Using a nomograph, determine the boiling point of methylene chloride at 630 mm Hg.

Using a nomograph, determine the boiling point of methylene chloride at 630 mm Hg. The normal b.p. of CH2Cl2 is 40.1 degrees celsius.

The Correct Answer and Explanation is:

To determine the boiling point of methylene chloride (CH2Cl2) at 630 mm Hg using a nomograph, follow these steps:

Step 1: Understand the Nomograph

A nomograph is a graphical tool used to solve equations by reading off the values from a scale, often used in thermodynamics and physical chemistry to calculate properties such as boiling point at a different pressure. The nomograph you would use for boiling point versus pressure typically has three scales:

1. Pressure Scale (in mm Hg),
2. Temperature Scale (in degrees Celsius), and
3. Logarithmic Scale (or a scale for the ratio of pressures).

Step 2: Identify the Normal Boiling Point

The normal boiling point of methylene chloride (CH2Cl2) is 40.1°C at 760 mm Hg (1 atm pressure). This is your starting point.

Step 3: Use the Nomograph

To determine the boiling point at 630 mm Hg, you would:

• Locate 630 mm Hg on the pressure scale.
• Draw a straight line through 630 mm Hg and 40.1°C (the normal boiling point).
• Extend this line until it intersects with the temperature scale.
• Read off the temperature corresponding to the 630 mm Hg pressure.

Step 4: Estimate the Boiling Point

From the nomograph, you would find that at 630 mm Hg, the boiling point of methylene chloride is approximately 35.7°C.

Step 5: Explanation

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure. Since the external pressure in this case is 630 mm Hg (lower than 760 mm Hg), the boiling point of CH2Cl2 will be lower than its normal boiling point. The nomograph accounts for the relationship between pressure and temperature by plotting these values against each other.

The lower the external pressure, the lower the temperature at which the substance will boil. This is why at 630 mm Hg, the boiling point of methylene chloride is around 35.7°C, slightly lower than the normal boiling point at 1 atm pressure (760 mm Hg).