Category: Chemistry Notes PPT

What Is Spectrum? 

Before understanding the colour spectrum, let us try to understand what is a spectrum? A spectrum is an array of certain elements that have been arranged together in an order of increasing wavelength.

Now, a colour spectrum is an array of 7 colours namely VIBGYOR, arranged in an order of increasing frequencies. The phenomenon was first observed by the profound scientist, Isaac Newton. He observed a white beam of light as it passed through a glass prism. To his surprise, the light from the other side was split into 7 different colour spectrum wavelengths. He studied the phenomenon further before he brought it to the notice of the public in 1665. 

Only after this, people started to believe that white light is composed of 7 different colour spectrum wavelengths, namely Violet, Indigo, Blue, Green, Yellow, Orange and Red. This led to the conclusion that ” whenever light passes through a medium which is capable of absorbing and reflecting light, spectrum formation is observed”. 

[]

What Causes the Spectrum? Let’s Dive Deeper!

Light has a characteristic property, called the wavelength of light. The wavelength of light differs from colour to colour. Each colour has a specific wavelength. The spectrum lies in the range of “Visible Spectrum” from wavelengths 700 Nm to 300 Nm. The visible spectrum is merely a small part of the vast electromagnetic spectrum. All the ranges of wavelengths are not visible to the human eye. The human eye can see the wavelengths only between 300 and 700 Newton Meter. 

Proof of Newtonian Theory of Spectrum

No theory in Science is acceptable, without optimal proof that validates it. For this, Newton provided excellent proof. He took a wheel that consisted of multiple colours, something like this: 

[]

Then, he rotated the wheel at an excessively high pace. As the speed of the wheel increased, all the colours appeared to merge into a single beam of white light. This merging of colours proved that white light is made of 7 different colours and when all these 7 colours merged, they formed a monochromatic white light. Through this simple experiment, Sir Isaac Newton managed to prove his theory of the spectral nature of light. 

Some Interesting Facts of the Spectrum

What is colour? To a common man, the word colour would just mean whatever we see in our surroundings. However, in Class 10 Chemistry Colour Spectrum, we understand the scientific point of view and conclude that the meaning of “colour” is completely different. From the Science perspective, an object has a colour when it absorbs all the wavelengths except one particular wavelength. The wavelength which the object is unable to absorb is reflected back and hence, our eyes can perceive the colour of the object. Objects appear to be colourful only because of the phenomenon of reflection and absorption. 

[]

So the colours you see above are just a result of the phenomenons of reflection and absorption! Sounds interesting, isn’t it? 

Phenomenons Around Us Based on Spectrum Formation of Light

Rainbow: As kids, all of us would have been extremely fascinated by rainbows. Have you ever pondered upon the science of rainbows? Rainbows are also a result of the scattering of light into its constituent colours. As we saw earlier, when a white beam of light is passed through a glass prism, it scatters into its constituent colours. In the case of rainbow formation, tiny droplets in the atmosphere act as little prisms. As the light passes through these water droplets, the light undergoes total internal reflection. Due to this, the white light splits into 7 different colours and forms a beautiful rainbow in the sky. 

[]

The Colour Effect on a CD: Have you ever observed a CD? If you’ve keenly observed it, you’d have surely noticed how it reflects light and produces a multi-coloured effect. This is another result of the scattering of light into its constituent colour spectrum wavelengths. The CD is smooth and shiny, it has a tiny gap in between layers which acts as the reflective surface, hence causing the colour spectrum effect. If you haven’t observed this effect, you should quickly grab a CD and take a look at it! 

[]

Colour of the Sky: What do you think is the colour of the sky? Blue right? Most of us think that the sky is blue. However, the sky isn’t coloured, it is colourless. The blue shade is because of the phenomenon of scattering of light. Blue light has the shortest wavelength and hence it gets scattered easily. Since blue light scatters more than all the other colours, it is the most prominent and therefore the sky appears to be blue.

[]

In this article we will learn about the conductors as well as the insulators. The Conductors are the materials we can say that permit the flow of electrons freely from particle to particle inside any object.

An object which is made up of a conducting material will permit the flow of charge to be transferred across the entire surface of the object inside which they are. If the transfer of charge to the object at a given location which charge is quickly distributed across the entire object’s surface.

The distribution of the charge is the result of movement of the electron inside it. Since the conductors are the conductive material so they  allow electrons to be transported from particle to particle.

An object which is  charged will always distribute its charge until the process of overall force repulsive which is between excess electrons is minimized.

If a conductor which is charged is touched to some other object, then the conductor can even transfer its charge to that object as well. 

The transfer of charge which takes place between objects occurs more readily if the second object is also made of a material which is conducting in nature. 

The Conductors mainly allow charge transfer through the movement which is free for electrons.

In contrast to the material which is conductive the insulators are materials that impede the electrons free flow from atom to atom or from molecule to molecule. 

The particles of the material of an insulator do not permit the free flow of electrons, that is we can say that the subsequent charge is seldom distributed evenly across the insulator’s surface.

The insulators are not useful for transferring charge. We can say that they do serve a role which is very critical in electrostatic experiments and demonstrations. The material which is conductive or objects which is conductive are often mounted upon insulating objects.

This arrangement which we have discussed also allows for a student or even the teacher to manipulate an object conducting without touching it.

The insulator basically serves as a moving handle for the conductor around on top of a lab table.

If experiments of charging are performed with pop aluminum cans, then the cans should be mounted on top as well as Styrofoam cups for better performance. The serve of the cups as insulators, is by the way preventing the pop cans from charge discharging. The cups also serve as a kind of handle when it becomes necessary to move the cans which are around on the table.

Conductors Definition Science Example

We take the examples of conductors including metals, and solutions of aqueous salts that are the ionic compounds dissolved in water in graphite, and the body of humans. If we take the examples of insulators including plastics objects, the Styrofoam and then the paper, glass, rubber and dry air; the materials division into the categories of insulators and of conductors is a somewhat division which is artificial.

It is more appropriate to think of the materials which are being placed somewhere along a continuum.

Those materials that are called as the super conductive which are known as superconductors that would be placed at one end and the least conductive materials. The best insulators would be placed at the other ends as well.

The metals which would be placed near the most conductive end and the glass as well would be placed on the opposite side of the continuum. 

The metals conductivity might be as much as a million trillion times greater than that of a glass.

Along we can say that the continuum of insulators and the conductors one might find the body of a human. Which is somewhere towards the conducting side of the middle. When the aquarius of the body is a charge which is static then it has a tendency to distribute that charge which is throughout the surface of the body.

The given size of the body of a human relative to the size of object is typically used in electrostatic experiments.

It would mainly require a large but abnormal quantity of excess charge before its notable effect. The effects of the charge which is excess on the body are often demonstrated by using the Van de Graaff generator.

When a student or a child places their hand upon the ball of static material then the excess charge from the ball is shared with the body of the human being. The conductor being, the charge which is excess charge could flow to the body of a human and spread throughout the surface of the body. We can say it even onto strands of hair. As the strand of individual hair becomes charged, they begin to repel each other. After looking to distance which is between themselves from their like-charged neighbors, we could note that the strands of hair begin to rise upward and outward direction this is a truly hair-raising experience.

Many of them are familiar with the humidity impact that can have upon charge which is of static buildups. In the months of winter it tends to be the driest months of the year with level up humidity in the air dropping to lower values.

A corrosion inhibitor is a chemical solvent that is applied in a given environment to decrease the pace of corrosion of the metal which is exposed to that particular condition, for example, air or water. CI can be the abbreviation of the Corrosion Inhibitor.

 

A corrosion Inhibitor can be defined as a chemical compound that can be added to fluids or gases and used to diminish the corrosion pace of a given material (usually a metal). One of the techniques for the Corrosion Inhibitor can be the addition of a coating on the metal’s surface which goes about as a passivation layer and denies access to the metal surface.

 

Kinds of Corrosion Inhibitor

Corrosion Inhibitors can be grouped into four general categories depending on the technique in which they prevent corrosion by working on the metal. These include anodic inhibitor, volatile corrosion inhibitor, cathodic inhibitor, and mixed inhibitor. These can be explained as follows:

 

1. Cathodic Inhibitor

Cathodic inhibitors are used for slowing down the cathodic reaction. They can also work to correctly hasten on the cathodic metal regions to confine the dispersion to the metal surface of the eroded elements.

 

Various examples of Cathodic Inhibitors include sulfite and bisulfite ions. These are the particles that can react with oxygen to form sulfates. Another example of a cathodic inhibitor includes nickel’s catalyzed redox reaction.

 

2. Anodic Inhibitor

These are another category of corrosion inhibitors that helps in the formation of a thin preventive oxide layer on the metal’s surface. This reaction prompts a significant anodic move, transforming the metallic exterior into a passivation area. This passivation region helps in lessening the corrosion of the metal.

 

Anodic Inhibitors Examples Include:

• Chromates,

• Nitrites,

• Orthophosphates, and

• Molybdates.

 

Volatile Corrosion Inhibitor

Volatile Corrosion Inhibitors can be utilized to stop the corrosion of condenser tubes in boilers. Another name for volatile corrosion inhibitors is vapour phase inhibitors of VPIs.

 

VPIs work by changing the exterior atmosphere pH to less acidic conditions to control corrosion. Morpholine and hydrazine are some of the examples of VPIs which are utilized to control the corrosion of the condenser pipes in boilers.

 

3. Mixed Inhibitors

These are other types of corrosion inhibitors that also form a film on the metal’s surface. Cationic reactions and anionic reactions are being reduced with the working of these inhibitors. This is done utilizing the precipitate formation on the surface of the metal.

 

Silicates and phosphates are a few of the examples of the mixed inhibitors which are utilized as water conditioners to stop the rusting of water.

 

Applications of Corrosion Inhibitors

Corrosion Inhibitors have a wide scope of applications in business, process, and industrial conditions. A few of these applications or their uses are as follows:

• These Inhibitors are utilized to quit rusting and anodic corrosion of metals. This is commonly done through the coating of the metal surface with a chromate layer.

• Oxygen scavengers can be utilized as CIs; this reacts with the environment’s dissolved oxygen and can also help in the prevention of corrosion of the cathodic.

• It is essential to prevent rusting and fuel pipeline corrosion. Hence, CIs are significant in making sure about these pipelines and diminishing the danger of mishaps.

• Metal pipes used in the heating systems are inclined to corrosion. CIs play a significant role in making sure about these pipes also.

 

Mechanisms of Corrosion Inhibitors

Cathodic Toxic Substances: These are utilized by smothering the procedures of cathodic decrease to adjust the reaction at the anode. The vulnerability of the metal to hydrogen-initiated breaking can be inclined to cathodic inhibition because the metal can retain hydrogen during cathodic charging or aqueous corrosion. In low-pH solutions, some decreased hydrogen diffuses as atomic hydrogen into the metal as opposed to the gas formation. This occurs during electroplating or pickling of the metal.

 

Oxygen Scavengers: These are synthetic chemicals that react with dissolved oxygen for a reduction in corrosion. The best examples are Sulfite and bi-sulfite ions that lead to the formation of sulfates while reacting with oxygen. Before any bringing down of oxygen dissolved in mud is finished by a scavenger, the air is expelled from the mud through mechanical foaming and degassing.

 

Cathodic Precipitates: These incorporate zinc, calcium and magnesium. They are accelerated on the metal surface to shape into a defensive layer. Since the task of an inhibitor is to diminish the anodic procedure rate, the possible corrosion change after an inhibitor has been included demonstrates a hindrance in the procedure. Positive displacement of the corrosion potential demonstrates an obstacle of the anodic method. The negative displacement of the potential shows the impediment of the cathodic process.

Inhibitors

An inhibitor is a chemical compound or mixture of chemicals that, when given at extremely low concentrations to a corrosive environment, effectively prevents or lowers corrosion while causing no substantial interaction with the environment’s components. Inhibitors are useful in closed environmental systems with excellent circulation because they ensure an appropriate and regulated concentration of inhibitors. These conditions can be reached in a variety of applications, including cooling water recirculation systems, oil refining, oil production and acid pickling of steel components. Antifreeze for vehicle radiators is one of the most well-known applications for inhibitors. Inhibitors can be organic or inorganic chemicals, and they are often dissolved in aqueous solutions. They reduce corrosion by acting as a barrier, by forming an adsorbed layer or by delaying the anodic, cathodic, or both corrosion processes.

Factors to Consider While Selecting an Inhibitor

• Cost of the inhibitor.

• The toxicity of the inhibitor can cause ill effects on human beings and other living species.

• The availability of the inhibitor determines its selection.

• Inhibitors should be environment friendly.

Corrosion Classification

Corrosion has been divided into the following methods:

Wet corrosion happens when a metal comes into touch with an electrolytic conducting liquid or when two different metals or alloys are submerged or partially immersed in the
electrolytic conducting solutions. This is always connected with low temperatures. Dry corrosion occurs mostly as a result of the direct chemical action of air gasses and vapours in the environment. This is usually linked with a high temperature.

Effective Method of Using Corrosion Inhibitor

One of the most effective ways to fight corrosion is to utilize corrosion inhibitors. Three elements must be addressed for them to be used effectively:

• Identification of corrosion problems

• Anodic inhibition (polarization of the anode to be increased)

• Cathodic inhibition (polarisation of the cathode to be increased)

• Resistance inhibition (increase in  circuit’s electrical resistance simultaneously with creating a thin or thick layer on the metal’s surface)

• Diffusion restriction (preventing the diffusion of depolarizers)

Cupric oxide is an inorganic chemical compound composed of cuprous ion and oxide ion. Cupric cuprous are the two forms of copper ions. Copper exists in two types of oxide, the one is with a higher oxidation state and another one is with a lower oxidation state, cupric oxide and cuprous oxide respectively. 

Cupric Oxide and Cuprous Oxide

The oxides of copper are of two types:

Cupric oxide- It is also known as copper cupric oxide. The oxidation state of copper in this compound is +2. +2 is the highest oxidation state of copper. Generally, in short, you can write it as oxide cupric. It exists in the monoclinic crystal system.

Cuprous oxide- the oxidation state of copper in this compound is +1. +1 is the intermediate oxidation state of copper. It can easily get oxidised or reduced.

The oxides of cupric cuprous are represented as CuO and Cu2O respectively.

Preparation of Cupric Oxide and Cuprous Oxide

Cupric Oxide can be prepared by the following methods:

1. It can be produced by the thermal decomposition of the cupric carbonate.

CuCO3 → CuO + CO2

The thermal decomposition of cupric carbonate forms cupric oxide as a product and carbon dioxide gas as a byproduct. 

2. Another method of Cupric oxide preparation is heating copper in the presence of air at a high temperature (around 300-800 degrees celsius).

Cu + O2 → CuO

3. Heating Copper Nitrate- The nitrate of copper is thermally unstable. On heating copper nitrate at a temperature around 180 degrees celsius. 

2Cu (NO3)2 → 2 CuO + O2 + 4 NO2 (this reaction takes place at a temperature around 180 degrees celsius)

4. Heating Cupric Hydroxide- cupric hydroxide is a thermally unstable compound. It gets easily decomposed into cupric oxide on heating.

Cu(OH)2 → CuO + H2O

Properties of Cupric Oxide

Physical Properties of Cupric Oxide

• Cupric oxide is a black colour compound.

• Cupric oxide exists in powder (amorphous) form.

• The melting point of cupric oxide is 1326 degrees celsius.

• Cupric oxide is insoluble in water.

• Cupric oxide is soluble in ammonium chloride and potassium cyanide.

Chemical Properties of Cupric Oxide

CuO + HNO3 → Cu (NO3)2 + H2O

CuO + 2HCl → CuCl2 + H2O

CuO + H2SO4 → CuSO4 + H2O

2KOH + CuO + H2O → K2 [Cu (OH)4]

CuO + H2 → Cu + H2O

CuO + CO → Cu + CO2

2CuO + C → 2Cu + CO2

Uses of Cupric Oxide

• Cupric oxide is used as a pigmenting agent in ceramic compounds. It gives blue, red, green, grey, pink, and black glazes.

• Cupric oxide is widely used in laboratories for the preparation of various copper salts.

• Cupric oxide is used in the manufacture of wood preservatives.

• Cupric oxide is used in the welding process.

• Cupric oxide is used in the manufacture of lithium batteries.

Did You Know?

• Paramelaconite is a copper mineral. In this mineral, copper exists in both +1 and +2 oxidation state.

• Do you think that copper was the first element used by man along with gold and iron?

• Copper is an essential element for the human body.

• Copper is used in alloy formation.

• The blood of octopus contains copper as an oxygen carrier. Therefore, the colour of the blood in them is blue.

• Copper is an essential trace mineral.

• Copper is used as a supplement with iron for the anaemic person.

Starch is quite crucial for our body but do you know how our body makes its starch? Well, for starters dehydration synthesis is the reaction which provides us with the starch that is necessary for our body to work correctly. Just like that, there are many uses of dehydration synthesis and many ways to do it. Today we are going to answer the following questions: what is a dehydration reaction, what are its applications and how to perform its chemical reaction. 

Dehydration Reaction

The first thing that comes to mind when you hear or read the word “dehydration” is the removal of water from a given object or a reaction. Dehydration synthesis occurs when there is a loss of water molecule for the formation of a larger molecule with the help of small reactants. Most of the dehydration synthesis that we see occur in nature forms a biological polymer where we get to see the addition of individual monomers along with the elimination of a single molecule of water. 

On the other hand, just like dehydration reaction condensation reaction works in the same way. In a condensation reaction, two molecules come together to provide a new compound, and the water molecule present in between them gets lost to form a larger molecule. You can use dehydration and condensation interchangeably.

Now let’s find out what happens when a dehydration reaction takes place in a given chemical system. 

Dehydration Synthesis of 2 Amino Acids

This is the basic structure of amino acids given in the diagram, which is shown in a picture below. Here we have two amino acids which are NH₂ and COOH. In addition to this, our body’s second most abundant material is amino acids. These acids have two functional groups and building blocks to the proteins that are present inside our body. The amino acid uses protein dehydration synthesis to give our body the required proteins so it can work properly. 

(example of amino acids, here we have NH₂ and amine group along with carboxyl group)

In the given image, you can see R in a box; it means a residual group is also present, which is a combination of individual elements that are attached here. As a result, amino acids are given different properties. This clears your definition for the synthesis reaction

When the dehydration of two amino acids takes place, the first amino acid releases oxygen that combines with the two hydrogen molecules present in the second amino acid. Thus, we get a covalent bond which links up the two monomers to form a dipeptide. During this process of dehydration synthesis water molecules are formed. 

Some of the reactions that you are going to perform under dehydration synthesis can be reversed if needed. Meaning if they are forming a mixture by using two different elements, you can get these two elements separated once again by performing a reversible reaction process. 

The most common reversible reaction to dehydration synthesis is hydrolysis in which we get H₂O which is taken away during the dehydration synthesis. 

Protein Dehydration Synthesis

There are several ways to define different dehydration chemistry synthesis. We can easily group them based on their reactants. Some of the elements that perform the synthesis have two functional groups. These two can react with each other quickly, a quick example of these reactions were the ones we showed you in the above image of two amino acids that are working as a functional group to make the reaction possible. 

The amino acid from the amine group can undoubtedly react to lots of acid groups to form amide bond, which is covalent. In addition to this, the newly formed acid still contains one free amine group along with one free carboxylic acid. Thus, making sure the reaction will proceed further with more amino acids. 

Another way to classify the dehydration synthesis is by separating it with the nature of the different catalysts. Just take an example of symmetrical ethers. In these, we have hydrogen ions which are working as a catalyst. The main reason why reactions need catalysts is because in living organisms when the reaction is taking place, the pH, temperature and salt concentration can be tweaked. As a result, for a reaction to complete and give its product in a short time, we need a catalyst.

Diatomic molecule or diatomic elements are the one which contains two chemically bonded atoms. If the two atoms are similar, such as in the oxygen molecule (O₂), they form a homonuclear diatomic molecule, while if the atoms are different, such as in the carbon monoxide molecule, they form a heteronuclear diatomic molecule (CO), where they make up the heteronuclear diatomic molecule.

Heat capacity

Diatomic molecules like oxygen and polyatomic molecules like water contain additional rotational motions, which also store the thermal energy in their kinetic energy of rotation. Every additional degree of freedom contributes more amount R to cV because the diatomic molecules can rotate about two axes.

Heteronuclear Molecules

All other diatomic molecules are the chemical compounds of two various elements. Several elements combine to produce heteronuclear diatomic molecules based on pressure and temperature.

Examples are gases nitric oxide (NO), hydrogen chloride (HCl), and carbon monoxide (CO).

Several 1:1 binary compounds are not regularly considered diatomic due to the reason they are polymeric at room temperature, but when evaporated, they produce the diatomic molecules—for example, gaseous SiO, MgO, and others.

Occurrence

In the Earth’s environment, hundreds of diatomic molecules have been identified in interstellar space and in the laboratory. About 99% of the atmosphere of Earth is composed of 2 species of diatomic molecules: oxygen (21%) and nitrogen (78%). The natural abundance of hydrogen in the atmosphere of Earth is only of the order of parts per million. However, hydrogen is the most universally abundant diatomic molecule. The interstellar medium can be dominated by hydrogen atoms.

Molecular Geometry

All the diatomic molecules are linear and characterized by a single parameter which is the bond length or distance between the two atoms. The diatomic nitrogen atom has a triple bond, the diatomic oxygen atom has a double bond, while the diatomic hydrogen, fluorine, chlorine, iodine, and bromine atoms all have single bonds.

Historical Significance

Since a number of the more important elements, such as carbon, are diatomic, they played a key role in the 19th-century elucidation of the principles of atom, molecule, and elements, like oxygen, nitrogen, and hydrogen takes place as diatomic molecules. The original atomic hypothesis of John Dalton assumed that all the elements were monatomic and that the atoms present in compounds would commonly have the simplest atomic ratios with respect to each other. For suppose, the formula of Dalton assumed water to be HO, giving the atomic weight of the oxygen as eight times that of hydrogen, instead of a modern value of up to 16. As a result, for almost half a century, there was uncertainty about molecular formulas and atomic weights.

As early as 1805, von Humboldt and Gay-Lussac exhibited that water is formed of one volume of oxygen and two volumes of hydrogen, and also by 1811, Amedeo Avogadro had arrived at the exact interpretation of the composition of the water, depending on what is currently known as Avogadro’s law and the diatomic elemental molecule assumption.

However, until the 1860s, these observations were dismissed, partly due to the assumption that atoms of one element would have no chemical affinity for atoms of a similar element, and partly due to obvious exceptions to Avogadro’s rule that were not clarified until later in terms of dissociating molecules.

Cannizzaro revived Avogadro’s theories and used them to construct a coherent table of atomic weights that largely agrees with current principles at the Karlsruhe Congress on atomic weights in the 1860s. These weights were said as prerequisites for the discovery of periodic law by Lothar Meyer and Dmitri Mendeleev.

Excited Electronic States

Normally, the diatomic molecules are in their ground or lowest state, which conventionally is also called the ‘X’ state. When the diatomic molecule’s gas can be bombarded by the energetic electrons, a few of the molecules can be excited to the higher electronic states as they take place. For suppose, in the natural aurora, nuclear explosions of high-altitude and the rocket-borne electron gun experiments. Such type of excitation can also take place when the gas absorbs either light or other electromagnetic radiation.

Also, the excited states are unstable and relax back to the ground state naturally. Over different short time scales after excitation (typically fraction of seconds, or at times longer than a second, if there is a metastable excited state), transitions occur from the higher to lower electronic states and finally to the ground state, and in every transition results, there emits a photon. This emission is called fluorescence.

And, successively, higher electronic states can be conventionally named as A, B, C, and so on. The excitation energy should always be either greater than or equal to the electronic state energy in order for the excitation to take place.

In the quantum theory, the diatomic molecule’s electronic state can be represented by the molecular term symbol as given below:

 2S + 1 _Λ(v)

Where S is given as the total electronic spin quantum number, Λ is given as the total electronic angular momentum quantum number along the internuclear axis, and v is given as the vibrational quantum number. Λ takes on the values of 0, 1, 2, and so on, which are represented by the symbols of electronic states such as Σ, π, Δ and so on.