Chem100_11.                                                                                      2011/2012

 

 

Assignment #2   CHAPTERS 2 and 3|

 

1.                  {10} How many protons, neutrons, and electrons are in the following atoms?

What element symbols do Q, X, Y, Z, and @ represent?

 

a)                                            7 protons, 7 neutrons, 7 electrons, N

 


b)                                             20 protons, 21 neutrons, 20 electrons, Ca

 


c)                                               53 protons, 78 neutrons, 53 electrons, I

 


d)                                             14 protons, 16 neutrons, 14 electrons, Si

 


e)                                             8 protons, 9 neutrons, 8 electrons, O

 

 

 

2.                  {5} Silver (Ag; Z=47) has two naturally occurring isotopes, 107Ag (106.90509 amu) and 109Ag (108.90476amu). Calculate the fractional abundance of the isotopes if the average atomic mass of silver is 107.8682 amu.

 

107.8682amu = 106.90509 amu x X + 108.90476 amu x (1-X)

107.8682 -108.90476  = 106.90509X-108.90476X

-1.0366 = -1.9997X;  X= 0.5184 ; 1-X = 0.4816

 

0.5184 of light isotope (107)    and  0.4816 of heavy isotope (109)

 

 

 

  1. {10} Locate iodine, mercury, bromine, silicon, and argon on the periodic table. Give the atomic symbol, atomic number, and label each as a metal, metalloid or nonmetal. Indicate physical state common for these elements (solid (s), liquid (l) of gas (g))

 

53I (s), nonmetal ;  80Hg(l),  metal;  35Br, (l), nonmetal; 14Si, metalloid, (s); 18Ar, nonmetal, (g).

 

Note: atomic number as a superscript is also acceptable, e.g., 53I.

 

  1.  {5} Name the following groups in the periodic table:

 

1A             2A       6A       7A       8A

Alkali metals, alkaline earths metals, chalcogens, halogens, noble gases.

 

  1. {5} What monoatomic ions do the following elements form? Give the atomic symbol and the charge.

(a)                Bromine                                  Br-

(b)               Magnesium                              Mg2+

(c)                Sodium                                    Na+

(d)               Phosphorus                              P3-

(e)                Aluminum                               Al3+                            

 

  1. {5} Write empirical formulas and name the ionic compound formed from the following pairs of elements:

 

(a)                sodium and chlorine                  NaCl  sodium chloride

(b)               calcium and fluorine               CaF2  calcium fluoride

(c)                iodine and aluminum                AlI3   aluminum iodide

(d)               sulfur and potassium                K2S,   potassium sulfide

(e)                lithium and oxygen                   Li2O, lithium oxide.

 

  1.  {15} Give the systematic names for the formulas or the formulas for the names of the following compounds:

 

(a)                chromium (II) nitrate                          Cr (NO3)2

(b)               FeI2                                                     ferrous iodide or iron (II) iodide

(c)                Ferric oxide                                         Fe2O3

(d)               ScS                                                      scandium (II) sulfide

(e)                sodium dihydrogen phosphate            NaH2PO4

(f)                Ag2S                                                    Silver (I)  sulfide

(g)               FeCl3                                                   iron (III) chloride or ferric chloride

(h)               Mercurous fluoride                             Hg2F2

(i)                 Cu(ClO4)2                                            cupper (II) perchlorate or cupric perchlorate

(j)                 Potassium dichromate                         K2Cr2O7

(k)               Dichlorine trioxide                              Cl2O3

(l)                 SF4                                                      Sulfur tetrafluoride

(m)             Dinitrogen pentoxide                          N2O5                           

(n)               Sulfuric acid                                        H2SO4

(o)               Nitrous acid                                        HNO2

 

 

 

  1. {5} How many grams of oxygen are in 65 g of C2H2O2?

 

mol C2H2O2 = 65g x 1mol/58g= 1.12 mol;

mol O = 2x1.12= 2.24mol

g O =  2.24 mol x 16g/1mol = 36g

 

 

  1. {15} A compound is composed of only C, H, and O. The combustion of a 0.519 g sample of the compound yields 1.24 g of CO2 and 0.255 g of H2O. What is the empirical formula of the compound?

 

mol C:  1.24 g x 1mol/(12.01 +32)g = 0.02818 mol C; gC: 0.02818mol x 12.01g/1mol    = 0.3384g C

molH:    0.255g x 1mol /(2x1.008 +16) x2= 0.02831mol H;  = 0.02853g H

mol O:    0.515 g – 0.3384g -0.02853g = 0.149g;  0.149g/16 =0.00928 mol

0.02818/0.00928 = 3.04;    0.02831/0.00928=3.05

 

C3H3O

 

  1. {10}  Sulfur and fluorine react in a combination reaction to produce sulfur hexafluoride:

 

S(s) + 3 F2 (g) à SF6 (g)

 

You run this reaction in the lab using 2.0 g of S and 2.0 g of F2 and obtained 1.5 g of SF6. What is the percent yield of this reaction?

 

mol S= 2.0 /32.1 = 0.0623mol;   mol F2 = 2.0/38 =0.0526mol;    F2 is limiting

theoretical yield:  0.0526 mol /3 = 0.0175 mol SF6 = 0.0175x (32+6x19) = 2.56g

%yield= 1.5/2.56 x100 = 58.6%= 59%

 

 

 

  1.  {5}  What is the empirical formula of a compound, which contains 29%  Na, 41%  S, and 30% O by mass?

 

assume 100g of compound

mol Na:   29g /23g = 1.26 mol

mol S:  41/32 = 1.28 mol

mol O:  30/16 = 1.88 mol

 

1.28/1.26 =1.01;   1.88/1.26 =1.5     1, 1, 1.5    multiply by 2

2:2:3

 

Na2S2O3 

 

 

 

  1. {10} GeF3H  is formed from GeH4 and GeF4 in the combination reaction:

 

 

GeH4 + 3GeF4 à 4GeF3H

 

If the reaction yield is 92.6%, how many grams of GeF4 are needed to produce 8.00 moles of GeF3H?

 

 

theoretically, for 8 mol of GeF3H,  6 mol GeF4 are needed

 

actually:   6 mol/0.926 = 6.48 mol of GeF4 ;   6.48mol x (72.6 + 4x19)g/mol = 962.9 g