2.6 H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If

the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant

To calculate Henry's law constant for hydrogen sulfide (H2S) in water, we need to understand the relationship defined by Henry's law. This law states that the amount of gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of that gas above the liquid. The formula for Henry's law can be expressed as:

Understanding Henry's Law

Henry's law is mathematically represented as:

C = kH * P

Where:

• C = concentration of the gas in the liquid (in mol/L)
• kH = Henry's law constant (in mol/(L·atm))
• P = partial pressure of the gas (in atm)

Given Data

In this case, we know the solubility of H2S in water at standard temperature and pressure (STP) is 0.195 m. The unit "m" refers to molality, which is moles of solute per kilogram of solvent. To convert this to molarity (mol/L), we need to consider the density of water, which is approximately 1 kg/L at STP. Thus, 0.195 m can be approximated to 0.195 mol/L.

Calculating Henry's Law Constant

Next, we need to find the partial pressure of H2S at STP. At STP, the pressure is 1 atm. Therefore, we can rearrange the Henry's law equation to solve for the Henry's law constant:

kH = C / P

Substituting the values we have:

• C = 0.195 mol/L
• P = 1 atm

Now, plug these values into the equation:

kH = 0.195 mol/L / 1 atm = 0.195 mol/(L·atm)

Final Result

The Henry's law constant for hydrogen sulfide (H2S) in water at STP is approximately 0.195 mol/(L·atm). This value indicates how much H2S can dissolve in water under a pressure of 1 atm, reflecting its solubility and potential toxicity in aquatic environments.

Real-World Implications

Understanding Henry's law constant is crucial in environmental science and chemistry, especially when dealing with toxic gases like H2S. It helps predict how gases behave in natural waters, which is vital for assessing risks to aquatic life and human health.