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Titrations

Titrations Titrations are used to find out the concentration of an acid or an alkali solutions using a suitable indicator . The method for a titration is described below: Using a pipette, add a measured volume of alkali into a clean conical flask. Add a few drops of indicator. The most commonly used indicators are phenolpthalein, methyl orange and litmus. Fill a burette with acid and record the starting volume. Adds the acid from a burette until the indicator changes colour from pink to colourless (for phenolphthalein) or yellow to red (for methyl orange) or blue to red (for litmus). Record the final volume reading and repeat the titration until you get concordant titres. Pipette measures a fixed volume. burette measures variable volume.

The development of the model of the atom

Early ideas about atoms New experimental evidence may lead to a scientific model being changed or replaced over time. In 1804, John Dalton presented his atomic theory that all matter was made up of tiny hard particles or spheres called atoms that could not be broken up. In 1897, J J Thomson proposed that the atom looked like a plum pudding. J J Thomson discovered that atoms contained even smaller negatively charged particle called electrons which could be removed from atoms. He said that the atoms were spheres of positive charge with a lot of negative electrons stuck in it like fruit in a pudding. In 1909 Rutherford and his assistants had proven the existence of the nucleus. Rutherford performed alpha scattering experiment in which a beam of alpha particles was fired at a gold foil. They realised that most of the mass of the atom m

Reversible reactions

Reversible Reactions In some chemical reactions, the products of the reaction can react with each other to re-form the original reactants. These reactions are called reversible reactions . Reversible reactions are ones which happen in both directions at the same time. Reversible reactions can be represented in the following way: A + B ⇌ C + D Reversible reactions are shown using a double headed arrow ⇌ one pointing in each direction. If a reversible reaction is exothermic in one direction it is endothermic in the other direction. When a reversible reaction takes place in a closed container, an equilibrium will be reached. This means that the forward and the backward reactions have the same rate of reaction. If the conditions are changed then the position of equilibrium will move to counteract the change. If we increased the temperature of a reaction at equilibrium, the position of equilibrium moves in the endothermic direction to reduce the temper

Rates of Reaction

Rates of Reaction The rate of reaction means how fast or how slow a reaction happens. Increasing the temperature increases the frequency of collisions and energy of the particles also increases and the rate of reaction increases. If the concentration of a reacting solution or the pressure of a reacting gas is increased , the particles are closer and the collisions between reactant particles increases . Higher concentration increases the rate of reaction . The larger the surface area , the more particles are exposed and the frequency of collisions between particles increases and the rate of reaction increases . A catalyst is a substance that speeds up the rate of a reaction . Catalyst is not chemically changed or used up during the reaction . Biological catalysts used in our bodies are called enzymes . Catalysts increase the rate of reaction by providing a different pathway for the reaction that requires less energy

Potable water

Potable Water Water is essential for life. Potable water means water that is safe to drink . Potable water is not pure in the chemical sense because it contains dissolved solid substances . Pure water has a pH of ~7 and contains no dissolved substances. The method to obtain potable water depends on the source. The methods used to make water potable with fresh water is easier than sea water . This is because removing the large amount of sodium chloride present in sea water requires a lot of energy . Fresh water is water that comes from rain . In the United Kingdom, rain provides water with low levels of dissolved substances . Rainwater collects in the ground, lakes and rivers. Fresh water still needs to be treated before it is safe to drink. Most potable water in the UK is produced from fresh water . If supply of fresh water are limited, desalination of sea water may be required. In warmer countries, drinking water mos

The Earth’s Early Atmosphere

The Earth’s Early Atmosphere Theories on the development of Earth’s atmosphere have changed and developed over the years as science has progressed. Evidence for the early atmosphere is not enough because the Earth formed approximately 4.6 billion years ago. Scientists do not know the accurate composition of the Earth’s early atmosphere because it was too long ago. One theory suggests that the Earth’s early atmosphere was intense volcanic activity . The surface of the Earth was covered by volcanoes that released gases that formed the Earth’s early atmosphere. Earth’s early atmosphere was very similar to the atmospheres of Mars and Venus today. Earth's early atmospheres have a large amount of carbon dioxide with little or no oxygen gas . As the earth cooled, water vapour condensed to form the oceans . When the oceans formed, most of the carbon dioxide was taken out of the atmosphere by being dissolved into the oceans. Carbonate compounds were then precipitated as