Conversions, unit mole-gram

Molarity (M) A concentration unit defined to be the number of moles of solute per liter of solution, 95q, 259 concentration unit conversion, 261-262 potassium chromate, 263 Mole A collection of6.0122 X 1023 items. The mass in grams of one mole of a substance is numerically equal to its formula mass, 55. See also Amount Mole fraction (X) A concentration unit defined as the number of moles of a component divided by the total number of moles, 116-117,261 Mole-gram conversions, 55-56,68-68q... 

This balanced equation can be read as 4 iron atoms react with 3 oxygen molecules to produce 2 iron(III) oxide units. However, the coefficients can stand not only for the number of atoms or molecules (microscopic level) but they can also stand for the number of moles of reactants or products. So the equation can also be read as 4 mol of iron react with 3 mol of oxygen to produce 2 mol ofiron(III) oxide. In addition, if we know the number of moles, the number of grams or molecules may be calculated. This is stoichiometry, the calculation of the amount (mass, moles, particles) of one substance in the chemical equation from another. The coefficients in the balanced chemical equation define the mathematical relationship between the reactants and products and allow the conversion from moles of one chemical species in the reaction to another. 

Since molar masses have units of grams and moles, they are conversion factors between grams and moles. 

You make unit conversions everyday when you determine how many quarters are needed to make a dollar or how many feet are in a yard. One unit that is often used in calculations in chemistry is the mole. Chapter 11 shows you equivalent relationships among mole, grams, and the number of representative particles (atoms, molecules, formula units, or ions). For example, one mole of a substance contains 6.02 X 10 representative particles. Try the next example to see how this information can be used in a conversion factor to determine the number of atoms in a sample of manganese. 

The conversion factor between atomic mass units and grams is numerically equal to the inverse of Avogadro s number Na, and the mass of a single atom in atomic mass units is numerically equal to the mass of one mole of atoms in grams. Thus, one atom of has a mass of 1.007825 u because 1 mol of has a mass of 1.007825 g. The dalton is a mass unit that is equivalent to the atomic mass unit and is used frequently in biochemistry. 

For pure solids and liquids, this means converting grams to moles using the molar mass of the substance. (It might be necessary to insert one or more additional conversion factors to convert from the given mass unit to grams.)... 

What conversion factor do we need to convert between grams and moles Arrange the appropriate conversion factor so that grams cancel and the unit moles is obtained for your answer. 

The conversion factor on the right is the correct one. Moles will cancel, leaving unit of grams for the answer. The number of grams of Zn is... 

Notice that we write the conversion factor in such a way that the mol unit wiU cancel, leaving only units of grams in the answer.) Thus, there are 23.3 g of Zn in 0.356 mole of Zn. 

The molar mass of a compound can be used as a conversion factor to relate an amount in moles to a mass in grams for a given substance. Recall that molar mass usually has the units of grams per mole. To convert a known amount of a compound in moles to a mass in grams, multiply the amount in moles by the molar mass. 

This route requires two additional pieces of data the molar mass of the given substance and the mole ratio. The molar mass is determined by using masses from the periodic table. We will follow a procedure much like the one used previously by using the units of the molar mass conversion factor to guide our mathematical operations. Because the known quantity is a mass, the conversion factor will need to be 1 mol divided by molar mass. This conversion factor cancels units of grams and leaves units of moles (see Figure 2.3 below). 

Ans. There are 6.02 X 10 i atoms in 1.00 mol Na (Avogadro s number). There is 23.0 g of Na in LOO mol Na (equal to the atomic weight in grams). This problem requires use of two of the most important conversion factors involving moles. Note which one is used with masses and which one is used with numbers of atoms (or molecules of formula units). With numbers of atoms, molecules, or formula units, use Avogadro s number with mass or weight use the formula weight. 

The mole is defined as the number of atoms in exactly 12 g of which is 6.02 X 10 —Avogadro s number. Equal numbers of moles of two (or more) different substances have the same number of formula units but not the same mass. The molar mass is the mass in grams of one mole of a substance. The number of grams per mole—the molar mass— is a frequently used conversion factor, used for converting between grams and moles. (Section 7.3)... 

What conversion factor is used to convert a number of moles of a substance to (a) the number of grams of the substance (b) the number of formula units of the substance ... 

It always makes sense to think about orders of magnitude as you do a calculation. In Example 3.3, the 5.68-milligram sample of silicon is clearly much less than l mole of silicon (which has a mass of 28.09 grams), so the final answer of 1.22 X 1020 atoms (compared with 6.022 X 1023 atoms) is at least in the right direction. Paying careful attention to units and making sure the answer is sensible can help you detect an inverted conversion factor or a number that was incorrectly entered in your calculator. 

Other convenient units for pointwise permeability are g-moles/ cm -sec-atm/cm., applicable to both liquids and gases. The conversion for gaseous pointwise permeabihty utilizes the value of 22,414 cm (STP) per gram-mole, and a value of 76 cm Hg/atm. Thus... 

We expect that the mass of a single atom in grams would be a very small number. We know that one mole of Fe atoms has a mass of 55.85 g and contains 6.022 X 10 Fe atoms. We use this information to generate unit factors to carry out the desired conversion. 

Remember that the units of molar mass are grams per mole, which can be used as a conversion factor. 

First, determine the mass of NaCl to add to a 1.0-L container. The 0.15M solution must contain 0.15 moles of NaCl per liter of solution. You will need to use the molarity of the solution (0.15 mol NaCl/L solution) as a conversion factor to get from molarity to number of moles of NaCl. You win then use the molar mass of NaCl as a conversion factor to change moles of NaCl to grams of NaCl. To find the molar mass of NaCl (58.5 g/mol), add the atomic masses of Na and Cl, and apply the unit grams/mole to the sum. 

Determine that the molar mass of KCl is 74.6 g/mol by adding the atomic masses of K and Cl and applying the unit grams/mole to the srun. The conversion factor that must be used to convert from grams to moles of KCl is 1 mol KCl/74.6 g KCl. 

The functions of the above conversion factors are convert starting information from grams to moles using the coefficients in the balanced equation convert to moles of desired substance convert from moles to grams of desired substance. Be sure to label each factor completely with its units. Then if canceling of units does not result in the correct units for the answer you will know that there has been an error in your reasoning. 

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. 

Step 1 is a prerequisite to any stoichiometric calculation. We must know the identities of the reactants and products, and their mass relationships must not violate the law of conservation of mass (that is, we must have a balanced equation). Step 2 is the critical process of converting grams (or other units) of substances to number of moles. This conversion allows us to analyze the actual reaction in terms of moles only. 

A mole of substance is the amount that contains Avogadro s number (6.022x10 ) of chemical entities (atoms, molecules, or formula units). The mass (in grams) of a mole has the same numerical value as the mass (in amu) of the entity. Thus, the mole allows us to count entitles by weighing them. Using the molar mass (jM., g/mol) of an element (or compound) and Avogadro s number as conversion factors, we can convert among amount (mol), mass (g), and number of entities. The mass fraction of element X in a compound is used to find the mass of X in any amount of the compound. 

Figure 3.8 Summary of the mass-mole-number relationships in a chemical reaction. The amount of one substance in a reaotion is related to that of any other. Quantities are expressed in terms of grams, moles, or number of entities (atoms, molecules, or formula units). Start at any box in the diagram (known) and move to any other box (unknown) by using the information on the arrows as conversion factors. As an example, if you know the mass (in g) of A and want to know the number of molecules of B, the path involves three calculation steps ...

Ans. The formula mass of oxygen is 32.0 therefore there are 32.0 g per mole of oxygen. To determine the number of moles of oxygen in 52.0 g of oxygen, we must convert grams of oxygen to moles of oxygen. To do this we require a unit conversion factor ... 

Ans. Converting percent to grams by assuming 100 g of the compound, we determine the number of moles in each mass using atomic masses of each as unit conversion factors ... 

The value of Avogadro s number will also be given in a table of useful information or, sometimes it is included with the question itself. Since you use this value so often, you probably already know it. These two conversion factors are arranged so that the units cancel in making the change from grams through moles to atoms. If the conversion were desired in the reverse direction, then both factors would be inverted. ... 

MMa Often problems of this type will involve the heat of combustion in units of kJ per mole rather than per gram. The molar mass of the g tance undergoing combustion can be used to make the necessary conversions. ... 

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