Significant figure molecular mass

If the numbers being added do not have the same number of significant figures, we are limited by the least-certain one. For example, the molecular mass of KrF2 is known only to the third decimal place, because we only know the atomic mass of Kr to three decimal places ... 

Express the molecular mass ( uncertainty) of C9H906N3 with the correct number of significant figures. 

Modern mass spectrometers are so precise that molecular masses can often be measured to seven significant figures. A 12Ci01H8 molecule of naphthalene, for example, has a molecular mass of 128.0626 amu as measured by mass spectrometry. 

Colloidal systems are generally of a polydispersed nature - i.e. the molecules or particles in a particular sample vary in size. By virtue of their stepwise build-up, colloidal particle and polymer molecular sizes tend to have skew distributions, as illustrated in Figure 1.2, for which the Poisson distribution often offers a good approximation. Very often, detailed determination of relative molecular mass or particle size distribution is impracticable and less perfect experimental methods, which yield average values, must be accepted. The significance of the word average depends on the relative contributions of the various molecules or particles to the property of the system which is being measured. 

With the development of high resolution mass spectroscopy the mass of the molecular fragment can be measured to seven significant figures. These very accurate relative atomic masses make it possible to distinguish molecules with very similar molecular mass values. 

Figure 8.1) [28]. Thus the molecular mass determined by these techniques corresponds to that calculated using the chemical mass of each element present in the protein. Both values are significantly different from one another. Indeed, the difference between the isotopic mass and the chemical mass of a peptide or of a protein is about 1 Da per 1500 Da. Hence, specifying the mass we are talking about is important. The choice is determined by the resolution of the analyser and the mass of the ion being analysed. 

A newly synthesized compound has the molecular formula ClF202PtFg. Compute, to four significant figures, the mass percentage of each of the four elements in this compound. 

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