Molecular formulae, of compounds

J.10 (a) White phosphorus, which has the formula P4, burns in air to form compound A, in which the mass percentage of phosphorus is 43.64%, with the remainder oxygen. The mass spectrum of A yields a molar mass of 283.9 g-mol. Write the molecular formula of compound A. (b) Compound A reacts with water to form compound B, which turns litmus red and has a mass percentage composition of 3.087% 11 and 31.60%... 

This is a critical chapter in your study of chemistry. Our goal is to help you master the mole concept. You will learn about balancing equations and the mole/mass relationships (stoichiometry) inherent in these balanced equations. You will learn, given amounts of reactants, how to determine which one limits the amount of product formed. You will also learn how to determine the empirical and molecular formulas of compounds. All of these will depend on the mole concept. Make sure that you can use your calculator correctly. If you are unsure about setting up problems, refer back to Chapter 1 of this book and go through Section 1-4, on using the Unit Conversion Method. Review how to find atomic masses on the periodic table. Practice, Practice, Practice. 

The molecular formula of compounds A and B (C6H10O2) indicates an index of hydrogen deficiency of 2. Because we are told the compounds are diketones, the two carbonyl groups account for all the unsaturations. 

In section 6.4, you learned several practical methods for determining empirical and molecular formulas of compounds. You may have noticed that these methods work because compounds react in predictable ways. For example, you learned that a compound containing carbon and hydrogen reacts with oxygen to produce water and carbon dioxide. From the mass of the products, you can determine the amount of carbon and hydrogen in the reactant. You also learned that a hydrate decomposes when it is heated to form water and an anhydrous compound. Again, the mass of one of the products of this reaction helps you identify the reactant. In Chapter 7, you will learn more about how to use the information from chemical reactions in order to do quantitative calculations. 

Use these data to determine the molecular formulas of compounds, I, II, and III and to determine the relative values for the atomic masses of hydrogen and nitrogen. 

The molecular formula of compound 44 was established as CssHsgOnNSNa on the basis of the pseudomolecular ion peak at m/z 762.3481 [M + Na]" in the HRFABMS. Examination of the H- and C-NMR spectra indicated that 44 possessed the same 3p,6a,8,isp-tetrahydroxy steroidal nucleus as glycosides 43 and 45 bonded to a monosaccharide unit. 

In Section 2-10 we distinguished between simplest and molecular formulas of compounds. We showed how simplest formulas can be calculated from percent compositions of compounds. The molecular weight must be known to determine the molecular formula of a compound. For compounds that are gases at convenient temperatures and pressures, the ideal gas law provides a basis for determining molecular weights. 

Write the empirical (or molecular) formulas of compounds that the elements in the third period (sodium to chlorine) should form with (a) molecular oxygen and (b) molecular chlorine. In each case indicate whether you would expect the compound to be ionic or molecular in character. 

Solution (a) The molecular formula of compounds A, B and C is of the general form 2n-2 formula indicates... 

Examine the following IR spectrum and the molecular formula of compound E, C9Hi20 Tell (See Examples 11.4-11.7)... 

High-resolution mass spectra were obtained for unidentified compounds a, b, c, d, and f. The molecular formula of compounds a, b, c, and d is C12H22O. Proposed structures are isomers of ketones, e.g., a and b might be 2- or 4-isomers of ethylisopropyl cyclohexyl ketone and c and d might be cyclohex-4-ylhexan-2-one or cyclohex-4-yl-4-methylpentan-2-one, respectively. An unidentified compound (e) was found also for the quasi-molecular ion M + 1105. The only fragment was M - 18 in chemical ionisation mass spectroscopy. The molecular formula of unidentified compound f is C15H14O. The proposed structure is... 

The mass spectrum of compound B, a colorless liquid, shows these peaks in its mass spectrum. Determine the molecular formula of compound B and propose a structural... 

High resolution mass spectra were obtained for unidentified compounds a, b, c, d (Tables 3.4 and 3.5). The molecular formula of compounds a, b, c is Proposed structures are isomers of ketones, for example, a and b might be 2- or 4-... 

The molecular formula of compound A, C7H14O, turns into that of compound B, CgHi S. 

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