Experiment 6 Standardization of a Solution

The concentration of a solution is determined by titration with a sample of known composition. (See the Stoichiometry chapter.) 

The mass of the sample is calculated from the differences between masses 1 and 2. The volume added is calculated by taking the difference between measurement 3 and either measurement 4 or 5. 

A plot of pH versus the volume added is made. This graph or the difference between measurements 3 and 5 gives the volume of titrant. 

The mass of the sample is converted to moles by using the molar mass. The moles of titrant may be calculated from a consideration of the moles of sample and the balanced chemical equation. The moles of titrant divided by the liters of solution gives the molarity of the solution. 

A solution could be prepared by dissolving a known amount of solute in a volumetric flask and diluting to volume. 

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Experiment 6 Standardization of a Solution Using a Primary Standard... 

A student performed an acid-base titration. The student began Part I of the experiment by determining the exact concentration of a base through the standardization of a basic solution using a primary acidic HCl standard. The student measured out approximately 10 mL of 6.00 M NaOH and diluted it to approximately 600 mL. The student discovered that 48.7 mL of the NaOH solution was needed to neutralize exactly 50.0 mL of a 0.100 M HCl solution. 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

All solvents used for general applications were of reagent grade. For special purposes, purification of solvents was effected using standard procedures. All other reagents were used as supplied commercially except as noted. A solution of chloromethyl methyl ether (6 mmole/mL) in methyl acetate was prepared by adding acetyl chloride (141.2 g, 1.96 mol) to a mixture of dimethoxy methane (180 mL, 2.02 mol) and anhydrous methanol (5.0 mL, 0.12 mol).20 The solution was diluted with 300 mL of 1,1,2,2-tetrachloroethane and used as a stock solution for the chloromethylation experiments. 

In a typical experiment, 50 g of NaOH flakes were first dissolved in 120 g of water. The required amount of catalyst was then wet loaded into the caustic solution and 72 g of ethanolamine added. Before heating the autoclave was closed and the air inside purged out with N2. The autoclave was then heated with the set temperature (433 K) reached after about 80 minutes. This time is taken as zero in the plots that follow. The standard operating conditions used for catalyst evaluation unless otherwise stated were as follows temperature 433 K pressure 0.9 MPa ethanolamine concentration 2.9 M NaOH concentration 6.2 M stirrer speed 80 rpm catalyst 8 g with particle size 106-211 pm. 

Similarly, to standardize a solution means to determine its concentration to three or more significant figures. For example, if a solution of NaOH is made up to be approximately 0.1 M, a standardization experiment may be performed and the concentration determined to be 0.1012 M. We will discuss the details of such an experiment in Section 4.6. 

Biochemical oxygen demand (BOD) is one of the most widely determined parameters in managing organic pollution. The conventional BOD test includes a 5-day incubation period, so a more expeditious and reproducible method for assessment of this parameter is required. Trichosporon cutaneum, a microorganism formerly used in waste water treatment, has also been employed to construct a BOD biosensor. The dynamic system where the sensor was implemented consisted of a 0.1 M phosphate buffer at pH 7 saturated with dissolved oxygen which was transferred to a flow-cell at a rate of 1 mL/min. When the current reached a steady-state value, a sample was injected into the flow-cell at 0.2 mL/min. The steady-state current was found to be dependent on the BOD of the sample solution. After the sample was flushed from the flow-cell, the current of the microbial sensor gradually returned to its initial level. The response time of microbial sensors depends on the nature of the sample solution concerned. A linear relationship was foimd between the current difference (i.e. that between the initial and final steady-state currents) and the 5-day BOD assay of the standard solution up to 60 mg/L. The minimum measurable BOD was 3 mg/L. The current was reproducible within 6% of the relative error when a BOD of 40 mg/L was used over 10 experiments [128]. 

EXAMPLE 2.6 Temperature Dependence of Diffusion Coefficients. Suppose the diffusion coefficient of a material is measured in an experiment (subscript ex) at some temperature Tex at which the viscosity of the solvent is qgx. Show how to correct the value of D to some standard (subscript s) conditions at which the viscosity is j s. Take 20°C as the standard condition and evaluate D°20 for a solute that displays a D° value of 4.76-10 11 m2 s 1 in water at 40°C. The viscosity of water at 20 and 40°C is 1.0050-10 2 and 0.6560 -10 2 P, respectively. 

The density stepping method was then run on a spiked soil sample. Five grams of soil were spiked with the same solution of herbicide standards used to spike the celite sample and the solvent was allowed to evaporate. The spiked sample was then placed into an extraction thimble and extracted. The results were different than those obtained from the spiked celite. Even at a high density of C02 the herbicides were not extracted. Previous experience showed that using water as a modifier aided in the extraction of diuron from soils (6)(7). Therefore 1 ml. of water was added to the spiked soil and the sample rerun at a density of 0.9 g/ml of C02. The results showed a significant increase in recovery of the herbicides with the addition of water. This demonstrates that the addition of a modifier added to the extraction cell can have a significant effect upon the extraction recoveries (8)(9). The results are summarized in Table VIII. 

Figure 15. Effect of segregation on polymerization of styrene in cyclohexane solution. Standard CSTR with h baffles and a 6-blade turbine, V = 670 cm, T = 75 °C. Dispersion Index DI vs. space time. Influence of agitation speed. Curves S (segregated flow) and M (well-micromixed flow) calculated from batch experiments. Initiator PERKAD0X l6, A = 0.033 mol L - -, kd = 5 x 10 5 s-1, f = 0.85 Mq = 6.65 mol L l, SQ = 2.22 mol IT1.

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