Atomic Mass of Lead

Determining the Approximate Value of the Atomic Mass of Lead from Its Specific Heat Capacity. To determine the specific heat capacity of a metal, use a calorimeter and a device for heating the metal. A very simple calorimeter can be made from several beakers inserted one into another (Fig. 38). The inner beaker should have a volume of 100 ml, the middle one—300-400 ml, and the outer one—500 ml. Water is poured into the small beaker, while the others are needed to produce an air thermal-insulating layer. 

A device for heating a metal also consists of three beakers of different volumes inserted one into another so that the bottom of one beaker does not contact that of its neighbour. Unlike a calorimeter, water is poured into all three beakers. 

Pour 50 ml of water into the small beaker of the heating device and an amount of it into the other two beakers such that the level 

Weigh the small beaker of the calorimeter and pour exactly 50 ml of water into it. Measure and record the temperature of the boiling 

Form 6. DETERMINATION OF THE ATOMIC MASS OF LEAD FROM ITS 

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To determine the amount of heat absorbed by the glass of the calorimeter beaker, mark the level of the water in the beaker when running the experiment. Use the data obtained to approximately determine the mass of the glass heated by the water. Consider that the mass of the thermometer glass immersed in the liquid is about 2 g. Use the found specific heat capacity to calculate the atomic mass of lead by the Dulong and Petit law. 

Transfer the bowl into a muffle furnace and roast the precipitate at 400-450 °C during one hour. Cool the bowl with the substance to room temperature in a desiccator and weigh it. Use the found value of the equivalent and the approximate value of the atomic mass of lead to determine its valence. Calculate a more accurate value of the atomic mass of lead from the obtained data, compare your result with the value of the atomic mass of this element given in Mendeleev s periodic table, and establish the magnitude of the error in per cent. 

At the time, Soddy was seeking evidence that lead from thorium ores had different atomic weights from normal lead. When Soddy announced the discovery of a sample of lead of atomic mass 207.74, he acknowledged the contribution of Hitchins for the separation and analysis work. Thus, Hitchins precise and accurate measurements on the atomic masses of lead from different sources were among the first evidence for the existence of isotopes.51 In addition, Hitchins took over the research on protactinium from Cranston when the latter was drafted for the First World War. 

Like carbon, most elements are a mixture of isotopes. In most cases, the fraction of each isotope is the same no matter where the sample comes from. Most average atomic masses can be determined to several decimal places. However, some elements have different percentages of isotopes depending on the source of the sample. This is true of native lead, or lead that occurs naturally on Earth. The average atomic mass of lead is given to only one decimal place because its composition varies so much from one sample to another. 

The element lead (Pb) consists of four naturally occurring isotopes with masses 203.97302,205.97444,206.97587, and 207.97663 amu. The relative abimdances of these four isotopes are 1.4,24.1,22.1, and 52.4%, respectively. From these data, calculate the average atomic mass of lead. 

Solution. The formula mass of PbS is obtained by adding the atomic masses of lead and sulfur, which we obtain from the table inside the back cover ... 

Example 4-5. A 1.0000-g sample of lead sulfide, PbS, prepared from an ore of uranium (Katangan curite) was found to give 0.8654 g of metallic lead on reduction. Another 1.0000-g sample of lead sulfide prepared from an ore of thorium (Norwegian thorite) was found to give 0.8664 g of metallic lead on reduction. Assuming the atomic mass of sulfur to be 32.064, calculate the two values of the atomic mass of lead. 

In 1914 the American chemist T. W. Richards reported the chemical atomic mass of lead from an ore of uranium to be about 2 d less than that of lead from an ore of thorium. Can you explain this difference ... 

Lead consists of four naturally occurring isotopes. Calculate the atomic mass of lead. (4.5)... 

Use the mass spectrum of lead to estimate the atomic mass of lead. Estimate the mass and percent intensity valnes from the graph to three significant figures. 

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