Category: Chemistry Notes PPT

The process of calculating the ratio of radioactive argon to radioactive potassium of rock to find out its time of origin is called potassium argon dating or K Ar dating. This method is used in many fields to determine the age of a sample. The process in rocks is based on the decay of radioactive potassium-40 to radioactive argon-40. Some parts also decay to calcium-40. The ratio of these components in a sample or rock is the measure of its age. The potassium argon method calculates the ages of several objects like meteorites, volcanic rocks, different types of minerals, etc. Some meteorites have dated back to 450 crore years, and some volcanic rocks are aged just 20,000 years.

Potassium Argon Dating Formula

The potassium argon dating process follows a particular formula to determine the age of a rock or a sample. The decay profile of radioactive potassium determines the age and origin of radioactive argon. Radioactive potassium also decays to radioactive calcium. The radioactive form of potassium and argon are potassium-40 and argon-40. The ratio of radioactive potassium, radioactive argon, and radioactive calcium is measured. This ratio is compared with the time of radioactivity. The entire process is completed through a particular formula of radioactivity. Thus, the age of a rock or a sample can be found out. 

How Does K Ar Dating Work?

One of the most abundant components in the earth’s crust is potassium, about 2.4% of the mass. Out of every 10,000 potassium atoms, one radioactive potassium is present there. 19 protons and 21 neutrons are present in the nucleus of the radioactive potassium. When a proton of the radioactive potassium collides with a beta particle, it becomes neutral and converts into a neutron. The number of neutrons and protons in the nucleus becomes 22 and 18. It is the nucleus structure of radioactive argon. Thus, radioactive potassium atoms convert into radioactive argon atoms. By observing the transformation of potassium into argon, the age of a sample can be determined. 

Importance of Radioactivity

The potassium argon dating process is mainly dependent on radioactivity. By observing the transformation of radioactive potassium into radioactive argon, the age of a sample is determined. Every radioactive atom has a particular life. Relating the ratio of the particles in the sample and their life, the age is calculated. Therefore, radioactivity is a vital matter to determine the age of a sample.

 

Limitations of Potassium Argon Method

As K Ar dating is a sensitive geological process, there are some limitations to the method. The limits are mentioned below. 

• The volcanic rocks leave no evidence of going through a heating- recrystallization process after initial formation. Expert geologists should process the entire method. If there is any fault in the sample collection process, it can create problems in determination.

• This process has a strong relationship with the time duration. As the transformation of radioactive atoms concerning time is observed in this process, the time duration of the sample and the ratio of the atoms should be measured correctly.

• When a sample becomes higher than one million years old, it is difficult to determine the actual age and origin. Therefore, the ratio of the radioactive potassium and radioactive argon atoms present in the sample should be measured sincerely. 

During a potassium argon dating process, the things mentioned above should be considered. Otherwise, the actual age and origin of a sample cannot be determined correctly. 

Did You Know?

Now, we are going to discuss some unknown facts about the potassium argon dating process. 

• K Ar dating is one of the most used processes in archaeology and geochronology. 

• The potassium argon dating process is dependent on the abundance of nonradioactive calcium, potassium, and argon in the earth. 

• This process is related to the atmosphere and its changes, and volcanism. 

• Many meteorites have been found, dating back to 4,500,000,000 years through the potassium argon method of dating objects. Some volcanic rocks have been found just 20,000 years old by examination by the same process.

Potassium oxide is made up of potassium and oxygen, joined together by ionic bonds. Potassium has an oxidation state of +1. So it can easily lose one electron. Potassium belongs to the group of alkali metals. It has a high tendency of combining with any other counter ion to complete its valency. So, it is highly reactive in free form. It readily reacts with oxygen to form Potassium Hydroxide. It has a pale yellow appearance and is widely used as a fertilizer. It is a strongly corrosive alkali when dissolved in water.  Here, we will study about Potassium oxide formula, structure, physical and chemical properties, and uses. Potassium oxide is a strongly corrosive alkali when dissolved in water.

Structure

The potassium Oxide formula contains two atoms of potassium and one atom of Oxygen. These atoms are joined by bonds. Potassium is in a +1 oxidation state. Oxygen has an oxidation state of -2. To balance the valency, Two atoms Of potassium combine with One atom of oxygen. So, the formula of potassium oxide is K2O

Physical Properties 

• It is solid and pale yellow in color.

• The molecular weight is 94.2 g/mol.

• The density of K2O is  2.35 gm/cm3.

• The melting Point of potassium oxide is 740℃.

• It is soluble in ether and ethanol.

Chemical Properties

​4K + O2 → 2K2O

K2O + H2O → KOH

K2O + HCl → KCl + H2O

2K + 2H2O → 2KOH + H2

Applications and Uses

• It is used as a fertilizer in the agriculture industry.

• It is not soluble in water and highly stable. This makes it useful in the ceramic industry. It is used in making lightweight bowls and structural compounds in aerospace.

• It is used for preparing soaps and glass. It is commonly known as pure potash.

• It is used to cure fungal infections such as zygomycetes

• It is also used in the treatment of animal-related diseases.

Conclusion

In this article, we learned about potassium oxide, the formula of potassium oxide, its chemical and physical properties, and its applications of it. It is an ion compound. It forms salt and water on being treated with an acid. It is also used as a fertilizer in the agricultural industry. It may be toxic when inhaled and ingested. It is useful in ceramic, glass, and optic industries.

Did You Know?

It must be noted that potassium oxide has the chemical formula K2O. While potassium Superoxide is an inorganic compound with the chemical formula KO2. It is a yellow-colored paramagnetic solid which decomposes in moist air. The oxidation state of oxygen in potassium superoxide is calculated as -1. These two compounds are totally different from each other in terms of chemical and physical properties.

Alkynes are unsaturated hydrocarbons with the general formula (C_nH_n-2). Hydrocarbons are compounds containing C and H atoms. Unsaturated hydrocarbon means there is a presence of double or triple bonds between the atoms. Alkynes have a triple bond between C and H atoms. They are hard to find in their pure form, They are sp hybridised and the bond angle between them is 180°. Synthesis of alkynes is useful because of its antibacterial, antifungal, and antiparasitic properties. Here, we will discuss the various methods of preparation of alkynes. 

Methods of Preparation of Alkynes

Dehydrohalogenation

The loss of a hydrogen and halogen atom from adjacent alkane carbon atoms leads to the formation of an alkene. Further, the loss of additional hydrogen and halogen atoms from the double‐bonded carbon atoms leads to the formation of alkyne. The halogen atoms may be located on the same carbon or the adjacent carbon atoms.

During the second dehydrohalogenation process, in the presence of a strongly basic medium and high temperature, Vicinal tetra haloalkanes can be dehalogenation with zinc metal to form alkynes. This process is called dehydrohalogenation because hydrogen is eliminated along with a halogen in order to obtain an alkyne.

Preparation of Alkynes from Vicinal Dihalides

Alkynes are prepared from vicinal dihalides by the process of dehydrohalogenation. We know the group 17 elements are known as halogens. So, dehydrohalogenation means the removal of Hydrogen and Halogen atoms. The vicinal term is used when two similar atoms are attached at adjacent positions. Dihalides simply mean two halogen atoms. laboratory preparation of alkynes is done by this method.

The first step involves the preparation of unsaturated halides. These are vinylic halides and are not reactive in nature. These halides are reacted with a strong base which results in the formation of alkynes. By using Metal acetylides small alkynes are converted into large ones.

Preparation of Alkynes from Calcium Carbide

At the industrial level, the synthesis of alkynes is done using calcium carbide. Calcium Carbide is prepared by heating quicklime (CaO) in the presence of coke (C). When calcium carbide is made to react with water, It results in the formation of calcium hydroxide and acetylene.

CaCO₃  → CaO + CO₂

CaO + 3C → CaC₂ + CO

CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂

This method is now replaced by another method called pyrolysis of methane, In which methane is heated at a temperature of 1500^oC in an airless chamber. It forms the product within a fraction of a second with the liberation of hydrogen. (Air must be excluded from the reaction or oxidation process will occur).

The reaction is endothermic at ordinary temperatures and is thermodynamically favoured at high temperatures.

Chlorine is a dense green-yellow gas with a strong odour. It has twice the density of air. The symbol of Chlorine is ‘Cl’ and it belongs to the halogen group. Chlorine was discovered in the 1770s and became a commercial agent ever since. It is easily detected in its natural state. Since it is toxic at low concentrations, it should be treated with caution. Due to its highly toxic nature, it has been used as a chemical weapon in wars.

The molecular formula of Chlorine gas Cl2.

Uses of Chlorine gas 

• During the First World War, the Germans used chlorine gas as a chemical weapon against the allied forces.

• Chlorine is most commonly used in wastewater treatment for disinfection.

• In the activated sludge phase, it is used to monitor odours and filamentous species.

• Despite this, it is most widely used in disinfection methods of preventing the spread of waterborne diseases.

Production and Use of Chlorine 

Here is a brief on Chlorine production and use (some main methods and applications).

Typically, rock salt deposits are mined; on rare occasions, water is pumped down, and brine containing around 25% sodium chloride is brought to the surface. Impurities separate first and can be absorbed as the brine evaporates. In warm climates, salt is made by the Sun evaporating shallow seawater, resulting in bay salt.

Chlorine is processed on a large scale using a variety of methods, including:

1. Electrolysis of Concentrated Sodium Chloride Solution in Water:

The cathode produces hydrogen, while the anode produces Chlorine. Since sodium hydroxide is formed in the electrolyte simultaneously, this process is known as chlorine-alkali electrolysis.

The following equations describe the chemical reactions that occur at each electrode as well as the overall cell process:

At Cathode (Iron Cathode) = 2H20 + 2e– → 2OH + H2

At Anode (Graphite Anode) = 2Cl– → Cl2 + 2e–

Cell Process = 2H20 + 2Cl– → 2OH– + H2 + Cl2

The symbol e- represents a single electron. Free Chlorine and hydroxide ions should not come into contact in the reaction tank; otherwise, Chlorine would be absorbed due to the reaction.

Cl2 + 2OH– → (ClO)– + Cl– + H2O

One can insert a porous wall between the electrodes to separate the chlorine gas. The hydroxide ion (diaphragm process), or the iron cathode, is substituted with a mercury cathode (mercury cathode process), which prevents the formation of hydroxide ions at the electrode. Instead, at the cathode, free sodium is discharged, and this metal readily dissolves in mercury, forming an amalgam, as shown below:

2Na+ + 2e– ⇔ 2Na (amalgam)

The amalgam can then react with the water outside the cell as:

2Na (amalgam) + 2H2O → 2Na+ + 2OH– + H2

This entire process is equivalent to the cell process.

2. Electrolysis of Fused Sodium Chloride:

It also contains metallic sodium, and at the anode, Chlorine is emitted once more.

3. Electrolysis of Fused Magnesium Chloride:

Chlorine is generated as a by-product of the Production of metallic magnesium in this process.

4. Hydrogen Chloride’s Oxidation:

As seen in the following equation, gaseous hydrogen chloride mixed with air or oxygen is passed over pumice in contact with cupric chloride as a catalyst:

4HCl + O2 (in presence of catalyst) ⇔ 2H2O + 2Cl2

With increasing temperature, the equilibrium constant for this reaction decreases, implying that the reaction continues more slowly at higher temperatures. However, to achieve a fair conversion rate, a temperature of 400 °C (750 °F) is needed in practice.

5. The Reaction Between Solid Chloride and Manganese Dioxide:

The method of producing Chlorine from a mixture of almost any solid chloride and manganese dioxide (MnO2) when heated with concentrated sulfuric acid (H2SO4) is historically interesting. The following is how the reaction happens:

2NaCl + 3H2SO4 + MnO2 ⇔ MnSO2 + 2NaHSO4 + 2H2O + Cl2

What is Protactinium?

Protactinium (which was formerly protoactinium) is defined as a chemical element having the symbol Pa and the atomic number 91. It is a metal of silvery-grey colour, dense actinide that readily reacts with water vapour, oxygen, and also inorganic acids. It produces different chemical compounds in which protactinium is usually present in the oxidation state of +5, but it can also assume with +4 and even +3 or +2. Protactinium concentrations present in the crust of Earth are typically a few parts per trillion but can reach up to some parts per million in a few uraninite ore deposits.

Properties of Protactinium

Let us look at the important protactinium properties given as follows:

Physical Properties of Protactinium

Chemical Properties of Protactinium

The chemical properties of Protactinium can be listed as follows:

• The group of the Protactinium is Actinides

• Its period is 7

• Its block is f

• It has an atomic number of 91

• The state of protactinium at 20 ⁰C is Solid

• Its electronic configuration is [Rn] 5f26d17s2

• It has the ChemSpider ID as 22387

• Protactinium melting point is 1572°C, 2862°F, 1845 K

• Its boiling point is 4000°C, 7232°F, 4273 K

• Its Density (g cm⁻³) is 15.4

• The Key isotopes are 231Pa

• Its Relative atomic mass is 231.036

• Its CAS number is given as 7440-13-3

Preparation of Protactinium

Protactinium was separated for scientific experiments from uranium ores before the nuclear reactor’s advent. Nowadays, it is produced mostly as an intermediate product of nuclear fission in thorium high-temperature reactors:

[_{90}^{232}textrm{Th}] + [_{0}^{1}textrm{n}] [rightarrow]  [_{90}^{233}textrm{Th}]  [xrightarrow[22.3 min]{beta^{-}}] [_{91}^{233}textrm{Pa}] [xrightarrow[26.967 d]{beta^{-}}] [_{92}^{233}textrm{U}] 

The 231 isotopes are prepared by radiating thorium-230 with slow neutrons, converting to the beta-decaying thorium-231, or by irradiating thorium-232 with fast neutrons, generating two neutrons and thorium-231.

Occurrence of Protactinium

Protactinium is described as one of the most expensive and rarest naturally occurring elements. It can be found in the form of two isotopes – 234Pa and 231Pa, with the isotope 234Pa occurring in two different states of energy. Approximately all the natural protactinium is protactinium-231. It is an alpha emitter, and it can be formed by the uranium-235 decay, whereas the beta radiating protactinium-234 can be produced as a result of uranium-238 decay. Nearly all uranium-238 (nearly 99.8%) decays first to the shorter-lived 234mPa isomer.

Protactinium takes place in uraninite (pitchblende) at concentrations of nearly 0.3-3 parts 231Pa per million parts (ppm) of ore. At the same time, the usual content is closer to 0.3 ppm (for example, in Jáchymov, Czech Republic, a few ores from the Democratic Republic of the Congo have about three ppm. Protactinium is defined as homogeneously dispersed in most of the natural materials and in water, but at much lower concentrations in the order of one part per trillion, which corresponds to the radioactivity of 0.1 picocuries (pCi)/grams. There is up to 500 times more protactinium in sandy soil particles than in water, including in identical soil samples. Higher ratios of 2,000 and above are measured in clays and loam soils, such as bentonite.

Properties of Protactinium 

• The protactinium metal is a radioactive, silvery, and shiny metal that slowly degrades in the presence of air to produce oxides. This metal contains up to 5 isotopes with their mass numbers ranging between 212 to 238, and protactinium 231 can be considered to be the most stable isotope containing a half-life of about 32,760 years. This isotope is formed by the decay of the element uranium 235 by emitting gamma radiation.

• Protactinium is well known to be one of the rarest and most expensive naturally occurring elements on Earth. This metal also occurs about three parts per trillion and at times in parts per million in uranium ores. And, the uranium processing obtains it as a by-product. This element was discovered by two persons named O.H. Gohring and K.Kajans in 1913.

• Protactinium is in a dense form as metal, and it is a silvery-grey having a bright metallic look. At temperatures below 1.4K, it is superconductive in nature. It reacts with inorganic acids, water vapour, and oxygen, producing its compounds. Also, a few of its compounds are coloured. In the state of the solid compound, protactinium is said to be the most stable in its oxidation state of +5. At the same time, it exists in the oxidation state of +4, even +3, and +2. The oxidation state of +5 rapidly gets hydrolyzed by combining with the hydroxide ions and forming both soluble and insoluble hydroxy-oxide solids in the solution state.

Protactinium Facts

Let us look at some of the protactinium facts.

• The leading causes of exposure to this element in the human body are the intake of water and food and the inhalation of contaminated dust that consists of protactinium.

• When ingested into the body, protactini
  um is considered to be toxic. It also affects the lungs and the gastrointestinal tract.

Quartz is a widely distributed mineral of several varieties that primarily consists of silicon dioxide (SiO2) or silica. Minor impurities such as sodium, lithium, titanium, and potassium can be present. This mineral has attracted more attention from the earliest times; ancient Greeks know water-clear crystals as krystallos. Thus, the name crystal, or more generally rock crystal, is applied to this variety. The term quartz is an old German word of uncertain origin, which was first used by Georgius Agricola in 1530.

Importance of Quartz

Quartz contains greater economic importance. Several varieties are given as gemstones, including citrine, amethyst, rose quartz, and smoky quartz. Sandstone, which is composed majorly of quartz, is an essential building stone. Huge amounts of quartz sand (which is also called silica sand) are used in the manufacture of ceramics and glass for foundry molds in metal casting. Crushed quartz can be used as an abrasive in silica, sandpaper, and it is employed in sandblasting. Still, sandstone is used as a whole to make millstones, grindstones, and whetstones. Silica glass (which is also known as fused quartz) can be used in optics to transmit ultraviolet light. Tubing and other different vessels of fused quartz have more important laboratory applications, and quartz fibres can be employed in extremely sensitive weighing devices.

Quartz is given as the second most abundant mineral in the crust of the Earth after feldspar. It takes place in approximately all metamorphic, sedimentary and acid igneous rocks. It is an important mineral in such silica-rich felsic rocks as granodiorites, rhyolites, and granites. It is highly resistant to weathering and also tends to concentrate in sandstones, including other detrital rocks. On the other side, secondary quartz serves as a cement in the sedimentary rocks of this type by forming the overgrowths on detrital grains. Microcrystalline varieties of silica such as flint, chert, jasper, and agate consist of a fine quartz network. Typically, metamorphism of the quartz-bearing sedimentary and igneous rocks increases the quartz amount and its grain size.

Etymology

The term “quartz” has derived from the German term named “Quarz,” which had a similar form in the first half of the 14th century in East Central German and the Middle of High German and which came from the Polish dialect word “kwardy,” that corresponds to the Czech word tvrdý (“hard”).

Existence of Quartz

The element of quartz exists in two forms. Let us discuss the types of quartz or quartz types and meanings.

(1) alpha-, or the low, quartz – It is stable up to the temperature of 573 °C (1,063 °F),

(2) beta-, or the high quartz – It is stable above the temperature of 573 °C.

These two are closely related, only with small movements of their constituent atoms at the alpha-beta transition. The beta-quartz structure is hexagonal, either with left- or right-handed symmetry groups, which are equally populated in crystals. The alpha-quartz structure is trigonal, again either with a right-handed or left-handed symmetry group. Whereas, at the transition temperature, the beta-quartz’s tetrahedral framework twists, which is resulting in the symmetry of alpha-quartz; the atoms move from special space group positions to the more general positions.

At temperatures more than 867 °C (1,593 °F), the beta-quartz changes into tridymite, but the transformation is slower because the bond breaking occurs to form a more open structure. At very high pressure, the alpha-quartz transforms into the coesite and still, at higher pressures, as stishovite. Such types of phases have been observed in the impact craters.

Quartz Production

Quartz is also defined as piezoelectric, which is a crystal that develops both positive and negative charges on an alternate prism edge when it is subjected to either tension or pressure. These charges are proportional to the same change in pressure. Due to its piezoelectric property, a quartz plate is used as a pressure gauge, as in the apparatus of depth-sounding.

Just as tension and compression form opposite charges, the converse effect is, alternating opposite charges will cause the alternating contraction and expansion. A section that cuts from a quartz crystal with the definite dimensions and orientation contains a natural frequency of this contraction and expansion (that is, vibration) that is very high, which is measured in millions of vibrations per one second. The quartz, which is the properly cut plates, can be used for the frequency control in televisions, radios, including other electronic communications equipment, and also for crystal-controlled watches and clocks.

Japan, Russia, and China are given as the world’s major and primary quartz producers. Brazil, Belgium, France, Bulgaria, South Africa, the United Kingdom, and Germany also mine significant amounts of this mineral.

Synthetic and Artificial Treatment

Not all quartz varieties are naturally occurring. A few clear quartz crystals are also treated using gamma or heat irradiation to induce the colour where it would not otherwise occur naturally. Susceptibility to such treatments will depend on the location where the quartz was mined.

Prasiolite, which is an olive-coloured material, can be produced by the heat treatment; natural prasiolite has also been observed in the Lower Silesia in Poland. Although the citrine takes place naturally, the majority is given as the result of smoky or heat-treating amethyst quartz. To deepen its colour, carnelian is widely heat-treated.