Limiting-reactant problem calculating

Mixing the two solutions will produce 2.50 X 10 mol of Fe (0H)3 precipitate, which is 2.67 g. The mixed solution contains Na cations and Cl anions, too, but we can ignore these spectator ions in our calculations. Notice that this precipitation reaction is treated just like other limiting reactant problems. Examples and further illustrate the application of general stoichiometric principles to precipitation reactions. 

Any of the types of problems discussed in Chapters 3 and 4 can involve gases. The strategy for doing stoichiometric calculations is the same whether the species involved are solids, liquids, or gases. In this chapter, we add the ideal gas equation to our equations for converting measured quantities into moles. Example is a limiting reactant problem that involves a gas. 

C05-0040. Summarize the strategy for calculating final pressures of gases in a limiting reactant problem. 

New NH3/NH4+ buffer When 0.142 mol per liter of HC1 is added to the original buffer presented in (a), it reacts with the base component of the buffer, NH3, to form more of the acid component, NH4+ (the conjugate acid of NH3). Since HC1 is in the gaseous phase, there is no total volume change. A new buffer solution is created with a slightly more acidic pH. In this type of problem, always perform the acid-base limiting reactant problem first, then the equilibrium calculation. 

For the rest of the exercise, the plan is straightforward for the neutralization reaction between HN03 and NaOH, perform the limiting reactant problem. The pH is determined from the concentration of excess HN03 or NaOH. Each calculation is totally independent of the other calculations. 

Before the equivalence point, the pH is determined by the buffer solution consisting of the unreacted CH3COOH and NaCH3COO produced by the reaction. Each calculation is a limiting reactant problem using the original concentration of CH3COOH. 

Given a set of initial masses of reactants and a balanced chemical equation, determine the limiting reactant and calculate the masses of reactants and products after the reaction has gone to completion (Section 2.6, Problems 47 and 48). 

To solve limiting quantities problems, the first step is to recognize that it is such a problem. In these problems, the quantities of two (or more) reactants are given. Make sure that all the quantities are in moles, or convert them to moles. Select one of the quantities and calculate how much of the other(s) will react with that quantity, as we did in Section 5.1. If we calculated that we need more moles of the second reactant than is present, then the second reactant is in limiting quantity. If we calculated that we have more moles of the second reactant than is needed, the first reactant is in limiting quantity. We use the number of moles of limiting reactant to calculate the quantity of reaction that will occur. 

Plan We first write the balanced equation. Because the amounts of two reactants are given, we know this is a limiting-reactant problem. To determine which reactant is limiting, we calculate the mass of N2 formed from each reactant assuming an excess of the other. We convert the grams of each reactant to moles and use the appropriate molar ratio to find the moles of N2 each forms. Whichever yields less N2 is the limiting reactant. Then, we convert this lower number of moles of N2 to mass. The roadmap shows the steps. Solution Writing the balanced equation ... 

Analyze We are asked to calculate the number of moles of product, NH3, given the quantities of each reactant, N2 and H2, available in a reaction. This is a limiting reactant problem. 

To determine the pH of the solution, we first calculate the amount of each reactant and each product present at the completion of the reaction. Because you can assume this neutralization reaction proceeds as far toward the product side as possible, this is a limiting reactant problem. 

Plan We are asked for the amount of product formed in a reaction, given the amounts of two reactants, so this is a limiting reactant problem. If we assume that one reactant is completely consumed, we can calculate how much of the second reactant is needed in the reaction. By comparing the calculated (juantity with the available amount, we can determine which reactant is limiting. We then proceed with the calculation using the quantity of the itmiting reactant. 

Plan We are asked to calculate the amoimt of product, given the amoimts of two reactants, so this is a limiting reactant problem. TTius, we must first identify the limiting reagent. To do so, we must calculate the number of moles of each reactant and compare their ratio with that required by the balanced equation. We then use the quantity of the limiting reagent to calculate the mass of Ba3(P04)2 that forms. 

If you can t decide how to solve a limiting reactant problem, as a last resort you could do the entire calculation twice—once based on each reactant amount given. The mwUer answer is the correct one. 

In a limiting reactant problem, a certain quantity of each reactant is given and you are usually asked to calculate the mass of product formed. If 10.0 g of Y2 is reacted with 10.0 g of XY, outline two methods you could use to determine which reactant is limiting (runs out first) and thus determines the mass of product formed. 

Solving Limiting-Reactant Problems In limiting-reactant problems, the quantities of two (or more) reactants are given, and we first determine which is limiting. To do this, just as we did with the cars, we use the balanced equation to solve a series of calculations to see how much product forms from the given quantity of each reactant the limiting reactant is the one that yields the least quantity of product. 

Calculating Quantities in a Limiting-Reactant Problem Amount to Amount... 

Plan This is a limiting-reactant problem because the quantities of two reactants are given. After balancing the equation, we determine the Umiting reactant. From the molarity and volume of each solution, we calculate the amount (mol) of each reactant. Then, we use the molar ratio to find the amount of product (HgS) that each reactant forms. The limiting reactant forms fewer moles of HgS, which we convert to mass (g) of HgS using its molar mass (see the road map). We use the amount of HgS formed from the limiting reactant in the reaction table. 

Plan (a) and (b) From the depictions, we note the charge and number of each kind of ion and use Table 4.1 to determine the ion combinations that are soluble, (c) Once we know the combinations. Table 4.1 tells which two ions form the solid, so the other two are spectator ions, (d) This part is a limiting-reactant problem because the amounts of two species are involved. We count the number of each kind of ion that formed the solid. We multiply the number of each reactant ion by 0.010 mol and calculate the amount (mol) of product formed from each. Whichever ion forms less is limiting, so we use the molar mass of the precipitate to find mass (g). 

We can summarize the limiting-reactant problem as follows. Suppose you are given the amounts of reactants added to a vessel, and you wish to calculate the amount of product obtained when the reaction is complete. Unless you know that the reactants have been added in the molar proportions given by the chemical equation, the problem is twofold (1) you must first identify the limiting reactant (2) you then calculate the amount of product from the amount of limiting reactant. The next examples illustrate the steps. 

A type of reasoning frequently used in science involves what if thinking. A scientist will assume that a particular condition or set of conditions is true and then calculate the answer based on this assumption. If the answer proves to be impossible—if it contradicts known facts—that answer is discarded and another is considered. In limiting-reactant problems, we need to identify the limiting reactant. We can answer this question by assuming that each reactant is limiting. 

The quantities of the reactants can also be given in grams. The calculations to identify the limiting reactant are the same as before, but the grams of each reactant must first be converted to moles, then to moles of product, and finally to grams of product. Then select the smaller mass of product, which is from complete use of the limiting reactant This calculation is shown in Sample Problem 9.6. 

Sometimes our interest in a limiting reactant problem is in determining how much of an excess reactant remains, as well as how much product is formed. This additional calculation is illustrated in Example 4-12. 

Five tasks must be performed in this problem (1) Represent the reaction by a chemical equation in which the names of reactants and products are replaced with formulas. (2) Balance the formula equation by inspection. (3) Determine the limiting reactant. (4) Calculate the theoretical yield of sodium nitrite based on the quantity of limiting reactant. (5) Use... 

A table of amounts is a convenient way to organize the data and summarize the calculations of a stoichiometry problem. Such a table helps to identify the limiting reactant, shows how much product will form during the reaction, and indicates how much of the excess reactant will be left over. A table of amounts has the balanced chemical equation at the top. The table has one column for each substance involved in the reaction and three rows listing amounts. The first row lists the starting amounts for all the substances. The second row shows the changes that occur during the reaction, and the last row lists the amounts present at the end of the reaction. Here is a table of amounts for the ammonia example ... 

The problem asks for a yield, so we identify this as a yield problem. In addition, we recognize this as a limiting reactant situation because we are given the masses of both starting materials. First, identify the limiting reactant by working with moles and stoichiometric coefficients then carry out standard stoichiometry calculations to determine the theoretical amount that could form. A table of amounts helps organize these calculations. Calculate the percent yield from the theoretical amount and the actual amount formed. 

The quantitative treatment of a reaction equilibrium usually involves one of two things. Either the equilibrium constant must be computed from a knowledge of concentrations, or equilibrium concentrations must be determined from a knowledge of initial conditions and Kgq. In this section, we describe the basic reasoning and techniques needed to solve equilibrium problems. Stoichiometry plays a major role in equilibrium calculations, so you may want to review the techniques described in Chapter 4, particularly Section 4- on limiting reactants. 

Again, we use the standard approach to an equilibrium calculation. In this case the reaction is a precipitation, for which the equilibrium constant is quite large. Thus, taking the reaction to completion by applying limiting reactant stoichiometry is likely to be the appropriate approach to solving the problem. 

If the quantities of both reactants are in exactly the correct ratio for the balanced chemical equation, then either reactant may be used to calculate the quantity of product produced. (If on a quiz or examination it is obvious that they are in the correct ratio, you should state that they are so that your instructor will understand that you recognize the problem to be a limiting quantities problem.)... 

---