More About Formulas Formulas n n Tell the
More About Formulas
Formulas n n Tell the type & number of atoms in a compound. Microscopic level: imagine 1 atom, molecule, or formula unit. • Formula gives atom ratios. n Macroscopic level: imagine working in the lab • Formula gives mole ratio
Formulas n Ex: 2 H 2 O can mean • 2 molecules of water • 2 moles of water. 2 H 2 O molecules have 4 hydrogen atoms & 2 oxygen atoms. 2 Moles of H 2 O molecules have 4 moles of hydrogen atoms & 2 moles of oxygen atoms.
What can you say about Cu. SO 4 5 H 2 O? n n n It’s a hydrated salt. For every mole of Cu. SO 4, there are 5 moles of water. If it’s heated, it dries out. The water goes into the air and you’re left with the anhydrous salt, Cu. SO 4. The mole ratio in the formula can be used to predict how much water would be given off by any size sample. If you had 2 moles of Cu. SO 4 5 H 2 O, how much water would you lose on heating?
Percent Water in Cu. SO 4 • 5 H 2 O n Step 1: Calculate the formula mass. • Mass of salt + Mass of water n n Percent = (Part/Whole) X 100% % H 2 O = Mass H 2 O/Formula Mass X 100 %
Ionic vs. Covalent Formulas n By looking at the type of atoms, we can decide if the substance is an ionic compound or a molecular (covalent) compound. Molecular compounds have all nonmetals. Ionic compounds usually have metal + nonmetal.
Empirical Formula n n n Smallest whole number ratio of the elements in the compound. Ionic compounds have only empirical formulas. Covalent compounds have empirical and molecular formulas. They can be the same or different.
Molecular Formulas n n n For covalent (molecular) compounds. Give the exact composition of the molecule. Molecular compounds have both empirical and molecular formulas. They can be the same or different.
Say everything you can about: Na. Cl Ionic, empirical CH 4 C 6 H 6 Covalent, molecular Covalent, empir. , molec? C 8 H 18 Covalent, molecular Ca. Br 2 Ionic, empirical CF 4 Covalent, empirical, molecular? KI Ionic, empirical Cu. SO 4 5 H 2 O Ionic, empirical C 6 H 12 O 6 Covalent, molecular Be. SO 4 Ionic, empirical C 2 H 4 Cl 2 Covalent, molecular
Say everything you can about PH 3 C 2 H 4 Al 2 O 3 Sr. I 2 NF 3 H 2 Se CH 3 OH Si. O 2 H 2 O 2 CCl 4 Xe. F 4 P 4 O 10
Relationship between empirical and molecular formulas n n n The molecular formula is a whole number multiple of the empirical formula. Molec. Formula = n (Empirical Form. ) n is a small whole number, which multiplies the subscripts. Sometimes, n = 1.
Molecular Formula n n If you know the empirical formula and the molar mass, you can find the molecular formula. Step 1: Find the mass of the empirical formula. Step 2: Molar mass Empirical mass = small whole number, n Step 3: Multiply the subscripts in the empirical formula by n.
Finding Molecular Formulas n n n Find the molecular formula for the substance whose empirical formula is CH and whose molar mass = 78. 0 g Step 1: Empirical mass = 13. 0 g Step 2: Molar mass = n = 78. 0/13. 0 Empirical mass n = 6. Step 3: 6 X subscripts in CH = C 6 H 6.
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