MyChemistryHomework

The photoelectric effect is the emission of electrons (called photoelectrons) from a material caused by electromagnetic radiation, viz ., ultraviolet light. The effect is not only studied in condensed matter physics, solid state, and quantum chemistry to draw inferences about the properties of atoms, molecules and solids but also has profound applications in electronic devices specialized for light detection and precisely timed electron emission. Einstein's formula explained the photoelectric effect, and had far-reaching consequences in the development of quantum mechanics. Question: Following results are observed when Sodium metal is irradiated with different wavelengths. Calculate the threshold wavelength. l (nm) 500 450 400 v × 10 –5 (cm s –1 ) 2.55 4.35 5.35 Click to enlarge the image Solution: Click to enlarge the image K max = Maximum kinetic energy, h = Planck constant, n = Frequ...

Multistep synthesis  is the artificial execution of multiple organic chemical reactions to obtain one or more products by physical and chemical manipulations. Retrosynthetic analysis is a problem-solving approach in the organic syntheses, achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents, and repeated until a simple or commercially available structure is reached, which can be used as a starting material to synthesize the target molecule. Question: How would you do the following transformation? Click/tap here to enlarge the image Solution infographic: Click/tap here to enlarge the image S N 2 = Nucleophilic substitution bimolecular, Nu = Nucleophile, LG = Leaving group A radical-substitution reaction is a substitution reaction involving free- radicals as a reactive intermediate. A strong Nu forms a new bond to an sp 3 -hybridized C- atom via a backside attack, while the LG detaches from ...

The  Kjeldahl method  (or  digestion ) is a quantitative analytical method for a sample's organic nitrogen plus ammonia/ammonium ( NH 3 /NH 4 + ). Other forms of inorganic nitrogen, for instance, nitrate, are not included in this measurement without modification. It has been an important method for indirectly quantifying protein content of a sample using an empirical relation between Kjeldahl nitrogen and protein; however, adulteration by substances,  viz ., Melamine fails this method for the quantification of proteins.  An advanced method, say, mass spectrometry may be used for a precise and accurate measurement of a protein. Question: A sample of 0.50 g of an organic compound was treated according to Kjeldahl method. The ammonia evolved was absorbed in 50 mL of 0.50 M H 2 SO 4 . The residual acid required 60 mL of 0.50 M solution of NaOH for neutralization. Find the percentage composition of nitrogen in the compound. Solution:   Click/tap to enlarge ...

pH  is a logarithmic scale used to specify the acidity or basicity of aqueous solutions. Acidic solutions (with higher concentrations of hydrogen ( H + ) cations) are measured to have lower  pH  values than basic or alkaline solutions. The neutral pH is 7.  A 𝑝𝐻 meter may be used for a precise and accurate measurement of the 𝑝𝐻 of a solution. The pH of weakly acidic chemical solutions can be estimated using the Henderson-Hasselbalch equation : The equation relates the pH of a weak acid to the acid dissociation constant, K a , and the ratio of the concentrations of the acid (unionized) and its conjugate base ( cB , ionized). Aspirin aka Acetylsalicylic acid ( ASA ) is an NSAID (non-steroidal anti-inflammatory drug) used to reduce pain, fever, and inflammation, and as an antithrombotic. Question: The pK a of Aspirin is 3.5 . The pH of the gastric juice in human stomach is ~ 2.5 & that in the small intestine is ~ 8 . Predict the ionization statuses of ...

Henry's law , a gas law, states that the amount of dissolved gas in a liquid is directly proportional at equilibrium to its partial pressure above the liquid. The depth-dependent dissolution of Oxygen and Nitrogen in the blood of underwater divers which changes during decompression, possibly causing decompression sickness if the decompression occurs too fast, is an application of Henry’s law. Once the bottle of a carbonated soft drink is opened, almost pure Carbon dioxide above the liquid in the container at a pressure higher than the atmospheric pressure escapes decreasing the pressure above the liquid, resulting in fast degassing as the dissolved gas is liberated from the solution. This is an everyday example of Henry’s law. Question: K H values for some gases at the same temperature are given: Gas K H /k bar Ar 40.3 CO 2 1.67 HCHO 1.83 x 10 -5 CH 4 0.413 where K H i...

Solubility equilibrium is a type of dynamic equilibrium that exists when a solid chemical compound is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation, or with chemical reaction with another component of the solution, viz. , acid, base or salt. Each solubility equilibrium is characterized by a temperature-dependent solubility product which functions like an equilibrium constant. Question: K sp (Ag 2 C 2 O 4 ) = 1.29 x 10 -11 mol 3 /L 3 at 25 0 C . A solution of K 2 C 2 O 4 containing 0.152 mol in 500 mL water is shaken at 25 0 C with excess Ag 2 CO 3 till the following equilibrium is reached: Ag 2 CO 3 + K 2 C 2 O 4 ⇌ Ag 2 C 2 O 4 + K 2 CO 3 At equilibrium, the solution contains 0.0358 mol of K 2 CO 3 . Assuming the degree of dissociation of K 2 C 2 O 4 & K 2 CO 3 to be equal, calculate the K sp (Ag 2 CO 3 ) . Solution: Click to enlarge the image Stirred up by the solubility product❓ Let Chemaf...

The  periodic table ( PT ) aka the periodic table of the elements is an arrangement of the chemical elements into rows (called periods) and columns (called groups) in order of their atomic numbers so that an approximate recurrence of their properties takes place (referred to as periodicity). To aid to memorize the elements, mnemonics have been popular. On the tables below, you will find a few engaging, valuable mnemonics (some modified by Chemaficionado ). Stay tuned for more (as this post will be updated)! Looking for a cool periodic table for learning/teaching or as a souvenir/gift at a reasonable price? Click HERE ! Click/tap to enlarge the images Propelled by the periodic table❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ NOTE: Post updated since published References: (1)      Wikipedia Contributors.  Periodic table . Wikipedia. https://en.wikipedia.org/wiki/Periodic_tabl...

Isomers  are different compounds that have the same molecular formula ( MF ). When the group of atoms that form the molecules of different isomers are bonded together in fundamentally different ways, constitutional/structural isomers are formed. Isomers that differ only in the spatial orientation/configuration of their component atoms are referred to as stereoisomers or spatial isomers. Question: How many isomers (including stereoisomers) do exist with the molecular formula C 6 H 11 Br  &   5 carbon parent ring? Solution infographic: Click/tap to enlarge the image Intimidating or inspiring isomers❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)       Structural isomer . Wikipedia. https://en.wikipedia.org/wiki/Structural_isomer. (2)      Stereoisomerism . Wikipedia. https://en.wikipedia.org/wiki/Stereoisomerism. (3)     Stereocenter . Wikipedia. https://en.wikipedia....

The term ‘spontaneous’ has historically been used to describe processes for which the change in Gibbs free energy in the standard state, ΔG Ѳ < 0 . The phrase ‘thermodynamically favored’ is preferred instead so that common misunderstandings equating ’spontaneous’ with ‘suddenly’ or ‘without cause’ can be avoided. Knowing the values of ΔH Ѳ & ΔS Ѳ (change in enthalpy and entropy in the standard state respectively) for a process at a given temperature T (absolute value) allows ΔG Ѳ to be calculated directly: ΔG Ѳ = ΔH Ѳ ─ TΔS Ѳ If ΔH Ѳ < 0 & ΔS Ѳ > 0, no calculation of ΔG Ѳ is necessary to determine that the process is thermodynamically favored ( ΔG Ѳ < 0 ). If ΔH Ѳ > 0 & ΔS Ѳ < 0, no calculation of ΔG Ѳ is required either to conclude that the process is thermodynamically unfavored ( ΔG Ѳ > 0 ). However, in some cases, it is necessary to consider both enthalpy and entropy to determine if a process will be thermodynamically favore...

pH is a logarithmic scale used to specify the acidity or basicity of aqueous solutions. Acidic solutions (with higher concentrations of hydrogen ( H + ) cations) are measured to have lower pH values than basic or alkaline solutions. The neutral pH is 7.  A 𝑝𝐻 meter may be used for a precise and accurate measurement of the 𝑝𝐻 of a solution. Question: What is the pH of a 10 ─8 M solution of HCl ? Solution: Click/tap to enlarge the image For a dilute solution, the [H + ] from water cannot be ignored. NOTE: Post updated since published Pivotal pH ❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  pH . Wikipedia. https://en.wikipedia.org/wiki/PH. (2)    Brown, C.; Ford, M.  Higher Level Chemistry ,  2nd  ed.; Pearson Education: Harlow, Essex, 2014.

The Kjeldahl method (or digestion ) is a quantitative analytical method for a sample's organic nitrogen plus ammonia/ammonium ( NH 3 /NH 4 + ). Other forms of inorganic nitrogen, for instance, nitrate, are not included in this measurement without modification. It has been an important method for indirectly quantifying protein content of a sample using an empirical relation between Kjeldahl nitrogen and protein; however, adulteration by substances, viz ., Melamine fails this method for the quantification of proteins.  An advanced method, say, mass spectrometry may be used for a precise and accurate measurement of a protein. Question: During the estimation of nitrogen present in an organic compound by Kjeldahl’s method, the ammonia evolved from 0.50 g of the compound in Kjeldahl’s estimation of nitrogen, neutralized 10 mL of 1 M H 2 SO 4 . Find out the % of nitrogen in the compound. Solution:   Click/tap to enlarge the image Absorbed in analysis in organic chemistry❓ ...

Chemical equilibrium is the state in which both the reactants and products in a chemical reaction are present in concentrations that have no more propensity to change with time, s.t. there is no visible alteration in the system properties. This state results when the forward reaction proceeds at the same rate as the reverse/backward reaction, and is known as dynamic equilibrium. Le Chatelier's principle ( aka Chatelier's principle, Braun–Le Chatelier principle , Le Chatelier–Braun principle or the equilibrium law) states if a system in a chemical equilibrium is subjected to a change in conditions, viz. , concentration, temperature or pressure, the equilibrium shifts in such a way that the effect of change is nullified. An electrophilic addition ( A E ) reaction is an addition reaction where a chemical compound containing a double/triple bond has a π bond broken, with the formation of two new σ bonds. The conversion of Ethylene to Ethyl alcohol by steam in presence o...

A separation process is a scientific method or technique that converts a mixture or a solution of chemical substances into two or more distinct product mixtures to obtain purity. Centrifugation is a mechanical process which uses the centrifugal force to separate particles from a solution as per their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate away from the centrifugal axis, while the less dense components drift toward the axis.  The clear liquid remaining above the centrifuged solid phase (called precipitate) is known as the supernate or supernatant. In chromatography the mixture of analytes (often called a sample) to be separated into its components, based on the differences of their polarities ( Mnemonic: like likes like), is dissolved in a fluid solvent (gas or liquid) called the mobile phase, which carries it through a system (a column, a capillary tube, a plate, or a sheet) on which a material known as the...

You are visiting Chemmemento , a webpage dedicated to offering chemistry related gifts and souvenirs for learning & teaching chemistry, and for a lot of fun. NOTE: I will keep adding products as and when listed and available (feel free to suggest anything you may like). TABLETOP PERIODIC TABLE Looking for a cool periodic table for learning/teaching or as a souvenir/gift? The periodic table ( PT ) aka the periodic table of the elements is an arrangement of the chemical elements into rows (called periods) and columns (called groups) in order of their atomic numbers so that an approximate recurrence of their properties takes place (referred to as periodicity). Click to enlarge the images Why Periodic Table from amiciCare/amicikart? ✅ Desktop/tabletop display with a robust wooden stand ✅ Premium acrylic panel for crystal-clear visibility and years of durability ✅ Hard laminated (waterproof and dustproof) fonts ✅ One year manufacturer warranty f...