Chemical formulas molar masses

In this chapter, you will learn about the relationships between chemical formulas, molar masses, and the masses of elements in compounds. 

Chemical formula, molar mass and mass percentages... 

We illustrate how the mass percent composition of a compound is related to its chemical formula using ammonium nitrate (NH4 NO3). The molar masses of NH4 NO3 and its constituent elements can be used to convert the chemical formula into mass percentages. 

It is remarkable that no empirical mixture parameters and no experimental data are required to use the equation. The only parameters in the Flory-Huggins equation are the hard core volumes V, which are a pme-component property, and the atomic or group contribution values are found in standard compilations. Since the v/s are significant in the FH equation only in terms of their ratios, pure-liquid molar volumes are often used for V in place of hard core volumes. For solutions of polymers of the same chemical formula, molecular masses are legitimate substitutes for V , for the same reason. Thus the volume fractions ( ) can be substituted by mass fractions W . Either volume fraction or mass fraction is directly related to laboratory data. To avoid mole fractions, the activity tti from Equations (4.368) and (4.369) can be used to calculate by / = aj. ... 

The general topic of this chapter is stoichiometry (stoy-key-OM-e-tree), the study of mass relations in chemistry. Whether dealing with atomic masses (Section 3.1), molar masses (Section 3.2), chemical formulas (Section 3.3), or chemical reactions (Section 3.4), you will be answering some very practical questions that ask how much or how many—." For example—... 

Calculate the molar mass of a compound, given its chemical formula. 

P, with the remainder oxygen. The mass spectrum of compound B yields a molar mass of 97.99 g-mol. Write the molecular formula of compound B. (c) Compound B reacts with an aqueous solution of calcium hydroxide to form compound C, a white precipitate. Write balanced chemical equations for the reactions in parts (a), (b), and (c). 

Just as each element has a characteristic molar mass, so does every chemical compound. Chemical compounds are composed of atoms bound together into molecules or ions clustered together in electrically neutral aggregates. In either case a chemical formula describes the atomic composition of a compound. 

As chemical formulas become more complicated, the calculation of molar mass requires more steps, as shown in Examples 3-10 and 3-11. 

The line drawing and chemical formula of Sevin, a common insecticide, appear in the margin. Determine the molar mass of Sevin. 

To determine the molar mass of a substance, we need its chemical formula and elemental molar masses. From the chemical formula, determine the number of moles of each element contained in one mole of the substance. Multiply each elemental molar mass by the number of moles of that element, and add. 

Before we can calculate a molar mass, we need a chemical formula. Then we can calculate the masses of each of the elements in one mole of the compound. 

The chemical formula of a compound contains essential information about its composition. The formula identifies which elements are present, and it states the number of atoms of each kind present in one unit of the compound. We need the chemical formula of a substance to calculate its molar mass. In fact, almost all chemical calculations require the correct chemical formula. How are chemical formulas determined in the first place ... 

Sometimes chemists have to analyze substances about which they know very little. A chemist may isolate an interesting molecule from a natural source, such as a plant or an insect. Under these conditions the chemical formula must be deduced from mass percentage data, without the help of an expected formula. A four-step procedure accomplishes this by using mass-mole conversions, the molar masses of the elements, and the fact that a chemical formula must contain integral numbers of atoms of each element. 

Analysis of ibuprofen, the active ingredient in several over-the-counter pain relievers, shows that it contains 75.7% carbon, 8.8% hydrogen, and 15.5% oxygen. The mass spectrum of ibuprofen shows that its molar mass is less than 210 g/mol. Determine the chemical formula of this compound. 

To get from elemental analysis to a chemical formula, we begin by dividing each mass by the appropriate molar... 

As with all calculations of chemical amounts, we must work with moles. Because grams are asked for, we must do a mole-mass conversion this requires the molar mass of the substance, which in turn requires that we know the chemical formula. 

C03-0105. The line stmctures of three different plant growth hormones are given below. For each one, write the chemical formula for the compound and calculate its molar mass. 

Does it bother you to find that neither the chemical formula nor the molar mass is needed for these calculations Remember that not all data are necessarily required for any particular calculation. Because average kinetic energy depends on temperature but not on molar mass, we do not need mass information to do this problem. 

We can use the ideal gas equation to calculate the molar mass. Then we can use the molar mass to identify the correct molecular formula among a group of possible candidates, knowing that the products must contain the same elements as the reactants. The problem involves a chemical reaction, so we must make a connection between the gas measurements and the chemistry that takes place. Because the reactants and one product are known, we can write a partial equation that describes the chemical reaction CaC2(. ) +H2 0(/) Gas -I- OH" ((2 q) In any chemical reaction, atoms must be conserved, so the gas molecules can contain only H, O, C, and/or Ca atoms. To determine the chemical formula of the gas, we must find the combination of these elements that gives the observed molar mass. 

C05-0021.A 2.96-g sample of a compound of mercury and chlorine is vaporized in a 1.000-L bulb at 307 °C, and the final pressure is found to be 394 torr. What are the molar mass and chemical formula of the compound ... 

C05-0072. Gaseous hydrocarbons, which contain only carbon and hydrogen, are good fuels because they bum in air to generate large amounts of heat. A sample of hydrocarbon with m— 1.65 g exerts a pressure of 1.50 atm in a 945-mL bulb at 21.5 °C. Determine the molar mass and chemical formula of this hydrocarbon. 

CHEMICAL NAME = aluminum(lll) oxide CAS NUMBER = 1344-28-1 MOLECULAR FORMULA = Al203 MOLAR MASS = 102.0 g/mol COMPOSITION =AI(52.9%) 0(47.1%)... 

CHEMICAL NAME = ammonia CAS NUMBER = 7664-41-7 MOLECULAR FORMULA = NH3 MOLAR MASS = 17.0 g/mol COMPOSITION = N(82%) 0(18%)... 

CHEMICAL NAME = biphenyl CAS NUMBER = 92-52-4 MOLECULAR FORMULA = C12H10 MOLAR MASS = 154.2 g/mol COMPOSITION = C(93.5°/o) H(6.5%)... 

CHEMICAL NAME = butane MOLECULAR FORMULA = C4H10 MOLAR MASS = 58.1 g/mol COMPOSITION = C(82.66°/o) H( 17.34%)... 

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