An aqueous solution containing 10 g of an optically pure compound was diluted to 500 ml with water and was found to have a specific rotation of −129°. if this solution were mixed with 500 ml of a solution containing 7 g of a racemic mixture of the compound, what would the specific rotation of the resulting mixture of the compound? what would be its optical purity?

Specific rotation = -258°

Optical purity = 200%

Explanation:

Substances that have a chiral carbon ( a carbon which has four different atoms or compounds bond to it) have optical isomers. The different molecules are called enantiomers, and they differ by the side they deflect polarised light. A mixture contained the same number of the enantiomers is not optical and doesn't deflect polarized light. It's called a racemic mixture.

The specific rotation (spec.rot.) can be calculated by the equation:

spec.rot. = α/lc

Where α is the observed rotation of the plane polarised light in degrees, l is the path length in decimeters, and c is the concentration of the solution in g/100 mL.

The initial concentration is 10g/500mL = 2g/100 mL. The racemic mixture doesn't change the specific rotation, so the final concentration is 10g/1000 mL = 1g/100 mL. Then:

with α and l the same:

spec.rot.1/spec.rot.2 = c2/c1

spec.rot.2 = c1xspec.rot.1/c2

spec.rot.2 = 2x(-129°)/1

spec.rot.2 = -258°

If for a -129° the optical purity was 100%:

-129° ---------- 100%

-258° --------- x

By a direct simple three rule:

129x = 25800

x = 200%

h let me think

answer: option (4) is the correct answer.

explanation:

areas which are at low altitudes and near the equator tend to receive direct sunlight from the sun. hence, heat energy or radiations from the sun make these areas warmer and they have warmest water.

whereas areas which are at high altitudes and away from the equator do no receive direct sunlight. hence, no direct contact from the sun makes these regions colder and thus, they have colder water.

thus, we can conclude that the statement areas at low latitudes near the equator have the warmest water because they receive the most direct sunlight best explains the relationship between an area's geography and the temperature of its surface water.