Precipitation reactions have been widely used in chemical analysis of the titration-titration, in the determination of gravimetric, in separating a sample into its components. Precipitation titration is a titration where the outcome groups titrasinya reaction is difficult to precipitate or dissolve the salt.
The precipitate is a substance that separates itself as a solid phase out of solution. The precipitate formed when the solution becomes too saturated with the substance in question. Solubility of a precipitate is the molar concentration of saturated solution. Solubility depends on various conditions such as temperature, pressure, concentration of other ingredients in solution, and on the composition of the solvent.
In some cases, the solution changes with changing temperature can be the basis for the separation. For example, the separation of lead ions of silver and mercury (I) can be achieved with the three ions precipitate it. First as chloride, followed by adding hot water to the mixture. The hot water will dissolve lead and mercury chloride but silver does not dissolve in it. The precipitate of lead chloride (PbCl 2) is the sediment was slightly soluble in water. The precipitate of lead chloride solution can be obtained by reacting lead nitrate with potassium chloride solution. To understand the solubility of lead chloride, the experiment was conducted.
1.2 Experiment Objectives
1.2.1 Purpose Experiment
The purpose of this experiment that is studying methods of determining the value of the solubility product (KSP).
1.2.2 The purpose of Experiment
The purpose of this experiment are:
Calculating the solubility of which is slightly soluble electrolyte.
Calculating the heat solubility of PbCl 2 by using the properties of KSP dependence on temperature.
1.3 Principle Experiment
The principle of this experiment was to determine the solubility product (KSP) PbCl 2 through the formation of a precipitate formed from PbCl 2 Pb (NO 3) 2 and KCl, and measure the temperature of dissolution of PbCl 2 precipitate through the heating process.
It has been commonly known in chemistry that the compounds do not larutpun still have solubility. Therefore, such compounds are more appropriately described as a difficult soluble compounds. When the compounds are difficult to dissolve it into contact with water, then some of the ion leaving the crystal lattice of sediments and into the solution, some other ions take the place left on it. After a few moments, the dynamic equilibrium is reached so that the rate of release of ions from exactly the same as the rate of sediment deposition. Thus, the solution is said to have been saturated. Concentrations of the saturated solution, expressed in units of mol / L or g/100 mL, represents a unique constant value at a certain temperature and is called the solubility (denoted by the letter S, which comes from the word Solibility). Solubility is also dependent on the nature or the true nature and sensitivity of other substances that exist in solution (Rival, 1995).
Factors affecting the solubility is as follows (Khopkar, 1990):
Solubility increases with increasing temperature. Sometimes the sediment was well formed in the heat of solution, but do not do filtering on the condensation heat.
Organic salts more soluble in water. The reduced solubility in organic solvents can be used as a basis the separation of the two substances.
Effect of ion type
Sediment in the water solubility is reduced if the solution containing one of the authors ions precipitate, because the restrictions KSP (solubility product constant).
Effect of other ions
Some deposits increased solubility in aqueous solution when there are different salts with sediment.
Effect of pH
Solubility of salts of weak acids depends on pH.
Effect of hydrolysis
If the salt of weak acid dissolved in water, would produce a change (H +). Cation of the species experiencing salt hydrolysis thereby increasing solubility.
Influence of complex
Solubility of slightly soluble salts is a function of the concentration of another substance that forms a complex with the salt cations.
The precipitate is a substance that separates itself as a solid phase out of solution. The precipitate may form crystals (crystalline) or colloidal, and can be removed from the solution by filtration or centrifugation (centrifudge). The precipitate formed when the solution becomes too saturated with the substance in question. Solubility (S) of a deposition by definition is equal to the molar concentration of saturated solution (Svehla, 1990).
Precipitation titration is a titration where the outcome groups titrasinya reaction is difficult to precipitate or dissolve the salt. The basic principle is a fast precipitation reaction reaches equilibrium at each addition of titrant; there are no impurities that interfere with and necessary indicator to see the end point titration. Only the precipitation reactions that can be used in titration (Khopkar, 1990).
The deposition that occurred during the titration can be expressed with the aid of the titration curve. This titration curve provides useful information for selecting the most appropriate atmosphere for chemical examination (Rival, 1995).
In some cases, especially in the titration of a dilute solution, the reaction rate is too low so that the titration is cumbersome. When the equivalence point was approached and titrant added slowly, there is no high kelewatjenuhan and precipitation can be very slow. One other difficulty is that the composition of sediment is often not known because the influence of coprecipitation. Although this kopresitasi can be minimized or corrected by some kind of aging process of deposition, this is not possible in direct titrations involving the formation of a sediment (Underwood, 1996).
The precipitation titration, a substance that reacts with the substance defined pentiter difficult to form compounds that dissolve in water. Because it was determined that concentrations of substances which decreased during the titration process. Changes in concentrations were observed near the point of equality with the help of appropriate indicators or equipment. However, this method actually requires strict requirements, so its use is limited in titrimetry.
Requirements are as follows:
Miscellaneous equilibration occurs must take place fast enough;
substance to be determined must react stoichiometrically with pentiter substances;
precipitate formed must be quite difficult to dissolve so that the reaction to perfection guaranteed 99.9%;
Should be available method of determining the appropriate end point.
Because of the above requirements must be met in precipitation titration, the precipitation reactions that are commonly used in gravimetry can not be used entirely in precipitation titration. Actually, only the precipitation reaction with silver ions are commonly used in the precipitation titration, although sometimes it can also be used with ion precipitation reactions of mercury (I) (Rival, 1995).
When a strong electrolyte added to a weak electrolyte, or to a solution containing soluble salts is difficult, of solution ionic strength will change (strong electrolytes dissociate completely). Therefore, activity coefficients and dissociation constants or the solubility of weak electrolytes are difficult to dissolve the salt will change (Dogra, 1990).
Some conclusions can be drawn from the solubility product equation, namely (Rival, 1995):
The bigger one ion concentrations are elevated, the greater the concentration of other ions decreased and vice versa.
Whether the sediment will be formed or not, can be predicted from the concentrations of the constituent ions. If the product of the concentrations of ions existing in solution is greater than the product of solubility, it can be estimated that the deposit will arise.
Formation of these compounds are difficult to dissolve is one easy way for the separation and determination of chemical compounds.
From the solubility product, solubility of compounds can be predicted. The lower the solubility of the product, the more specific stoichiometry.
PbCl 2 precipitate soluble in hot water, but separated again as long crystals such as needles and a half cold. He is also soluble in concentrated hydrochloric acid or potassium chloride solution. If the sediment washed by decantation, and dilute ammonia is added, no changes are visible, although there is an exchange reaction with sediments, and including lead hydroxide (Svehla, 1990).
KSP compounds can be determined from laboratory experiments to measure the solubility (mass compounds that can be dissolved in each liter of solution) until the right circumstances saturated. In that state, has a maximum capacity of solvent to dissolve or mengionkan solute. Excess solute although little will be precipitated. Solubility product in the real situation is the final value achieved by the product ions when equilibrium is reached between the solid phase of which is only slightly soluble salt and the solution was (Shukri, 1999).
Result times the concentration of its constituent ions for each given temperature is constant, the ion concentration raised to the same number with the number of each ion in question. Solubility is the amount of dissolved substances can be dissolved in a solvent to form a saturated solution. While the solubility of the product is the final result achieved by the product ion when equilibrium is reached antra solid phase of which is only slightly soluble salts in the solution (Keenan, 1991) .
Solubility of sediments that were found in quantitative analysis increased with increasing temperature. With some substances temperatu effect is small, but with other substances that influence can be very real. So the solubility of silver chloride at 10 and 100 o C, respectively, are 1.72 and 21.1 mg dm -3, while the solubility of barium sulfate at both temperatures were, respectively, are 2.2 and 3.9 mg dm -3. In some cases, the effect of reducing the solubility of ions allies have become so small that the temperature effect, which no effect will be obvious allies ions, becomes very small (Bassett, 1994).
KSP = HKK = calculated by multiplying the [cation] with [anion] of a saturated solution of electrolyte is difficult to dissolve by heterogeneous equilibrium. Solubility of an electrolyte is the number of moles of electrolyte which can dissolve in each liter of solution. If the total ion concentration in solution increases, the ion drag force becomes more apparent and the activity (effective concentration) was smaller than the concentration stoikhiometri or measurability. For the ions involved in the process of dissolution, this means that higher concentrations should occur before equilibrium is reached in other words, the solubility will increase (Oxtoby, 2001).
Materials used in this experiment was Pb (NO 3) 2 0.075 M, 0.1 M KCl, distilled water, tissue rolls, paper label.
The tools used in the experiment is a test tube rack, test tubes, measuring cup 50 ml and 250 ml, 50 ml burette, thermometer 0 to 150 o C, the wire gauze, tweezers.
3.3 Experimental Procedure
work procedure for this experiment is
a. Put up the tools that are used along with the ingredients.
b. Cleaned instruments are clean.
c. Solution of Pb (NO 3) 2 and KCl were included in two different Biuret, using the measuring cup.
d. Entered Pb (NO 3) 2 into a test tube of 10 ml, then added with a solution of KCL as much as 1 ml.
e. Do the same thing at the points (d) for the three other test tubes, but with the volume of KCl different, namely to the second tube 1.5 ml, 2 ml for the third tube and four tubes of 2.5 mL.
f. Observed changes that occur, whether or not to precipitate.
g. Precipitate that formed was dissolved on the bath, but not before first measured the initial temperature of sediment formation.
h. Stirring the solution using a thermometer to dissolve sediments back.
j. Condensation temperature recorded at the time sediments were dissolved again.
k. Processed all the data obtained to find the value of the solubility of the solution-solution.
RESULTS AND DISCUSSION
RESULTS AND DISCUSSION
In this experiment, using the principles of solubility product, KSP. The principle of this experiment states that the product of the concentration of its constituent ions for any given temperature is constant, the ion concentration raised to the same number with the number of each ion in question.
The experiment was carried through the formation of PbCl 2 precipitate. A sample solution of a difficult or insoluble, in this case Pb (NO 3) 2, the value of the concentration of ions is greater than the product of the concentration of electrolyte. Addition of KCl resulted in the formation of a substance settling of sediment. These deposits will dissolve with heating.
At the time experimenting with the process of formation of sediments, not at all precipitate the addition of KCl. The precipitate formed on addition of KCl only a certain volume, among them is the addition of 1 M KCl 1.5 mL, 2 mL, and 2.5 mL. While the addition of KCl 1 M 1 mL did not precipitate. This shows that the more volume of KCl were added, the more precipitate formed.
Sediment deposition that PbCl 2 is slightly soluble in water. Dissolution of sediment carried by the method of heating. This is done with the aim to accelerate the dissolution process of sediment. The more sediment that is formed, the longer the process of dissolution and the bigger the temperature required to dissolve deposits.
In addition, the volume of added KCl was also affecting the value of the solubility product (KSP). The greater the volume of KCl were added, the smaller the value of the solubility product (KSP) are obtained. This is because the large volume of KCl affects the amount of sediment that is formed, thus affecting the value of solubility product (KSP).
The results showed that the dissolution heat PbCl 2 in this experiment is at -8.4566 . As for the reaction is endothermic reaction, ie chemical reaction accompanied by the absorption of heat by the system, so the system temperature increases.
From the experiments have been conducted, the data obtained as follows:
1. Solubility (s) PbCl2 addition of KCl at 1 M:
- Vol. KCl 1.5 mL, KSP = 5.5 x 10-4
- Vol. KCl 2 mL, KSP = 9.76 x 10-4
- Vol. KCl 2.5 mL, KSP = 8.64 x 10-4
2. Heat PbCl2 dissolution of -8.4566.
We suggest in this experiment was also conducted to determine the value of the solubility product (KSP), on the other sediment, so the results can be compared with each other.
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