Science lab concentration | Chemistry homework help
- Find the formula mass (FM) of lead chromate, PbCrO4. Use the periodic table in Appendix A of this lab
Concentration PHSC 1021 online 3 | P a g e to look up the atomic masses of the elements. 323.2 u - Lead chromate is made up of 1 atom of Pb, 1 atom of Cr, and 4 atoms of O. The atomic masses of those elements are: Pb (207.2 u), Cr (52.0 u), O (16.0 u) Therefore, the formula mass of PbCrO4 is 207.2 u + 52.0 u + (4 × 16.0 u) = 323.2 u ---------------------------------------------------------------------------------------------------------------------------- Concentration and Moles Now that we know what a formula mass is, we can talk about the mole again. A mole of any substance has a mass equal to the same number of grams as its formula mass (FM). For example, copper has a FM of 63.5u. Therefore, a mole of Cu has a mass of 63.5 grams, and copper has a molar mass of 63.5 g/mol. Water (H2O) has a FM of 18.0u, and a mole of H2O has a mass of 18 grams. Therefore, water has a molar mass of 18 g/mol. If the concentration of a solution is 1 mol/L, then there is 1 mole of the solute for every liter of solution. Sometimes chemists need to make solutions with specific concentrations such as 2.4 mol/L or 7.6 mol/L. To make the solution, first they find the mass of the solute needed, using the relationship between mass and moles. -----------------------------------------------------------------------------------------------------------------------------