8.4: Procedure
- Page ID
- 537579
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Part 1: Factors Affecting Reaction Rates
Procedure:
1. Weigh 0.05 g of magnesium turnings.
2. Measure 50 mL of 0.75 M HCl and place it in a 125 mL Erlenmeyer flask.
3. Drop the magnesium turning into the Erlenmeyer flask and start your timer.
4. Feel the side of the flask, what do you notice?
5. Stop the timer when the reaction (bubbling) stops. Record the time.
6. Repeat steps 1-4 with magnesium ribbon.
What the is the reaction taking place in the flask? Be sure to balance the reaction and provide states of matter.
Which magnesium metal (turnings or ribbon) has the faster reaction rate? Explain why.
What did you feel when you felt the flasks? Is this indicative of an endothermic or exothermic reaction?
How would the reaction rate be affected if the reaction flask was placed in ice?
Part 2: Determining the Order of the Reaction
In this part of the laboratory we will be determining the order of the overall reaction. In order to do this, we will be collecting the hydrogen gas produced by the reaction in a balloon covering the Erlenmeyer flask. We can approximate the amount of hydrogen gas produced by measuring the diameter of the balloon and using the equation for the volume of a sphere at various time points.
In order to graph an integrated rate law, we need to plot the time of the reaction vs. the concentration of a reactant. Because we are not changing the volume, we will use moles as our y-axis unit. We are able to convert the amount of product (H2) to reactant (HCl) using stoichiometry.
Procedure:
1. Cut a piece of magnesium ribbon that is approximately 4.5 cm long. Place the ribbon inside of a balloon.
2. Measure 25 mL of 0.75 M HCl and place it in a 25 mL Erlenmeyer flask.
3. Set up a clamp holding a ruler according to the photo below.
4. Place the balloon over the mouth of the flask and drop the magnesium ribbon into the flask. With your phone, begin recording the set up. Be sure to keep the phone steady so that accurate measurements can be taken from the recording.
5. Hold the balloon upright until enough gas is produced to hold itself up. Adjust the height of the ruler so that the cm side of the ruler is at the diameter of the balloon.
6. Record the reaction for 2.5 minutes.
Data analysis:
1. In excel, plot the diameter of the balloon at approximately 10 second intervals. Start once the balloon began to hold itself up.
For example: Time Diameter
30 seconds 10.42 cm – 8.11 cm = 2.31 cm
40 seconds 10.94 cm – 8.56 cm = 2.38 cm
50 seconds ….
2. Using the functions provided by excel, convert each diameter of the balloon to volume.
Volume of sphere = (4/3)*Π*r3
3. Continuing to use the functions provided by excel, convert the volume (app. the volume of H2 gas) to
a. mass of H2
b. mol of H2
c. mol of HCl
4. Assuming the starting amount of moles of HCl was 3, subtract moles of HCl used (3c) from 3 to determine the amount of HCl mol remaining at each time point.
5. Plot the amount of mol of HCl remaining vs. time. This represents a zeroth order reaction.
6. Plot the ln of the amount of mol of HCl remaining vs. time. This represents a first order reaction.
7. Plot the inverse of the amount of mol of HCl remaining vs. time. This represents a second order reaction.
8. For each plot, display the trendline equation and r2 value on the graph.
Using this information from step 8, determine what the overall order for this reaction. (Hint: the higher the r2, the better fit)
According to the order you chose, what is the reaction rate for this reaction?
If the initial moles of HCl was tripled, what would happen to the reaction rate?
Draw a plot of moles of HCl vs. reaction rate.
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