Molar Mass as a Conversion Factor

The molar mass of O2 is therefore 32.00 g/mol. Now do the calculation shown in step 2. 

The answer is correctly given to three significant figures and is close to an estimated value of 75 g (2.50 mol x 30 g/mol). 

To convert a known mass of a compound in grams to an amount in moles, the mass must be divided by tbe molar mass. Or you can invert the molar mass and multiply so that units are easily canceled. 

Sample Problem I Ibuprofen,Cj3Hjg02, is the active ingredient in many nonprescription pain relievers. 

What is the total mass in grams of carbon in 33 g of ibuprofen  

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If we want an amount other than 1 mol, we use the molar mass as a conversion factor from the stated number of moles to the mass required ... 

Now that we know how many moles of ethylene we have (0.536 mol), we also know from the balanced equation how many moles of HC1 we need (0.536 mol), and we have to do a mole-to-gram conversion to find the mass of HC1 required. Once again, the conversion is done by calculating the molecular mass of HC1 and using molar mass as a conversion factor ... 

The problem gives the number of moles of NaHC03 and asks for a mole-to-mass conversion. First, calculate the formula mass and molar mass of NaHC03. Then use molar mass as a conversion factor, and set up an equation so that the unwanted unit cancels. 

Next, find how many moles of ethyl alcohol are in 40.0 g by using molar mass as a conversion factor ... 

If you measure 165 g of manganese on a balance, you will have the 3.00 moles of manganese you need for the reaction. The reverse conversion—from mass to moles—also involves the molar mass as a conversion factor, but it is the inverse of the molar mass that is used. Can you explain why ... 

Most chemical reactions that occur on the earth s surface, whether in living organisms or among inorganic substances, take place in aqueous solution. Chemical reactions carried out between substances in solution obey the requirements of stoichiometry discussed in Chapter 2, in the sense that the conservation laws embodied in balanced chemical equations are always in force. But here we must apply these requirements in a slightly different way. Instead of a conversion between masses and number of moles, using the molar mass as a conversion factor, the conversion is now between solution volumes and number of moles, with the concentration as the conversion factor. 

For pure liquids and solids, as we have seen, the most convenient measurable property is mass. It is very easy to measure the mass of a pure solid or liquid, and we can convert between that and the number of particles it represents using the molar mass as a conversion factor. 

Between this chapter and Chapter 10, we have now seen three different ways to convert between a measurable property and moles in equation stoichiometry problems. The different paths are summarized in Figure 13.10 in the sample study sheet on the next two pages. For pure liquids and solids, we can convert between mass and moles, using the molar mass as a conversion factor. For gases, we can convert between volume of gas and moles using the methods described above. For solutions, molarity provides a conversion factor that enables us to convert between moles of solute and volume of solution. Equation stoichiometry problems can contain any combination of two of these conversions, such as we see in Example 13.8. 

You are given 2.50 mol of ( 3115)25 and must convert the moles to mass using the molar mass as a conversion factor. The molar mass is the sum of the molar masses of all the elements in ( 3115)25. 

Step 3 Calculate the number of moles of each element present in the sample. Use molar mass as a conversion factor. 

Before you can use molar mass as a conversion factor, you must calculate its value. This first requires the formula of barium chloride. 

Unfortunately, we cannot count particles—at least, not directly. Instead, we measure masses or other macroscopic quantities. These can be converted into numbers of particles. You already know how to do this conversion with mass, using molar mass as a conversion factor between mass (in grams) and number of particles (in moles) (see Section 7.5). Equation 10.1 can also be interpreted as, Four moles of NH3 molecules react with five moles of O2 molecules to produce four moles of NO molecules and six moles of H2O molecules. ... 

STRATEGIZE The heat of vaporization gives the relationship between heat absorbed and moles of water vaporized. Begin with the given amount of heat (in kJ) and convert to moles of water that can be vaporized. Then use the molar mass as a conversion factor to convert from moles of water to mass of water. 

Using Molar Mass as a Conversion Factor (7.2) Using Mole-Mole Factors (7.6)... 

Molar Mass as a Conversion Factor (7.2), Balancing a Chemical Equation (7.3), Classifying Types of Chemical Reactions (7.4), Identilying Oxidized and Reduced Substances (7.5), Using Mole-Mole Factors (7.6), and Converting Grams to Grams (7.7). 

The conversion pathway for this problem is given above. First, convert the volume of the sample to mass this requires density as a conversion factor. Next, convert the mass of halothane to its amount in moles this requires the inverse of the molar mass as a conversion factor. The final conversion factor is based on the formula of halothane. 

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