A student is asked to perform and analyze the result of just buret portion of a

Question

A student is asked to perform and analyze the result of just buret portion of a glasware experiment to determine the accuracy and precision of the buret. The student prepared their buret as shown in the picture below: What is the volume indicated on the buret to the correct number of significant digits? If the student wanted to deliver 10.00 mL of water from the buret into a beaker, what should the final volume reading of the buret read? When measuring the mass of water, the student used the weighing by difference method. What is the result of the following subtraction operation, to the correct number of significant figures:should the final volume reading of the buret read? The student obtained the following measurements: What are the correct calculated values? Mass of dry beaker (g) 30.123 g Mass of beaker plus 1^st water sample 40.110 g Mass of beaker plus 1^si & 2^nd wafer samples 50.234 g Mass of 1^st sample (g) Mass of 2^nd sample (g)

Explanation / Answer

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Burets: Burets are graduated in 0.1 mL increments, with the 0.00 mL mark at the top and the 50.00 mL mark near the bottom. There are also burets with liquid capacities of 25.00 mL and 10.00 mL. A buret must be scrupulously clean before it is used, and its valve must be liquid-tight.

Reading the buret: The volume should be recorded noting the bottom of the meniscus. In reading volumes, the eye must be at the level of the liquid surface to avoid an error due to parallax. Parallax is a condition that causes the volume to appear smaller than its actual value if the meniscus is viewed from above and larger if the meniscus is viewed from below. To avoid parallax be sure that the meniscus is at eye level. If this reading is exactly “0,” record 0.00 mL. Otherwise, count the number of markings between each number, and estimate to the nearest 0.01 mL.

Question 1a) your answer is correct. You can estimate the volume to the nearest 0.01 mL and the uncertainty will be +0.01 mL. Buret division is 0.1 mL

Question 1b) If you observe the numeration in the buret you will see that it increases toward the tip. This means that as you discharge volume form the buret the value in the scale will increase. So the reading after you deliver the 10.00 mL would be 21.33 + 10.00 = 31.33 mL

Question 2: Your answer is correct. To weight mass in the lab we use an analytical balance. The precision and accuracy of many modern analytical balances are very good. The readings in the problem are in grams to the third decimal figure so the precision will be +0.001 g (or 1 mg). The final weight can be reported as (23.110 +0.001)g

Question 3:

Mass of first sample: 40.110 g – 30.123 g = (9.987 +0.002)g

Mass of second sample: 40.110 g – 30.123 g = (9.987 +0.002)g

Explanation: The uncertainty in a measured number carries into calculations made using the number. A calculated result has to be expressed consistently with the uncertainties in the numbers used in the calculation. When adding or subtracting two numbers the uncertainty is the sum of their individual uncertainties.

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