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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.