Chemical Formulas 5 Pre-lab Questions Before beginning this experiment in the la

Question

Chemical Formulas 5 Pre-lab Questions Before beginning this experiment in the laboratory, you should be able to answer the following questions. 1. Give the chemical symbols for the following elemets: (a) lead, (b) iron, (e) fluorine, and (e) potassium 2. What are the formula weights of (a) KBr and (b) PbCo,? 3. Define the term compound 4. The molecular formula for benzene is CH. What is its empirical formula? 5. Balance the following equation: Al(s)+Cl2(g)ACIS(s). 6. What is the percentage composition of PbCO,? A substance was found by analysis to contain 45.57% tin and 54.43% chlorine, what is the empirical formula for the substance? 7. Copyright C 2015 Pearson Education, Inc.

Explanation / Answer

1. a. pb
   b. Fe
   c. F
   d. K
2. formula weight of KBr = 39+80 = 119
formula weight of PbCO3 = 208+ 12+ 48 = 268
3. compound is a substance is composed of two or more different elements.
eg .H2So4

4. CH
5.2Al(s) +3Cl2(g)------> 2AlCl3(s)
6.Pb% = 208*100/268 = 77.6%
C%     = 12*100/268   =4.47%
O%     =3* 16*100/268 = 17.9%

7. element   %      atomic weight    relative4 number       simple ratio

    Sn       45.57   118.7            45.57/118.7 = 0.3839   0.3839/0.3839 =1
    Cl        54.43 35.5             54.43/35.5 = 1.53      1.53/0.3839 =4

      Empirical formula is SnCl4

8.chemical compound always contains exactly the same proportion of elements by mass.

9. A formula which gives simplest whole number ratio is called empirical formula.

A formula which gives actual number atoms is called molecular formula.

10. mass of CaI2 = no of moles * molar mass of CaI2
                 = 1.73*294 = 508.62g

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