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, … Read more
PHYSICAL PROPERTIES OF ACIDS Acids have a characteristic sour taste Most acids are colourless liquids Mineral acids are odourless. Organic acids have characteristic smell All acids have pH less than 7 All acids turn blue litmus paper red, methyl orange red and phenolphthalein colourless. All acids dissolve in water to form an acidic solution. Most … Read more
Substances are either pure or impure. A pure substance is one which contains only one substance. An impure substance is one which contains two or more substances. A pure substance is made up of a pure solid, pure liquid or pure gas. A mixture is a combination of two or more pure substances which can … Read more
Pure Substance Pure means that only one substance is present in the material and can be a pure element or compound. A simple physical test for purity, and properties that can help identify a substance, is to measure the boiling point or melting point. Every pure substance melts and boils at a fixed temperature. … Read more
Which apparatus? You wouldn’t dream of trying a chicken using a spoon, or of drying your hair in over a stove! In everyday life, we need to use the right tools for the job we are doing. The same is true in the science lab. There are lots of types of different chemical apparatus, all … Read more
Corrosion The eating up of metals by the action of air and moisture on their surface is called corrosion. The corrosion of iron is called rusting. While other metals are said to ‘corrode’, iron metal is said to ‘rust’. Rusting of Iron When an iron object is left in damp air (or water) for a … Read more
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 … Read more
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 … Read more
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 … Read more
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 … Read more
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 … Read more
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 … Read more
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 … Read more
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 … Read more
Characteristics of periods The first period starts with hydrogen (H) and ends with helium (He). It has just two elements H (Z=1) and He (Z = 2). H has one electron in the first-shell. He has 2 electrons in the first-shell. As we have seen in the chapter on the structure of atoms, the first-shell … Read more
Ionic (Electrovalent) Bonding Noble gases like neon or argon have eight electrons in their outer shells (or two in the case of helium). These noble gas structures are thought of as being in some way a “desirable” thing for an atom to have. When other atoms react, they try to organize electrons such that their … Read more
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 … Read more
Diamond Has a very high melting point (almost 4000°C). Very strong carbon-carbon covalent bonds have to be broken throughout the structure before melting occurs. Is very hard. This is again due to the need to break very strong covalent bonds operating in 3-dimensions. Doesn’t conduct electricity. All the electrons are held tightly between the atoms, … Read more
The higher the metal in the reactivity series the more reactive the metal with water. The following experiments show the reaction of metals with cold water and water vapour/steam. Reaction of sodium/ potassium with cold water: Procedure Put about 500cm3 of water in a beaker. Add three drops of phenolphthalein indicator/litmus solution/universal indicator solution/methyl orange indicator … Read more
Physical properties Hydrogen is a neutral, colourless and odourless gas. When mixed with air it has a characteristic pungent choking smell It is insoluble in water thus can be collected over water. It is the lightest known gas. It can be transferred by inverting one gas jar over another. Chemical properties. Burning Hydrogen does not … Read more