Category: Chemistry
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Cell, Electrochemical Cell, Diagram, and Structure
Continue ReadingWhat is Cells?
The device which convert electrical energy into chemical energy or chemical energy into electrical energy is called cell.
Types of Cells
Cells are of two types;
1. Electrochemical Cell
The cell which convert chemical energy into electrical energy is called electrochemical cell.
Eg: Daniell cell
Daniell Electrochemical Cell Diagram
2. Electrolytic Cell
The cell which convert electrical energy into chemical energy is called electrolytic cell.
Ex- electrolysis of NaCl.
o In electrolytic cell redox reaction takes place.
o In electrolytic cell non-spontaneous (ΔG = positive) reaction type is proceed.
o For this cell, the value ΔG is positive.
The Electrolysis of Molten NaCl
If H Cl solution is take place in electrolytic cell then the following reaction takes place at cathode and at anode
H CL ⇔ H+ Cl–
At cathode: H+ + e- → ½ H2(g)
At anode: Cl– → ½ Cl2(g) + e-
Electrochemical Cell Citations
- An electrochemical cell for in operando studies of lithium/sodium batteries using a conventional x-ray powder diffractometer. Rev Sci Instrum . 2014 Oct;85(10):104103.
- Electrochemical cell-based chip for the detection of toxic effects of bisphenol-A on neuroblastoma cells. Biosens Bioelectron . 2011 Mar 15;26(7):3371-5.
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Electrolytes: Definition, Type, and Functions
Continue ReadingWhat are Electrolytes?
An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrolytes are essential minerals such as sodium, calcium, and potassium. Electrolytes play an important role in many key functions in the body.
Classification of Electrolytes
All electrolytes do not dissociate in same amount at all the given dilution. on the basis, electrolytes are divided mainly in two parts strong electrolytes and weak electrolytes.
i. Strong Electrolytes
Strong electrolytes are those substance which are completely ionized in their aqueous solution. Generally, this class contains strong acids , strong bases and salt of acid-base (strong), salts of strong acid-weak base and weak acid-strong base.
Eg: HCl , NaOH , NaCl , CH3COONa , NH4Cl etc.
These salts are completely dissociated at normal dilution.
ii. Weak Electrolytes
Weak electrolytes are those substances which are not completely dissociated in their aqueous solution and degree of dissociation increase with increase in solution.
Ionic part of weak electrolytes is called “degree of dissociation” or “degree of ionization”. It is denoted by α. This class contains weak acids, weak bases and salt of weak acid and weak base.
Eg: CH3COOH, H2CO3, H3BO3, NH4OH, Al(OH)3, CH3COONH4
Factors Affecting Electrolyte Conductance
The conductance depends upon the following factors;
a) Inter-ionic Attraction
If strong ionic attraction is present between the ions of solute then they do not dissociate easily, when they dissolve in solvent, due to this the value of conductivity become less. The energy released in ion-solvent reaction is called “salvation-energy” and if water is solvent then it is called ‘hydration energy’. So, if the amount of ion -ion attraction energy is more than ion-solvent attraction then electrolytes are taken in class of weak electrolytes.
b) Salvation of Ions
It depends on attractive forces present between ions and solvents, which are called “ ion-solvent interactions”. If this attractive force is very strong then ion becomes solvate in which the layers of solvent molecules are attached to ions and decrease its size. In this condition, the movement of ions towards electrode decreases, so the conductivity decreases.
c) Viscosity of Solvent
Viscosity of solvent depends on solvent-solvent interactions. Greater the attraction, greater is the viscosity of solvent, which decreases the conductivity .
d) Concentration of Solution
Concentration of solution is greater than concentration of electrolyte solution, lesser is the value of its conductivity. The amount of dissociation increases with the increase in dilution due to which, the conductivity of solution of electrolyte increases.
e) Effect of Temperature
The average kinetic energy of ions of electrolyte increases with increase in temperature, which increases the degree of dissociation of electrolyte. Hence, the amount of conductivity increases with increase in temperature.
Electrolytes Citations
- Investigation of the role of electrolytes and non-electrolytes on the cloud point and dye solubilization in antidepressant drug imipramine hydrochloride solutions. Colloids Surf B Biointerfaces . 2008 Aug 1;65(1):74-9.
- Electrolytes. Isha Shrimanker; Sandeep Bhattarai.
- Selection of an electrolyte to enhance the electrochemical decolourisation of indigo. Optimisation and scale-up. Chemosphere . 2005 Aug;60(8):1080-6.
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Conductors: Definition, Types, and Examples
Continue ReadingWhat are Conductors?
Conductors are those substance from which electric current can pass through are called conductors. Metals are good conductor of electricity.
eg: copper, silver, tin.
Types of Conductors
Conductors can be classified into two types:-
I. Metallic Conductors
Metallic conductors are those conductors in which electricity is flow due to the presence of free e- are called metallic conductors.
Factors Affecting Metallic Conductor
The nature and structure of the matter.
The no valence electrons per atom.
The density of matter.
Temperature: if we increase the temperature then the conductivity of metallic conductor decreases.
II. Electrolytic Conductors
Electrolytic conductors are those conductors which do not flow electricity in solid state but in molten state.
This type conductor, conduct electricity due to the presence of free ions, are called electrolyte conductor.
Metallic Conductors vs Electrolytic Conductors
Metallic Conductors Electrolytic Conductors In these conductors, conductivity is produced due to movement of e-. In these conductor conductivity is produced due to movement of free ions. In metallic conductors, no chemical change take place during the conduction of electricity. In these conductors chemical change take place. In metallic conductor flow of substance does not take place. In these conductors flow of substance take place. The conductivity of these conductor decrease with increase in temperature. The conductivity of electrolyte increase with increase in temperature. Electrochemistry
o The branch of chemistry which deals with the study of relationship between electrical and chemical energy and their interconversion is called electrochemistry.
o The basis of such processes is redox-reactions.
o The redox reactions take place in various chemical and biological reactions.
o Redox reactions are used in – burning of fuels, industrial processes, digestion of food by organism, photosynthesis for getting energy from sun, metal extraction, preparation of important chemicals, preparation of dry and moist batteries, fuel cell etc.
o The chemical reactions which are take place by electrochemical processes are energy rich and produce less pollution.
o Hence, the study of electrochemistry is very important to develop new eco-friendly techniques.
o Biological system like transfer of sense actions from brain to cells to opposite to opposite to this is also coordinated by electrochemistry.
Conductors Citations
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Drawbacks of Rutherford Model: Experiments and Conclusion
Continue ReadingWhat is Rutherford Model?
Greek philosopher Democritus was concerned to know that how a piece of matter can be cut into so many smaller pieces. He also believed that it could reach a point where it wouldn’t be able to be cut further into smaller pieces. These smallest pieces of matter are named as Atomos. It was an incident in about 450 B.C. However, this idea was not further discussed for more than 2000 years.
Then, British Chemist named John Dalton restored the idea of atom in 1800 and provided suggestion for atoms. After the discovery of atom, many atomic models were projected by scientists to define the atomic structure and discovery of subatomic particles such as electron, proton, and neutron.
Then, around 1911, a great physicist, Rutherford discovered the nucleus and proposed Rutherford’s Atomic Model. Rutherford upturned Thomson’s model in 1911 with his the most famous experiment which came to known as gold foil experiment in which he discussed that the atom has a tiny and heavy nucleus which is present in the centre of an atom.
Rutherford proposed an experiment to use the alpha particles which are emitted by a radioactive element. He projected that if Thomson model of atom was correct, then the beam of alpha particles would go straight through the gold foil. It was then noted that most of the beams went straight through the foil, but a few of them were deflected. Rutherford thus presented his physical model for subatomic structure of particles, as a description for the amazing experimental results.
He stated that the atom comprises of a central charge, this is at present termed as atomic nucleus, though Rutherford himself did not use the term nucleus in his research paper and this nucleus is surrounded by a cloud of circling electrons.
Features of Rutherford Model
The main points of Atomic Nuclear Model proposed by Rutherford is given below;
• Most of the atom has empty spaces within it as most of the alpha particles go straight through gold foil.
• Most of the mass that was present inside the atom was focused in a small area in the Centre, which is named as the nucleus.
• The electrons rotate around the nucleus in their fixed paths termed as orbits.
• The size of the nucleus is very small as compared to the size of an atom. According to calculation of Rutherford. He stated that the size of the nucleus is 105 times smaller than an atom.
• There is also a very strong electrostatic force of attraction present between the positive and negative charges of an atom which makes the atom stable.
Drawbacks of Rutherford Model
The model of the atom projected by Rutherford is still known as the classical model and was very much acknowledged at that time, though, later, it was proved that there were certain facets that this model was not able to explain.
Therefore, the certain drawbacks of Rutherford’s model of an atom is given below, and it was felt that some findings still need to be done in the field of atomic structure. Drawbacks of Rutherford model of atom:
1. According to Maxwell, electrons should release electromagnetic radiations because an accelerated charged particle has the tendency to release electromagnetic radiation. Rutherford also stated that the electrons revolve around the nucleus in their fixed paths named as orbits. But due to the presence kinetic motion of the electrons, the radiations further cause the shrinking of the electrons. Hence, electron should fall in nucleus of an atom in less than 10 seconds because electrons will keep on losing energy. Consequently, Rutherford’s model was unable to explain Maxwell’s theory.
2. If electrons would fall in nucleus this should make the atom very unstable, but it is shown that atoms are very stable particles.
3. Rutherford further explained the revolving of electrons around the nucleus of atoms in fixed paths or orbits, though, he was unable to explain how the electrons were placed inside the atom, thus results in making the model an incomplete model of the atom.
4. The Rutherford model of atom also helped to concentrate a great deal of charge on atom and mass of atom to a very small space, but was unable to feature any structure to the remaining electrons and atomic mass of atom. It did give reference to the atomic model of Hantaro Nagaoka, in which the electrons are commonly arranged in more than one rings, with the definite symbolic structure as of the stable rings of Saturn.
Rutherford Model Citations
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Molality: Definition, Calculation, Equation, and Formula
Continue ReadingWhat is Molality?
A final way to express the concentration of a given solution is by calculating its molality. The molality (m) of a solution is defined as the moles of solute divided by the kilograms of solvent in which solute is dissolved. For instance; A solution that comprises of 1.0 mol of NaCl dissolved into 1.0 kg of water is referred to as a “one-molal” solution of sodium chloride. The symbol for molality is represented in a lower-case m.
Molality Formula
Molality(m)=Number of moles of solute divided by Mass of solvent in kgs.
SI unit of molality = mol kg-1.
Molality (m) = moles of solute/kilograms of solvent = mol/kg
Molality Characteristic
1. Molality is denoted as a property of a solution.
2. It is an intensive property thus it will not differ from sample to sample for a given solution.
3. The number of moles of solute and the mass of solvent are generally not affected by pressure and temperature of system. Henceforth, molality unlike molarity, is not dependent on temperature and pressure.
4. Molality is referred to a non-volumetric concentration such as mole fraction and mass fraction.
Molality vs Molarity
Molarity (M) is commonly defined as the number of moles of solute per liter of solution.
Molarity = moles of solute/liters of solution
Molality (m) is commonly defined as the number of moles of solute per kilogram of solvent.
Molality = moles of solute/kilograms of solvent
Molarity is referred to measurement of the moles in the total volume of the solution, whereas molality is a measurement of the moles in connection to the mass of the solvent.
Molality varies from molarity only in its the denominator. While molarity is expressed in the liters of solution, molality is expressed in the kilograms of solvent.
Concentrations expressed in molality are commonly used to study properties of solutions which are related to vapor pressure and temperature changes. Molality is often used because its value generally does not change when temperature of system is change thus it is an independent quantity. On the other hand, the volume of a solution, is somewhat dependent upon temperature.
Molality and molarity are related in value for dilute aqueous solutions because of the fact that the density of those solutions is fairly close to 1.0 g/mL. This further means that 1.0 L of solution has approximately a mass of 1.0 kg. As the solution becomes more and more concentrated, its density will not even be close to 1.0 g/ml and the molality value will differ from molarity.
How to Calculate Molality? Example 1
What is the molality when 0.830 mol is dissolved in 1.60 L of solvent?
Molality = 0.830 mol / 1.60 kg
The answer is 0.518 m.
How to Calculate Molality? Example 2
Calculate the molality of a solution prepared from 30.22 grams of NaCl in 5.00 kg of water.
Given;
Solute = 30.22 gm of NaCl
Solvent = 5.00 Kg of water
Molar mass of solute that is NaCl = 58.44 gm/mol
number of moles of solute = 30.22 / 58.44
= 0.51 mol
Molality or m = number of moles of solute (n)/ weight of solvent in kg
Thus,
m = 0.51 / 5.00 = 0.102 moles/kg
Molality Citations
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Mass Number: Definition, Calculation, and Examples
Continue ReadingWhat is Mass Number?
The sum of number of protons and neutrons is termed as the mass number of an atom.
It is represented by using the letter ‘A.’
The symbol A is derived from a German word Atomgewicht means atomic weight. Protons and neutrons present in the nucleus of an atom together, are also called nucleons.
For instance, an atom of Oxygen has 8 protons and 8 neutrons in the nucleus of its atom. Thus, its mass number is 8+8= 16.
The number of protons is the same in all atoms of an element that means, it is unique for all elements, the number of neutrons can vary. Therefore, atoms of the same element can have different mass numbers.
These types of structure are named as isotopes.
The weight of an electron in an atom is nearly insignificant. Therefore, the atomic mass of an atom is approximately the same as its mass number.
Mass Number vs Atomic Number
Atomic Number Mass Number The atomic number is defined as the total number of protons present in the nucleus of an atom. The total number of protons and neutrons present in the nucleus of an atom gives us the mass number of an atom. It is commonly signified with the letter ‘Z.’ It is commonly represented using the letter ‘A.’ All the atoms of a specific element have the same number of protons, and henceforth they have the same atomic number. Protons and neutrons present in the nucleus of an atom together, are called nucleons. For example, all carbon atoms have an atomic number equal to 6, however all atoms of Oxygen have 8 protons in their nucleus thus atomic number of oxygens is 8. For instance, an atom of carbon has 6 protons and 6 neutrons. Thus, the mass number of carbon atom is 12. If we want to find the valency of a substance, then we see the electrons present in the outermost shell of the atom. But to further find the atomic number or the mass number, we need to know the total number of protons and neutrons present in the nucleus of an atom.
Uses of Mass Number
The mass number of an element is convenient to determine the isotopic mass which is generally calculated in the atomic mass units or amu.
An isotope of an element is referred to the elements having same atomic number but different mass number. Isotope thus differs in the number of neutrons.
Usually, atomic mass and mass numbers are two different terms and can vary only by an insignificant value. In most of the cases, they are different. Though, as the weight of an electron is insignificant so it can be said that the atomic mass of an atom is almost equal to mass number.
There are some substances which are named as Isobars. These are defined as the atoms of different elements having the same mass number, but different atomic numbers.
For example, Chlorine-37 and Argon-37 have the same mass number. But their atomic numbers are 17 and 18 respectively. Hence, they are called isobars.
The heavier atoms frequently practice alpha decay where they terminate 2 protons and 2 neutrons from their radioactive nucleus respectively, the mass number of elements is then altered consequently.
In conclusion, the mass number is altered by total 4 units.
Notation of Atom
To write the notation of any atom, we need to know the symbol of the element, the atomic number, and also the mass number.
The mass number of the atom goes in superscript of the symbol and the atomic number is written below as a subscript as shown below.
For example: potassium (K) has an atomic number 19 and mass number is 39 is written as;
19K39
Mass Number Calculation
If the number of protons and the mass number of an element is given, then we can also find the number of neutrons simply by subtracting its atomic number from its mass number as shown below;
No of neutron = mass number – atomic number
Or
N = A – Z
Mass Number Calculation Example
An atom has an atomic number of 11 and a mass number of 23.
1. Find the number of protons
2. Determine the number of neutrons in the nucleus of an atom.
3. The number of electrons present in nucleus of atom
Solution:
1. As we know the atomic number is always equal to the number of protons present in the nucleus of an atom therefore,
Number of Protons = 11.
2. As we now know that the number of neutrons is always found by deducting the atomic number from the mass number as shown below;
N = A -Z
Therefore,
Number of neutrons = 23 – 11 =12 3.
As the number of protons is always equal to number of electrons present in a neutral atom.
So, Number of electrons = number of protons which is = 11
Mass Number Citations
- Dependence upon mass number and neutron excess of the real part of the proton optical potential for mass numbers 44 <= A <= 72. Phys Rev C Nucl Phys . 1986 Aug;34(2):468-479.
- Dependence of actinide production on the mass number of the projectile: Xe +248Cm. Phys Rev C Nucl Phys . 1987 Jan;35(1):204-212.
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Thomson Atomic model: Definition, Experiments, and Limitation
Continue ReadingWhat is Thomson Atomic Model?
Thomson atomic model was proposed by William Thomson in the year 1900. This model described the inner structure of the atom theoretically.
This theory was strongly supported by Sir Joseph Thomson, who had discovered the electron initially.
Thomson presumed that an electron is two thousand times lighter as compared to proton and thought that an atom is made up of thousands of electrons.
In this atomic structure model, he stated that the atoms are fenced by a cloud having positive as well as negative charges.
Thomson atomic model of an atom is reffered to as a plum pudding. However, at that time the atomic nucleus was yet to be discovered. So, Thomson projected a model on the basis of known properties of atom that was available at that time.
The known properties are mentioned below:
• Normally, atoms are neutrally charged particles.
• Negatively charged particles named as electrons are present in an atom.
Thomson Pudding Atomic Model
Thomson projected that the shape of an atom is similar to that of a sphere having a radius of 10-10 m.
The positively charged particles are uniformly scattered with electrons arranged in such a way that the atom is thus electrostatically stable.
Thomson atomic model was also named as the plum pudding model or the watermelon model.
The electrons present in an atom resembled the seeds that are embedded in a watermelon whereas the watermelon’s red mass signified the positive charge distribution in atom.
Postulates of Thomson Atomic Model
An atom generally contains a positively charged sphere with electrons that are embedded in it.
An atom as an entire particle is electrically neutral because the negative and positive charges present are equal in magnitude.
Thomson stated that the model of an atom is similar to the structure of watermelon.
Where he considered:
• Watermelon seeds are represented as negatively charged particles.
• The red part of the watermelon is represented as positively charged.
• According to the postulates of Thomson’s atomic model, an atom is similar to a sphere of positive charge with electrons or negatively charged particles that are present inside the sphere.
• The positive and negative charges present in atom is equal in magnitude.So, an atom has no charge and is considered to be electrically neutral.
• Thomson’s atomic model is similar to a structure of a spherical plum pudding and a watermelon.
Limitations of Thomson Atomic Model
• Thomson was unable to explain the stability of an atom because his model of atom failed to describe how a positive charge particles holds the negatively charged electrons in an atom. Consequently, Thomson’s theory also failed to justify the position of the nucleus in an atom.
• Thomson’s model was unable to explain the scattering of alpha particles by thin metal foils that was explained by Rutherford.
• Even though Thomson’s model was not a precise model to account for the atomic structure, it still proved to be the base for the expansion of other atomic models. The study of the atom and its structure has flagged a way for several inventions that have played an important role in the development of humankind.
Thomson Atomic model Conclusion
Even though Thomson’s atomic model was not precise and had a few drawbacks, it still provided the base for several other atomic structure models that were later discovered. It is thus one of the foundation models that led to important and revolutionary discoveries.
Thomson Atomic model Citations
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Rutherford Atomic Model: Definition, Experiments, and Limitation
Continue ReadingWhat is Rutherford Atomic Model?
In 1904, J.J. Thomson proposed the plum pudding model of an atom. He stated that an atom is a positive charge sphere in which electrons (negative charge) are embedded.
He also stated that the atom is electrically neutral as positive charge and negative charge present inside the nucleus of an atom are equal. But this model could not describe the stability of the atom.
Ernest Rutherford, a British scientist conducted an experiment named ‘alpha gold-foil, and thus based on those observations, he proposed the atomic structure of elements and which came to known as the Rutherford Atomic Model.
Rutherford Atomic Model and His Alpha Scattering Experiment
Rutherford performed an experiment by bombarding a thin sheet of gold with alpha particles and then studied the path of these particles after they contacted with the gold foil.
Rutherford, in his experiment, bombarded high-energy streams of α-particles from a source of radioactive element of a thin sheet (100 nm thickness) of gold.
He placed a fluorescent zinc sulfide screen around the thin gold foil to study the variation in path of alpha particles.
Rutherford’s observations thus opposed Thomson’s atomic model. Reason for using gold foil in the experiment Gold is the most malleable metal of all metals.
Thus, It can easily be converted into very thin sheets. Reason for choosing alpha particles in the experiment Alpha particles are referred to as double-charged Helium atoms, and they have more momentum. Furthermore, they deviate least from their path.
Alpha Scattering Experiment's Observation
The observations made by Rutherford are mentioned below:
1. A greater fraction of the α-particles that were bombarded on the gold sheet passed through it without any deflection, and hence that means that most of the space in an atom is empty.
2. Some of the α-particles were deflected by the gold sheet at minor angles, and it was found that the positive charge in the atom is not distributed uniformly.
3. Very few of the α-particles were commonly deflected back, that is only a few α-particles one in every 12000 alpha particles bombarded were deflected at an angle 180o. So, the volume occupied by the positively charged particles in an atom inhabits a small volume as compared to the total volume of an atom.
Rutherford Atomic Model
Based on the above finding and conclusions, Rutherford further proposed the atomic structure of elements. Hence, the Rutherford’s atomic model proposed that:
1. The positively charged particles and most of the mass of an atom was concentrated in a very small volume inside an atom. This small positively charged body present in the atom is named as nucleus.
2. He also proposed that the negatively charged electrons surround the nucleus present in an atom. He demonstrated that the electrons that surrounds the nucleus revolve around it at a very high speed in circular paths. These circular paths are termed as orbits.
3. He stated that the electrons having negatively charged and the nucleus having the positively charged constituents are generally held together by a strong electrostatic force of attraction.
Rutherford Atomic Model and Modern Science
Rutherford’s finding helped the scientists to realise that the atom is not just made up of a single particle, but instead it consists of smaller subatomic particles.
Rutherford’s gold foil experiment also helped the scientists to find the exact atomic structure of an atom. Scientists eventually discovered that atoms have a positively charged nucleus present in the centre and radius of atom found to be 1.2 × 10−15 meters × [atomic mass number]1⁄3.
Subsequently, scientists found the number of electrons present in an atom by using X-rays. When an X-ray is passed through an atom, some part of it usually scatter, while the remaining rays pass through the atom.
As the X-ray commonly loses its intensity when electrons are scattered, then the number of electrons contained in an atom can be accurately estimated thus by finding the rate of decrease.
Limitation of Rutherford Atomic Model
The Rutherford atomic model was based on experimental observations, yet it failed to explain few things as mentioned below;
• Rutherford’s model was unable to explain the stability of an atom.
• Rutherford model did not discuss anything about the arrangement of an electron in orbit as well.
• According to Rutherford’s atomic model, electrons revolve around the nucleus in a circular path called orbits. But particles that are in motion around the nucleus on a circular path would experience acceleration, and this acceleration causes radiation of energy by charged particles. Ultimately, the electrons should lose energy and fall into the nucleus of an atom.
• Other drawback of the Rutherford model was a that he was unable to explain anything about the distribution of electrons in an atom.
• Definite lines in the hydrogen spectrum could also not be clarified by this model of atom.
Rutherford Atomic Model Citations
- Simulation of Rutherford backscattering spectrometry from arbitrary atom structures. Phys Rev E . 2016 Oct;94(4-1):043319.
- Comparison of Rutherford’s atomic model with the Standard Model of particle physics and other models.
- Rutherford’s Contribution. Science 25 Apr 1997: Vol. 276, Issue 5312, pp. 513-517
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Molarity: Definition, Calculation, Equation, and Formula
Continue ReadingWhat is Molarity?
The molarity (M) of a solution is defined as the number of moles of solute dissolved in one liter of solution.
To analyze the molarity of a solution, divide the moles of solute present in a solution by the volume of the solution stated in liters.
Molarity Equation
Equation used for finding the molarity of a solution is given below;
Molarity (M) = moles of solute / liters of solution = mol/L
When a molarity is reported, the unit used to represent is M and it is generally read as “molar”.
For instance, a solution labeled as 1.9 M NH 3 is read as “1.9 molar ammonia solution”.
One molar is referred to as the molarity of a solution where one gram of solute is dissolved in one liter of solution.
Molarity vs Molality
1) Molarity is referred to as concentration of a substance that is calculated as the number of moles of solute that is dissolved in one liter of solution while molality is defined as concentration of a substance that is calculated as the number of moles of solute found in one kg of solvent.
2) The molarity is represented by the symbol M, whereas molality is represented by a symbol m .
3) The formula for molarity is written as moles / liter whereas the formula for molality is written as moles / kg.
4) Molarity is generally affected by changes in temperature of the system while molality is not affected by changes in temperature of system.
5) Molarity is usually affected by changes in pressure whereas molality is not affected by changes in pressure of system.
6) Molarity may result in a vague and inexact concentration, whereas molality always results in an accurate and exact measurement of concentration of solution.
How to Calculate Molarity #1
A solution is prepared by dissolving 52.23 g of NH 4 Cl into enough water to make 600.0 mL of solution. Calculate its molarity.
Given; Mass – 52.23 g NH4Cl
Molar mass of NH4Cl = 53.50 g/mol
Volume of solution given = 600.0 mL = 0.600 L
Initially, the mass of the ammonium chloride given is converted to moles. Then the molarity is calculated of the solution by dividing by liters.
52.23 g NH4Cl x (1mol of NH 4 Cl / 53.50 g NH 4 Cl) = 0.9762 g
The given volume has to be converted to liters.
0.9762 / 0.600 = 1.621 M
The molarity is 1.621 M, this means that a litre of the solution would contain 1.621 mol NH4Cl.
How to Calculate Molarity #2
A chemist needs to make 4.00 L of a 0.350 M solution of potassium permanganate (KMnO4). What mass of KMnO4 does she need to make the above solution?
Given; molarity = 0.350 M
volume = 4.00 L
molar mass KMnO4 = 158.04 g/mol
Unknown ; mass KMnO4 = ? g
Moles of solute can be calculated by multiplying molarity of solution by liters. Then, moles has to be converted to grams.
Mol KMnO4 = 0.350 M KMnO4 x 4.00 liter = 1.4 mol KMnO4
1.4 mol KMnO4 x (158.04 g/mol/ 1 mol KMnO4) = 221.5 g KMnO4
When 221.5 g of potassium permanganate is dissolved into water to make 4.00 L of solution, and the molarity is 0.350 M.
Molarity Citations
- Relationship between Molarity and Color in the Crystal (‘Dramada’) Produced by Scytalidium cuboideum, in Two Solvents. Molecules . 2018 Oct 9;23(10):2581.
- The Relationship between Effective Molarity and Affinity Governs Rate Enhancements in Tethered Kinase-Substrate Reactions. Biochemistry . 2020 Jun 16;59(23):2182-2193.
- Effective molarity redux: Proximity as a guiding force in chemistry and biology. Isr J Chem . 2013 Aug;53(8):567-576.
- The effect of buffer molarity on the size, shape and sheath thickness of peripheral myelinated nerve fibres. J Anat . 1982 Aug;135(Pt 1):183-90.
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Mole Fraction: Definition, Calculation, and Formula
Continue ReadingWhat is Mole Fraction?
The mole fraction is defined as the ratio of number of moles of a given component present in a solution to total number of moles present in the given solution.
Mole fraction is one of the ways to find the concentration of the given solution.
A unit of concentration is termed as a mole fraction.
The mole fraction thus calculates the relative amount of solute and solvents present in each solution.
Mole fraction are unitless quantity, have no dimensions, and the sum of all fraction in a mixture is always equal to 1.
Mole fraction is represented by a symbol X.
Mole Fraction Formula
if a mixture is composed of two substance that are A and B, then the mole fraction is calculated as given below:
XA = mol A / (mol A + mol B) and XB =mol B / (mol A + mol B)
Mole Fraction of Solute = Moles of solute / (Mole of Solute + Mole of Solvent)
For instance, if a mixture contains 0.80 mol A and 1.0 mol B
mole fraction of A =0.8/1.5 =0.44
mole fraction of B = 1.0/1.8 = 0.55
The Mole fraction can also be converted into mole percentage by multiplying it by 100.
Properties of the Mole Fraction
The mole fraction is used broadly in the construction of phase diagrams. It has a lot of advantages which are mentioned below:
Mole fraction does not generally depend on temperature as compared to molar concentration, and it does not need knowledge of the densities of the involved phases.
It is very easy to make a mixture of known mole fractions by weighing the appropriate masses of the constituents used to form a mixture.
A mole fraction of a substance is referred to as the function of other component present in a tertiary mixture.
Disadvantages of Mole Fraction
The one disadvantage of mole fraction is that mole fraction is not suitable for liquid solutions.
How to Find Mole Fraction in Mixtures?
A mixture of gases is made by combining 6.8 moles of O2 and 4.6 moles of N2, find the mole fraction of nitrogen in this mixture?
Total number of moles = 6.8 +4.6 = 11.4
moles of N2 = 5.6 /11.9
= 0.403
So, mole fraction of N2 = 0.403
How to Find Mole Fraction in Solution?
Find the mole fraction of NaCl if 0.200 moles of sodium chloride are dissolved in water.
Primarily, convert volume of water into mass and then to moles
Density is defined as mass divided by its volume.
Density = Mass / Volume
M = D*V = 1g/ml * 100 ml =100 g
So, Moles of water = Mass / total molar mass
= 100 / 18 = 5.55 moles
Total number of moles = 5.55 + 0.200 = 5.75 moles
Thus, Mole fraction of NaCl = 0.200 / 5.75 = 0.0347
How to Find Mole Fraction Multi-Component Mixtures?
To find the mole fraction of Hexane in the mixture of 10.0 g of pentane(C5H12), 10.0 f of hexane (C6H14) and 10.0 g of benzene (C6H6).
Primarily, find the number of moles in 10.0 g of each component by the formula:
Number of moles = Given mass /Molar Mass
Number of moles of Pentane is equal to 0.138 moles
Moles of hexane is equal to 0.116 moles
Moles of benzene is equal to 0.128 moles
Hence, Total number of moles present = 0.138 + 0.116 + 0.128 = 0.382
Lastly, The mole fraction of hexane is = 0.116 / 0.382 = 0.303.
How to Find Mole Fraction from Molality?
If 1.82 m solution of table sugar (C6H12O6) is formed in water, find the mole fraction of the table sugar?
As the molality of a solution is given thus, we can convert it to the equivalent mole fraction, which is a mass ratio as given below;
Molality = moles solute / kg of solvent.
As per the definition of molality, we have 1.82 moles of sugar solution and 1.00 kg (1000 g) of water. We know the number of moles of sugar, thus we need to find the moles of water using its molecular weight as given below;
Moles of water = 1000 / 18 = 5.55 moles
Total number of moles is equal to 5.55 + 1.82 = 7.37 moles
Mole fraction of sugar = 1.82 / 7.37 = 0.246
How to Find Mole Fraction from Mass Percent?
Find the mole fraction of cinnamic acid with a mole percent of 60.00% urea in cinnamic acid. The molecular weight of urea is 60.16 g/mol and the molecular weight of cinnamic acid is 148.16 g/mol.
By assuming a total mass of 100.0 g which means that we have 60.0 g of urea and 40.0 g of cinnamic acid.
Thus, we can then find the moles present of Urea and Cinnamic acid by dividing each by its molecular weight as shown below;
Numbers of moles of Urea = 60.0 / 60.16 g/mol = 0.997 moles
Numbers of moles of cinnamic acid = 40.0/148.16g/mol = 0.269 moles
Total number of moles is equal to 1.266 moles
Mole fraction of cinnamic acid = 0.269/1.266 = 0.2124
Citations
- The reciprocal calculation procedure for setting occupational exposure limits for hydrocarbon solvents: An update. Journal of Occupational and Environmental Hygiene Volume 14, 2017 – Issue 8.
- Anomalous mole fraction effect, electrostatics, and binding in ionic channels. Biophys J . 1998 May;74(5):2327-34.
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