Mole converting between grams and

To convert between moles and grams, chemists use the molar mass of a substance. The molar mass of an element is the mass in grams of one mole of the element. Molar mass has the unit grams per mol (g/mol). The mass in grams of 1 mol of an element is numerically equal to the element s atomic mass from the periodic table in atomic mass units. For example, the atomic mass of copper to two decimal places is 63.55 amu. Therefore, the molar mass of copper is 63.55 g/mol. Skills Toolkit i shows how to convert between moles and mass in grams using molar mass. 

Strategy We are trying to solve for grams of zinc. What conversion factor do we need to convert between moles and grams Arrange the appropriate conversion factor so that moles cancel and the unit grams are obtained for your answer. 

Solution The conversion factor needed to convert between moles and grams is the molar mass. In the periodic table (see inside front cover) we see the molar mass of Zn is 65.39 g. This can be expressed as... 

Use the molar mass of aluminum to convert between moles and grams. 

We use the molar mass to convert between grams and moles, and the stoichiometric relationship between moles of C3H8 and kJ to convert between moles and kJ, as shown in the following example. 

Such problems as this one involve many steps or conversions. Try to break the problem into simpler ones involving fewer steps or conversions. It may also help to remember that solving a stoichiometry problem involves three steps (1) converting to moles, (2) converting between moles, and (3) converting from moles. Use molarities and molar masses to carry out volume-mole conversions and gram-mole conversions, respectively, and stoichiometric factors to carry out mole-mole conversions. The stoichiometric factors are constructed from a balanced chemical equation. 

This last example uses a dimensional analysis to convert between moles, mass, and volume. How many liters will 150 grams of S02(g) occupy at STP Remember the importance of keeping careful track of the numbers, units, and substance in a problem such as this one. Start by converting to moles and then to volume ... 

This example can be extended by asking What mass of carbon dioxide is produced when 96.1 grams of propane is combusted with oxygen In this case we must convert between moles of propane and moles of carbon dioxide. This conversion can be done by inspecting the balanced equation, which shows that 3 moles of CO2 is produced for each mole of C3H8 reacted ... 

The conversion factor for converting between mass and amount in moles is the molar mass of the substance. The molar mass is the sum of atomic masses from the periodic table for the atoms in a substance. Skills Toolkit 3 shows how to use the molar mass of each substance involved in a stoichiometry problem. Notice that the problem is a three-step process. The mass in grams of the given substance is converted into moles. Next, the mole ratio is used to convert into moles of the desired substance. Finally, this amount in moles is converted into grams. 

Mass is often the most easily measured property, and we now know how to convert between mass in grams and moles of a substance using the substance s molar mass. The solutions to many problems will therefore follow these steps ... 

For each of the elements (a) iron and (b) krypton, write a conversion factor that converts between mass in grams and moles of the substance. 

There is a lesson here Choose or develop the most efficient conversion factor to solve the problem. If you re converting grams to atoms, find the equality that relates grams and atoms for the conversion factor. If it s mole to atoms, find the connection between mole and atoms. Use the units g Fe, mole Fe, and atoms Fe to guide the correct use of the conversion factor. 

This equation means that 1 mole of C3He reacts with 5 moles of O2 to produce 3 moles of CO2 and 4 moles of H2O. To use this equation to find the masses of reactants and products, we must be able to convert between masses and moles of substances. Thus we must first ask How many moles ofpropane are present in 96.1 grams ofpropane The molar mass of propane to three significant figures is 44.1 (that is, 3 X 12.01 + 8 X 1.008). The moles of propane can be calculated as follows ... 

Converting between amount and mass. If you know the amount of a substance, you can find its mass, and vice versa. The molar mass (tK), which expresses the equivalence between 1 mole of a substance and its mass in grams, is the conversion factor. From amount (mol) to mass (g), multiply by the molar mass ... 

Molar mass is used as a conversion factor to convert between the moles and grams of a substance. 

STRATEGIZE Determine which of the reactants makes the least amount of product by converting from kilograms of each reactant to moles of product. Convert between grams and moles using molar mass. Convert between moles of reactant and moles of product using the stoichiometric relationships derived from the chemical equation. Remember that the reactant that makes the least amount of product is the limiting reactant. 

Molal units are used predominately by engineers and scientists studying electrolytes because the concentration calculation is independent of density and, hence, temperature. Molal concentration is the number of gm-moles per 1000 gm of solvent. Equations 2-lc and 2-ld show how to convert between molal and molar concentrations. Note that as the acid or base weight fraction approaches one (the grams of solvent approaches zero), the molal concentration approaches infinity. 

Plan Rather than convert from tons to grams to moles and back again, let s find the mole-to-mole ratio between Fe203 and coke, then use a unit factor similar to that used in Exercise 26-44. 

THE PERIODIC TABLE HELPS US CONVERT BETWEEN GRAMS AND MOLES... 

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