Chemistry

SIMPLE MACHINE

Definition of Simple Machine A machine is a tool or device that makes work easier. It is defined as a tool which uses force applied (effort) at one point to overcome another resisting force (effort) at another point. Examples of machine include: a plier, the human arm, a gear, a pulley etc. Types of Machine There are six types of simple machines. They are; Lever Wheel and axle Pulley Wedge Inclined plane Screw Lever A lever is a simple machine built on the principle of a stiff bar resting on a pivot or fulcrum with a load placed at one end and effort applied on the other end. There are three parts of the lever; Load: This is the point of the resisting force. Effort: This is the point where force is applied. Fulcrum: This is the turning point of the lever. Types of Lever There are… Read More »SIMPLE MACHINE

AIR AND COMBUSTION

Percentage of Oxygen in Air We have read that Air consists mainly of molecules of oxygen and nitrogen with important yet trace amounts of other gases. We know that the combustion of organic material requires oxygen. The idea here is to capture a quantity of air in a measured and isolated volume and then use up all the oxygen by burning something. The remaining volume will be mostly molecular nitrogen. Equipment needed flasks water container candles rulers thermometer Procedure The volume of a flask is measured. Water is placed in a container along with a thermometer, and a flask inverted over a lit candle resting in the water. Eventually the candle goes out. Measure the height of water relative to the original water height. Calculate the volume. From the total volume, assumed to be oxygen and nitrogen, compute the percentage of oxygen. Suppose the heights of air were measured… Read More »AIR AND COMBUSTION

AN ALKALI

Alkali is pronounced like alcohol, with ‘lie’ at the end instead of ‘hol’. An alkali is any substance which produces OH– ions in water. OH– ions are called hydroxide ions. If there are excess of (OH)– ions when a compound is dissolved in water, the solution is called a base or an alkaline solution. A base is generally a metal hydroxide solution. Table below lists some of the common alkalis available in our everyday lives. Name of alkali Chemical Formula Dissociation in water Sodium Hydroxide NaOH Na+ + (OH)– Potassium Hydroxide KOH H+ + NO3– Ammonium Hydroxide NH4OH NH4+ + (OH)– A substance which will neutralize an acid, but does not dissolve in water, is called a base. For example, copper (II) oxide, iron (II) oxide and zinc carbonate are bases. They do not dissolve in water. Any base which dissolves in water is called an alkali. The outer circle encloses all bases, while the inner… Read More »AN ALKALI

ACIDS, BASES AND INDICATORS

WHAT IS ACIDS, BASES AND INDICATORS? All the elements in nature fall into three classes: metals, non-metals and gases. Non-metals are also sometimes called metalloids. The compounds formed by combination of the elements can also be classified as organic and inorganic compounds. Organic compounds are formed from a combination of carbon and hydrogen; they are also sometimes known as hydrocarbons. In addition to this, all these compounds taste sour, bitter or salty. The sour tasting substances are known as acids. Bitter tasting compounds are generally soapy to feel also; they are known as bases or alkalis. What is an acid? When a substance dissolves in water, the solution may be acidic, neutral or alkaline. An acid is any substance which produces H+ ions or H3O+ ions in water. H+ ions are called hydrogen ions; H3O+ ions are called hydroxonium ions. You will mostly see acids in reactions as forming H+ ions.… Read More »ACIDS, BASES AND INDICATORS

EVAPORATION AND BOILING

EVAPORATION AND BOILING (LIQUID TO GAS) On heating particles gain kinetic energy and move faster. In evaporation and boiling the highest kinetic energy molecules can ‘escape’ from the attractive forces of the other liquid particles. The particles lose any order and become completely free to form a gas or vapour. Energy is needed to overcome the attractive forces in the liquid and is taken in from the surroundings. This means heat is taken in, so evaporation or boiling are endothermic (require heat to be added) processes. If the temperature is high enough boiling takes place. Boiling is rapid evaporation anywhere in the bulk liquid and at a fixed temperature called the boiling point and requires continuous addition of heat. The rate of boiling is limited by the rate of heat transfer into the liquid. Evaporation takes place more slowly at any temperature between the melting point and boiling… Read More »EVAPORATION AND BOILING

CAREERS IN CHEMISTRY

Chemists are the people who transform the everyday materials around us into amazing things. Some chemists work on cures for cancer while others monitor the ozone protecting us from the sun. Still others discover new materials to make our homes warmer in the winter, or new textiles to be used in the latest fashions. The knowledge gained through the study of chemistry opens many career pathways. Here are just a few of the careers chosen by chemists. Agricultural Chemistry Biochemistry Chemical Education Chemical Engineering Consumer Product Chemistry Environmental Chemistry Food and Flavor Chemistry Forensic Chemistry Medicinal Chemistry Some Career Descriptions: Biochemistry Biochemistry is the study of the structure, composition, and chemical reactions of substances in living systems. Biochemistry emerged as a separate discipline when scientists combined biology with organic, inorganic, or physical chemistry and began to study such topics as how living things obtain energy from food, the chemical… Read More »CAREERS IN CHEMISTRY

SODIUM HYDROGEN CARBONATE AND SODIUM CARBONATE

Sodium Carbonate (Na2CO3) Popularly known as washing soda or soda ash, sodium carbonate is a commercially important compound. In earlier days, it was obtained from the ash of plants and from natural deposits in India and Egypt. Manufacture of Sodium Carbonate Raw Materials Sodium chloride – NaCl (brine solution) Ammonia – NH3 Limestone – CaCO3 (for carbon dioxide supply) Principal Reactions Process The first step in the manufacture of sodium carbonate is to generate carbon dioxide. This can be got by heating limestone. The Plant Used in the Solvay Process Saturation of Brine With Ammonia Brine solution is pumped into the ammonia absorber. From the ammonia recovery tower, ammonia mixed with a little carbon dioxide enters the absorber and saturates brine. Impurities of calcium and magnesium present in brine are precipitated as carbonates. These impurities can be removed by pumping the liquid through the filter press and then passed… Read More »SODIUM HYDROGEN CARBONATE AND SODIUM CARBONATE

CARBON (II) OXIDE (CARBON MONOXIDE)

What is Carbon monoxide?. Carbon monoxide is an odourless, tasteless and colourless gas, which is insoluble in water. It is extremely poisonous. Under no circumstances must the gas be inhaled or smelled. It is not usually prepared in a school laboratory. If need be, the gas should be prepared in a fume chamber. Preparation of carbon monoxide 1.By dehydrating oxalic acid with hot concentrated sulphuric acid Carbon monoxide is prepared with the help of oxalic acid and concentrated sulphuric acid as shown below. Oxalic acid has the formula . Sulphuric acid reacts with oxalic acid and removes from it one molecule of water (both the hydrogen atoms, along with an oxygen atom). The product left behind due to this reaction, is a molecule of carbon dioxide and a molecule of carbon monoxide. The carbon dioxide can be removed by passing it through a concentrated solution of potassium hydroxide. … Read More »CARBON (II) OXIDE (CARBON MONOXIDE)

CHEMICAL PROPERTIES OF CARBON

CHEMICAL PROPERTIES OF CARBON The combustion of carbon: Carbon reacts with oxygen to form two oxides, carbon dioxide, CO2, and carbon monoxide CO. The proportions of these two oxides formed during combustion depend on the conditions. At about 500 ºC, carbon dioxide is produced almost exclusively, provided that oxygen is in excess: C(s) + O2(g) CO2(g) At higher temperatures, or when the supply of oxygen is restricted, carbon monoxide is the main product. 2C(s) +O2 (g) 2CO (g) Reaction with acids Carbon reacts with concentrated sulphuric acid and concentrated nitric acid. Nitric acid is a powerful oxidizing agent. Both acids oxidize carbon to carbon dioxide gas. Carbon + sulphuric acid carbon dioxide + sulphur dioxide +water C(s) + 2H2SO4(conc) CO2(g) + SO2(g) + 2H2O(l) Carbon + nitric acid carbon dioxide + Nitrogen (IV) oxide + water C(s) + 4HNO3 (conc) CO2(g) + 4NO2(g) + 2H2O(l) Reducing action of carbon When… Read More »CHEMICAL PROPERTIES OF CARBON

AMORPHOUS CARBON

AMORPHOUS CARBON Apart from diamond and graphite, which are crystalline forms of carbon, all other forms of carbon are amorphous allotropes of carbon. Coke Coke is the amorphous allotrope of carbon, which is derived from coal. When coal undergoes destructive distillation, it yields two allotropes of carbon, namely coke and gas carbon. Destructive distillation is a chemical process, which involves is the breaking up of a complex substance by heating it in the absence of air. Uses of coke It is a very good fuel and when ignited it burns almost with no smoke. It is a non-conductor of heat and electricity. It acts as a good reducing agent and is extensively used in the production of producer gas, water gas and hydrogen. Sugar Charcoal Sugar charcoal can be obtained by dehydrating cane sugar, either by treating it with concentrated sulphuric acid or by heating it in the… Read More »AMORPHOUS CARBON

GRAPHITE

What is graphite? Unlike the tetrahedral arrangement of atoms in diamond, the carbon atoms in graphite are arranged in the form of hexagonal rings in layers (Fig.10.2). Each carbon is bonded to only three other carbon atoms in that layer. Different layers of graphite are held together by rather weak forces. Hence they can slide over one another. This is one reason why graphite scales off easily and can mark impressions on substrates. Because of this property, it is also used as a lubricant. Physical Properties of Graphite Graphite is greyish black crystalline substance. It has a soft and greasy texture, but has a metallic luster. The specific gravity of graphite is only 2.2 g cm-3. Due to the presence of a free valence electron, it is a good conductor of electricity. It is also one of the stable forms of carbon. The structure of graphite has hexagonal rings arranged… Read More »GRAPHITE

DIAMOND

DIAMOND What is diamond? Diamond is the purest form of natural carbon. It occurs as small crystals embedded in rocks. These are supposed to have been formed by the crystallization of carbon under extreme pressure and temperature in the interior of the earth. Nowadays, synthetic industrial diamonds are being manufactured by subjecting graphite to very high temperatures and pressures. Carbon atoms in diamond have tetrahedral structure. Each atom of carbon is surrounded by four other atoms that together forms the tetrahedral structure, as shown in the figure 10.1. Physical Properties of Diamond Diamond is the purest form of carbon. It is the densest of all allotropes of carbon. Diamond’s tetrahedral structure, makes it the hardest naturally occurring substance. It is brittle and transparent. Pure diamond is colourless. Diamond has very high refractive index. When properly cut and polished, it allows the light to undergo total internal reflection that makes… Read More »DIAMOND

ELECTRODE REACTIONS

Cathode reactions (reduction) (-) negative cathode where reduction of the attracted positive cations is by electron gain (reduction) to form metal atoms or hydrogen [from Mn+ or H+, n = numerical charge]. The electrons come from the positive anode. Hydrogen ions are reduced to hydrogen gas molecules. Electrolysis of many dilute salts or acid solutions make hydrogen gas by reduction as shown. 2H+(aq) + 2e- H2(g) Copper (II) ions are reduced to copper atoms in the electrolytic purification or electroplating using copper (II) sulphate solution. Cu2+(aq) + 2e– Cu(s) Silver ions reduced to silver atoms in silver electroplating Ag+(aq) + e- Ag(s) Anode reactions (oxidation) Positive anode is where the oxidation of the atom or anion is by electron loss. Non-metallic negative anions are attracted and may be oxidised to the free element. For example, in the electrolysis of molten chloride salts or their concentrated aqueous solution or conc. hydrochloric… Read More »ELECTRODE REACTIONS

ELECTROPLATING

Electroplating is a process of depositing a thin layer of a fine and superior metal (like chromium, zinc, nickel, gold etc.) over the article of a baser and cheaper metal (like iron, copper, brass), with the help of electric current. Uses Electroplating is very useful because of the following reasons: Surface protection e.g. nickel plating of iron to prevent corrosion. Makes the article attractive e.g., electroplating of silver or gold on brass etc. Repair of finer machine parts. Process The process of electroplating involves the following steps: Before electroplating the metal surface is cleaned thoroughly. Firstly, an alkaline solution is used to remove grease and then it is treated with acid to remove any oxide layer. It is then washed with water. The article to be electroplated is made cathode since metallic ions are positive and thus get deposited on the cathode. The… Read More »ELECTROPLATING

ELECTROLYTES AND NON-ELECTROLYTES

However, if the compound is unable to ionise it does not conduct electricity it is called a non-electrolyte. In general, the extent to which an electrolyte can break up into ions categorises an electrolyte. This gives a measure of the degree of dissociation (a) of an electrolyte. Based on this degree the electrolytes can be classified as strong or weak electrolyte and non-electrolyte. Strong Electrolyte A strong electrolyte, such as a solution of sodium chloride dissociates or ionises completely or almost completely to form free mobile ions in the solution or molten form. The more the availability of free mobile ions in an electrolyte, the greater is its capacity to carry or conduct current i.e. the stronger the electrolyte. The ability to conduct current can be observed by setting up a cell as shown in figure 4.4. The bulb glows brightly. For e.g., Sodium chloride even in crystalline… Read More »ELECTROLYTES AND NON-ELECTROLYTES

EFFECT OF AN ELECTRIC CURRENT ON SUBSTANCES

Introduction In any chemical reaction, the existing chemical bonds are broken and new chemical bonds are formed. Hence, all chemical reactions are fundamentally electrical in nature since electrons are involved in some way or the other in all types of chemical bonding. Many chemical reactions utilize electrical energy, whereas others can be used to produce electrical energy. As electrical energy involves the flow of electrons, these reactions are concerned with the transfer of electrons from one substance to the other. Conductors and insulators The ability to conduct electricity is the major simple distinction between elements that are metals and non-metals. Conductors A conductor is a material that conducts electricity but is not chemically changed in the process. All metals and graphite are conductors of electricity. Insulators An insulator is a material that does not conduct electricity. Such materials have no free electrons. Summary of Common Electrical Conductors These… Read More »EFFECT OF AN ELECTRIC CURRENT ON SUBSTANCES

SALTS

General Preparation of Salts Salts are generally ionic compounds formed by the reaction of an acid with a base. The preparation of these salts involves the treating of different metals and non-metals and their compounds with various acids, bases etc. However, some of them can be prepared by direct combination of the concerned elements or also by indirect routes. Insoluble Salts by Precipitation Precipitation is the reaction in which a solid is formed by the action between two or more fluids, e.g., calcium carbonate is precipitated when carbon dioxide is passed through limewater. See also: BONDING IN METALS INTERMOLECULAR BONDING – VAN DER WAALS FORCES THE PHYSICAL PROPERTIES OF SILICON DIOXIDE THE PHYSICAL PROPERTIES OF GRAPHITE THE PHYSICAL PROPERTIES OF DIAMOND

BONDING IN METALS

Bonding in metals Metal atoms have relatively few electrons in their outer shells. When they are packed together, each metal atom loses its outer electrons into a ‘sea’ of free electrons (or mobile electrons). Having lost electrons, the atoms are no longer electrically neutral. They become positive ions because they have lost electrons but the number of protons in the nucleus has remained unchanged. Therefore the structure of a metal is made up of positive ions packed together. These ions are surrounded by electrons, which can move freely between the ions. An ion is a charged particle made from an atom by the loss or gain of electrons. Metal atoms most easily lose electrons, so they become positive ions. In doing so they achieve a more stable electron arrangement, usually that of the nearest noble gas. These free electrons are delocalized (not restricted to orbiting one positive ion)… Read More »BONDING IN METALS

INTERMOLECULAR BONDING – VAN DER WAALS FORCES

Van Der Waals Forces Intermolecular attractions are attractions between one molecule and a neighbouring molecule. The forces of attraction which hold an individual molecule together (for example, the covalent bonds) are known as intramolecular attractions. All molecules experience intermolecular attractions, although in some cases those attractions are very weak. Even in a gas like hydrogen, H2, if you slow the molecules down by cooling the gas, the attractions are large enough for the molecules to stick together eventually to form a liquid and then a solid. In hydrogen’s case the attractions are so weak that the molecules have to be cooled to (-252°C) before the attractions are enough to condense the hydrogen as a liquid. Helium’s intermolecular attractions are even weaker – the molecules won’t stick together to form a liquid until the temperature drops to (-269°C). Hydrogen Bonding Polar molecules, such as water molecules, have a weak,… Read More »INTERMOLECULAR BONDING – VAN DER WAALS FORCES

THE PHYSICAL PROPERTIES OF SILICON DIOXIDE

Silicon dioxide Has a high melting point – varying depending on what the particular structure is (remember that the structure given is only one of three possible structures), but around 1700°C. Very strong silicon-oxygen covalent bonds have to be broken throughout the structure before melting occurs. Is hard. This is due to the need to break the very strong covalent bonds. Doesn’t conduct electricity. There aren’t any delocalized electrons. All the electrons are held tightly between the atoms, and aren’t free to move. Is insoluble in water and organic solvents. There are no possible attractions which could occur between solvent molecules and the silicon or oxygen atoms which could overcome the covalent bonds in the giant structure. Uses of Silica i) Quartz glass is used for manufacturing optical instruments. ii) Colored quartz is used for manufacturing gems. iii) Sand is used in manufacture of glass, porcelain, sand paper and… Read More »THE PHYSICAL PROPERTIES OF SILICON DIOXIDE

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Chemistry

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