Q
QuestionChemistry

(+)-Tartaric acid has a specific rotation of + 12.0°. What is the specific rotation of a mixture of 75% (+)-tartaric acid and 25% (-)-tartaric acid? A. + 4.0° B. + 6.0° C. + 8.0° D. + 9.0°
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Answer

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Step 1
: Understand the problem

In this problem, $\alpha_{1} = +12.0°$, $m_{1} = 0.75 \times m_{total}$, and $\alpha_{2} = -12.0°$, $m_{2} = 0.25 \times m_{total}$.
We are given the specific rotation of pure (+)-tartaric acid and the percentage of a mixture containing (+)-tartaric acid and (-)-tartaric acid. We need to find the specific rotation of the mixture. The specific rotation of a chiral molecule is a measure of its optical activity, which describes the ability of the molecule to rotate plane-polarized light. When two enantiomers are present in a mixture, their optical activities partially cancel each other out. The specific rotation of the mixture can be calculated using the following formula: Where:

Step 2
: Calculate the specific rotation of the mixture

[\alpha]_{mixture} = +6.0°
Plug the given values into the formula:

Final Answer

The specific rotation of the mixture is + 6.0°.