1) Calculate each of the following quantities. (a) mass in kilograms of 3.9 1020

Question

1) Calculate each of the following quantities.

(a) mass in kilograms of 3.9 1020 molecules of NO2
- kg
(b) moles of Cl atoms in 0.0379 g C2H4Cl2
- mol
(c) number of H - ions in 3.74 g SrH2
- ions

2) What is the molecular formula of each compound? (Type your answer using the format C6H12O6 for C6H12O6 and use the same order of the elements as in the empirical formulas.)

(a) empirical formula C7H4O2 ( = 240.20 g/mol)
  
(b) empirical formula CH2Cl ( = 98.95 g/mol)
  
(c) empirical formula NO2 ( = 92.02 g/mol)
  
(d) empirical formula HgCl ( = 472.1 g/mol)

3) Chromium(III) oxide reacts with hydrogen sulfide (H2S) gas to form chromium(III) sulfide and water.

Cr2O3(s) + 3 H2S(g) Cr2S3(s) + 3 H2O(l)
- mol

(b) How many grams of Cr2O3 are required?
- g

4) Calculate the mass of each product formed when 137 g of silver sulfide reacts with excess hydrochloric acid.

a) Ag2S(s) + HCl(aq) AgCl(s) + H2S(g) [unbalanced]
AgCl
- g

b) H2S
- g

Explanation / Answer

1. a) 1 mole contains = 6.023*10^23 atom/molecules

6.023*10^23 atom/molecules of NO2 = 46.0055 g/mol

3.9*10^20 molecules of NO2 = (46.0055*(3.9*10^20))/( 6.023*10^23)

     = 0.0298 grams = 2.98*10^(-2)*10^(-3) kg

= 2.98*10^(-5) kg

b) No of moles = w/mwt

w of C2H4Cl2 = 0.0379 grams , Mwt of C2H4Cl2 = 98.9592 g/mol

= 0.0379/98.9592 = 0.00038 mole

c) No of moles = w/mwt

   mwt os srh2 = 89.6359 g/mol

     = 3.74/ 89.6359 = 0.042 mole

1 mole srh2 = 2 mole h-

No of moles of H- = 2*0.042 = 0.084 mole

2 (a) empirical formula C7H4O2 ( = 240.20 g/mol)

n = molecularformula weight/empirical formula weight   =

= 240.20/120.11 = 2

molecularformula = 2*C7H4O2 = C14H8O4

(b) empirical formula CH2Cl ( = 98.95 g/mol)

n = 98.95/49.4796 = 2

molecularformula = 2*CH2Cl = C2H4Cl2

(c) empirical formula NO2 ( = 92.02 g/mol)

n = 92.02 /46.0055 = 2

molecularformula = 2*no2 = N2O4

(d) empirical formula HgCl ( = 472.1 g/mol)

n = 472.1/236.0430 = 2

molecularformula = 2*HgCl = Hg2Cl2

3. question is in complete.

4. Ag2S(s) + 2HCl(aq) ---> 2AgCl(s) + H2S(g)

1 mole ag2s = 2 mole hcl = 2 mole agcl = 1 mole h2s

No of moles of Ag2S= 137/247.8 = 0.553 mole

mass of Agcl produced = 0.553*143.32 = 79.256 grams

mass of H2S Produced = (0.553/2)*34.0809 = 9.42 grams

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