General Chemistry - Basic Concepts

Dissolving sugar in water is a physical change because if you were to dissolve the sugar in water and then let the water evaporate, the sugar would still be left. All of the components that you started with are still there, even if you can't see them. A physical change is a change of matter that does not alter the chemical properties of that matter. A chemical change is when bonds are broken and new bonds are being formed between different atoms. Chemical Change: Baking soda and vinegar fizzing and creating bubbles Physical Change: When water freezes, it doesn't create a new substance. Ice is still H₂O just in a solid form.

Sublimation is the phase transition in which a substance passes directly from the solid to the gas state without passing through the liquid phase.

Bauxite is the primary ore of aluminium and is chemically a mixture of hydrated aluminium oxides, typically Al2O3.nH2O.

Gobar Gas contains:
Methane (CH₄) about 60% 
Carbon Dioxide (CO₂) about 30% 
Hydrogen (H₂) about 8% 
Nitrogen (N₂) about 1% 
Water vapour (H₂O) about 1%
So, we see that methane is the main constituent of the Gobar gas.

One should not sleep in a closed room where a charcoal fire is burning as it produces CO. The produced CO will combine with the Hemoglobin present in the blood, which cause death of a person.

Ice cream is a emulsion of milk or water in cream. i.e. oil in water type. Gelatin is act as an emulsifier, i.e. it helps to stabilize the emulsion. So, it avoids the formation of crystals.

Water that contains mineral salts (as calcium and magnesium ions) that limit the formation of lather with soap called hard water. Such water contains metal ions (calcium, magnesium, iron) which, instead of lather form precipitate with soap. The rain water dissolves sulphates, chlorides and carbonates of calcium and magnesium present in many rocks. These salts cause hardness of water. This water also dissolves carbon dioxide from air which converts the carbonates of calcium and magnesium into bicarbonates. These bicarbonates being soluble in water cause hardness. The hardness of water is of two types:- temporary hardness and permanent hardness. Temporary hardness is due to the presence of bicarbonates of calcium and magnesium in water. These salts are soluble in water and exist in the form of positive and negative ions. The name temporary is given to this type of hardness because these ions are removed merely by boiling. Temporary hardness is removed by boiling water. Due to this calcium and magnesium bicarbonates are converted into insoluble carbonates witch are easily removed. Permanent hardness is due to the dissolved chlorides or sulphates of calcium and magnesium. These salts can not be decomposed by boiling and hence the name permanent is given to this type of hardness. These salts are soluble in water and produce corresponding ions in solution. Both temporary and permanent hardness can also be removed by ion exchange method which involves the replacement of one ion by another.

Carbon monoxide is hazardous to man as CO combines with hemoglobin of the blood which causes the death of a person when a person takes inside the large amount of it in the body.

When hydrogen chloride gas (from a chloride test) reacts with ammonia (often from an ammonia solution), it forms white fumes of solid ammonium chloride (NH4Cl).

Milk is pasteurized to destroy the microorganisms. Pasteurization is a process of heating a food, usually a liquid, to a specific temperature for a definite length of time and then cooling it immediately. This process slows spoilage due to microbial growth in the food.
Unlike sterilization, pasteurization is not intended to kill all micro-organisms in the food. Instead, it aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurized product is stored as indicated and is consumed before its expiration date). Commercial-scale sterilization of food is not common because it adversely affects the taste and quality of the product. Certain foods, such as dairy products, may be superheated to ensure pathogenic microbes are destroyed.

Temporary hardness of the water is due to the presence of calcium bicarbonate. Water's hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are cations (positively charged metal complexes) with a charge greater than 1⁺. Usually, the cations have the charge of 2⁺. Common cations found in hard water include Ca²⁺ and Mg²⁺.

Atomic weight of uranium is 238.

In metallurgy, a non-ferrous metal is a metal that is not ferrous, that is, any metal, including alloys, that does not contain iron in appreciable amounts. Generally, more expensive than ferrous metals, non-ferrous metals are used because of desirable properties such as low weight (e.g. aluminium), higher conductivity (e.g. copper), non-magnetic property or resistance to corrosion (e.g., zinc). Some non-ferrous materials are also used in the iron and steel industries. For example, bauxite is used as flux for blast furnaces, while others such as wolframite, pyrolusite, thus making ferrous metals not like in ferrous metals.

A metalloid is a chemical element with properties that are in-between or a mixture of those of metals and non-metals, and which is considered to be difficult to classify unambiguously as either a metal or a non-metal. There is no universally agreed or rigorous definition of a metalloid. Classifying any particular element as such has been described as 'arbitrary'. The term was first popularly used to refer to non-metals. Its more recent meaning as a category of intermediate or hybrid elements did not become widespread until the period 1940-1960. The six elements commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony and tellurium. They or their compounds find uses in glasses, alloys or semiconductors. So, boron behaves chemically with both metals and non-metals.

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal. However, since bronze is a somewhat imprecise term, and historical pieces have variable compositions, in particular with an unclear boundary with brass, modern museum and scholarly descriptions of older objects increasingly use the more cautious and inclusive term copper alloy instead.

Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms, ascorbate acts as an antioxidant by protecting the body against oxidative stress. It is also a cofactor in at least eight enzymatic reactions including several collagen synthesis reactions that, when dysfunctional, cause the most severe symptoms of scurvy. In animals, these reactions are especially important in wound-healing and in preventing bleeding from capillaries.

Lead is used in the storage battery, so we also say it as a lead acid battery.  A lead-acid battery is a electrical storage device that uses a reversible chemical reaction to store energy. It uses a combination of lead plates or grids and an electrolyte consisting of a diluted sulphuric acid to convert electrical energy into potential chemical energy and back again. The electrolyte of lead-acid batteries is hazardous to your health and may produce burns and other permanent damage if you come into contact with it. Thus, when dealing with electrolyte protect yourself appropriately.

Francium, cesium, gallium, and rubidium are four elements that melt at temperatures slightly higher than room temperature. Francium (symbol Fr and atomic number 87), a radioactive and reactive metal, melts around 300 K. Francium is the most electropositive of all the elements. Cesium (symbol Cs and atomic number 55), a soft metal that violently reacts with water, melts at 301.59 K. The low melting point and softness of francium and cesium are a consequence of the size of their atoms. In fact, cesium atoms are larger than those of any other element. Gallium (symbol Ga and atomic number 31), a grayish metal, melts at 303.3 K. Gallium can be melted by body temperature, as in a gloved hand. Rubidium (symbol Rb and atomic number 37) is soft, silvery-white reactive metal, with a melting point of 312.46 K. Rubidium spontaneously ignites to form rubidium oxide. Like cesium, rubidium reacts violently with water.

An element is defined by the number of protons in the nucleus of its atoms, but its chemical reactivity is determined by the number of electrons in its outer shell property fundamental to the organization of the periodic table of the elements. So, atomic number is good to defined the different properties of the elements.

Sodium benzoate is a common food preservative used to prevent the growth of bacteria and fungi in acidic food products, including grains.

Mercury (Hg) is a metal that exists in a liquid state at room temperature.

Butane is a highly flammable hydrocarbon gas that is easily liquefied under pressure, making it ideal for use in cigarette lighters.

Depending on various geographical locations these may change, but for the most part, air is made up of 78% nitrogen (N₂), 21% oxygen (O₂), and trace amounts of carbon dioxide (CO₂), methane (CH₄), hydrogen (H₂), argon (Ar) and helium (He). The CO₂, CH₄, H₂, Ar, and He, when combined together, make up about 1% of air.

Burning of a candle involves a chemical change because the wax reacts with oxygen to produce new substances like carbon dioxide and water vapor. Evaporation is a physical change.

Liquefied Petroleum Gas or LPG (also called Autogas) consists mainly of propane, propylene, butane, and butylene in various mixtures. It is produced as a by-product of natural gas processing and petroleum refining. The components of LPG are gases at normal temperatures and pressures. One challenge with LPG is that it can vary widely in composition, leading to variable engine performance and cold starting performance. At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is stored in pressurized steel bottles. Unlike natural gas, LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. Such accumulations can cause explosion hazards, and are the reason that LPG fuelled vehicles are prohibited from indoor parkades in many jurisdictions.