Rates of Reaction Lab Report – Magnesium and Hydrochloric Acid Essay Sample

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BACKGROUND INFORMATION:

Chewing is an extremely important, yet oftentimes overlooked, part of healthy digestion. Most people put food in their mouth, chew a few times and swallow their food, as if their sole focus was how quickly they could get their foods to their stomachs. The action of chewing mechanically breaks down very large aggregates of food molecules into smaller particles. This results in the food having increased surface area, an important contributing factor to good digestion.

HYPOTHESIS: The longer the chewing period and intensity, the larger the resultant surface area, which should result in a faster rate of reaction.

INDEPENDENT VARIABLE: Reactant surface area (mm2)

DEPENDENT VARIABLE: Time (sec)

CONTROLLED VARIABLES:

HOW it was controlled:

1. Reactant

Magnesium was used throughout the experiment.

2. Acid

HCL was used throughout the experiment.

3. Molarity of HCL acid {M}

A molarity of 1 was used throughout the experiment.

4. Pressure (on the hydrogen bubble) {Pa}

a. Depth of measuring cylinder

This was kept generally constant by keeping the general depth of the measuring cylinder constant; although this isn’t an accurate way for controlling the variable, small differences in the depth would have a negligible effect on the pressure.

b. Volume of HCL acid in the large beaker {mL}

This was kept constant by keeping the volume at 500 ml, using the marked increments on the beaker itself.

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.

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.

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