ap chemistry free response practice unit 2
name:
2022 ap chemistry free-response questions
6. a student wants to determine the concentration of permanganate, $mno_4^{-}(aq)$, in a solution. the student plans to use colorimetric analysis because solutions containing $mno_4^{-}(aq)$ have a purple color.
(a) to determine the optimum wavelength for an experiment that measures the concentration of $mno_4^{-}(aq)$, the student takes a sample of the solution and measures the amount of light absorbed by the sample over a range of wavelengths. the data are plotted in the graph shown. identify the optimum wavelength that the student should use for the experimental procedure.
(b) the student uses a stock solution of $2.40 imes10^{-3}m kmno_4(aq)$ to prepare the standard solutions of $mno_4^{-}(aq)$ that are needed to construct a calibration curve.
(i) the student uses a 100.0 ml graduated cylinder to measure a certain volume of $kmno_4(aq)$ stock solution, as shown in the diagram given. what volume should the student record?
(ii) calculate the volume, in ml, of $2.40 imes10^{-3}m kmno_4(aq)$ that is required to produce 100.0 ml of a standard $1.68 imes10^{-3}m mno_4^{-}(aq)$ solution.

Question

ap chemistry free response practice unit 2
name:
2022 ap chemistry free-response questions
6. a student wants to determine the concentration of permanganate, $mno_4^{-}(aq)$, in a solution. the student plans to use colorimetric analysis because solutions containing $mno_4^{-}(aq)$ have a purple color.
(a) to determine the optimum wavelength for an experiment that measures the concentration of $mno_4^{-}(aq)$, the student takes a sample of the solution and measures the amount of light absorbed by the sample over a range of wavelengths. the data are plotted in the graph shown. identify the optimum wavelength that the student should use for the experimental procedure.
(b) the student uses a stock solution of $2.40	imes10^{-3}m kmno_4(aq)$ to prepare the standard solutions of $mno_4^{-}(aq)$ that are needed to construct a calibration curve.
(i) the student uses a 100.0 ml graduated cylinder to measure a certain volume of $kmno_4(aq)$ stock solution, as shown in the diagram given. what volume should the student record?
(ii) calculate the volume, in ml, of $2.40	imes10^{-3}m kmno_4(aq)$ that is required to produce 100.0 ml of a standard $1.68	imes10^{-3}m mno_4^{-}(aq)$ solution.

Accepted Answer

# (a)
## Brief Explanations:
The optimum wavelength for colorimetric analysis is the wavelength at which absorbance is maximum. Looking at the graph, the peak of the absorbance curve gives this value.
# Answer:
$525\space nm$ (approximate value from the peak of the absorbance - wavelength graph)

# (b)(i)
## Brief Explanations:
When reading a graduated cylinder, we read the bottom of the meniscus. The markings on the graduated cylinder in the diagram are in $1 - mL$ increments.
# Answer:
$92.0\space mL$

# (b)(ii)
## Step - by - Step Format:
## Step1: Use the dilution formula $C_1V_1 = C_2V_2$
where $C_1$ is the initial concentration, $V_1$ is the initial volume, $C_2$ is the final concentration, and $V_2$ is the final volume.
We are given $C_1=2.40\times 10^{-3}\space M$, $C_2 = 1.68\times 10^{-3}\space M$, and $V_2=100.0\space mL$
## Step2: Solve for $V_1$
From $C_1V_1 = C_2V_2$, we can express $V_1=\frac{C_2V_2}{C_1}$
Substitute the values: $V_1=\frac{1.68\times 10^{-3}\space M\times100.0\space mL}{2.40\times 10^{-3}\space M}$
$$V_1=\frac{1.68\times100.0}{2.40}\space mL$$
$$V_1 = 70.0\space mL$$
# Answer:
$70.0\space mL$

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QUESTION IMAGE

Question

Explanation:

(a)

Answer:

(b)(i)