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20 Experience 2. Trilonometric determination of calcium in water. 100 ml of water pour to the flask, 2 ml of NaOH solution and a small amount of crystalline murexide indicator is added. Titrate with a solution of Trilon B until the red color changes into lilac. Titration is repeated twice. The calcium content is calculated by the formula: 2+ eq 2 (Tr B) (Tr B) (Ca )= 1000 (H O) eq C V C V ⋅ ⋅ , mmol/l where C eq (Tr B) – normality of the Trilon B solution, mol/l; V (Tr B) – volume of the Trilon B solution, consumed for titration, ml; V (H 2 O) – volume of water, which underwent the analysis, ml. To recalculate the calcium content in mg/l water use the formula: C m (Ca  2+ ) = C eq (Ca  2+ ) × 20 where 20 g/mol is the molar mass of the equivalent of calcium. Calculate content of Mg  2+ ions in mol/l in the water, based on experimentally determined values of the total hardness and calcium ion content of Ca  2+ : C eq (Mg  2+ ) = H (H 2 O) – C eq (Ca  2+ ) LESSON 10. CHEMISTRY OF BIOGENIC ELEMENTS Required base level. The principles of dividing the elements into s‑, p‑ and d‑blocks. Conditions for the course of the ion exchange reaction. Oxidation-reduction reactions: the concept of an oxidizer, a reducing agent, possession of the electronic balance method. Properties of amphoteric compounds. Questions for the preparation for the lesson. 1. General characteristics: electronic structures of atoms, cations and anions, oxidation states of s–, p–, d  – elements. 2. Comparative evaluation of chemical properties of s–, p–, d  – elements: complexation reactions; precipitation formation; c) oxidation-reduction reactions. 3. Content of biogenic elements in the body and its biological role. Chemical similarity and biological antagonism (sodium-potassium, magnesium-calcium). Compounds of lithium, sodium, potassium, magnesium, calcium as medicines. Toxicity of beryllium and barium.