A. Standard solution of Primary
Primary standard solution is a solution made of materials that the concentration of the solution can be directly determined from the weight of the dissolved material is very pure.
A. A standard substance should qualify as below:
a.zat be easily obtained, easily purified, easy to dry (preferably at a temperature of 100-120oC)
b.zat must have the equivalent of high, so weighing aberration can be ignored.
c. substances must be readily soluble in the conditions in which it was in use.
d. substances should be tested against the impurity substances with qualitative tests or other tests of sensitivity in the know (the total amount of impurity substances, generally should not exceed 0.01 to 0.02%)
e. reaction with the standard solution must be stoichiometric and practically instant \. Tutrasi aberration can be ignored, or easily in tetapakan closely with experiment.
f. substances should be no change in the air during the weighing, these conditions imply that the substance should not be hygroscopic, was also in the oxidation by air or carbon dioxide is influenced by the NII. These standards must be on guard so that its composition does not change during penyimpana.
Primary standard solution standard solution whose concentration is obtained by weighing.
2. Examples of compounds that can be used for primary standards are:
a. Arsenic trioxide (As2O3) is used to make sodium arsenit NaASO2 used to standardize a solution of sodium periodat NaIO4, I2 iodine solution, and cerium (IV) sulphate Ce (SO4) 2.
b. Bensoat acid is used to standardize a solution of ethanolic sodium, isopropanol, or DMF.
c. Potassium bromate KBrO3 to standardize a sodium thiosulfate solution Na2S2O3.
d. Potassium hydrogen phtalat (KHP) was used to standardize a solution of perchloric acid and acetic acid.
e. Sodium Carbonate is used to standardize a solution of H2SO4, HCl and HNO3.
f. Sodium chloride (NaCl) to standardize a solution of AgNO3
g. Sulfanilik acid (4-aminobenzene sulfonic acid) is used to standardize a solution of sodium nitrite.
As2O3, bensoat acid, KBrO3, KHP, Na2CO3, NaCl, and acid sulfanilik above is the primary standard so this compound is weighed by a certain weight and then dissolved in distilled water to obtain a certain volume of primary standard solution.
Secondary standard solution is a solution whose concentration is obtained by titrating with a solution of primary standard. NaOH can not be used for the primary standard because NaOH is hygroscopic and therefore it should be titrated NaOH with KHP advance that can be used as a primary standard. So also with H2SO4 and HCl can not be used as a primary standard, to make the secondary standard solution can be titrated with a solution of primary standard NaCO3.
B. Secondary standard solution
while the secondary solution is a solution made from materials that the concentration of the solution can not be directly determined. To determine the concentration of this solution must be standardized prior to the primary standard solution.
Examples of kinds of kinds of secondary standard solutions that can be used in the titration alkalimetri:
A. NaOH solution to titrate Strong - Strong Bases
example:
- Strong acids: HCl
- Weak Bases: NH4OH
The reaction equation:
NH4OH + HCl → NH4Cl + H2O
2. NH4OH solution in the titration of strong acid - Weak base
example:
- Strong acids: HCl
- Weak Bases: NH4OH
The reaction equation:
NH4OH + HCl → NH4Cl + H2O
3. NaOH solution in the titration of Weak Acid - Strong Bases
example:
- Weak acid: CH3COOH
- A strong base: NaOH
The reaction equation:
CH3COOH + NaOH + H2O → NaCH3COO
Ionic reactions:
H + + OH-→ H2O
Preparation of Secondary NaOH solution can be done by weighing a number of crystalline NaOH and then diluted with a precise volume. To standardize the NaOH solution can be used a standardized solution H2C2O4 first as a primary standard substance and add pp indicators. The achievement of the equivalence point is marked with a violet color change young.
The reaction between NaOH and H2C2O4 are as follows:
2NaOH (aq) + H2C2O4 (aq) → Na2C2O4 (aq) + H2O (l)
Please note that a solution of known concentration is called the titrant. Titrant is added little by little (from the buret) in titrat (titrated solution) until the color changes and titrat good indicator is usually a solution of titrant. When the color change indicator, the titration is stopped. When the indicator changes color and is called the titration end point and the expected end of the titration end point equal to the equivalence point titration. The farther end point titration equivalence point titration, the greater the error and, therefore, the selection of indicators is very important that the indicator changes color at the equivalence point is reached. At the equivalence point is reached pH 7 (neutral).
C. Indicator
Various indicators have different ionization constants, and consequently they show color at different pH range (Keenan, 2002).
Fenolphtalein classified as very weak acid in a state that is not ionized indicator is colorless. If the ionized alkaline environment fenolphtalein will give more color and light as the anion (Day, 1981).
Methyl orange is salt Na from an acidic sulphonic where in a solution of many ionized, and the environment alkali anion gives the yellow color, whereas under acidic methyl orange is a weak base and take the ions H +, there is a change in the structure and gives the red color of the ions(Day, 1981).
An indicator can change color at certain pH regions, for example:Metal orange: red pH 3.1 - pH 4.4 yellow
Bromtimol blue: yellow pH 6.0 - pH 7.6 bluePhenolphthalein: Clear pH 6.0 - pH 9.6 red
Ways of making alkalimetri indicators for examination:
A. phenolphthalein
a. Weigh as much as 1 gram phenolphthalein.
b. Dissolve in 250 ml of alcohol (ethanol)
c. Mix together, make the solution to 500 ml by adding distilled water.
2. Methyl orange
a. Weigh as much as 1 gram of methyl orange.
b. Dissolve in 500 ml 95% alcohol.
c. Mix together, make a 1 liter by adding distilled water.
3. Brom thymol blue
a. Brom thymol Blue weigh as much as 0.1 gram
b. Dissolved in 1.5 ml of 0.1 M NaOH solution
c. Dilute with water to a volume of 100 ml
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