Suppose a sample of an initially pure single enantiomer of tartaric acid [α]D​ =+12.4⁰ (H₂O) underwent a chemical isomerization reaction which yielded 10% of the other enantiomers and 20% meso isomer in addition to 70% of the starting compound.
If 1.0 g of total mixture (including meso) was dissolved in 1.0 mL of water and the optical rotation measured in a 1.0dm cell, what would be the observed rotation of the solution?