Chapter 13, Problem 2Q

Interpretation Introduction

Interpretation:

The reason for the use of ethanol or isopropyl alcohol instead of water or acetone to clean the surface of the refractometer should be determined.

Concept introduction:

Refractive index is an important physical property that determines the composition of the substance. It determines the amount of refraction the light undergoes due to the change in speed because of the difference in densities.

Refractive index $\left(n\right)$ is defined as the ratio of the velocity of light in vacuum or air to the velocity of light in another medium of the substance under study that is given as follows:

  $n=\frac{V_{\text{air/vacuum}}}{V_{\text{another}\text{medium}\text{under}\text{study}}}$

Where,

• $V_{\text{air/vacuum}}$ is the velocity of light in vacuum or air.
• $V_{\text{another}\text{medium}\text{under}\text{study}}$ is the velocity of light in another medium of the substance under study.

The density of organic compounds varies with temperature so does velocity of light passing through it. Density is inversely proportional to the temperature of the substance.To determine the refractive index an instrument called refractometer is used.

The formula to calculate the variation of refractive index with temperature is given as follows:

  $\Delta n=4.5\times {10}^{-4}\times \left(T_1-T_2\right)$

Where,

• $\Delta n$is the change in the refractive index.
• $T_{\text{1}}$ and $T_2$ is the initial and final temperature, respectively.