Rates of Reaction Lab Report - magnesium and hydrochloric acid

---

APPARATUS & DIAGRAM:

---

METHOD:

1. Use the ruler, pencil and scissors to cut 15 magnesium strips down to a standardized length of 10 mm.
2. Fill the large beaker with 500ml of HCL acid, so that when you submerge the inverted measuring cylinder, its tip is well submerged as well (see Figure 2).
3. Fill the measuring cylinder completely with HCL acid, leaving only 1 mL empty (Figure 3). A process of trial and error, involving a pipette, was used for this particular experiment to achieve this. The cylinder in this situation was filled to 17 mL.
4. Practice step 5. Remember that once the cylinder is inverted and submerged, the increment markings need to be visible so that when the hydrogen bubble reaches 6 mL (5 mL actually, plus 1 mL air cavity), you stop the stopwatch.
5. Place 1 strip in the cylinder, start the stopwatch, clamp your thumb (or finger) over the top of the cylinder, invert the cylinder then submerge it in the acid in the large beaker, then release your thumb (finger). It is imperative all these steps are done at light speed.
6. Stop the stopwatch once the hydrogen air bubble reaches 6 mL.
7. Repeat steps 5 and 6 changing only the number of magnesium strips, essentially adding one more each time.
8. Repeat step 7 as many times as possible until consistent results are obtained.

DATA COLLECTION:

1 Strip:

2 Strips:

3 Strips:

4 Strips:

5 Strips:

Strip Dimensions:

Ruler uncertainty: ±0.5 mm

   Thickness:        0.5 mm ±100.0%

Width:        3.0 mm        ±16.7%

Length:        10.0 mm ±5.0%

DATA PROCESSING: 

Total Surface Area (SA) of Strips (mm2):

Rate of Hydrogen Production (mL/s):

Measuring cylinder uncertainty: ±0.2 mL

5.0 mL ±4.0%  

DATA PRESENTATION:

---

---

CONCLUSION:

        Obviously, there is no proportionality, although there certainly is a correlation that agrees with my hypothesis, that as surface area increases, the rate of reaction increases as well. This is clear, because the gradient of the line of best fit is clearly positive, indicating that as the total surface area (mm2) increases, so does the rate of hydrogen production (mL/s).

        

EVALUATION:

Clearly, the biggest weakness of the data is the massive uncertainty in SA, due to the measurement of the strip’s thickness with a ruler that wasn’t designed to measure miniscule lengths accurately. So technically, a measurement of 0.5mm with a ruler, whose smallest graduation is 1mm, will lead to 100% uncertainty; however, in reality, I doubt it that the uncertainty is actually that large; which is why this issue is only a weakness, and not a limitation. Therefore, the conclusion and data are accurate and reliable, because the trend is clear.

Another weakness is the method. In terms of safety, it’s generally unsafe to go about placing one’s hand in acid; even if the acid is really weak at 1 M. Also, the method was tedious and was rather manual and primitive, specifically the part where the chemist is required to clamp their thumb (finger) over the cylinder’s top.

IMPROVEMENTS:

        The most important improvement is to use a more accurate measurement device to measure the dimensions of the magnesium strips, particularly the thickness. Or using a different reactant that provides for a better shape, for a more accurate dimension measurement.

        Addressing the second weakness concerning the method; using a gas syringe would’ve been more efficient, and less tedious, not to mention safer.