Precipitation Calculations

Silver chromate, Ag2Cr04, precipitates when a demonstrator adds aqueous potassium chromate, K2Cr04(oq), to aqueous silver nitrate, AgN03(oq). 

The question just asked can be stated more generally Given the concentrations of substances in a reaction mixture, will the reaction go in the forward or the reverse direction To answer this, you evaluate the reaction quotient and compare it with the equilibrium constant K. The reaction quotient has the same form as the equilibrium-constant expression, but the concentrations of substances are not necessarily equilibrium values. Rather, they are concentrations at the start of a reaction. To predict the direction of reaction, you compare with K.  

Suppose you add lead(II) nitrate, Pb(N03)2, and sodium chloride, NaCl, to water to give a solution that is 0.050 M Pb and O.IOM Cl . Will lead(II) chloride, PbCl2, precipitate To answer this, you first write the solubility equilibrium. 

The reaction quotient has the form of the equilibrium-constant expression, which in this case is the K,p expression, but the concentrations of the products are starling values, denoted by the subscript i. 

Here Qc for a solubility reaction is often called the ion product (rather than reaction quotient), because it is the product of ion concentrations in a solution, each concentration raised to a power equal to the number of ions in the formula of the ionic compound. 

Sample Problem D Will a precipitate form if20.0mL of 0.010MBaCl2 is mixed with 20.0 mL of 0.0050 M Na2S04  

The two possible new pairings of ions are NaCl and BaSO. Of these, only BaSO is a slightly soluble salt. It will precipitate if the ion product [Ba +HSO ] in the mixed solution exceeds for BaSO. From the list of solubility products in 

First [Ba2+] and [SO -] in the above solution must be found. Then the ion product is calculated and compared with the 

The ion product, 1.2 x IO-2, is greater than the value of precipitation occurs. 

CHECK YOUR Th answer contains the appropriate number of significant figures and is close 

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Note on the gravimetric standardisation of hydrochloric acid. The gravimetric standardisation of hydrochloric acid by precipitation as silver chloride is a convenient and accurate method, which has the additional advantage of being independent of the purity of any primary standard (compare Section 10.38). Measure out from a burette 30-40mL of the, say, 0.1M hydrochloric acid which is to be standardised. Dilute to 150 mL, precipitate (but omit the addition of nitric acid), and weigh the silver chloride. From the weight of the precipitate, calculate the chloride concentration of the solution, and thence the concentration of the hydrochloric acid. 

The concentration of F ions can be measured by adding an excess of lead(II) chloride solution and weighing the lead(II) chlorofluoride (PbCIF) precipitate. Calculate the molarity of F ions in 25.00 mL of a solution that gave a lead chlorofluoride precipitate of mass 0.765 g. 

Fig. 26.4. Fracture sealing rates (cm yr 1) for the quartz precipitation calculations shown in Figure 26.3.

Fig. 3. Time scales in precipitation calculated for BaSC>4 precipitated from 0.5 m BaCl2- and 0.33 m H2S04-solutions at 25 °C. To quantify mixing, a specific power input typical for the applied T-mixer (s = 103 W/kg) was used.

Silver chromate, Ag2Cr04, is insoluble. It forms a brick-red precipitate. Calculate the mass of silver chromate that forms when 50.0 mL of 0.100 mol/L silver nitrate reacts with 25.0 mL of 0.150 mol/L... 

Theoretical calculations will always overestimate precipitator efficiencies, probably because of reentrainment. This overestimation could be as large as a factor of 2 or more (Rose and Wood, 1966). Even so, drift velocity or effective migration velocity is the basis for all precipitator calculations and does provide a good base for the comparison of various designs. 

Precipitation is the formation of a compound that exceeds its solubility limit in a given medium. Coprecipitation is the inclusion or trapping of an otherwise soluble compound when a precipitate is formed under the same conditions. Precipitation calculations, including equilibrium diagrams involving the solubility-precipitation of solids, are discussed in Section 5.3. 

Stas found that 100 gm. of pure silver (dissolved in nitric acid) required 54.2075 gm. of sodiur.x chloride for complete precipitation. Calculate the atomic weight of sodium. (Assume atomic weights of silver and chlorine and AgNOg + NaCl = AgCl + NaNOg.)... 

Kolthoff and Noponen mixed 25 ml of 0.11 Af barium nitrate, 10 ml of 0.1 M lead nitrate, and 25 ml of 0.1 M sodium sulfate. After precipitation and digestion for 1 h, 59% of the lead remained in the precipitate. Calculate the recovery and separation (enrichment) factors for barium. 

The calculation of rates based on changes in solute species concentrations in soils, aquifers, and watersheds requires partitioning the reactant between sources produced by primary mineral dissolution and sinks created by secondary mineral precipitation. Calculation of weathering rates based on solute transport requires knowing the nature and rate of fluid flow through soils, aquifers, and watersheds. 

Calculate the mass of the dry precipitate. Calculate the number of moles of precipitate produced in the reaction. (Hint Use the results from step 13.)... 

Fig. 11. Range of possible temperature and 8 0 j,jr conditions for calcite and dolomite (ankerite) precipitation. Calculated from the calcite-water fractionation equation in Friedman O Neil (1977). As in Fig. 10, 8 0 values plotted for dolomite/ankerite are adjusted -3%o from measured values to compensate for differences in fractionation relative to calcite (Land, 1980), thus allowing the same fractionation equation to be used for both minerals. (This correction effectively turns values for dolomite/ankerite into calcite values for the purpose of examining the range of temperature and 6 0 a,er conditions in effect during precipitation, and is approximate only.)...

In a group 1 analysis, a student adds HCl acid to the unknown solution to make [Cl ] = 0.15 M. Some PbCl2 precipitates. Calculate the concentration of... 

TABLE I Calculated and observed 7oo Tor different pHs assuming iron hydroxide precipitation. Calculated assuming initial carbon = 8 mmol/L, initial = -127oo dolomite = -17oo. = 2.8, starting water... 

When aqueous solutions of NaiS04 and Pb(N03)2 are mixed, PbS04 precipitates. Calculate the mass of PbS04 formed when 1.25 L of 0.0500 M PblNOsli and 2.00 L of 0.0250 M Na2S04 are mixed. 

For a system containing two or more possible precipitates, calculate the invariant point(s), or mutual saturation pointfs) using the Newton-Raphson technique. 

An equation of state can be used to calculate. (P, T). The expression for the PR-EOS for the calculation of (P, T) is provided by Eq. (3.22) of Chapter 3. Then with A/i, T[, and Ac/jp one can calculate fpure i( P)-order to proceed with the wax-precipitation calculations, one needs to dssume a proper solid model. Currently, there are two types of solid models. One is the solid-solution model, and the other is the multisolid-phase model. These models are presented below. 

Here, we provide both the equilibrium and the material balance equations for wax precipitation calculations for solid-liquid equilibria. At fixed temperature and pressure, for every component i, the multisolid-phase model must satisfy... 

Various methods have been used for asphaltene-precipitation calculations. Most models in the literature are based on the classical Flory-Huggins polymer-solution theory (see Chapter 1) coupled with the Hildebrand regular solution (see Chapter 1) (Hirschberg et al., 1984 Burke et al., 1990 Kokal et al., 1992 Kawanaka et ah, 1991 MacMillan... 

Gibbs free energy of the precipitated phase. In order to evaluate the Gibbs free energy of the precipitated phase, first the state of this phase should be ascertained. Most of the asphaltene precipitation calculations are based on the assumption that the precipitate is a solid phase. This assumption is most probably true at room temperature but may not be valid at reservoir temperatures which are often higher than 330 K. Experimental studies have shown that the precipitated phase is in the form of dark solid particles when a crude oil is diluted with propane at room temperature (Kokal et al., 1992), When the same crude oil is diluted with n-pentane or a heavier normal alkane at room temperature, the precipitated phase has a crystalline state (Kokal et al., 1992). Chung et al. (1991) also observed the precipitate to be in a solid state when a crude oil was mixed with n-pentane at room temperature. 

In asphaltene precipitation calculations, T, Pf.,co and interaction coefficients should be provided for the EOS, The calculations in Figs. 5.13 and 5.14 are based on the PR-EOS. The critical pressures of resins and asphaltenes were set to 8.8 and 8.2 bar, respectively. The acentric factors of resins and asphaltenes were set to 1.8 and 2.0, respectively. The Cavett (1964) correlation was used to estimated and except for asphaltenes and resins. The binary interaction coefficient between asphaltene and resin is set to zero, and between methane and asphaltene, and methane and resin are set to 0.14 and 0.1, respectively. Other binary interaction coefficients are set according to Table 3.3 of Chapter 3. 

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