![]() ![]() The molar mass of a compound is given by the sum of the standard atomic weight (namely, the standard relative atomic mass) of the atoms which form the compound multiplied by the molar mass constant. The molar mass of atoms of an element is given by the standard relative atomic mass of the element multiplied by the molar mass constant, 1 × 10−3 kg/mol = 1 g/mol. The molar mass is a physical property defined as the mass of a given substance (chemical element or chemical compound) divided by the amount of substance. You need to multiply the molar mass of the substance by the number of moles:Īs you can see, the most difficult task here is finding out the molar mass of the substance. ![]() You need to divide the mass of the substance by the molar mass of the substance: molar mass of the substance in grams/mole How to convert grams to moles? Key Concepts and Summaryĭensity relates a substance’s mass and volume. Density can be used to calculate volume from a given mass or mass from a given volume.There is a simple relation between grams and moles: Often, the unit of the given quantity must be first converted to the appropriate unit before applying density as a conversion factor. Make sure the mass units are the same, or the volume units are the same, before using density to convert to a different unit. What is the density of the metal?Ĭare must be used with density as a conversion factor. It is placed in 200.0 mL of water, and the water level rises to 742.1 mL. What volume should be measured to obtain 10.0 g of the liquid?ī) A cube of metal has a mass of 1.45 kg. Thus, in this case we must invert it.ĥ.00\ \ruleĪ) Isopropyl alcohol has a density of 0.785 g/mL. Look at the density value as a “conversion factor” (2.50 g/mL) and arrange it so it CANCELS what you already know. If a 5.00 g sample has a density of 2.50 g/mL, what volume does it occupy? Note how the mass units cancel, leaving the volume unit, which is what we’re looking for. Thus, if we want to know the volume of 45.9 g of gold, we would set up the conversion as follows: This reciprocal density is still a useful conversion factor, but now the mass unit will cancel and the volume unit will be introduced. In so doing, we move not only the units but also the numbers: When we want to use density to convert from mass to volume, the numerator and denominator of density need to be switched-that is, we must take the reciprocal of the density. That is, the density value tells us that we have 19.3 grams for every 1 milliliter of volume, and the 1 is an exact number. Take the density of gold, for example:Īlthough this was not previously pointed out, it can be assumed that there is a 1 in the denominator: We have already demonstrated that the number that goes with density normally goes in the numerator when density is written as a fraction. Use the density from Table 1 “Densities of Some Common Substances” as a conversion factor to go from volume to mass:ĭensity can also be used as a conversion factor to convert mass to volume-but care must be taken. ![]()
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