Crystallization and Recrystallization

In crystallization, crystalline precipitates are formed. Precipitates can be formed in two ways; by nucleation and by particle growth. In nucleation, a few ions, atoms or molecules come together to form a stable solid. These small solids are known as nuclei. Often, these nuclei form on the surface of suspended solid contaminants. When this nucleus is further exposed to the ions, atoms or molecules, additional nucleation or further growth of the particle can happen. If nucleation continues to take place, a precipitate containing a large number of small particles results. In contrast if growth predominates, a smaller number of larger particles are produced. Rate of nucleation increases with increasing relative supersaturation. Normally, precipitation reactions are slow. So when a precipitating reagent is added slowly to a solution of an analyte, a supersaturation can occur. (Supersaturated solution is an unstable solution which contains a higher solute concentration than a saturated solution.)

Crystallization

Crystallization is the process of precipitating crystals from a solution due to changes in solubility conditions of the solute in the solution. This is a separation technique which is similar to regular precipitation.

Precipitates are solids consisting of particles in a solution. Sometimes solids are a result of a chemical reaction in a solution. These solid particles will eventually settle down due to their density, and it is known as a precipitate. In centrifugation, the resulting precipitate is also known as the pellet. The solution above the precipitate is known as the supernatant. The particle size in the precipitate changes from occasion to occasion. Crystals can be easily filtered, and they are larger in size.

The difference in crystallization method from the normal precipitation is that, the resulted solid is a crystal. Crystalline precipitates are more easily filtered and purified. The crystal particle size can be improved by using dilute solutions and adding the precipitating reagent slowly while mixing. The quality of the crystal and the improvement in filterability can be obtained from the dissolution and recrystallization of the solid. Crystallization can be seen in nature too. It is most often carried out artificially for various types of crystal production and purification.

Recrystallization

Recrystallization is a technique to purify the crystals obtained from crystallization method. Though crystallization separates the compound in almost pure form, when the crystals form some of the impurities may trap in it. By recrystallization method, these impurities can be removed to a greater extend.

Normally the crystals are dissolved in very little amount of hot solvent and allowed to dissolve completely. When this is allowed to cool slowly (may be after filtering), the crystals may appear again. These crystals are free of the impurity. The crystals can be separated by filtering the solution again. Recrystallization process can be carried out in several ways, and several times to increase the purity of the desired crystal.

What is the difference between Crystallization and Recrystallization? • Recrystallization is done to crystals formed from a crystallization method. • Crystallization is a separation technique. Recrystallization is used to purify the compound received from crystallization.

Alloy and Composite

Alloy and composite materials are mixtures of two or more components. Both have different properties than the starting materials.

What is an Alloy?

Alloy is a mixture of two or more elements where at least one of them is metal. The resulting alloy can be a solution or a solid. If only two components are mixed to produce an alloy, it is known as a binary alloy. If there are three components, it is known as ternary alloy. The amount of element in the alloy is normally measured and given by mass (as percentages). Alloys can be also classified as homogeneous if they have a single phase. If have several phases, those alloys are classified as heterogeneous. If there isn’t a distinct phase boundary, then they are known as intermetallic.

Alloys are produced from elements, to have improved qualities than the reactant elements. They have different qualities than the reactant components. Normally alloys have metallic properties, but they differ from pure metal elements. For example, alloys don’t have a single melting point. Rather, they have a range of melting points.

Steel is an example for alloy. It is made out of iron and carbon. Steel is stronger than iron. The carbon percentage can vary depending on the grade, and mostly it is between 0.2% and 2.1% by weight. Though carbon is the main alloying material for iron, some other elements like Tungsten, chromium, manganese can also be used for the purpose. Different types and amounts of alloying element used determine the hardness, ductility and tensile strength of steel. Alloying element is responsible for maintaining the crystal lattice structure of steel by preventing dislocation of iron atoms. Thus, it acts as the hardening agent in steel. The density of steel varies between 7,750 and 8,050 kg/m3 and, this is affected by the alloying constituents too.

Brass is another alloy which is made out of copper and zinc, but more durable than copper and attractive than zinc. When producing jewelry from gold, silver, and platinum, they are mixed with other elements, to make them more ductile and flexible.

What is a Composite?

Composite is a material made out of two or more constituent materials which are chemically and physically different. Constituent materials are the individual materials which makes the composite. There are two categories of them as matrix and reinforcement. Usually matrix material supports the reinforcement material. The constituent materials stay separately within the finished structure because they are chemically and physically different, to mix with each other.

Composites can be synthetic or naturally occurring materials. Wood is a natural composite. It is made up of cellulose fibers and a matrix of lignin. When preparing composites, normally both matrix and reinforced materials are combined and compacted. After this, the shape of the composite is set, and it won’t change unless it is affected by certain conditions.

Alloy vs Composite

• Alloy is a homogenous or a heterogeneous mixture whereas composites are heterogeneous.

• There is at least one metal in alloy, but it is not necessary to have metals in composites.

Gold and Gold Plated

Gold is a metal, which has been known to man since ancient times. It has become a precious metal due to its brightness, softness, corrosion resistance in most chemical natures, ductility and scarcity. Many people confuse the gold with gold plated items. Plated gold is a coating of gold which is fused on another metal. The price of gold and the need to imitate gold make the need for gold plated items. Jewelry is the most common items made of gold.

Gold

Gold is a soft, malleable and ductile metal. Due to the softness of gold it is alloyed with other metals like copper. The percentage of gold in a gold alloy is indicated by karat. 24K (24 karat) gold is the pure gold, and it is not alloyed. 22K gold has 22 parts of gold and 2 parts of another alloying element by weight. The contents of gold and the alloying element are expressed out of 24. All the alloys are usually called gold. The gold content of the item should be stamped on it. 24K gold is not suitable for practical day to day usage on account of its softness. The resistance to corrosion is excellent in pure gold. With the decreasing content of gold in gold alloys, the resistant to corrosion decreases. Therefore, the durability of gold with a high percentage of gold is higher. It is a tenuous metal which can be thinned out to a very fine leaf. Because gold is one of the metals, which has a high electrical conductivity, it is used for circuits in the electronic industry. Because of the expensiveness of gold, gold plated items have become an option for gold items.

Gold Plated

Gold plated means that a coating of gold is applied on the surface of another metal. At least 10K gold is required to apply the coating. The widely used technique of gold plating is electro plating. A Potassium – Gold cyanide solution is taken as the bath for plating. Other than that, electro less plating and immersion plating techniques are also used. The plating of gold wears off quickly depending on the usage. Gold plated items are also prone to corrosion due to the base metals beneath the coating. Due to the metals under the coating, gold plated jewelry may cause allergies to some people. The durability of gold plated items depends on the thickness of the layer of gold, the gold content of the gold layer and the quality of the metal used beneath the gold layer. Gold can be identified from gold plated items by carrying out appropriate tests.

Gold and gold plated items are difficult to differentiate because of their same appearance. But they can be identified with tests. So the tests available can be used to identify whether the items are fake or not in the case of jewelry. Gold plated items are widely used as a substitute for gold.

What is the difference between Gold and Gold Plated? • Pure gold or gold alloys are called gold. Gold plated means that a coating of gold is applied on the surface of another metal. • The durability of gold is higher than that of gold plated metals. • Gold is more expensive than gold plated metals.

Gold and Platinum

Gold and platinum are considered to be metals used for jewellery making, and they are expensive. Both are less reactive elements and are ideal for jewelleries.

Gold

Gold is a transition metal with the chemical symbol Au. Au is from the Latin word ‘aurum’ which means ‘shining dawn’. Gold is in the group 11 of the periodic table, and its atomic number is 79. Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s¹. Gold is a shiny metal with a metallic yellow colour. Further, it is a malleable and ductile metal.

Gold is widely used to make jewellery and statues. It is considered as a very precious metal. One of the important properties of gold is its less reactivity. Gold doesn’t react with moisture and oxygen in the air. Therefore, no matter how long it is exposed to air, gold oxide layer won’t be forming; therefore, its colour doesn’t fade or change.

Since gold does not react with other chemicals easily, it occurs as a free element in the nature. Gold particles are found embedded in rocks. Johannesburg, South Africa has one of the largest gold deposits. Other than that, Russia, United States, Australia, and Peru are major gold producers in the world.

Gold creates alloy with other metals easily. Gold has +1 and +3 oxidation states commonly. Gold ions in a solution can be easily reduced to the 0 oxidation state, so gold can be precipitated out. ¹⁹⁷Au is the only stable isotope of gold. Among the applications of gold, it has been in use for centuries. It was considered precious from the history and was being used as a currency. When making jewellery, pure gold (24k) is not used. Usually it is alloyed with some other metals and 22k, 18k, 9k etc. gold are used for jewellery making process.

Platinum

Platinum or Pt is a transition metal with the atomic number 78. In the periodic table, it is in the group with Nickel and Palladium. So has the electric configuration similar to Ni with outer orbitals having s² d⁸arrangement. Platinum, most commonly, forms +2 and +4 oxidation states. It can also form +1 and +3 oxidation states.

Platinum is silvery white in colour and has a higher density. It has six isotopes. Among these, most abundant one is ¹⁹⁵Pt.  Atomic mass of Platinum is about 195 gmol^-1. Platinum doesn’t oxidize or react with HCl or nitric acid. It is highly resistant to corrosion. Pt also can withstand a very high temperature without melting. (Its melting point is 1768.3 °C) Also, it is paramagnetic.

Platinum is a very rare metal, which is used in jewellery making. Platinum jewellery is also known as white gold jewellery and is very expensive. Further it can be used as the electrode in electrochemical sensors, and cells.  Platinum is a good catalyst to use in chemical reactions. South Africa is the number one producer of platinum metal.

Gold vs Platinum

• Platinum has the atomic number of 78, and atomic number of gold is 79.

•  Platinum, most commonly, forms +2 and +4 oxidation states, but gold commonly forms +1 and +3 oxidation states.

•  Gold has a metallic yellow colour whereas platinum has a shiny white colour.

•  Platinum is used to make white gold jewelleries which are more expensive than gold jewelleries.

•  When making jewellery, platinum can be used in more pure form compared to gold.

Gold and White Gold

Gold and white gold are expensive materials used for jewellery making. People choose gold or white gold depending on their tastes. Except few differences, both are good starting materials for jewelleries.

Gold

Gold is a transition metal with the chemical symbol Au. Au is from the Latin word ‘aurum’ which means ‘shining dawn’. Gold is in the group 11 of the periodic table, and its atomic number is 79. Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s¹. Gold is a shiny metal with a metallic yellow colour. Further, it is a malleable and ductile metal.

Gold is widely used to make jewellery and statues. It is considered as a very precious metal. One of the important properties of gold in its less reactivity. Gold doesn’t react with moisture and oxygen in the air. Therefore, no matter how long it is exposed to air, gold oxide layer won’t be forming and, therefore, its colour doesn’t fade or change. Since gold doesn’t react with other chemicals easily, it occurs as the free element in the nature. Gold particles are found embedded in rocks. Johannesburg, South Africa has one of the largest gold deposits. Other than that Russia, United States, Australia and Peru are major gold producers in the world.

Gold creates alloy with other metals easily. Gold has +1 and +3 oxidation states commonly. Gold ions in a solution can be easily reduced to the 0 oxidation state, so gold can be precipitated out. ¹⁹⁷Au is the only stable isotope of gold. Among the applications of gold, it has been in use for centuries. It was considered precious from the history and was being used as a currency. When making jewellery, pure gold (24k) is not used. Usually it is alloyed with some other metals and 22k, 18k, 9k etc. gold are used for jewellery making process.

White Gold

White gold is an alloy made by mixing gold with some other white metal. This alloying metal could be silver, palladium or manganese. Depending on the alloying metal and the proportions used, properties of white gold can vary. For instance, when palladium is mixed with gold, the result white gold will be soft and pliable. When nickel and gold is mixed, it would be hard and strong.

White gold’s purity is given in karats. For example, white gold can be 18kt, 14kt, 9kt, etc. The colour of white gold we see is not the actual colour of white gold. The whitish colour comes from rhodium plating and normally the colour of white gold is a light grey colour. White gold is mainly used for jewellery making. The alloys used for this are gold,palladium,silver and gold, nickel,copper, and zinc. However, some people are allergic to nickel so it is no longer used widely in white gold.

Gold vs White Gold

• White gold is an alloy and gold is a pure chemical element.

• Gold has a yellow colour whereas white gold has a whitish colour.

• In white gold, other elements are mixed, so it can react with moisture and air, but gold is comparatively less reactive.

Gas and Petrol

Gas (LPG/Liquefied petroleum gas/ auto gas) and petrol (gasoline) consist of hydrocarbons, and they are used as fuels in internal combustion engines of vehicles. In recent years, there has been an increased move towards gas as an alternative fuel in vehicles. Both LP gas and petrol are obtained from petroleum, so both are fossil fuels.

Gas

Gas (LPG) is used as a fuel in vehicles as well as in domestic appliances. Gas, which is used in vehicles, is mainly a mixture of propane and butane. It can be liquefied under pressure, hence stored as a compressed liquid, and it is burnt as a dry vapour in the engine. Gas is non- corrosive, free from lead and has a high octane rating. In order to use gas in vehicles, they have to be converted to either dual fuel or dedicated gas operation. In dual fuels, vehicle can operate by petrol or gas alternatively. A separate gas tank should be installed in the vehicle along with the petrol tank. LPG and petrol have slightly different burning characteristics but, the engines can be set up to use both fuels alternatively without a problem. Dedicated gas vehicles don’t have a petrol fuel system, therefore operate using gas only. This conversion is costly, but in the long run, it saves money, because the gas price is much lower than petrol. All the vehicles cannot be converted to gas, and for the installation of the gas tank, a considerable space is needed which are some of the drawbacks.

Petrol

Petrol is a liquid form of hydrocarbon fuel. Hydrocarbons are like isooctane or benzene, and toluene is added to petrol, to increase its octane rating. It is volatile and has a higher density than LPG.

Difference between Gas and Petrol

When operating vehicles with gas, fuel consumption is higher than that of petrol. Also, the energy output is lower in gas compared to petrol. However, gas is lot cheaper than petrol, and that offsets its high consumption. Petrol combustion is partial, resulting lot of carbon dioxide and other particulate matter in the emissions. Comparatively gas is cleaner, and emissions are less than petrol. Therefore, gas is more environmental friendly and economical to use in vehicles than petrol. However, lot of people are still into using petrol for their vehicles; gas is less available than petrol in filling stations. Although, the gas is expected to be more efficient than petrol, this may not be observed unless the engine design is optimized for LPG fuel.

LNG & LPG

LNG and LPG are energy sources. They are flammable, and combustion releases energy. Both are mixtures which are mainly composed of hydrocarbons. Both LNG and LPG are composed of gases, but they are converted to liquid form in order to store and transport easily. So they are stored under high pressurised conditions to maintain it as a liquid. But after vaporized into gaseous state, it is a highly flammable mixture.

LNG (Liquified Natural Gas)

Liquified natural gas is abbreviated as LNG. This is a mixture of hydrocarbons, mainly composed of methane. It also contains small amounts of butane, propane, ethane, some heavier alkanes and nitrogen. LNG is odourless, non-toxic, colourless mixture. LNG is produced from natural gas. In a LNG plant, water, hydrogen sulphide, carbon dioxide and some other compounds (which will freeze under low temperatures) are removed. The environmentally harmful emissions from LNG are higher during the production, storage, and combustion. Therefore, special infrastructure facilities are there in production plants. So one disadvantage of LNG is the high cost associated with storage, transportation facilities, and infrastructure requirements.

LPG (Liquified Petroleum Gas)

Liquified petroleum gas is abbreviated as LPG. This is a mixture of hydrocarbon gases primarily containing propane and butane. Since it mostly contains propane gas, sometime LPG is referred to as propane. It is heavier than air. LPG is a flammable mixture of gases which is used as a fuel in motor vehicles and some other heating appliances (for cooking). LPG readily burns in air which makes it a good fuel for cooking and other purposes. When it is used to power the internal combustion engines in vehicles, LPG is named as auto gas. This is a clean fuel, and upon combustion, it produces fewer amounts of harmful emissions and carbon dioxide (which is a greenhouse gas).

Moreover, it is less expensive compared to gasoline. However, on the negative side, the availability of LPG is limited and also the number of miles a car can run from a full tank of fuel is fewer. So it has lower energy content. LPG is a fossil fuel, so it is produced as a by-product of petroleum refining. Further, it can be prepared by natural gas. LPG evaporates quickly at room temperature and pressure because it has a lower boiling point (which is lower than room temperature). So LPG is supplied in pressurised steel vessels. Leaking of LPG is hazardous. These leakages can be identified due to the odor of LPG. Although naturally LPG is odourless, addition of a stanching agent gives it a distinctive, unpleasant smell.

LNG vs LPG

• LNG mainly contains methane, and LPG mainly contains propane.

• LPG is commonly used in household whereas LNG is not. LNG is mainly used for other energy requirements.

• LNG is produced from natural gas, and LPG is produced from petroleum refining.