1.1. Physical and Chemical properties of interest

So now, will go back to the characteristics of some of the Chemicals. So, we are talking about physical and chemical characteristics of the chemicals now. So, so we are looking at the physical properties. From a fate and transport point of view, when we have already set up the problem, what could be what is our area of interest what is it that you are interested? We are interested in chemicals entering water, we are interested in chemicals entering air, chemicals entering plants and animals, soil, sediment and all that.

This initial part serves as an introduction to the discussion surrounding physical and chemical properties of chemicals. The focus is on understanding how these properties influence the behavior of chemicals when they enter various environmental mediums such as water, air, and soil. The terms 'fate' and 'transport' point towards how chemicals move and change states in the environment, making it crucial to understand their properties effectively.

Imagine pouring a fluorescent dye into a clear lake. The way the dye spreads and eventually settles or reacts with the lake's ecosystem symbolizes the importance of knowing the physical and chemical properties of substances as they interact with their environment.

So, there are some properties of chemicals that are of interest to in this context, ok. So, which are these properties that are affected. So, straight away can you what is one of, what is what are the properties that could be of interest? If I gave if I give a name of chemical and if I ask, is it going to be a health hazard in water, what is your first first question or response? Students: solubility. Professor: What is the? Student: solubility. Professor: what is the solubility? So aqueous solubility is usually referred see we are going to be in this class, we are going to be using absolute units.

The conversation shifts to identifying specific physical and chemical properties that impact the behavior of chemicals in the environment. The focus is on two primary properties: aqueous solubility, which measures how well a chemical dissolves in water, and vapor pressure, which reflects how readily a chemical vaporizes into the air. Both properties help assess potential health hazards and environmental risks associated with chemicals.

Consider salt in water. It dissolves easily, which means it has high solubility. If you think about a chemical spill into a river, knowing its solubility helps predict how widely it will spread and whether it will harm aquatic life.

So, what are these two? Aqueous Solubility and vapor pressure, these properties correspond to, correspond to something they can be classified as one particular this this measurements, when do this when how can you, how do you find solubility of a chemical? Student: we dissolve in water. Professor: you put it in water and then, how do you measure, because you are measuring it when you know it’s reached solubility?

This chunk delves into how to actually determine the aqueous solubility of a chemical. It involves dissolving a solid chemical in water and then measuring its concentration once equilibrium (or saturation) is reached, which means no more of the chemical can dissolve in the water under the given conditions. Understanding this measurement is vital for assessing water quality and the potential impact of pollutants.

Think of making a sugar solution in water. If you add sugar slowly and stir, at a certain point, no matter how much more sugar you add, it won't dissolve anymore. This point at which the sugar can't dissolve any longer is like the solubility limit.

Equilibrium is defined between two states, between two particular states. So, what is this equilibrium between? Students: vapour zone and liquid phase. Professor: So we are talking about the equilibrium of A between its pure form and water and pure form and air is solubility. So, equilibrium of pure substance of A between its pure form and air is saturated vapour pressure.

The concept of equilibrium is vital in chemistry as it describes a state where the concentrations of the solute in different phases (solid, liquid, or gas) remain constant over time. In this context, equilibrium refers to the state of a chemical when its concentration in water versus air (for vapor pressure) or when it is dissolved in water (for solubility) reaches a balance, indicating that the rate of the forward reaction equals the rate of the reverse reaction.

Consider a sealed bottle of soda. Initially, when you open it, carbon dioxide gas escapes, but eventually, a balance is reached between the gas in the liquid (soda) and the gas in the air above it. This balance point is akin to the vapor pressure of the carbon dioxide above the soda.

So if I have a mixture with A plus water and there is air, how much of A will go to the air if I leave it long enough to go to equilibrium? So this is the equilibrium between the concentration of A in air versus the concentration of A in water, air and water are in contact with each other and they go to equilibrium?

This chunk explains the concept of vapor-liquid equilibrium (VLE), which describes how a chemical distributes itself between its liquid form (in water) and its gaseous form (in air). When these two phases are in contact, a certain concentration of the chemical will reside in air and another in water until equilibrium is established. This understanding is crucial for predicting how pollutants behave in natural waters.

Think of a fish tank where there is water and air above it. Over time, some pollutants in the water may evaporate into the air, just as perfume scent spreads in the room. The extent to which this happens can be predicted with the principles of VLE.

Henry’s Law which says that there is this, this linear relationship is very linear. On the other hand, it is called as Raoult’s law on the higher end. So, Henry’s Law, the definition of Henry’s Law constant is very straightforward, simple. It’s a partition constant as we describe it.

Henry's Law helps establish the relationship between the concentrations of a gas in a liquid phase versus a gaseous phase at equilibrium. The Law states that the amount of gas that dissolves in a liquid is proportional to the pressure of that gas above the liquid. This law is crucial in environmental science when analyzing the behavior of volatile organic compounds in water bodies.

Imagine opening a can of soda. The carbon dioxide (gas) is under pressure, and when you open it, some escapes into the air. The amount of gas that remains dissolved in the soda depends on the pressure of the gas above it, which is what Henry’s Law describes.

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