Category: Chemistry Notes PPT

A metal ion is at the centre of a complex ion, which is surrounded by a number of other molecules or ions. These can be thought of as co-ordinate (dative covalent) bonds linked to the central ion. (In some circumstances, though, the bonding is more intricate.)

As we already discussed what is complex, now we will discuss what is the meaning of complex in detail.

What is the Meaning of Complex?

A covalent bond is established when two atoms share a pair of electrons. Because both nuclei are attracted to the electron pair, the atoms are stuck together. Each atom contributes one electron to the formation of a simple covalent connection, although this isn’t always the case.

A covalent link (a shared pair of electrons) in which both electrons come from the same place is known as a co-ordinate bond (also known as a dative covalent bond).

Example of a Complex Substance:

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Nomenclature in Complex Chemistry

Complex substances have their own naming convention: The central metal ion is the name given to the metal. Ligands are the anions or molecules that are bonded to the metal. The coordination number refers to the number of ligand-binding sites on the metal ion. A coordinate covalent bond is a link between a metal ion and a ligand in which the ligand gives both electrons. Water, ammonia, and chloride ions are examples of simple ligands.

Because coordination complexes are so common, their structures and reactions are explained in a variety of ways, which can be misleading. The donor atom is the atom in a ligand that is bound to the central metal atom or ion. A metal ion is bound to numerous donor atoms in a typical complex, which can be the same or different. A polydentate (many bonded) ligands is a molecule or ion having many bonds to the core atom; ligands with 2, 3, 4, or even 6 connections to the central atom are frequent. These complexes are known as chelate complexes, and the process of forming them is known as chelation, complexation, and coordination.

Ion in Complex Chemistry

All of these have active lone pairs of electrons in the outer energy level in common. The metal ion is employed to establish coordinate bonds with them.

Lone pair donors are present in all ligands. To put it another way, all ligands act as Lewis bases.

A complex substance is one in which one or more ligands are datively linked to a core metal cation. A ligand is a substance that can create a dative covalent connection with a transition metal by using its lone pair of electrons. H2O, NH3, Cl–, OH–, and CN– are examples of ligands.

Complex Ion-Forming Cations Must Have Two Characteristics:

1. The presence of a high charge density attracts electrons from ligands.

2. Low-energy empty orbitals that can accept the lone pair of electrons from ligands.

D-block metal (transition metal) cations are small, have a high charge, and have low-energy vacant 3d and 4s orbitals. When their partially full d subshell absorbs donated electron pairs from other ions or molecules, they readily form complex ions. The coordination number of a cation is the maximum number of lone pairs of electrons it can receive. This number is determined by the cation’s size and electronic configuration, as well as the ligand’s size and charge. The most common coordination number is six, but 4 and 2 are also popular. [Fe(H2O)6]2+, [CoCl4]2-, [Cu(NH3)4(H2O),2]2+, and [V(H2O)6]3+ are examples of complex ions.

Complex Ion Equilibria

When two reactants are combined, the reaction usually does not finish. Rather, until a condition is reached in which the concentrations of the reactants and products remain constant, the reaction will produce products. At this stage, the rate of product production is the same as the rate of reaction formation. Chemical equilibrium exists between the reactants and products, and it will continue to exist until it is disrupted by an external force. The reaction’s equilibrium constant (Kc) links the concentrations of the reactants and products. The reaction between the iron (III) ion and the thiocyanate ion, for example, is as follows:

Fe3+(aq)+SCN–(aq)→FeSCN2+(aq)

The deep red thiocyanatoiron (III) ion ([ FeSCN]2+) is generated when Fe3+ and thiocyanate ion solutions are combined. The initial concentrations of Fe3+ and SCN will drop as a result of the reaction. One mole of Fe3+ and one mole of SCN will react for every mole of [ FeSCN]2+ produced. 

Complex Substance Equilibria

At a fixed temperature, the value of Kc remains constant. This indicates that Fe3+ and SCN mixes will react until the equation above is met. Regardless of the initial amounts of Fe3+ and SCN utilised, the Kc value will be the same. The appearance of the red colour — indicating the developing [FeSCN]2+ ion — can be measured using spectrophotometry to find Kc for this reaction experimentally. At 447 nm, the wavelength at which the red complex absorbs the maximum light, the amount of light absorbed by the complex is measured. The complex’s absorbance (A) is proportional to its concentration (M) and can be directly measured using a spectrophotometer:

A = kM

The Beer-Lambert Law is a relationship between the amount of light absorbed and the concentration of the substance that absorbs the light, as well as the length of the path along which the light passes:

The observed absorbance (A) is proportional to the molar absorptivity constant (), route length (b), and molar concentration (c) of the absorbing species in this equation. The equation depicts the relationship between concentration and absorbance.

A = ϵbc

The coordination number refers to the total number of points of attachment to the centre element, which can range from 2 to 16 but is usually 6. In simple terms, the relative sizes of the metal ion and the ligands, as well as electronic parameters such as charge, which is reliant on the metal ion’s electron configuration, determine the coordination number of a complex. The phrase ionic potential, which is defined as the charge to radius ratio (q/r), is used to explain these opposing effects.

Did You
Know?

Electronic transitions caused by light absorption produce spectacular colours in transition metal complexes. As a result, they’re frequently used as pigments. D–d transitions or charge transfer bands are the most common transitions associated with coloured metal complexes. D–d transitions occur only for partially-filled d-orbital complexes (d1–9) because an electron in a d orbital on the metal is excited by a photon to another d orbital of higher energy. Charge transfer is still possible in complexes with d0 or d10 configurations, even though d–d transitions are not. An electron is promoted from a metal-based orbital to an empty ligand-based orbital in a charge transfer band (metal-to-ligand charge transfer or MLCT). 

Excitation of an electron in a ligand-based orbital into an empty metal-based orbital also happens (ligand-to-metal charge transfer or LMCT). Electronic spectroscopy, also known as UV-Vis, can be used to observe these phenomena. Tanabe–Sugano diagrams can be used to assign d–d transitions to simple compounds with high symmetry. With the help of computation, these assignments are becoming more popular.

Water conservation is a broad category that covers simple ways to save water at home to complex, long term measures taken to preserve water on a larger scale. 70% of the earth’s surface is covered with water, though it is not entirely useful to humans. 97% of saltwater covering oceans is not drinkable for humans and the remaining 3% is mostly frozen in glaciers. 

Water conservation is the practice of an efficient usage of water by reducing unnecessary wastage of the same. The importance of water conservation becomes even more necessary as there is a limited source of freshwater that is beneficial for all human beings for a Healthy lifestyle. The freshwater available for use is unevenly distributed. Human activities are polluting the water sources threatening the survival of living beings. So, water conservation focuses on the concept of “save water and save a life”.

The Need for Water Conservation

It comes as no surprise that water is one of the most essential elements for the survival of any lifeform on the surface of Earth. The presence of water is what makes Earth different from any other planet. The need to maintain the constant flow of water comes from its vitality for the survival of all flora and fauna on the Earth.  

Just because a portion of the human population has easy access to water resources, we keep forgetting why saving water is important. Saving water is not only a necessity for humans, our careless waste of water is also affecting the animals and plants around us. There are serious consequences of water depletion.

Ways to Conserve Water

Water conservation is essential and can be done by everyone. We can all contribute to saving water. Very small-scale changes can be made to preserve water. Even the people who aren’t facing water shortages should find ways to save water at home.

Several techniques can be implemented for the conservation of water that has been discussed below:-

• Careful Use of Water: Keep the taps turned off when not in use. Usage of efficient home appliances like washing machines and dishwashers can save a lot of water. Even without the appliances, make sure you don’t overuse water while washing dishes or clothes.

• Don’t Wash Down Garbage: Make sure to not wash down small bits of trash that use a large amount of water to flush down the drain. Always put them in the bin.

• Don’t Run The Faucet to Clean Vegetables: Fill a container with water to wash fruits and vegetables. Keeping them under the faucet while water runs down will lead to unnecessary wastage of water.

• Check for Leaks: Leaks can cause a significant amount of water loss if left unchecked. So, check the faucet, taps, and pipes for leaks regularly. While turning the tap off make sure to turn it all the way or it may keep dripping.

• Water the Plants Smartly: While watering your plants keep in mind the temperature and time of the day, so water doesn’t evaporate quickly. Reuse water from cleaning and laundry to water the plants.

• Reduce Bathing Water Amount: While bathing or taking a shower make sure to not let the water run down for a longer period or unnecessarily. 

• The best way to conserve water is to recycle and reuse it.

• Try limiting your shower time to 10 to 15 minutes because humans carelessly consume gallons of water for luxuriously long showers. So Reducing the shower time would prevent excessive wastage of water.

• Rusting pipes Leaky faucets dripping water from shower heads Earth science of unnecessary water wastage that needs to be fixed immediately to avoid wasting water.

• Try using a compost Bin instead of in-sink garbage disposal. Compost bins are environmentally friendly and reduce water wastage.

• Maintenance of appliances can prevent potential leaks and wastage of energy.

• We can save gallons of water by turning off the water while brushing our teeth, shaving, showering, and washing dishes as these daily routine activities have resulted in excessive consumption of water.

• Promote plantation of drought-resistant trees and plants as these can thrive even without irrigation.

• Trees and plants with a layer of mulch around them slow down the evaporation of moisture.

These are some of the many ways to save water. Moreover, people need to be educated and made aware of the ways of saving water. Make an effort to educate the people around you on why you think saving water is important.

Water Conservation Facts 

• Agriculture only accounts for 80% of India’s total water consumption.

• The biggest water rejuvenation plan launched by the Indian government is “Namami Gange” for the Ganges river basin.

• Rain accounts for 85% of the available water while the rest 15% is from melting snow.

• The water prerequisite of India is 1100 billion cubic meters per year.

• 84% of rural households do not have access to piped water lines.

• Lack of water causes a heavy loss in income since Indian women spend 150 million workdays every year carrying and fetching water.

• Around 10 crore people consume water with an excessive amount of fluoride.

• Almost 68% of the earth’s fresh water is contained in Ice and glaciers. Freshwater can be found in rivers, streams, and lakes and also in glaciers and groundwater.

• Do you know where the saltiest water in the world is found?

• Well, the saltiest water in the world is found in a small lake Don Juan Pond in Antarctica.

These facts tell more than enough about why conservation of water is important. The current situation regarding the depleting amount of water tells us about the dire need of why it is
essential to conserve water.

Dihydrogen, which is better known as H2, is the most abundant element in the world and it can combine with almost anything and form carbohydrates, proteins, hydrides, hydrocarbons and many other compounds. Dihydrogen or H2 combines with almost every element on earth, except noble gasses, and forms binary compounds called hydrides under certain conditions. MgH2, B2H6 are two examples of hydrides. These hydrides are broadly classified into three categories:

• Ionic or saline or salt like hydrides

• Covalent or molecular hydrides

• Metallic or non-stoichiometric hydrides

Ionic hydrides

These compounds of H2 are mostly formed with s-block elements which are highly electropositive in nature. Although lighter metal hydrides such as LiH, BeH2 have significant covalent character.

LiH is unreactive at a moderate temperature with O2 or Cl2, so it is used in the synthesis of other useful hydrides.

Covalent hydrides

H2 forms molecular bonds with most of the p-block elements and the most common compounds are H2O, NH3, CH4 and HF.

Covalent hydrides are further divided into three categories according to the relative numbers of electrons and bonds in their Lewis structure:

(i) electron-deficient – all the group 13 elements form electron deficient compounds with hydrogen and act as electron acceptor (Lewis acids), eg, B2H6,

(ii) electron-precise – all group 14 elements form electron precise compounds and see tetrahedral in geometry, eg, CH4,

(iii) electron-rich hydrides – elements from groups 15 through 17 form such bonds that have excess electrons which are present as lone pairs, eg, NH3 where 1 lone electron is present.

Metallic hydrides

Hydrides formed by many elements of d and f-block with H2 are called metallic hydrides. Elements from groups 7,8 and 9 do not form bonds with H2, and only Cr from group 6 forms a bond. Some of the metals can accommodate a large number of hydrogen making them highly potential for hydrogen storage, eg, Pt, Pd. In this type of hydride, hydrogen occupies the metal lattices in the interstitial spaces.

The introduction to the early theory of the atom was done by a scientist named John Dalton (1766-1844). He was a British physicist, chemist, and meteorologist who is well known for many of his contributions to the pioneering research of atoms, the law of partial pressures, Daltonism, etc. Dalton’s atomic model showed the way to many future works, researches regarding atomic theory, even though his conclusions were rather incorrect. He considered the atom as the smallest, indivisible unit of matter and wrote several postulates. Dalton’s model suggested the atom to be a ball-like structure that cannot be further divided. He also symbolized different atoms. Each atom was circular and bears different symbols.

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Dalton’s Atomic Model

The matter has been a subject of fascination since the beginning. Democritus was known to be the first to suggest that matter is made up of particles. Dalton’s model came almost two millennia later and brought further light to the topic. However, the ideas from researches of methane and ethylene might have helped define Dalton’s atomic theory at the time.  

 

The theory of Dalton was published in the paper “New Chemical Philosophy”. Dalton’s idea for the theory is believed to be inspired by the physical properties of gases. Although connections of his work have been made with several other chemists of the time. The definition of dalton’s atomic theory brought the novel concept of calculating relative atomic weights. 

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Postulates of Dalton’s Atomic Theory

The law of conservation of mass and constant proportions are the basis that helps explain Dalton’s atomic theory. Based on these laws Dalton’s atomic theory states the following postulates:

• Atoms are considered to be a matter which is made up of very small, indivisible particles.

• All the atoms in an element are identical. So, they have the same size, shape, mass, and chemical properties. Different elements have different properties i.e. masses, sizes, shapes, and other chemical properties.

• Atoms can neither be created nor be destroyed or subdivided into a chemical reaction.

• Atoms of different elements combine in whole numbers in a simple but fixed ratio to form compounds. Different types of atoms are joined together to form compounds.

• A chemical reaction is a rearrangement of atoms, where the formation of new products occurs due to the rearrangement of atoms in the reactant. The number of atoms before and after a chemical reaction remains the same. 

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Limitations of Dalton’s Atomic Theory

Although Dalton’s atomic theory marked a significant turning point in the research regarding the matter, the theory wasn’t entirely faultless. In further research, his theories were proven wrong.    

• As it was found, later on, atoms are not indivisible. Subatomic particles like protons, electrons, and neutrons have been discovered since then.

• Dalton’s atomic theory states atoms of an element are identical in mass. However, a single element having different atomic masses has been observed. These are called isotopes.

• According to the theory of Dalton, compounds are formed when atoms combine in whole numbers. This fails to explain the formation of complex organic compounds.

• Dalton’s model failed to explain the existence of isobars. Atoms of different elements when having the same mass, are called isobars.

• The theory fails to explain the difference in properties of allotropes. It can not prove the difference in properties of charcoal, diamond, and graphite; allotropes of carbon. 

 

Influences on Modern Atomic Theory

Dalton’s atomic theory contributed a lot to modern atomic theory. Dalton’s model was revolutionary for the period and gave much to the new chemists to research upon. The Atomic theory got modified with the contribution of many after Dalton, namely, Chadwick, JJ Thompson, Ernest Rutherford, Niels Bohr etc. Later, JJ Thompson discovered electrons and Rutherford worked on the model to discover the nucleus. 

 

Finally, Niels Bohr’s model and the Quantum mechanical model provided the modern atomic model as it is known today. Modern atomic theory, though evolved in two centuries, holds much of Dalton’s atomic theory. 

What is Destructive Distillation?

In this article, readers will be able to learn about the topic of destructive distillation. We will answer the question of what is destructive distillation by first beginning with the definition of destructive distillation. We will also explore other facets of the destructive distillation meaning.

When it comes to the definition of destructive distillation, then it can be said that this is a chemical process that is used to subject unprocessed materials to decomposition. This is done by heating those unprocessed materials. In this process, ‘cracks’ are produced in relatively large quantities.

It is also important to point here that usually, the term ‘destructive distillation’ is used to refer to the process through which organic materials are processed with certain reagents, limited amounts of oxygen, solvents, and catalysts like steam and phenols.

The destructive distillation definition can also be used to refer to the processing of organic materials in an environment that does not contain air or pyrolysis in the absence of air. One can also define destructive distillation as the application of the concepts of pyrolysis.

For students who are unfamiliar with the term, pyrolysis can be explained as the process of thermal decomposition of various substances. This is done at a very high temperature and under relatively inert atmospheres.

Let’s consider an example to understand this entire process in a better manner. Coal is often subjected to destructive distillation. This is done to form a wide range of products that are very important from a commercial point of view. Some of those commercially important products are coke, coal tar, coal gas, gas carbon, ammonium hydroxide, and coal oil.

Destructive Distillation of Coal Diagram

As of now, students must have learned how to define destructive distillation and learned the destructive distillation meaning. However, there might still be some doubts related to the destructive distillation definition.

To further solve these doubts, we believe that it is best for students to go through the destructive distillation of coal diagrams. Check the below diagram.

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Products Formed During Destructive Distillation

Have you ever wondered about what products are formed during destructive distillation? If you have, then in this section, you will be able to find the answer to the question of what are the products formed during destructive distillation.

The first thing that students need to learn about the products that are formed during destructive distillation is that in the case of inorganic materials, only a few products are generated. This is directly in contrast to the large number of products that are generated after processing organic materials through destructive distillation.

However, one must also remember that most of those products are not of major importance from a commercial point of view. Another important fact that one must know is that the distillates of destructive distillation processes often have a relatively low molecular weight.

There are also fractions of distillates that can go under the process of polymerization to form larger molecules. Tar and chars are good examples of products that can go under polymerization to form larger molecules. Both of these products are also stable under heat.

It is also important to note that the cracking of larger molecules in the feedstock and the further conversion of those compounds into volatile liquids and products, the polymerization of distillate molecules, and the formation of chars and solids can all occur during the same process. These products have great commercial value.

The process of destructive distillation and other forms of pyrolysis has helped in discovering new chemical compounds. These processes have also helped in the elucidation of chemical structures of different compounds.

Through these processes, chemists have also learned about the nature of several chemical materials. A good example of this is how insight was gained into the structures of furanoses and pyranoses.

The Process of Destructive Distillation

In this section, we will look at the process of destructive distillation. As we have mentioned before, this process involved the pyrolysis of organic and inorganic feedstock. This is done inside a distillation apparatus, and the volatile products are collected during the pyrolysis.

However, it is important to note here that only a fraction of the mass of the initial feedstock will be accounted for in the final products. This is mainly because a large portion of the initial feedstock is still retained by the distillation apparatus. This is usually in the form of ash, char, and non-volatile tar.

Further, if this process is compared with combustion, then a significantly lower amount of the organic matter is consumed during the entire process. Some experts also view this entire process as a modified version of the traditional practice of charcoal burning.

It is also vital to note the importance of this process in the industrial setting in many regions of the world – however, the most prominent place where this practice is performed in Scandinavia. Thankfully, modern destructive distillation processes have also been better optimized to maximize the number of valuable products extracted from the feedstock.

Application of Destructive Distillation

To help learners, we have created a list of various applications of destructive distillation. That list is mentioned below.

• This process can be used to obtain both turpentine and methanol from wood

• The destructive distillation of wood also tends to behind a residue of solid charcoal. This substance has a lot of commercial applications

• Processing wood through destructive distillation can also help one to obtain many other products that have a high commercial value. Some of those products are tar and terpenes

• Coal is processed through destructive distillation to obtain several commercially valuable products like ammonium hydroxide, coke, coal tar, and coal gas

• The waste obtained after polymerization can also be processed through destructive distillation. This process will give up the initial monomers, and those monomers can be reused in other proper procedures

Fun Facts about Destructive Distillation

Did you know that destructive distillation as a process has been used time and again to find various organic compounds? This statement is a fact as destructive distillation was used to discover isoprene.

Isoprene was discovered when natural rubber was processed through destructive distillation. Isoprene plays an important role in the formation of many synthetic rubbers. The most important synthetic rubber produced by using isoprene is neoprene.

Measurement is an essential factor for us to understand the external world. Through millions of life years, we have developed a measurement sense. Measurements need tools, which provide a quantity for scientists. The problem that occurs here is, the result of every measurement by any measuring instrument contains a sort of uncertainty, where this uncertainty is called an Error.

Accuracy and precision are more essential factors to consider while taking any measurements. These terms explain how close a measurement is to either a known or accepted value. Let us look at precision, accuracy, and their differences in detail.

Accuracy

Accuracy can be explained as the ability of an instrument to measure the accurate value. In other terms, the closeness of the measured value to a true or standard value. Accuracy is obtained by taking small readings, and these small readings reduce the calculation error. The accuracy of the system has been classified into three types as given below.

Point Accuracy

The accuracy of an instrument only at a particular point on its scale is called point accuracy. It is quite important to make a note; this accuracy does not give any info on the general accuracy of the instrument.

Accuracy as the Percentage of Scale Range

The uniform scale range defines the accuracy of a measurement. We can understand this better with the help of the below example:

Let us consider a clinical thermometer having a scale range of up to 5000 C. The thermometer has an accuracy of ±0.5; it means ±0.5 percent of increase or decrease in the instrument value, which is negligible. But if the same reading is more or less than 0.50 C, it is considered as a high-value error.

Accuracy as the Percentage of True Value

This type of accuracy of the instrument is defined by identifying the measured value with regards to their true value. The instruments’ accuracy can be neglected up to ±0.5 percent from the true value.

Precision

The closeness of either two or more measurements to each other is called the precision of a substance. If a given substance is weighed five times and gets 3.2 kg every time, the measurement is very precise but not necessarily accurate. Precision is always independent of accuracy. The example discussed below will explain to you how you can be precise but not accurate and vice versa. Precision can sometimes be separated as follows.

Repeatability

This is the variation, arising when the conditions are kept identical, and repeated measurements are taken in a short period of time.

ReproducibilityIt is the variation, arisen when using the same measurement process among different operators and instruments and over longer time periods.

Example of Accuracy and Precision

There are many real-time examples that can be discussed in the concept of Accuracy and Precision. Let us discuss one among them.

Let us go through a good analogy to understand the difference between precision and accuracy with an example. Imagine if a football player is shooting at the goal. If the player shoots the ball into the goal, he is said to be accurate. Also, a football player who keeps striking the same goalpost is precise but not accurate.

Thus, a football player can be accurate without being precise if he hits the ball all over the place but still, he scores. Also, a precise player will hit the ball to the same spot repeatedly, irrespective of whether or not he scores. A football player, who is accurate and precise, will not only aim at a single spot but also score a goal.

Considering the image, the image on the top left shows the target hit at a high precision point and accuracy. The image on the top right shows the target hit with high accuracy but low precision. The image listed on the bottom left shows the target hit at a high precision but with low accuracy. Finally, the image placed on the bottom right shows the target hit at low accuracy and at low precision.

List Out the Difference Between Accuracy and Precision in Tabular Form

The difference between accuracy and precision is tabulated below:

Accuracy and precision are tools used in measurement, this topic is briefly discussed in chapter 2 called units and measurement of the class 11 NCERT book. This chapter is prescribed by the Central Board of Secondary Education and it forms the basis of chemistry. Students preparing for NEET should get a clear foundation of the basic concepts that are taught in classes 11 and 12 as some extremely important questions can be asked in the NEET exam.

Measurement of physical quantities needs a comparison with a certain arbitrarily chosen, basic, internationally accepted method or reference standard called unit. Measurement is considered the basic foundation of all experimental science and technology. There is some form of uncertainty in the result of every measurement taken by any measuring instrument. This uncertainty can be termed as an error. Even calculated quantities which are based on measured values have some form of error. This is where the difference between accuracy and precision comes into existence.

 

Accuracy can be defined as the measure of how close the measured value is to the true value of the quantity. On the other hand, precision can be defined as the quality of being exact. It refers to how close two or more measurements are to each other, regardless of their accuracy, in some cases it is possible for precise measurements to not have accuracy. 

The study notes provided by on The difference between accuracy and precision are extremely important in the study of measurement, measurement forms the basis of chemistry and without it, experiments can’t be performed. Therefore, students who aspire to study further in this field should have their basics cleared. The difference between accuracy and precision is briefly discussed in the class 11th chapter, however, has created separate study notes that are related only to the study of the topic being discussed. The topi
cs are taken separately and explained because it helps to get a better understanding of the concept and also it covers all the minute details that may be missed by students otherwise. 

Both accuracy and precision help to determine how close measurement is to an actual value, however, both these concepts are not the same. Accuracy represents how close a measurement is to the actual value, on the other hand, precision represents if the measurements are reproducible or not even if they are far from the actual value. Both precise and accurate measurements are close to the true values and are also repeatable.

Accuracy and precision are terms in chemistry that have a critical meaning in science and they are constantly used incorrectly. Therefore it is extremely important to know their workings.

Important Concepts that Help to Understand the Difference between Accuracy and Precision

2.2 The international system of units

2.3 Measurement of length

2.4 Measurement of mass

2.5 Measurement of time

2.6 Accuracy, the precision of instruments and errors in measurement

2.7 Significant figures

2.8 Dimensions of physical quantities

2.9 Dimensional formulae and dimensional equations

2.10 Dimensional analysis and its applications