Equations Lead chromate

Lead chromates are prepared by precipitation techniques from soluble salts ia aqueous media. The raw material Hst iacludes a number of different lead compounds, eg, Htharge, lead nitrate, basic lead acetate, basic lead carbonate, as well as acids, alkahes, sodium bichromate, and sodium chromate. The typical reaction can be represented by the foUowiag equation ... 

Write a balanced net ionic equation for the production of the yellow precipitate when potassium chromate is added to the paint chip and yellow lead chromate precipitate is formed. 

J ) Recall the properties of lead chromate. Complete the equation —... 

If 100 gm. of lead nitrate produce 97.576 gm. of lead chromate, what is the atomic weight of chromium (Equation is K2Cr04 + Pb(N03)2 = PbCr04 + 2 KNO3.)... 

The common ion effect and Le Chatelier s principle A saturated solution of lead chromate (PbCr04) is shown in Figure 18-17a. Note the solid yellow PbCr04 in the bottom of the test tube. The solution and solid are in equilibrium according to this equation. 

Substitution of typical values into equation 6.39 leads to some interesting observations. Small crystals of reasonably soluble salts may dissolve in fractions of a second, but those of sparingly soluble substances can take very long periods of time. For example, a Ipm crystal (r = 5 x 10 m) of lead chromate (D 10 m s V 5 X 10 m moP c 10 molm ) would take about 7h to dissolve in water at room temperature. A 10 pm crystal would take about 30 days. Tiny crystalline fragments of relatively insoluble substances may therefore remain undissolved in unsaturated solutions and act as nuclei in subsequent crystallization operations. The behaviour of precipitates attributed to the past history of the system may well be associated with this behaviour. 

Consider a saturated solution of lead(II) chromate. See Figure 9.5(A) on the next page. The following equation represents this equilibrium. 

Pour potassium chromate and dichromate solutions into separate test tubes and add a solution of a barium salt to each of them. What is the composition of the precipitates See how the obtained salts react with dilute acids. Perform similar experiments with a lead salt. Write the equations of the reactions. 

Consider the unbalanced chemical equation corresponding to the formation of solid lead(II) chromate, PbCr04 ... 

Potassium chromate and lead(II) acetate are both dissolved in a beaker of water, where they react to form solid lead(II) chromate. What is the balanced net ionic equation describing this reaction ... 

Figure 4.4 An aqueous ionic reaction and its equations. When silver nitrate and sodium chromate solutions are mixed, a reaction occurs that forms solid silver chromate and a solution of sodium nitrate. The photos present the macroscopic view of the reaction, the view the chemist sees in the lab. The blow-up arrows lead to an atomic-scale view, a representation of the chemist s mental picture of the reactants and products. (The pale ions are spectator ions, present for electrical neutrality, but not involved in the reaction.) Three equations represent the reaction in symbols. (The ions that are reacting are shown in red type.) The molecular equation shows all substances intact. The total Ionic equation shows all soluble substances as separate, solvated ions. The net Ionic equation eliminates the spectator ions to show only the reacting species.

This is the precipitation of lead(ll) chromate, PbCr04, that occurs when a solution of sodium chromate, N02CrO4, is added to a solution of lead(ll) nitrate, Pb(N03)2- The equation for the doublereplacement precipitation reaction is Na2Cr04(aq) + Pb(N03)2(aq) PbCr04(s) + 2 NaN03(aq). The question that this chapter asks-and answers—is, "How many grams of lead(ll) chromate will precipitate if 123 g Na2Cr04 reacts "... 

---