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Stoichiometry I: Calculations Based on Formulas
(a) Compute possible values of the atomic weight of M, for each of the following formulas: MCI, MCl 2 , MCl 3 , MCl 4 .
(b) It is found by other methods that the atomic weight of M is about 27.
Which of the above formulas is the correct one?
12. A metal forms two different chlorides. Analysis shows one to be 54.1% Cl and
the other to be 64.4% Cl by weight. What are the possible values of the atomic
weight of the metal?
13. An organic compound containing C, H, O, and S is subjected to two analytical
procedures. When a 9.33 mg sample is burned, it gives 19.50 mg of CO 2 and
3.99 mg of H 2 O. A separate 11.05 mg sample is fused with Na 2 O 2 , and the
resulting sulfate is precipitated as BaSO 4 , which (when washed and dried)
weighs 20.4 mg. The amount of oxygen in the original sample is obtained by
difference. Determine the empirical formula of this compound.
PROBLEMS B
14. Find the percentage composition of (the percentage by weight of each element
in) each of the following compounds.
(a) NH 3
(g) (NH 4 ) 2 Cr0 4
(b) N 2 H 4
(h) CaCN 2
(c) HN 3
(i) PtP 2 0 7
(d) Zn(NO 2 ) 2
(j) BiONO,-H 2 O
(e) Zn(NO,.i) 2
(k) Streptomycin, C 21 H 29 O 12 N 7
(f) Zn(NO.,) 2 -6H 2 O
15. What is the weight of 1.00 mole of each compound in Problem 14?
16. How many moles are in 1.00 Ib of each compound in Problem 14?
17. Determine the number of molecules in
(a) 50.0 g of mercury
(b) 0.500 Ib of chloroform, CHCI :i
(c) 1.00 nanogram of HC1
(d) 25.0 ml of benzene, C,jH 6 , whose density is 0.879 g/ml
(e) a copper bar 1" x 2" x 24". The density of copper is 8.92 g/ml.
18. From the following analytical results (percentage by weight), determine the
empirical formulas for the compounds analyzed.
(a) 42.9% C, 57.1% O
(f) 32.4% Na, 22.6% S, 45.0% 0
(b) 27.3% C, 72.7% O
(g) 79.3% Tl, 9.9% V, 10.8% O
(c) 53.0% C, 47.0% O
(h) 25.8% P, 26.7% S, 47.5% F
(d) 19.3% Na, 26.8% S, 53.9% O
(i) 19.2% P, 2.5% H. 78.3% I
(e) 29.1% Na, 40.5% S, 30.4% O
(j) 14.2% Ni, 61.3% I, 20.2% N,
4.3% H
19. Weighed samples of the following hydrates are heated to drive off the water,
and then the cooled residues are weighed. From the data given, find the
formulas of the hydrates.
Stoichiometry I: Calculations Based on Formulas
(a) Compute possible values of the atomic weight of M, for each of the following formulas: MCI, MCl 2 , MCl 3 , MCl 4 .
(b) It is found by other methods that the atomic weight of M is about 27.
Which of the above formulas is the correct one?
12. A metal forms two different chlorides. Analysis shows one to be 54.1% Cl and
the other to be 64.4% Cl by weight. What are the possible values of the atomic
weight of the metal?
13. An organic compound containing C, H, O, and S is subjected to two analytical
procedures. When a 9.33 mg sample is burned, it gives 19.50 mg of CO 2 and
3.99 mg of H 2 O. A separate 11.05 mg sample is fused with Na 2 O 2 , and the
resulting sulfate is precipitated as BaSO 4 , which (when washed and dried)
weighs 20.4 mg. The amount of oxygen in the original sample is obtained by
difference. Determine the empirical formula of this compound.
PROBLEMS B
14. Find the percentage composition of (the percentage by weight of each element
in) each of the following compounds.
(a) NH 3
(g) (NH 4 ) 2 Cr0 4
(b) N 2 H 4
(h) CaCN 2
(c) HN 3
(i) PtP 2 0 7
(d) Zn(NO 2 ) 2
(j) BiONO,-H 2 O
(e) Zn(NO,.i) 2
(k) Streptomycin, C 21 H 29 O 12 N 7
(f) Zn(NO.,) 2 -6H 2 O
15. What is the weight of 1.00 mole of each compound in Problem 14?
16. How many moles are in 1.00 Ib of each compound in Problem 14?
17. Determine the number of molecules in
(a) 50.0 g of mercury
(b) 0.500 Ib of chloroform, CHCI :i
(c) 1.00 nanogram of HC1
(d) 25.0 ml of benzene, C,jH 6 , whose density is 0.879 g/ml
(e) a copper bar 1" x 2" x 24". The density of copper is 8.92 g/ml.
18. From the following analytical results (percentage by weight), determine the
empirical formulas for the compounds analyzed.
(a) 42.9% C, 57.1% O
(f) 32.4% Na, 22.6% S, 45.0% 0
(b) 27.3% C, 72.7% O
(g) 79.3% Tl, 9.9% V, 10.8% O
(c) 53.0% C, 47.0% O
(h) 25.8% P, 26.7% S, 47.5% F
(d) 19.3% Na, 26.8% S, 53.9% O
(i) 19.2% P, 2.5% H. 78.3% I
(e) 29.1% Na, 40.5% S, 30.4% O
(j) 14.2% Ni, 61.3% I, 20.2% N,
4.3% H
19. Weighed samples of the following hydrates are heated to drive off the water,
and then the cooled residues are weighed. From the data given, find the
formulas of the hydrates.