
- Then we readied a thermometer to record the temperatures.
- We then recorded the initial temperatures.
- We then placed the reactants into a single 100mL beaker
- Then we carefully and swiftly recorded the temperature until it stopped changing, then the data and observations were recorded.
Part 2
- First we got all the necessary equipment and tools to perform the lab.
- We then took the masses of the 50mL beakers.
- Then, after solving for the amounts needed of the reactants, we acquired the amount of reactants needed.
- We then placed each reactant (HCl and KOH) into the separate 50mL beakers and their masses were then subtracted by the original mass of the 50mL beakers to find the masses of the reactants.
- Both were diluted with 5mL of water while being stirred with a stirring rod.
- We then placed both of the solutions into a single, 100mL beaker and we recorded the changes in the temperature.
- After all this had transpired, we recorded our data and solved for ∆H.
Part 3
- First we got all the necessary equipment and tools to perform the lab.
- We then made sure that we had our safety goggles, gloves, and a fume hood to let out the ammonium gas, due to the harmfulness associated with these chemicals.
-
Before any lab reactions were done, we solved for the correct amount of reactants (1.5 grams of both NH4Cl and Ba(OH)2) and placed them in separate 50mL beakers.
- We then took their masses and subtracted the original 50mL beaker weight to find the masses of the reactants.
- Then, we put both of the reactants in the mortar and we began to mash the substance with the pestle while recording the temperature and observations. The temperature was recorded until it stopped changing.
- We then analyzed the data and we solved for the actual ∆H.
Data
*Heat capacity for water is 4.18 degrees Celsius
∆H=mc∆t where m= mass of solution, c= heat capacity and ∆t= change in temperature
Part 1
HCl + NaOH → H2O + NaCl
(P – R)
(-167.3 -470) - (-286 -407)
(-693 - -63 7.3) ∆H = -55.7 kJ/mol
50 mL NaOH – 51.1 g
23.1º C
50 ml HCl – 48.9 g
22.1º C
Mix of NaOH & HCl – 99.6 g
∆H=(99.6)(4.18)(.8)=333.062
333.062/1000=.0333062/
(-52.46 kJ/mol / -55.7 kJ/mol) x 100 = (94.2% yield) (5.8% error)
Part 2
KOH + HCl —> H2O + KCl
(-481) (-167.3) (-286) (-419) = ∆H = -56.7 kJ/mol
Dilution
HCl –
(1 M)V = (0.5 M)(10 mL)
V = 5 mL HCl
& 5 mL H2O
KOH –
(1 M)V = (0.5 M)(10 mL)
V = 5 mL KOH
& 5 mL H2O
Diluted HCl – 7.1 g & 18.6º C
Diluted KOH – 11.7 g & 19.4º C
∆H= (50.4)(4.18)(5)=1053.36
1053.36/1000=1.05336/.05= 21.07 KJ/mol
-21.07 KJ/mol / -56.7 KJ/mol= (62.84% error) (37.16% yield)
Part 3
Ba(OH)2 x 2H2O (s) + 2NH4Cl (s) → BaCl2 x 2H2O (s) + 2NH3 (aq) + 8H2O (l)
(-3342) (-628) (-858.1) (-572) (160.58) (-2288)
(-858.1+(-572)+(-160.58)+(-2288)-(-3342)+(-628)= ∆H=91.32 KJ/mol
ΔH= (7.9)(.361)(4)= 11.41 KJ/mol for BaCl2
ΔH= (7.9)(4.7)(4)= 148.52 KJ/mol for NH3
ΔH= (7.9)(4.18)(4)= 132.09 KJ/mol for H2O
ΔH= 11.41+148.52+132.09 / 3= 97.34 KJ/mol
Percent yield= (actual/theoretical) x 100
97.34-91.32/91.32 x 100= (6.59% yield) (93.41% error)
Graphs and Pictures
Goggles Gloves
Potassium Hydroxide
Hydro chloric Acid Sodium Hydroxide
Ammonium Chloride
Barium Hydroxide
Digital Scale Mortar and Pestle
Conclusion
Ultimately, this lab was a success. A lot was learned about not only enthalpy and chemical reactions, but also basic chemistry skills. This lab could be considered somewhat of a success according to the research question and hypotheses as well. While none of our actual ΔH values matched up exactly with the theoretical ΔH values, all of the values successfully and accurately portrayed whether the reactions were endothermic or exothermic, which is principally what the lab is about, and none of our actual ΔH values were astronomically off, or at least not off enough to make a significant difference. Furthermore, we were able to calculate the ΔH’s with a moderate amount of accuracy. This lack of exact accuracy indicates several errors in this lab. Firstly, human error is a gigantic factor. With so many calculations, sign changes, eyeball measuring, and other human inaccuracies undetected and therefore unaccounted for indefinitely contribute to the lack of accuracy. Also, inaccurate measuring tools and devices may have played a role. Finally, a lack of understanding of what was actually transpiring would have been tremendously helpful. When you don’t fully understand the concepts being employed, you are going completely on “empty” formulas without an understanding of what you are actually doing, making it virtually impossible to detect error.
If this lab were to be conducted again, there would be several different things I would do different. I would alter my methods of conducting this lab to minimize human error. Also, I would use more accurate measuring tools and devices. Finally, I would make my best effort to come into the lab with as much prior knowledge about the subject as possible, and also bring to the table a superb grasp of what was actually going on.