Category: Chemistry Notes PPT

When we study the isomers in chemistry, we come across different forms of isomers. Although isomers are divided into two different groups – stereoisomers and constitutional isomers, there are other sub-divisions of isomers as well, such as cis and trans isomers. However, there is a difference between cis and trans isomers.

Generally, the cis and trans isomerism is found in both organic and inorganic compounds. The ‘cis’ and ‘trans’ are Latin words that refer to this side of and another side of respectively. Cis isomers are the isomers that have two similar atoms lying on the same side of the double bond in a molecule. The trans isomers have molecules with two similar atoms that are placed on opposite sides of the double bond. Both the cis and trans isomers possess the same molecular formula but differ in a few aspects. In this article, we will learn about the difference between cis vs trans-isomers.

What is Cis and Trans Form of Isomers?

The atoms that make up isomers in stereoisomerism join up in the same order, but have a different spatial arrangement. Geometric isomerism is a type of stereoisomerism. These kinds of isomers tend to occur when the rotation in a molecule is restricted. The examples of stereoisomers generally consist of the carbon-carbon double bond.

Difference between Cis and Trans Isomers

Talking about the difference between the cis and trans stereoisomers, the main difference between the two lies in the arrangement of the atoms in the double bonds. However, some of the major difference between the isomers cis and trans are tabulated below. Let us take a look at them.

Boiling Points and Melting Points of Cis and Trans Isomers

1. Boiling Point

The boiling point of a cis- isomer is higher than the boiling point of a trans- isomer of the same molecule. For example, boiling points of cis- isomer and trans- isomer of 1,2-dichloroethene are 60 degrees Celsius and 48 degrees Celsius respectively. This is because, in cis- isomer, the heavy groups are on the same side of the bond which makes the cis-isomer polar and results in dipole attraction between the molecules. 

2. Melting Point

The melting point of the cis-isomer is lower than the melting point of the trans- isomer of the same molecule. For example, melting points of cis- isomer of 1,2- dichloroethene are -80 degrees celsius and -50 degrees celsius respectively. This is because the molecules of the trans- isomers(straight-chain) well- packed than the molecules of the cis-isomers (U-chained). Therefore, the intermolecular forces are stronger in trans-isomers as compared to the cis-isomers. 

The Polarity of Cis – Isomers and Trans – Isomers

Both the cis-isomers and trans-isomers have an equal number of the same type of atoms joined together. However, the cis-isomers are polar and trans-isomers are non-polar because, in trans-isomers, the groups are attached in opposite directions. Due to this, the dipole moment of the bond cancels out making the trans- isomer non-polar. Since the cis-isomers are polar, they are also unstable in nature whereas the trans-isomers, being non-polar are stable in nature. 

Acidic Strength of Cis and Trans – Isomers 

The cis-isomers have greater acidic strength than the trans-isomers. The cis-isomer also called the maleic acid has greater acidic strength than the trans-isomer also called the fumaric acid because the maleic acid is able to form an intra-hydrogen bond. This bond forms because the maleic acid is able to lose its hydrogen ion. No such bond is formed in fumaric acid because in trans- isomers, strong interaction with the oxygen atoms of the carboxylic group exists. 

Examples of Cis and Trans Isomers in Alkenes

1. But-2-ene is one of the most common examples of geometric isomerism in Alkenes.  

But-2-ene can show both cis and trans isomerism because of the restricted rotation around the double bond. The double-bonded carbons in cis- isomer and trans- isomer have the same two groups attached to them that are hydrogen and methyl groups. The only difference is in the placement of these groups. In the cis-isomer, the two groups are present on the same side of the double bond whereas, in the trans- isomer, the two groups are present on the opposite sides of the double bond. Both the compounds have different geometrical structures, physical properties and chemical properties. 

Examples of Cis and Trans Isomers in Cyclic Compounds

1. 1,3-dimethylcyclobutane is one of the most common examples of cis and trans isomers in cyclic compounds. 

1,3-dimethylcyclobutane can show both cis and trans isomerism because of the restricted rotation around the double bond. This is because if the rotation occurs, then the cyclic ring will break. The groups attached to the ring system will vary in their positions. The cis-isomer will have the groups attached to the same side of the ring whereas the trans- isomer will have the groups attached to the opposite sides of the ring. 

A cell in chemistry is used to convert chemical energy to electrical energy or we can say for the purpose of conversion of energy. The chemical reactions occur inside the cells and as a result of these, electrical current flows. In this article, we will study about two main cells; these are galvanic cells and electrolytic cells in detail. The chemical energy is converted into electrical energy in galvanic cells while electrical energy is converted into chemical energy into electrolytic cells. These electrochemical cells are used for different applications.

What are Galvanic Cells?

Galvanic cells consist of two half-cells, which convert the chemical potential energy into electrical potential energy. It happens through a spontaneous chemical reaction. On the two half-cells of galvanic cells, each half-cell contains an electrode in an electrolyte. The separation is required to prevent a direct chemical contact of the reduction and oxidation reactions by creating a potential difference. Electrons that are released in the oxidation reaction passes through an external circuit before it is being used by the reduction reaction.

Working of Galvanic Cells

The working of galvanic cells is very simple. It involves a chemical reaction that allows the electrical energy to use as an end product. During a redox reaction, the galvanic cell uses the energy transfer between electrons to convert chemical energy into electrical energy. Reactions of Daniel cell (galvanic cell) at cathode and anode are as follows:

At cathode: Cu²⁺ + 2e⁻→ Cu

At anode: Zn → Zn²⁺ + 2e⁻

The galvanic cell has the power to separate the flow of electrons through the cycle of oxidation and reduction, creating a half-reaction and connecting both of them to a wire such that a path may be created for the flow of electrons across that wire. This kind of electron flow is essentially called a current. And, such current can be made to pass through a wire to complete a circuit and to obtain the output in any device like a wristwatch, a television, and so on.

The galvanic cell may be composed of any two metals. If left in contact with each other, these two metals will form an anode and a cathode. This combination makes the galvanic corrosion more anodic. A connecting circuit is necessary to prevent this corrosion.

Terms to Remember

A few of the important terms brought into use in galvanic cells are mentioned below.

• Phase Boundaries, which refers to two metals acting as a cathode and anode.

• Salt Bridge, a connecting medium that allows a redox reaction to occur.

• Oxidation and reduction, a chemical process that allows the electric current to form and pass through a galvanic cell. 

What are Electrolytic Cells?

Electrolytic cells are much the same as galvanic cell as it requires a salt bridge, two electrodes in addition to the flow of electrons from the anode to the cathode. However, still, the two electrodes manage to differentiate from others in various aspects. For one, the electrolytic cell transforms electrical energy into chemical energy and, not the other way round.

Working of Electrolytic Cells

With the help of an electrolysis cell, molten sodium chloride (which contains dissociated Na+ cations and Cl^– anions) can be electrolyzed.

In the figure given below, two inert electrodes are dipped into molten sodium chloride. The cathode becomes rich in electrons when the electric current passes through it and develops a negative charge. The positively charged Na+ are attracted towards the negatively charged cathode. 

The atoms of chlorine move towards the positively charged cathode. The chlorine gas is formed at the anode as a result of this. The chemical equations and the overall cell reaction are as follows:

Reaction at Cathode: [Na⁺ + e⁻ → Na] x 2

Reaction at Anode: 2Cl⁻ → Cl2 + 2e⁻

Cell Reaction: 2NaCl → 2Na + Cl₂

Process of Electrolysis

In simple terms, the process of electrolysis refers to the decomposition of an element that is provided under the influence of an electric current. The first electrolysis was conducted by Sir Humphrey Davey, in 1808. This analysis provided important knowledge into how other elements act and how they vary from compounds and ions.

The subsequent redox reaction in the process is not natural, so for the start-up reaction, electrical energy must be added to the apparatus. Unlike the galvanic cell, the electrolytic cell requires both metals to be positioned in the same container. In this case, the positive electrode is considered an anode, and the negative electrode is considered a cathode.

What is an Electrochemical Cell?

An electrochemical cell is a device that would generate electrical energy by performing the chemical reactions in it or using the electrical energy supplied to it, facilitating chemical reactions in it. These devices have the capability to convert electrical energy into chemical energy and vice versa.

A good example of an electrochemical cell is a standard 1.5 Volt battery used to power up many electrical devices like a TV remote, a wall clock, and more.

Such types of cells are capable of generating electricity forming the chemical reactions in them, these types of cells are called Galvanic Cells or Voltaic Cells. As an alternative, cells that cause chemical reactions to happen in them when an electrical current is passed through them are referred to as electrolytic cells.

Difference Between Galvanic Cells and Electrolytic cells

There are numerous differences between galvanic and electrolytic cells to explain. Some of them are tabulated below.

Conclusion

From the above differences between galvanic and electrolytic cells, we can conclude that a galvanic cell produces an electric current with a chemical reaction that happens spontaneously in it, whereas an electrolytic cell does the opposite. This means it brings about the chemical reaction using an electric current from an external source.

Polysaccharides are the most abundantly available in nature among carbohydrates and perform a variety of functions, such as energy storage or as components of plant cell walls. Polysaccharides are very large polymers made up of tens to thousands of monosaccharides, linked by glycosidic linkages. Common polysaccharides: Starch, glycogen, and cellulose.

Heteropolymers can include, in addition to monosaccharides, sugars, amino sugars, or non-carbohydrate substances. Heteropolymers are common in nature and are non reducing carbohydrates (with no sweet taste).

Starch

Starch is a glucose polymer in which all repeat units are directed in one direction and connected by alpha bonds. Starch is edible and can be eaten safely by humans as we have the enzymes which can break it down into glucose.

It is a grain, with the main source for starch being potatoes, wheat, corn, and rice. These carbohydrates are broken down into glucose and used as a source of energy and a metabolism aid when reaching our bodies.

Starch is less crystalline and is weaker than cellulose. Despite the fact that raw starch is not soluble in cold water, it can be dissolved in warm water and can be used in different ways.

It’s most commonly used as food but has other uses as well. It can be used as glue, for tightening up clothes and weaving linen, for thickening sauces and for paper treatment.

Cellulose

Cellulose is a glucose polymer whose units can be rotated around the axis of a backbone of glucose unit polymer chains, and are connected by beta links. It is the most natural organic compound and is a fundamental component of plant cells.

While humans can easily consume any type of cellulose, such as the outer shells of corn, the only animals that can digest cellulose are termites and cud-chewing goats, deer, or buffalo because they have some enzymes that can break down cellulose into glucose.

It has many commercial uses and is the main component of the paper and the fibre used to make clothes such as linen and cotton. Cellophane and rayon are also made from cellulose through dissolving the pulp by viscose, causing it to degrade and then dissolve into cellulose xanthate in caustic soda.

Structure of Starch

Starch is made from a chain of α-glucose monomers. The glycosidic bonds are present in its linkage which is formed through the reaction of condensation. Water is released in this reaction. Mainly starch is made up of sugar glucose. Glucose is a molecule made up of carbon (C), hydrogen (H), and oxygen (O) whose basic chemical formula of C₆H₁₂O₆. An α- glucose monomer structure is drawn below.

Structure of Cellulose

The successive unit of glucose monomer present in the structure of starch is rotated 180 o around the polymer backbone chain’s axis and cellulose structure is obtained. At high temperatures, cellulose can be broken down into glucose (C₆H₁₂O₆) by treating with concentrated minerals acids. (C₆H₁₀O₅)n is the general formula used for cellulose.

Structural Difference Between Starch and Cellulose

Starch consists of two ingredients-amylose and amylopectin. Amylose is a long linear chain of ­-D-(+)-glucose units joined by glycosidic association C1-C4 (along-link).

Amylopectin is a branched-chain polymer consisting of ‐D-glucose units in which the chain is formed by glycosidic connection C1-C4 and glycosidic connection C1-C6 branches.

Cellulose, on the other hand, is a straight-chain polysaccharide with β – D-glucose units joined by glycosidic linkage C1-C4 (β-link).

Starch vs Cellulose

There are some parameters to differentiate between starch and cellulose. The difference between starch and cellulose are given below on the basis of parameters.

Starch and cellulose are made from the same monomer i.e. glucose hence they are very similar polymers. As their monomer is the same so they also have the same glucose-based repeat units. Cellulose is comparatively much stronger than starch. Hence cellulose is used for making fibres, clothes, papers, rope etc. while starch is practically not that useful in making things.

You have been learning about osmosis and diffusion for a very long time now. These two terms are not being heard for the first time by 90 percent of you all. But what makes this topic so important? Why do these two words keep on popping up out of nowhere and what exactly makes the entire idea of osmosis and diffusion so interesting?

 

Before we get into the details of everything and tell you what makes diffusion and osmosis so interesting, we must tell you that these two terms are going to be talked a lot about even in your higher studies. However,

 

One of the most interesting things is that both diffusion and osmosis are fairly easy to remember and understand because they have a very simple principle behind them that can be understood by anyone.

 

Another thing that we must tell you is that these two terms are also something that many people get confused about. Many students face difficulty in knowing what diffusion is and what osmosis is and end up writing the answers for the opposite. Therefore we want the students reading this article to pay full attention to the content being discussed here so that they do not get confused. This is because both of these concepts are very similar to each other but with practice and repetition revision, there will be no doubt at all.

 

Several processes can be performed as an experiment in a lab. Also such processes do pre-exist in our body as well as naturally and are in function to maintain the proper functioning of the body and nature. Out of many such processes, diffusion and osmosis are the most discussed ones. In this chapter, we are going to learn about diffusion and osmosis separately and in detail, we will also learn about the significance of diffusion and osmosis about how they are different or similar to each other and also though these two are different processes you will be surprised to know that osmosis is a special kind of diffusion. We will learn about all of this further in the chapter. So let’s get started with osmosis.

 

Osmosis

This refers to a process in which solvent particles (water molecules) move from a dilute solution into a concentrated solution across a semipermeable membrane. Osmosis occurs to dilute the concentrated solution and also to ensure the equalization of concentration on both sides of the membrane.

 

Examples of osmosis

• The roots of the plant absorbing water are a natural example of osmosis.

• The swelling up of red blood cells, when exposed to fresh water, is another example of osmosis.

 

Diffusion

Diffusion refers to the process in which particles from a higher concentration tend to move or transport to a lower concentration medium to attain equilibrium. In diffusion, the concentration is equalized throughout the medium. Now we will try to understand this process of diffusion with the help of a diagram given below 

 

As we can see the diagram dye molecules are added to the water molecules and later when the mixture is kept undisturbed for some time water molecules as well as the dye molecules tend to diffuse independently.

 

Types of Diffusion

There are two types of diffusion namely

• Simple diffusion

• Facilitated diffusion

 

Let’s Understand Simple Diffusion First

In simple diffusion, the substances move through the semipermeable membrane without any help from a transporter. A transporter can be anything like a bacteria.

 

While Facilitated Diffusion Refers to:

Movement of molecules from a higher concentrated substance to the lower concentrated substance with the help of a transporter or a carrier molecule across the cell membrane.

 

Examples of Diffusion

• Have you ever added a drop of food colour to water? If not, try it today you will be amazed at the results and you will be able to see an example of diffusion right in front of your eyes.

• When a food colour drop is added to the water the entire solution turns into the colour of food colour which shows that molecules of both water and food colour diffuse independently.

 

Significance of Diffusion and Osmosis

Both diffusion and osmosis are really important as these ensure the equalization of forces inside cells and also inside an organism as a whole by spreading all the necessary chemicals and nutrients from a highly concentrated area to the low concentration area inside an organism

 

Similarities between Osmosis and Diffusion

Both of these processes we discussed are similar in many ways. Let’s have a look at the similarities between these two processes.

• Both of these processes, diffusion and osmosis tend to equalize the concentration of the solution.

• Both of these processes do not require any extra energy or input hence these are called passive processes.

• Both of these processes observe the movement of molecules from higher concentration areas to lower concentration areas.
  

Differences Between Osmosis and Diffusion

Conclusion

There is not a lot of complicated information whenever we talk about what osmosis and what diffusion is. The concepts are fairly simple to understand and learn and that is why we suggest that students keep this article handy so that they do not forget about the main differences between the two topics being discussed here. encourages students to work on their revision skills whenever they are studying this topic and that is why we wish you the best in your preparation as well. Revision is a very important thing that many people miss out on but if you want yourself to score the best, then revising things in the best way to score well!

Temperature Effects on Reactions

Our world is full of things which we don’t know off, things which are taking place right in front of our eyes and still we are not aware of them. One of the most common occurrence that we can’t see from our eyes are chemical reactions. In some cases, they might be too slow, while on the other hand, some are too fast, but most of them are unrecognisable to us in daily lives. From putting mentos in your coke bottle to the engine of a car, we have reactions taking place all around us. Today we are going to discuss how temperature could affect a given reaction, and in this case, we react with Sodium thiosulphate and Hydrochloric acid. Not only does the temperature have some severe effect on this reaction, but other reactions get manipulated by the temperature in big industries to get the most from the reaction.  

Properties of Hydrochloric Acid

Before we dive deep into the reaction of these two compounds, it is fair to have some background about them to make it easier for us to understand how the temperature affects each of them individually. 

Hydrogen oxide being a liquid solution of hydrochloric acid is one of the most potent mineral acids. As a result, industries use it extensively in their production. We represent Hydrochloric acid as HCl when writing its chemical formula., and it is the mixture of hydrogen and chloride present in water. 

The acid is clear and doesn’t have any colour, but it does have a high pungent odour which can smell even from a distance if its bottle gets opened. The boiling hydrochloric acid rate and the melting point varies depending on its concentration in water. 

The fuming hydrochloric acid forms when the hydrogen and chlorine hold 38% of the total concentration with the water. The HCl which is used in industries has a concentration of 30%-35%. On the other hand, if we look at the commercial side of HCl, we get muriatic acid which is in between 20% to 32% of concentration. 

HCl can release only one hydrogen positive ion. Thus, it comes in the list of one of the strong acids and also called monoprotic acid. It gives us hydronium and chloride ions when it gets to react with water. If you want to dissolve a strong metal, you can take the help of Hydrochloric acid as it can from oxidised metal chlorides and hydrogen gas. Any biological sample which you break down HCl can help you digest it in no time. You can see its use in photographic, textile, and rubber industries. 

Properties of Thiosulphate

Thiosulphate is said to be an important inorganic salt that provides several medical uses to doctors. In other words, we can call it ‘hyp’; it’s the acronym of sodium hyposulfite. The chemical formula of this compound is Na2S2O3. It is also present in the state of pentahydrate salt. Thiosulphate is an ionic compound that has two sodium cations present along with thiosulfate anion. In this compound, we have sulfur atoms at the centre which is bonded with three oxygen atoms and with one sulfur atom. All of these are connected via single and double bonds with the characteristics of resonance. 

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Furthermore, the compound is highly soluble in water and has a physical property as a crystalline solid which is odourless. Under normal temperature and conditions, it remains solid, but when some extra heat is applied, it dissolves to give sodium sulfate and sodium polysulfide. 

Effects of Temperature on Rate of Reaction

From this reaction, we get precipitate of sulfur forms. The time which is taken to produce a certain amount of precipitate of sulfur is used to show us the rate of reaction for lab report discussion. One thing you need to keep in mind is to wear glasses and keep your face away from the test tube while the reaction is taking place. Because of sulfur dioxide as a by-product of this reaction which is a toxic gas, it can cause you breathing issues if you inhale it. 

The rate of reaction of the two compounds is directly proportional to the increase in temperature. When we increase the temperature, the molecules of a compound start to vibrate at a much faster rate resulting in a collision with particles of another compound. As a result, their collision leads to the reaction of the two compounds, and more the collision, the shorter will be the time in which the reaction gets completed.

But hold on, that’s not it when we increase the temperature the activation energy also reaches to its potential. Meaning the particles have now enough energy to start the reaction. The minimum energy which is required to start up a reaction between two compounds or chemicals is called activation energy.

The term “electrolyte” stands for particles that carry a positive or a negative charge. From the nutrition point of view, it refers to essential minerals found in blood, sweat and urine. Electrolytes found in our body include sodium, potassium, chloride, calcium, magnesium, phosphate, bicarbonate, etc. Electrolytes play a significant role in various bodily processes like maintaining proper nerve and muscle function, maintaining a proper pH in the body and keeping us hydrated. In simple words, electrolytes are minerals that carry an electric charge.

Why do we Need Electrolytes?

We need electrolytes in our body simply because they help facilitate various essential bodily functions like:

1. Maintenance of the Nervous System

Signals are sent from the central nervous system to different parts of the body through the nerve cells. These signals are called nerve impulses and are generated by the electrical charge of the nerve cell membrane. These changes occur due to electrolytes’ movement, particularly sodium, in and out of the membrane. This initiates a chain reaction that helps transfer signals along the length of the nerve cells.

2. Functioning of Muscles

Calcium is the electrolyte needed for muscle contraction. Muscle fibres slide and pass over each other due to the action of calcium ions, which in turn results in contraction and relaxation of muscle fibres.

3. Hydration

It is essential to maintain a fluid balance inside and outside of each cell in our body. Water must be kept in the right amounts. Electrolytes, especially sodium, help in maintaining fluid balance through osmosis.

4. Regulating Internal pH Levels

pH is nothing but the measure of how acidic or basic a substance is, and buffers, weak acids and bases regulate it. A pH of around 7.5 is essential for the proper functioning of the body. Even a slight deviation in the pH levels can make you unwell. The right balance of electrolytes in the body helps in maintaining the right pH level in your body.

Electrolyte imbalances are common but can be fatal in some cases. The main reasons for electrolyte imbalance are dehydration, which may be caused due to excess heat, drinking less water, or diarrhoea. Hence you should always drink adequate water to replace the lost electrolytes in your body.

Extended electrolyte imbalance levels can lead to fatigue, weakness, dizziness, confusion, cramping, etc.

Tests for Electrolytes

Tests for electrolytes in the body are carried out primarily to know the imbalance of a particular electrolyte in the body. They are also carried out when you are prescribed certain medications. An electrolyte test can also figure out the effectiveness of a specific type of treatment in your body.

Fluid and Electrolyte Balance

Electrolyte contains electric charge inside the body usually found inside blood, urine and tissue fluids. Sometimes due to the change in the water level inside the body, the electrolytes’ level becomes too high or low. There is a thumb rule for the amount of water you should take; you should lose them through urination or sweating. Due to dehydration or some other mechanism, this balance changes.

Usually, the body fluid has many dissolved chemicals, which may be electrolytes or non-electrolytes. In electrolytes, there are ionic bonds, and in the non-electrolyte, a covalent bond is there.

However, there is a proper balance maintained inside the body because of the flow of electrolytes’ movement whenever necessary. To understand this, let’s take an example. The concentration or the pH of blood remains the same after taking various acidic or alkaline foods. This is mainly because of the proper balancing of bicarbonate electrolyte.

Electro-Chemical Cell 

These are mainly of three types such as galvanic cell, concentration cell, an electrolytic cell. All these three cells consist of a similar mechanism.

The electrolyte is the conducting medium for electrons’ movement between anode and cathode in an aqueous medium. The anode is the medium in contact with the electrolyte and has the capacity to conduct electricity in combination with other chemicals. A cathode is a substance that is rich in protons and has the ability to receive electrons. The conductor is the substance that links between anode and cathode and helps in the current flow mechanism.

Types of Electrolytes

Electrolytes are broadly classified into two types, strong and weak electrolytes. Vital electrolytes ionize entirely in water, i.e. every fraction of the dissolved chemicals breaks into anions and cations. However, we should not assume that the compound completely dissolves in water. It just means that the whole combination that gets dissolved in water is broken into anions and cations. Some examples of vital electrolytes are strong acids, strong bases and salts. Weak electrolytes partially ionize in water. A fraction of the compound dissociates. Examples are weak acids and weak bases.