Concentration of Sulphuric Acid

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Medical Chemistry and Dental Materials 2005/2006 Practical Lesson No 4 TITRATIONS Reagents: 1. 2. 3. 4. 5. 6. NaOH standard solution H2SO4 Phenolphthalein Na2S2O3 standard solution Starch solution Solutio Lugoli 0.1 mol/l solution of unknown concentration 0.1 mol/l 6 g/l 13 g I2 in KI 25 g/l Theory of titrations In general, chemistry often analyses unknown samples to answer two questions: what substances are present and what is their amount. There are therefore two parts of analytical chemistry: the qualitative and the quantitative analysis. As analytical methods for inorganic substances differ from those for the organic ones, there are two kinds of analytical chemistry: the inorganic and the organic analytical chemistry. In this lesson we present some examples of the quantitative analysis of inorganic substances. An important method for determination of the amount of a particular substance is based on measuring volumes of reactant solutions. The method is called a titration, and can be defined as a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with known concentration of substance B until the reaction of substance A with the substance B is just complete. To make the course of the reaction visible, it is necessary to add another substance called an indicator. An indicator is a substance that undergoes a colour change when the reaction approaches completion, i.e. at the equivalence point. The titration analysis can be based on various sorts of chemical reactions, from which we give three examples here: A. Neutralisation reaction When an acid is mixed with an alkali (base), neutralisation reaction occurs, e.g.: HCl + NaOH ⎯→ NaCl + H2O In ionic terms: H+ + OH− ⎯→ H2O An acid-base titration is a special kind of titration, used for measuring the amount of acid

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