Determine the observed rotation angle (α) (for part A). Determine the observed rotation angle (α) (for part B).

Question

Part A: The specific rotation ([α]) of Unknown molecule (name is censored on this website but is not relevant for answering the question) in chloroform solvent is -16.3 degrees. determine the observed rotation angle (α) when 5g of this compound is dissolved in chloroform to give a total volume of 25ml and this solution is placed in a polarimeter with a path length of 2dm. ((This answer must be a Negative value so it is clockwise).

Part B: Determine the observed rotation angle (α) when a mixture of 1.5 g of Unknown molecule and 3.5 g of its enantiomer are dissolved in chloroform to give a total volume of 25ml and this solution is placed in a polarimeter with a path length of 2 dm. (This answer must be a Positive value so it is clockwise).

Answer 1

To determine the observed rotation angle (α) for Part A and Part B, you can use the formula:

\[α = \frac{[α] \cdot l \cdot c}{10}\]

Where:

- \(α\) is the observed rotation angle.

- \([α]\) is the specific rotation of the compound in degrees (given).

- \(l\) is the path length in decimeters (given as 2 dm).

- \(c\) is the concentration in g/100 mL.

First, you need to calculate the concentration (\(c\)) for both Part A and Part B:

Part A:

Concentration (\(c\)) = \(\frac{\text{mass of Unknown molecule}}{\text{total volume}}\)

Concentration (\(c\)) = \(\frac{5g}{25ml}\)

Concentration (\(c\)) = \(\frac{5g}{0.025L}\) = 200 g/100 mL

Part B:

Concentration (\(c\)) = \(\frac{\text{mass of mixture}}{\text{total volume}}\)

Concentration (\(c\)) = \(\frac{1.5g + 3.5g}{25ml}\)

Concentration (\(c\)) = \(\frac{5g}{0.025L}\) = 200 g/100 mL

Now, you can calculate the observed rotation angles (α) for both parts:

Part A:

\[α_A = \frac{(-16.3°) \cdot 2 \cdot 200}{10}\]

\[α_A = \frac{-6520}{10}\]

\[α_A = -652°\]

Part B:

\[α_B = \frac{(-16.3°) \cdot 2 \cdot 200}{10}\]

\[α_B = \frac(-6520}{10}\]

\[α_B = -652°\]

Both Part A and Part B result in a negative observed rotation angle (α), which indicates clockwise rotation. The specific rotation ([α]) of the compound doesn't change in these scenarios; it's the concentration and path length that affect the observed rotation.