Calculate Molecular/Formula Mass
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Chapter 7 Examples
Types of mass 1. Cl2
2. ICl
3. LiCl
4. NaCl
Calculate molecular/formula mass 1. CO2
2. H2O
3. (NH4)2SO4
4. Cr(ClO2)3
Mole Concept
Calculate the: 1. number of moles of water molecules in 25.0 g of water.
2. number of grams of water in 4.75 mole of water
3. number of water molecules in 2.65 moles of water
4. number of water molecules in 20.0 g of water
5. number of moles of water in 7.75 x 1024 water molecules
6. number of grams of water in 4.50 x 1023 water molecules
7. number of hydrogen atoms in 5.75 g of hydrogen
8. number of moles of hydrogen atoms in 4.50 g of hydrogen
9. number of grams of oxygen in 2.50 mole of magnesium phosphate
10. number of grams of phosphorous in 7.75 x 1024 formula units of magnesium phosphate
Percent Composition 1. Calculate the percent composition of Cr(ClO2)3
2. Calculate the percent composition of C2H5Cl
3. A student found that 1.00 g of a metal combined with 0.65 g of oxygen to form an oxide of the metal. Calculate the percent of metal in the oxide.
4. A crude sample of zinc sulfide has a mass of 8.00 g. It contains 5.00 g of zinc sulfide. What is the percent of zinc in the crude sample?
5. Calculate the number of grams of carbon in 16.5 g of carbon dioxide.
Empirical Formulas
1. Determine the empirical formula for the compound containing 32.4 % Na, 22.6% S and 45.1% O.
2. Calculate the empirical formula for the compound of composition 26.6% K, 35.4% Cr, and 38.1% O.
Molecular Formulas
1. An oxide of nitrogen gave the following analysis: 3.04 g of N combined with 6.95 g of O. The molecular mass of this compound was found by experimentation to be 91.0 amu. Determine its molecular formula.
2. A hydrocarbon has the following composition: C = 82.7% and H = 17.4%. The molecular mass is 58.2 amu. Calculate the molecular formula of this hydrocarbon. Honors Chemistry Ex 7-1
Calculate the molecular mass of each of the following compounds:
1. PCl3 4. C6H12O6
2. NH3 5. CH4
3. SO3 6. N2O3
Calculate the formula mass of each of the following compounds: 7. KOH 10. ZnF2
8. Al2(SO4)3 11. Hg(NO3)2
9. K2CO3 12. Ba(C2H3O2)2
Honors Chemistry I Exercise 7-2
Show your work.
Calculate the number of :
1. Moles of aluminum atoms in 6.40 g of aluminum
2. Moles of silver chloride in 51.0 g of silver chloride
3. Moles of H2SO4 in 0.150 kg of H2SO4
4. Moles of sodium atoms in 1.65 x 1023 sodium atoms
5. Moles of water molecules in 8.64 x 1024 molecules of water
6. Moles of CH4 molecules in 105 g of CH4
7. Grams of carbon dioxide in 1.23 moles of carbon dioxide
8. Grams of nitrogen in 3.50 mole of nitrogen molecules
9. Grams of H2SO4 in 2.00 mole of H2SO4
21 10. Grams of CH4 in 1.27 x 10 molecules of CH4 Honors Chemistry Exercise 7-3
Show your work. Calculate the number of:
1. Moles of oxygen molecules in 54.0 g of oxygen
2. Moles of oxygen atoms in 54.0 g of oxygen
3. Mole of sulfur atoms in 0.350 mole of aluminum sulfate
4. Grams of phosphorus in 1.40 mole of sodium phosphate
5. Grams of oxygen in 1.25 mole of sodium phosphate
6. Grams of magnesium in 3.45 x 1023 atoms of magnesium
7. Milligrams of carbon in 0.240 mole of C6H12O6
8. Atoms in 0.400 mole of carbon atoms
9. Molecules in 15.0 g of carbon dioxide
10. Molecules in 16.0 g of hydrogen
Honors Chemistry Exercise 7-4
Show your work. Calculate the percent composition of the following: 1. C2H6O
2. Ca3(PO4)2
3. Fe(C2H3O2)3
Calculate the percent of the metal in the following: 4. 0.503 g of metal combines with 0.400 g of oxygen 5. 1.85 g of a metal combines with 1.30 g of sulfur
Calculate the number of : 6. Grams of cadmium in 25.4 g of CdS 7. Grams of calcium sulfide containing 5.37 g of sulfur 8. Grams of magnesium in 65.0 g of magnesium nitride 9. A crude sample of lye has a mass of 12.7 g. It contains 6.85 g of sodium hydroxide. What is the percent sodium in the crude sample?
10. Yolanda’s chemistry professor provides her with samples of crystals labeled A, B, and C. One of them is nickel (II) sulfate, another is nickel (II) sulfate hexahydrate. The remaining solid is nickel (II) sulfate heptahydrate. The professor does not tell Yolanda which solid is which. After heating the crystals and carrying out mass determinations, Yolanda collects the data in the following table:
Crystal Mass of solid before heating Mass of solid after heating (g) (g) A 12.0 6.6 B 14.6 14.6 C 17.5 10.3
Using this information, identify each crystal.
Chemistry I Exercise 7-5
Show your work.
Determine the empirical formula for each of the following compounds: 1. 38.8% calcium, 20.0% phosphorus, and 41.3% oxygen
2. 74.4% gallium and 25.6% oxygen
3. 1.99 g of aluminum combines with 1.76 g of oxygen
4. 1.07 g of carbon combines with 1.43 g of oxygen
5. 0.500 g of sulfur combines with 0.500 g of oxygen
Determine the molecular formula for each of the following compounds from the experimental data: 6. 41.4 % carbon, 3.5% hydrogen, 55.1% oxygen, and molecular mass of 116 g/mole
7. 37.8% carbon, 6.3% hydrogen, 55.8% chlorine, and molecular mass of 127.0 g/mole. Practice Problems
1. There is a 3.50 mole sample of magnesium nitride. a. How many moles of nitrogen atoms are present? b. How many formula units of magnesium nitride are present? c. How many grams of magnesium nitride are present?
2. What is the percent of carbon in carbon monoxide?
3. What is the mass of 3.76 x 1023 oxygen molecules.
4. The formula of elemental sulfur is S8. How many moles of sulfur atoms will 3 moles of elemental sulfur contain?
5. Determine the number of atoms in each: a. 16.0 g of oxygen b. 12.0 g of carbon c. 1.008 g of hydrogen
6. Determine the mass in grams of one hydrogen molecule. (Use scientific notation.)
7. How many hydrogen atoms are there in 0.80 moles of C6H12O6? (Use scientific notation.)
8. A crude sample of NaOH has a mass of 40.0 g. It contains 15.0 g of NaOH. What is the percent of sodium in the crude sample?
9. What is the number of moles of water that contains 2.71 x 1024 atoms of hydrogen?
10. A compound is found to contain 33.3% calcium, 40.0% oxygen, and 26.7% sulfur. What is the empirical formula for the compound?
11. A substance has a percent composition of 40.9% carbon, 4.58% hydrogen, and 54.5% oxygen. Its molecular mass is 176 g/mole. What is its molecular formula?
12. If 1.54 grams of an oxide of osmium (Os) are analyzed and found to contain 1.15 grams of osmium, calculate the simplest formula of this compound.
13. A compound if found to have a percent composition of 80.4% bismuth, 18.5% oxygen, and 1.16% hydrogen, what is the empirical formula of the compound?
14. The percent composition of a compound is 92.3% carbon and 7.7% hydrogen. If the molecular mass is 78 g/mole, what is the molecular formula?
15. A compound to contain 64.3% barium, 13.25silicon, and 22.5% oxygen. What is the empirical formula of the compound?