Everything Science Grade 10

(Marvins-Underground-K-12) #1

CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE 19.2


Use the ratios of molar numbers calculated above to find the empirical
formula.

units in empirical formula=smallest number of molesmoles of this element

In this case, the smallest number of moles is 2 , 175. Therefore:
Carbon

4 , 35


2 , 175 = 2


Hydrogen

12 , 871


2 , 175 = 6


Oxygen

2 , 175


2 , 175 = 1


Therefore the empirical formula of this substance is: C 2 H 6 O.

Example 9: Determining the formula of a compound


QUESTION


207 g of lead combines with oxygen to form 239 g of a lead oxide. Use this
information to work out the formula of the lead oxide (Relative atomic masses:
Pb= 207, 2 u and O= 16, 0 u).

SOLUTION


Step 1:Find the mass of oxygen

239 gāˆ’ 207 g= 32g

Chemistry: Chemical change 345

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