Category: Chemistry Notes PPT

The Debye Huckel equation is a mathematical expression developed to explain certain properties of electrolyte solutions, or substances found in solutions in the form of charged particles (ions). The Debye Huckel equation accounts for the interactions between the different ions, which are the primary cause of differences between the properties of dilute electrolyte solutions and those of so-called ideal solutions.

 

Introduction

The entropy, rather than the enthalpy, drives the mixing of the solutions. By definition, while an ideal gas does not have the interactions between particles, an ideal solution assumes that there are interactions. Without interactions, the solution would not be in the liquid phase. Rather, the ideal solutions can be defined as having an enthalpy of either mixing or enthalpy of the solution, which is equal to zero (ΔHmixing or ΔHsolution = 0).

Since the interactions between the two liquids, A-B, are calculated as the sum of the A-A and B-B interactions, this is the case. The average A-A and B-B interactions are similar in the ideal solution, so there is no distinction between the average A-B and the A-A/B-B interactions.

 

Since in chemistry and biology, the average interactions between A and B are not always equivalent to the interactions of A or B alone, the enthalpy of mixing is not zero. As a result, a new definition for the concentration of molecules in solution has emerged. The effective concentration, a1, is calculated by taking into account the deviation from ideal action, with the operation of the ideal solution equal to one.

 

To convert from the mole fraction of the solute, x1 (as the unit of concentration, mole fraction can be determined from other concentration units like molality, molarity, or percent by weight) to activity, a1, an activity coefficient, 1, is used.

a[_{1}] = γ[_{1}]x[_{1}]

 

Debye Huckel Theory

This theory is related to electrochemistry. This theory was proposed by Peter debye and Eric huckel to explain the departure of electrolytic solution from ideality, because the electrolytic solution shows the deviation from the ideal behavior.

Colligative properties of ideal solutions are directly proportional to the concentration of solute. But this does not happen in the case of real solutions. In Case of real solutions we cannot take the concentration term as a whole. In case of real solutions the concentration term is replaced by another term which is known as activity. Activity is represented by a.

So we can say that this activity is directly proportional to the concentration c. Or we can say a is equal to gamma (Greek letter) multiplied by c, where Gamma is the activity coefficient. 

For an ideal solution the value of Gamma is 1. If we take a dilute solution, they are near to ideality but concentrated solution shows departure from ideality that shows non ideality.

When we take an electrolytic solution, we know that in case of strong electrolyte they have the tendency to dissociate into cations and anions. You also know that the opposite charges attract each other while the same charges repel each other. So the cations will have the tendency to go near anions and the anions will have the tendency to go near cations. So we cannot say that the ions are randomly distributed throughout the solution, in case of real solutions.

We cannot measure the activity coefficient of a single ion. So we will measure the mean activity coefficient. There are formulas to calculate mean activity coefficient.

By Debye Huckel theory we can calculate the activity coefficient of a single ion. And we know that the departure from the ideal is due to the electrostatic interactions which are between the ions.

With the help of coulomb’s law we can calculate the forces of interaction between two electrical charges which are separated by a distance r. So in real solutions, anions are more likely to be found near cations and vice versa.

Debye Huckel Limiting Law

See Debye–Hückel theory for the concepts that were used to derive this equation.

To measure the activity a[_{C}] of an ion C in a solution, the concentration and activity coefficient must be known:

a[_{C}] = γ [frac{[C]}{[C^{Theta}]}],

This is also called the debye huckel limiting law equation.

Where, 

γ is given as the activity coefficient of C,

[left [C right ]] is the measure of concentration of C,

[[C^{Theta}]] is given as the concentration of chosen standard state, for example, 1 mol/kg if molality is used.

Dividing [left [C right]] with [[C^{Theta}]] gives the dimensionless quantity.

The Debye–Hückel limiting law can be used to calculate an ion’s activity coefficient in a dilute solution with a known ionic power. The following is the equation:

ln(γ₁) = [frac{Z_{i}^{2}q^{2}k}{8 prod epsilon_{r} epsilon_{0} k_{b} T}] = – [frac{Z_{i}^{2}q^{3}N_{A}^{1/2}}{4prod (epsilon_{r} epsilon_{0} k_{B}T)^{3/2}}] [sqrt{10^{3} frac{1}{2}}] = – AZ[_{i}^{2}][sqrt{I}]

where 

Z[_{i}] is given as the charge number of ion species i,

q is given as the elementary charge,

k is given as the  inverse of the Debye screening length,

[epsilon_{0}] is the permittivity of free space,

[epsilon_{r}] is given as the relative permittivity of the solvent,

k[_{B}] is given as the Boltzmann constant,

T is given as the temperature of the solution,

I is the ionic strength of the solution,

N[_{A}] is given as the Avogadro constant,

And A is the constant that is completely based on the temperature.

The scientists have determined that it is not that simple because the things such as the sizes of the ions including the amount of charge that they contain may affect properties like conductivity. This equation is their attempt to account for certain variables when assessing an ionic behaviour of the compound.

 

Experimental Verification of the Theory

Several experimental methods for calculating activity coefficients have been tried to check the validity of Debye–Hückel theory: the main problem is that we need extremely high dilutions. Measurements of the freezing point, vapour pressure, osmotic pressure (which is an indirect method), and electric potential in cells are just a few examples (which is a direct method). 

 

Using liquid membrane cells, it was possible to examine the aqueous media 104 M at high dilutions and obtain good results and it also has been found that for the ratio 1:1 electrolytes (as either KCl or NaCl) the Debye–Hückel equation is completely correct, but for the ratio 2:2 or 3:2 electrolytes it can be possible to find the negative deviation from Debye–Hückel limit law: this strange behavior may be noticed only in the very dilute area, and in many concentrate regions the deviation becomes positive.

 

It is also possible that Debye–Hückel equation is unable to foresee this particular behavior because of the linearization of Poisson–Boltzmann equation, or may be not: about this, studies have been started only during t
he last years of the 20th-century because prior to it, it was not possible to investigate the region of 10−4 M, so it can be possible that during the next years new theories will be come up.

 

Main Assumptions of the Debye Huckel Theory

• The solute or electrolyte is completely dissociated which means that the electrolyte is strong.

• Ions are spherical and the solvation of ions is ignored in this theory.

• According to this theory solvent plays no role. It only provides medium for the interactions.

• Individual ions surrounding a central ion can be represented by an average cloud of continuous charge density.

So there is a spherical haze around the Central ion having net charge equal in amount but opposite in sign and is called its ionic atmosphere. The energy and chemical potential of any given Central iron is lowered due to electrostatic interaction with its ionic atmosphere.

 

According to this model, at very low concentration, the activity coefficient is calculated by the debye huckel limiting law.

Before understanding, what pH determination is? It is essential to understand what is the meaning of pH. The full form of pH is the potential of hydrogen. It is a quantitative scale that is used to determine or measure the acidity or the basicity of any liquid solution.

For instance, in the case of pure water, the concentration of hydrogen ion is 10 – 7 gram-equivalents per litre, which is considered to be neutral as it falls in the pH 7 category. We say a liquid concentration is acidic if the pH level is less than seven and we say, the liquid concentration is basic or alkaline if the pH is more than 7. This is how the pH of a given solution is determined.

How to Determine the pH Through an Experiment?

There are several experiments through which the pH of a certain liquid concentration is determined; one such is given below.

The theory rests on the fact that each chemical has an inclination towards being a base, or an acid or being neutral. When an acidic liquid is dissolved in the water, it releases free hydrogen ions (H⁺ ions), whereas, when a base is dissolved in the water it produces hydroxyl ions (OH^– ions). The strength or weakness of the acidic solution or basic solution depends on the release of H⁺ ions or OH^– ions when it is dissociated.

Measurement of pH

pH was invented by a Danish chemist named Soren Peder Lauritz Sorensen. The value of the pH will be low if the concentration of the hydrogen atoms is high. pH is defined as the negative logarithm (base 10) of hydrogen ion concentration.

• Liquid concentration, whose level is lower than seven on the pH scale, is said to be acidic.

• Liquid concentration, whose level is higher than seven on the pH scale, is said to be basic.

• Liquid concentration, whose level is equal to 7 on the pH scale is neutral.

pH Determination Methods

There are several methods of pH determination.

pH Paper:

Special strips of paper are made by submerging them in the chemical compound and then drying it. When this paper is dipped on a liquid substance, it changes colour. The change of colour is then compared to the colour chart to determine the actual pH level or in which category that certain liquid belongs.

pH Meter:

there is a device known as the pH meter, which is used to determine the pH level of a substance. This electronic device has a special electronic bulb that is sensitive to hydrogen ions. The ones that are present in the solution. The bulb produces a signal which is then amplified by and is shown in a meter format in the electronic meter attached. The meter displays the pH level and in which category does the substance belong. For very precise measurement, the pH meter should be calibrated before each measurement.

The pH of Fruit Juices

People who are obsessed with the idea of dieting are quite taken by the pH levels of different fruit juices. A study has shown that juices which are lower than pH level 4 or belong to the category of pH 4 can be extremely damaging to the teeth as well as the person’s health. For this purpose, the pH of fruit juices is mentioned below:

• Lemon Juice – 2.25

• Very Fine Grapefruit Juice – 3.22

• Minute Maid Cranberry Grape – 2.71

• Ocean Spray Strawberry Kiwi Juice Cocktail – 2.90

• Ocean Spray Cranberry – 2. 56

• Minute Maid Natural Energy Pomegranate Berry – 3.33

• Ocean Spray Cran-Grape – 2.79

• Minute Maid Orange Juice – 3.82

• Minute Maid Cranberry-Apple Raspberry – 2.79

Study of pH of Some Fruit Juices Project Determination of pH of Acid Solutions

There is an easy way to determine the pH level or the acidic level of a given solution.

Aim

Using pH paper and a universal indicator, determine the pH of solutions such as fruit juices containing various acids, bases, and salts.

Apparatus

• Test tubes

• Universal indicator

• pH paper

• White tile

• Dropper

• Some juices

Procedure

Pour the liquid into separate test tubes. Take the white tile and place the strip of paper on it. Take the help of the dropper to extract the liquid which you want to test and put it on the strip of pH paper. As soon as the liquid solution gets in touch with the pH paper, it will start changing colour. Now, match the colour to the universal chart that has been given to you to know if the solution is alkaline or neutral or acidic.

In the case of Cranberry juice, it will be acidic. Cranberry juice falls directly under the category of acidity because its measurement on the pH scale is typically between 2.3 to 2.5. Foods or juices which are above pH level 7 are considered to be basic or alkaline.

Similarly, limes, lemons, and tangerines – all of which are rich in ascorbic acid – feature a pH of 2.4, 3.1, and 4.1, respectively.

Precautions to be Taken During the Experiment

• Make a careful match between the colour of the solution and the standard colour pH chart.

• Keep the pH strips out of the reach of any chemical fumes.

• Maintain the pH paper clean.

Conclusion

pH determination helps people to understand if the given solution is acidic, basic or neutral, which, in turn, helps them to determine which liquids are safe or easy to consume. The way of measuring the pH scale is extremely easy, either that person can use pH paper or pH meter.

Many aspects explain various things on adhesion and cohesion, meaning and examples, which we observe in our daily life. Although, at times, we miss to focus on these little things, and these help us to keep our lives going on earth. The adhesion and cohesion forces are one of both phenomena. Although they sound to be similar, they are completely known to occur in different terms.

Surface tension is one of the important physical properties of water that describes the relationship between adhesion and cohesion.

Coming to the definitions, the tendency of either two or more different molecules to bond with each other is called Adhesion. In contrast, the attraction force between the same molecules is referred to as Cohesion.

About Adhesion and Cohesion

Adhesion forces can be one of the electrostatic forces’ results exerted on various substances. Simultaneously, the cohesive forces are associated with the Van der Waals forces and hydrogen bonding that cause liquids like water to withstand the separation. 

When a glass surface is poured with water, the forces of both adhesive, cohesive act on the water’s surface. Also, a strong adhesive force tends the liquid to spread over the surface; on the other side, a strong, cohesive force is responsible for forming water droplets on the water surface.

Both the adhesion and cohesion forces vary in their strengths. For example, if the cohesion forces between water molecules are stronger compared to the adhesion forces between them, then the individual molecules present in them will attract towards each other hence resulting in settling. If the adhesion forces of the water surfaces are stronger than the water molecules’ cohesion forces, the water tends to disperse then.

Difference Between Cohesion and Adhesion

Let us discuss the adhesion and cohesion difference.

Adhesion and cohesion are attraction forces, exist between different and the same molecules, respectively. Though they sound to be similar, they differ from each other. Let us come to know how cohesion differs from adhesion, and the primary differences between them are tabulated below:

Relationship and the Meaning of Cohesion and Adhesion

In general, cohesion and adhesion forces exist together; you can find these respective forces in various activities and processes. Consider the example, meniscus, which is a liquid surface curvature stored in a tube or container, is caused by both adhesion and cohesion. The attraction force between the edges of liquid and the container wall is called adhesion. The attraction force between the water molecules, which makes the liquid surface curved in the middle, is given cohesion.

Also, the meniscus shape is decided by these forces. If the cohesion force, which exists between the liquid molecules, is more than that of adhesion force existing between the liquid and the tube’s inner surface, the meniscus shape will be convex. For example, mercury, filled in a glass tube. Similarly, if adhesion is more than that of cohesion, the meniscus will be concave. For example, water, filled in a glass tube. The surface will be horizontal if the cohesion is equal to adhesion.

Let us suppose you spill some water on a surface. If the adhesive force is strong, then the water will get absorbed soon by the surface, and also it will go wet. Whereas, if the cohesive force is strong, there will be more attraction between the water molecules than between the surface and water molecules. So, the surface absorbs less water.

Differences Cohesion vs. Adhesion

Based on the given information above, a few key differences between cohesion vs adhesion are listed. 

Electronegativity: The term electronegativity was first introduced by the scientist named Jöns Jacob Berzelius in the year 1811. In the year 1932, after many discoveries and discussions, Linus Pauling first discovered the property of electronegativity completely and he also created an electronegative scale that depends on the bond enthalpy. This has further helped in establishing the valence bond theory.

The property of attracting a shared pair of electrons towards itself is known as electronegativity. In simple words, electronegativity is the property and the ability to gain electrons from an atom. It ranges from 0.79 to 3.98 on a scale and is denoted by X. The measurement of electronegativity “e” is done in the Pauling scale.

When the atomic number increases, it means that the distance between the nucleus and the valence electron also increases and hence, the electronegativity also rises. Therefore, the atomic number and the location of the electron from the nucleus play a very important role in determining the electronegativity and are the factors that are affecting it. Also, the tendency of attraction of electrons increases with the increase in the number of protons which increases with the increase in the nuclear charge.

When the two electronegative atoms are taken, with the increase in the difference between the electronegativity of the atoms, the polarity of the bond between them also increases. The atom that has the more electronegativity will gain a negative charge on it. The electronegativity usually increases along a period from left to right and decreases on passing through a group that is from up to down. According to this funda, chlorine becomes the most electronegative element and Francium becomes the least electronegative element.

Electron affinity: Electron affinity is the measurement of the amount of energy released when an electron is added by an atom of a molecule to an individual neutral atom which is in a gaseous state that forms a negative ion post the gain of the electron. This property is measured in kilojoules per mole and is denoted by “Eea”.

The factors that determine the electron affinity of an atom on an element are the atomic size, the nuclear charge, and the electronic configuration of the molecules or atoms. An electron acceptor has a greater positive electron affinity value while the one with the lower positive value is referred to as an electron donator.

The property of the electron affinity is only used for the atoms and the molecules that are present in the gaseous state. The molecules and the atoms that are present in the solid in the liquid state get changed when they come in contact with other atoms or molecules.

A bunch of electron affinity of elements were used by Robert S Mulliken for developing the electronegativity scale. The theory of electron affinity is also involved in the concept building for chemical hardness and chemical potential.

Electronegativity vs Electron Affinity

Both electronegativity and electron affinity are two different chemical properties that are associated with the elements. The primary difference between electronegativity and electron affinity lies in the fact that electronegativity is the property related to the ability of an electron to attract towards an atom. On the other hand, electron affinity is related to the release of energy whenever an electron tends to get added to an atom. These two properties are often known to be interrelated but they are not interchangeable. Both electronegativity and electron affinity deal with the movement of the electrons. However, electronegativity is the result of the property of attraction, while electron affinity is the result of the change in energy. In this article, we will study electronegativity vs electron affinity in detail.

Understanding the differences between electronegativity and electron affinity is important so that we do not use them interchangeably. Given below is the table that consists of the detailed differences of both terms.

Difference Between Electronegativity and Electron Affinity

Conclusion

The property of electronegativity and electron affinity is associated with the concept of electron gain. While electron affinity is capable of precise measurement and definition, electronegativity is capable of neither of them. For this reason, the electron affinity is present in neutral atoms or atoms in a molecule and the electronegativity only deals with chemically bonded atoms.

The substance or mixture of substances intended to prevent, destroy or mitigate any pest is termed as a pesticide. It is sometimes referred to as insecticides. Even herbicides are also a type of pesticide. The product is often used to control pests and includes plant regulators, defoliants and desiccants. A herbicide is a type of pesticide which is used to kill unwanted plants or weed. Various types of herbicides offer the option to kill certain types of unwanted plants while not harming the crops. They are better used to interfere in the growth of weed and also act as plant hormones.

Effects of Pesticides

Pesticides contain toxic chemicals which are released in the environment. These affect the environment and are also harmful to organisms. The product is meant to kill certain pests, but excessive usage can be disastrous for the crops. When used in large quantities, the pesticides can enter the air, water and even end up in our food.

It can cause impacts such as headaches and nausea. In some cases, it can cause chronic diseases like cancer and is harmful to the reproductive system. The presence of a high amount of chemicals in soil degrades its bio-diversity and quality. It also reduces the land’s power of water retention, which affects the growth of plants.

Types of Pesticides

Pesticides can be grouped in many ways. One of the most common pesticide grouping methods is according to the pests they can kill.

They are also grouped based on their biodegradable quality.

Biodegradable: The pesticides that can be broken down by microbes and other living beings are biodegradable products. They are turned into harmless compounds, which can be absorbed by the soil.

Persistent: The pesticides which are known as persistent ones are also biodegradable, but they tend to take more time to degrade. The time gap is usually months or years for them to degrade completely.

What are Herbicides

Herbicides are types of pesticides used to kill certain types of pests. It can either be a type of weed or some plant species that can harm the cultivation process. They are designed to kill or control a specific type of pests. Hence, they are limited in their usage. They come in two forms, that is selective and non-selective. We can find their usage in normal farms as well as in industrial areas. Since they are designed to mainly target plants, they are the most widely used pesticides in agriculture.

Selective and Non-Selective Herbicides

Selective herbicides are the most common type of herbicides that are used in the market. They offer control over a specific type of pests, mainly weeds. Each selective herbicide is designed to kill a particular type of weed and cannot be used on other forms of pests. Non-selective herbicides, on the other hand, work on most forms of weed but are often not available as a common choice. Since they target more than one type of species, there is always a debate about them being herbicides. Nonetheless, both the products have wide industrial usages as well as in agricultural areas.

Definitions

Those properties of matter that depend on the amount of the substance present are called extensive properties. Example- mass and volume. Those properties which do not depend on the amount of the substance are called intensive properties. Example- colour and density. 

The two terms, intensive and extensive properties of matter were introduced by Richard C. Tolman in the year 1917. The ratio of two extensive properties is an intensive property. For instance, the ratio of the mass and the volume is equal to density. In order to find density, it is important to divide mass by volume. Density is the intensive property while mass and volume are the extensive properties. Here, we will learn more about the intensive and extensive property and also about the ways in which these two properties differ from each other.

What is An Intensive Property of Matter?

The intensive property of matter is dependent upon the amount of substance. The word intensive is derived from the word “intensivus”. The characteristic of substance with intensive property does not change. Moreover, the size of the intensive properties also does not go through any form of change. Some of the common examples of intensive property are density, pressure, temperature, the hardness of an object and also refractive index. IUPAC defines intensive property as the one whose magnitude is independent in the size of the system. It is the bulk property which means it is a local physical property of a system. This does not depend on the amount of material in the system or the size of the system. 

Another example of understanding intensive property is the temperature of a system in thermal equilibrium. It means that the temperature of the system in the thermal equilibrium is the same as the temperature in its other parts. Now, if the system is divided, then the temperature in each subsystem will be identical. Similarly, the density of a homogenous system if divided in half, the mass and the volume gets divided in half. However, the density remains unchanged. The boiling point of any substance can be regarded as the intensive property of the substance. For example, the 100-degree centigrade boiling point of water will be unchanged regardless of the quantity. 

What is An Extensive Property of Matter?

The extensive property of matter can be determined as the property of the matter that is also dependent upon the amount of substance present. The word extensive was derived from the word extensivus. The matter with extensive property can easily be identified. Also, the size of the extensive property varies and it can also be computed. Some of the common examples of the extensive property of matter are mass, size, volume, weight and length. IUPAC defines extensive property as the one whose magnitude is additive for subsystems. This also states mathematical ideas like mean and measure. 

By the term additive of the subsystems, it refers to the extensive properties like mass, volume and entropy of the systems. It is because they increase and decrease while they grow large and small respectively. Therefore, it can be said that extensive property is the physical property where the value is proportional to the size of the system. The mass of a substance is an extensive property. As stated earlier, the extensive property will vary from substance to substance due to differentiation in the mass, size, volume, weight and length. Another important thing to remember regarding the extensive property of a substance is that if one extensive property is divided by another extensive property then it gives an intensive value. For instance, if mass and volume are both extensive. Now if these two are divided by each other then it will give us the density of the substance which is an intensive property.

Definition of Properties of Matter

All properties of matter can be defined as the chemical and physical properties of matter. The physical properties of matter can be further divided into two properties, intensive and extensive properties of matter. The extensive properties of matter are volume and mass. However, that depends on the amount of mass that is being measured. On the other hand, intensive properties of matter are density and colour and they do not depend on the amount of substance present. 

But when it comes to physical properties of matter it can be measured without altering the chemical identity of the substance. Now, to understand the measurement of the chemical properties it is essential to change the chemical identity of the substance. It is important to understand that not all physical properties of a substance are exclusively intensive or extensive for that matter. For instance, the electrical impedance of two subsystems can be regarded as additive. However, they should be combined in a series but if they are combined in a parallel manner then the resulting impedance will be less than that of either subsystem. 

How to Measure The Physical Properties of A Matter? 

Physical properties of a substance can be referred to as the properties that if observed or measured without altering the chemical nature of a particular substance. Some of the examples of physical properties which involve both intensive and extensive property are like colour and density. Colour and density are intensive property of the substance whereas volume and mass of the same substance can be referred to as the extensive property of the substance. Similarly, the boiling and the melting point of a substance is an intensive property. 

What is The Chemical Property Of A Substance?

The chemical property of a substance can be referred to as the measurement of the substance after alteration in the chemical structure of the substance. Some of the examples of the chemical property of a substance are as follows:

• Chemical stability of any substance can be understood by identifying whether a compound will react with water or air. Having said that, it is important to know, the substances that have chemical stability will not react like hydrolysis and oxidation. 

• The most preferred oxidation state of a substance is the lowest energy oxidation state which is the common and preferred method for metal to undergo reactions. 

What is The Heat of Combustion?

When a compound undergoes complete combustion or to say burning with oxygen, the energy that is released is referred to as the heat of combustion. The symbol for the heat of combustion is ΔHc.

What is Flammability?

Flammability is referred to as the state when anything is easily ignited and is capable of burning rapidly. Therefore, to understand the flammability of a compound, it is important to understand that whether a compound will burn or not when exposed to flame. Burning is a high-temperature reaction in the presence of oxygen which is a chemical reaction.