-Empirical formula --gives the largest term ratio of atoms (or moles) in the formula
*all ionic compounds are empirical formula
Ex: C4H10---molecular formula
C2H5----Empirical formula
Ex: -consider that we have 10.87g of Fe and 4.66g of O, what is the empirical formula?
MM of Fe---55.8g----- 10.87g x (1mole/55.8g) =0.195mol
MM of O------16g---------4.66 x (1mole/16g) = 0.291mol
-divide both by 0.195(the smallest molar amount)
Fe 1(0.195/0.195) x2 O 1.5(0.291/0.195)x2
Fe 2 O 3
- scale ratio to whole number----Fe2O3
Ex: A compound contains 31.9%K , 28.9%Cl2, 39.2%O, what is the empirical formula
*assume you have a hundred gram
K--31.9g x (1mole/39.1g)=0.816mole/0.814-------------1
Cl2--28.9g x (1mole/ 35.5g)=0.814mole/0.814----------1
O--39.2g x (1mole/16g)=2.45mole/0.814-----------------3
*KClO3---empirical formula
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-Molecular formula: is a multiple of the empirical formula and shows the actual number of atoms that combine to form a molecule.
**To multiple
N= molar mass of the compound/molar mass of the empirical formula**
Ex : A molecule has an empirical formula of C2H5 and a molar mass of 58g /mole, what is the molecular formula?
MM of C2H5= 29g/mole
N= (58g/mole)/(29g/mole)=2
2 x C2H5 = C4H10---molecular formula
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