Titration Using Molarity

14 Given the volume of a solution that reacts with a known mass of a primary standard and the equation for the reaction, calculate the molarity of the solution. 

Notice that the water in the hydrate is not a part of the equation. When one mole of H2C2O4 2 H2O dissolves, the hydrate water becomes a part of the solution and one mole of H2C2O4 is available for reaction. The hydrate water must be taken into account in weighing the H2C2O4 2 H2O, however. 

A chemist dissolves 1.18 g H2C2O4 2 H2O (126.07 g/mol) in water and titrates the solution with a solution of NaOH of unknown concentration. She determines that 28.3 mL NaOH(aq) is required to neutralize the acid. Calculate the molarity of the NaOH solution. 

The general plan for any titration problem is outlined by Equation 16.12. You 

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Solution Stoichiometry Titration Using Molarity Titration Using Normality (Optional)... 

In this chapter, you learned about solutions and how to use molarity to express the concentration of solutions. You also learned about electrolytes and nonelectrolytes. Using a set of solubility rules allows you to predict whether or not precipitation will occur if two solutions are mixed. You examined the properties of acids and bases and the neutralization reactions that occur between them. You then learned about redox reactions and how to use an activity table to predict redox reactions. You learned about writing net ionic equations. Finally, you learned how to use the technique of titrations to determine the concentration of an acid or base solution. 

Methyllithium (1.4 M, low halide) in diethyl ether, was purchased from the Aldrich Chemical Company, Inc., and was used without further purification. Titration using the method of Watson and Eastham5 was used to determine the molarity. The best and most reproducible results (ca. 88% yield) were obtained when freshly opened methyllithium was used. The yield was severely depressed when 0.86 M methyllithium was used (< 33%). The checkers used a recently purchased, freshly opened bottle of methyllithium and did not determine its molarity by titration. 

The normality or molarity of the acid can be determined by titration with a standard solution of sodium hydroxide using a color indicator, or by potentio-metric titration using a pH meter or a millivoltmeter. The sulfate anion in dilute acid can be measured by precipitation with barium chloride or by ion chromatography. 

These questions have been probed using a variety of solution techniques including visible absorption spectra (101), chiroptical and MCD spectra (102), 2H NMR spectra (103), rapid kinetic measurements (92), pH titrations (98), molar volumes (97), and electrochemical methods (98,104). 

The advantages of using molarity are twofold (1) Stoichiometry calculations are simplified because numbers of moles are used rather than mass, and (2) amounts of solution (and therefore of solute) are measured by volume rather than by mass. As a result, titrations are particularly easy (Section 3.10). 

Available from Ventron Corporation, Alfa Products, Beverly, MA 01915. t The molarity of the butyllithium solution may be checked before use by the procedure devised by Gilman.3 This involves careful hydrolysis of a measured sample using excess distilled water, followed by titration against standard hydrochloric acid solution with phenolphthalein as indicator. Since the butyllithium solution may contain some lithium hydroxide, it is necessary to carry out an identical titration of a sample which has undergone complete reaction with benzyl chloride in order to determine the lithium hydroxide present. From the difference between the two titrations, the molarity of the butyllithium may be calculated. 

A student performs a titration using 1.00 M NaOH to find the unknown molarity of a solution of HC1. The student records the data as shown below. What is the molarity of the solution of HC1 ... 

In a measurement for end-group analysis, 0.8632 g of a CTPB sample dissolved in 1 3 mixture of ethanol and toluene consumed 5.2 ml of 0.1240 N alcoholic potassium hydroxide solution in titration using phenolphthalein as the indicator. Calculate the molar mass of the polymer. 

In a titration, the molarity of one of the reactants, acid or base, is known, but the other is unknown. The known reactant molarity is used to find the unknown molarity of the other solution. Solutions of known molarity that are used in this fashion are called standard solutions. 

An acid-base titration uses an acid-base reaction to determine the molarity of an unknown acid or base. 

In this chapter (as in Chapter 9) molality, which is number of moles of solute per kilogram of solvent and indicated by the symbol M, will be used. Molarity, defined as the number of motes of solute per liter of solution, is another commonly used concentration unit, but can be somewhat more difficult to deal with since the volume of a solution varies with composition and temperature. However, if the solvent is water and the solution is dilute in solute (so that one liter of solution contains one kilogram of water), as-is generally the case in this chapter, molality and molarity are equal. Therefore, in some of the calculations that follow, especially the titration calculations in this section, we may ignore the distinction between molality (moles of solute per kilogram of water) and molarity (moles of solute, per liter of solution.) -... 

Activity coefficient data for ions in solutions of the types commonly used in oxidation-reduction titrations and electrochemical work arc somewhat limited. As a result, we must use molar concentrations rather than activities in many calculations.. sing molar concentrations may cause appreciable errors. Such calculations... 

In view of the above observations it seems appropriate to follow the reaction between heparin and antibiotics by conductometric titration, using the usual method. 0.5 x 10 molar solutions of antibiotic were used because these are well-characterized chemical entities and the concentrations are reasonably close to the practical therapeutic range. Heparin, however, is not well characterized and its concentrations are usually indicated in terms of a unit of activity which is defined in terms of... 

Titrate the sample with retinoid using a Hamilton-style syringe. Perform the titration rapidly to minimize photoisomerization and to keep changes in signal due to instability to a minimum. Aim to titrate one molar equivalent of retinoid (compared to the amount of protein) in -5-10 additions (see Note 8) Close the lamp shutter while adding retinoid to minimize photoisomerization. For later reference, record or mark the points of addition... 

For example, consider a student who has determined via a back titration using sodium hydroxide (Chapter 1) the molar mass of an organic acid (molar mass 126gmol ). The total experimental uncertainty is calculated to be 1.5%. The student s experimentally determined value for the organic acid is (130 2) gmohh This means that the student s result lies between 132 and 128gmoH. 

This amount of acid must be in the 10.0 mL of the HCl solution used for the titration. The molarity of the HCl solution can now be calculated. 

The choice of a concentration unit is based on the puipose of the experiment. For instance, we typically use molarity to express the concentrations of solutions for titrations and gravimetric analyses. Mole fractions are used to express the concentrations of gases—and of solutions when we are working with vapor pressures, which we will discuss in Section 13.3. 

An aqueous solution containing Pb and Cd can be titrated using EDTA. If an excess of cyanide is added to the solution, the cadmium is said to be masked by the formation of a cyanide complex. Suppose 20.00 mL of a solution containing only lead and cadmium is first titrated against 45.94 mL of a 0.02000 M solution of EDTA. After adding an excess of sodium cyanide, only 34.87 mL of the same EDTA solution produces an end point. Calculate the molarities of both the lead and the cadmium in the original solution. 

Sweetser and Bricker determined a variety of cations by spectrophotometric titrations with EDTA. Bruckenstein determined water in acetic acid by an ultraviolet photometric titration. C4 and higher molecular-weight olefins in automobile exhausts have been determined by spectrophotometric titration, using the high molar absorptivity of free tribromide ion at 290 m/x. 

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