Buret reading

Gordus, A. A. Statistical Evaluation of Glass Data for Two Buret Readings, /. Chem. Educ. 1987, 64, 516-511. 

C04-0141. A student prepared 1.00 L of a solution of NaOH for use in titrations. The solution was standardized by titrating a sample of potassium hydrogen phthalate whose mass was 0.7996 g. Before titration, the buret reading was 0.15 mL. When the indicator changed color, the buret reading was 43.75 mL. Calculate the molarity of the NaOH solution. 

Alkalinity is usually expressed as the millimoles of H+ required to titrate 1 L of water. Millimoles is calculated by multiplying the molarity of the acid (millimoles per milliliter) by buret reading in milliliters, as shown in the solution to Example 5.1 below. 

Record the buret readings at the end points for all three beakers. Calculate the percent KHP in the sample for all three titrations and include at least a sample calculation in your notebook, along with all results and the average. Calculate the ppt relative standard deviation. If your three results do not agree to within 10.0 ppt relative standard deviation, repeat until you have three that do or until you have a precision satisfactory to you instructor. 

Pipet a 25.00-mL aliquot of this standard calcium solution into each of three 250-mL Erlenmeyer flasks, add the buffer solution, and titrate each to the same end point as before, but use only two drops of EBT. All buret readings should agree to within 0.05 mL. If they do not, repeat until you have three that do. 

In titrimetric analysis (Figure 6.3), a weight or volume of the prepared sample is needed and the sample may need to be dissolved or otherwise pretreated following the weight or volume measurement. The most important part, however, is that a standard solution (the titrant) needs to be prepared and standardized. This solution is used to titrate the sample, and the buret reading is the datum needed for calculating the results. 

The critical datum is not a buret reading, as it was in the case of the volumetric method. Rather, the amount of iodine used is determined coulometrically by computing the coulombs (total current over time) needed to reach the end point. The coulombs are calculated by multiplying the current applied to the anode-cathode assembly (a constant value) by the total time (seconds) required to reach the end point. The modern coulometric titrator automatically computes the amount of moisture from these data and displays it. 

Set up the titration again with 25.00 mL of the degassed soda pop, as in step 3, and titrate to the chosen equivalence point. Repeat at least twice and average the buret readings. 

There is no buret reading in the coulometric Karl Fischer method. How can the results be calculated without a buret reading ... 

For gravimetric analysis, a solution may be needed to react with the analyte. Otherwise it consists of just physical separation operations and usually initial and final weight measurements. For titrimetric analysis, solutions are always needed to react with the analyte and these solutions must be standardized. Also, a critical measurement is a volume measurement (buret reading). 

Using the molar mass, calculate the moles of all weighed samples. The moles of substances are converted to molarities by dividing by the volume (in liters) of the solution. Molarities may also be determined from pipet or buret readings using the dilution equation. (If a buret is used, one of the volumes is calculated from the difference between the initial and final readings.) The dilution equation may be needed to calculate the concentration of each reactant immediately after all the solutions are mixed. 

If a gas is being generated, plot the volume of gas formed versus time. The volume of the gas formed is the difference between the initial buret reading and the buret reading at a particular time. The slope of this graph is the rate. 

The difference in the buret readings is the volume of NaOH solution added (convert this to liters). 

Figure 3-3 Calibration curve for a 50-mL buret. The volume delivered can be read to the nearest 0.1 mL. If your buret reading is 29.43 mL, you can find the correction factor accurately enough by locating 29.4 mL on the graph. The correction factor on the ordinate (y-axis) for 29 4 mL on the abscissa (x-axis) is 0.03 mL (to the nearest 0.01 mL).

A key feature of systematic error is that it is reproducible. For the buret just discussed, the error is always —0.03 mL when the buret reading is 29.43 mL. Systematic error may always be positive in some regions and always negative in others. With care and cleverness, you can detect and correct a systematic error. 

Relative uncertainty compares the size of the absolute uncertainty with the size of its associated measurement. The relative uncertainty of a buret reading of 12.35 0.02 mL is a dimensionless quotient ... 

C. Example Analysis of Active Hydrides or Alkyl Compounds Using a Gas Buret. This procedure utilizes the gas buret illustrated in Fig. 1.19 to analyze active hydrides or alkyls. First, the water levels in the reservoir and buret sides are adjusted to equal height and an initial buret reading is taken. A sample of known weight is introduced into the hydrolysis flask using a syringe. After gas... 

The reagent of known concentration is usually used as the titrant. The titrant is poured into a buret (also spelled burette) until it is nearly full, and an initial buret reading is taken. Buret numbering is close to zero when nearly full. A known volume of the solution of unknown concentration is added to a flask and placed under the buret. The indicator is added or the pH meter probe is inserted. 

The buret s stopcock is opened and titrant is slowly added until the solution permanently changes color or the pH rapidly changes. This is the end point of titration, and a final buret reading is made. 

Example A 20.0 mL sample of an HCI solution is titrated with 0.200 M NaOH. The initial buret reading is 1.8 mL and the final buret reading at the titration endpoint is 29.1 mL. What is the molarity of the HCI sample ... 

Reaction time (min.) Buret readings before titration (A) Buret readings after titration (B) mL acid titrated (B) - (A) mL 0.05 N HC1 used up in the reaction (B) - (A) - blank... 

Place the flask that contains the vitamin C sample under the buret and add the iodine solution dropwise, while swirling, until the indicator just changes to dark blue. This color should persist for at least 20 sec. Record the final buret reading (3b). Calculate the total volume of iodine solution required for the titration (3c), the weight of vitamin C in the sample (4), and percent (w/v) of vitamin C in the drink (5). Repeat this titration procedure twice more, except using 20- and 30-mL portions of the same fruit drink instead of 10 mL. Record the volumes of iodine solution that are required for each titration. 

You have analyzed a 15.0-mL sample of orange juice for vitamin C. Using a 0.005 M iodine solution for titration, your initial buret reading was 1.0 mL and the final reading was 7.4 mL. What was the concentration of vitamin C (mg/100 mL) in your orange juice Show your work. 

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