2.4 Chemical Formulas
Which contains the greatest number of moles of oxygen atoms: 1 mol of ethanol (C2H5OH), 1 mol of formic acid (HCO2H), or 1 mol of water (H2O)? Explain why.
Formic acid. Its formula has twice as many oxygen atoms as the other two compounds (one each). Therefore, 0.60 mol of formic acid would be equivalent to 1.20 mol of a compound containing a single oxygen atom.
Determine which of the following contains the greatest mass of hydrogen: 1 mol of CH4, 0.6 mol of C6H6, or 0.4 mol of C3H8.
1 mol CH4 x (4 mol H/1 mol CH4) x (1.01 g/1 mol H) = 4.04 g <----- 0.6 mol x C6H6 x (6 mol H/1 mol C6H6) x (1.01 g/1 mol H) = 3.64 g 0.4 mol C3H8 x (8 mol H/1 mol C3H8) x (1.01 g/1 mol H) = 3.23 g
One 55-gram serving of a particular cereal supplies 270 mg of sodium, 11% of the recommended daily allowance. How many moles and atoms of sodium are in the recommended daily allowance?
100 / 11 = 9.09 × 270 mg × (1 g/1*10^3mg) × (1 mol Na/22.99g) = 0.107 mol × (6.02 ×10^23 atoms Na/1mol) = 6.43 ×10^22
Which of the following represents the least number of molecules? (a) 20.0 g of H2O (18.02 g/mol) (b) 77.0 g of CH4 (16.06 g/mol) (c) 68.0 g of CaH2 (42.09 g/mol) (d) 100.0 g of N2O (44.02 g/mol) (e) 84.0 g of HF (20.01 g/mol)
20.0 g H2O represents the least number of molecules since it has the least number of moles.
A molecule of metaldehyde (a pesticide used for snails and slugs) contains 8 carbon atoms, 16 hydrogen atoms, and 4 oxygen atoms. What are the molecular and empirical formulas of metaldehyde?
Molecular formula, C8H16O4; empirical formula, C2H4O
Compare 1 mole of H2, 1 mole of O2, and 1 mole of F2. (a) Which has the largest number of molecules? Explain why. (b) Which has the greatest mass? Explain why.
a) As each mole consists of same number of atoms or molecules i.e. (6.022 ×10^23) , therefore one mole of H2, one mole of O2 and one mole of F2 have same number of molecules. b) Mass of 1 mole of substance is known as its molar mass. Thus , mass of 1 mole of H2 = 2× (1.0 g/mol) = 2.0 g/mol Mass of 1 mole of O2 = 2× (16.0 g/mol) = 32.0 g/mol Mass of 1 mole of F2 = 2× (19.0 g/mol) = 38.0 g/mol Therefore, 1 mole of F2 ha sthe highest mass among the given options.
Determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon, ZrSiO4, a semiprecious stone.
zirconium: 2.038 × 10^23 atoms; 30.87 g; silicon: 2.038 × 10^23 atoms; 9.504 g; oxygen: 8.151 × 10^23 atoms; 21.66 g
Determine which of the following contains the greatest mass of aluminum: 122 g of AlPO4, 266 g of Al2C16, or 225 g of Al2S3.
AlPO4: 1.000 mol Al2Cl6: 1.994 mol Al2S3: 3.00 mol
A packet of an artificial sweetener contains 40.0 mg of saccharin (C7H5NO3S), which has the structural formula:
0.0400-g saccharin x 1 mole/183.18 g x 6.022 x 10 23/ 1 mole .001314 1.31 x 10^20 molecules in saccharin 0.0400g C7H5NO3S(molC7H5NO3S/183.18gC7H5NO3S)(6.022×1023C7H5NO3Smolecules/1molC7H5NO3S)=1.31×10^20C7H5NO3S molecules c7 1.31 x 10^20 molecules in saccharin x 7 C atoms/molecules in saccharin 9.17 9.2 x 10 21 (??? why 21st power 1.31×10^20 C7H5NO3S molecules (7C atoms/1C7H5NO3S molecule)=9.17×10^20C atoms
Deriving Moles from Grams for a Compound Our bodies synthesize protein from amino acids. One of these amino acids is glycine, which has the molecular formula C2H5O2N. How many moles of glycine molecules are contained in 28.35 g of glycine?
28.35g glycine x 1mole/ 75.07 glycine C 2x12.01 H 5X1.008 O 2X16 N 1x 14.007 75.07 28.35g glycine(mol glycine/75.07g)=0.378mol glycine .378 mole glycine
Determine the mass of each of the following: (a) 2.345 mol LiCl (b) 0.0872 mol acetylene, C2H2 (c) 3.3 × 10−2 mol Na2 CO3 (d) 1.23 × 103 mol fructose, C6 H12 O6 (e) 0.5758 mol FeSO4(H2O)7
(a) 99.41 g; (b) 2.27 g; (c) 3.5 g; (d) 222 kg; (e) 160.1 g
Beryllium is a light metal used to fabricate transparent X-ray windows for medical imaging instruments. How many moles of Be are in a thin-foil window weighing 3.24 g?
Answer: 0.360 mol 3.24g x 1 mole/9.012 =0.360
What is the mass of 0.443 mol of hydrazine, N2H4?
Answer: 14.2 g
A prospector panning for gold in a river collects 15.00 g of pure gold. How many Au atoms are in this quantity of gold?
Answer: 4.586 × 10^22 Au atoms 15.00g Au x 1mole/196.96 x 6.022 X 10 23/1mole = 4.5862 x 10^22
What is the mass of 2.561 mol of gold?
Answer: 504.4 g 2.561 mol Au x 96.96g/1mole = 504.4g
A liter of air contains 9.2 × 10^−4 mol argon. What is the mass of Ar in a liter of air?
The molar amount of Ar is provided and must be used to derive the corresponding mass in grams. Since the amount of Ar is less than 1 mole, the mass will be less than the mass of 1 mole of Ar, approximately 40 g. The molar amount in question is approximately one-one thousandth (~10^−3) of a mole, and so the corresponding mass should be roughly one-one thousandth of the molar mass (~0.04 g): In this case, logic dictates (and the factor-label method supports) multiplying the provided amount (mol) by the molar mass (g/mol): 9.2×10^−4molAr(39.95g/molAr)=0.037g Ar The result is in agreement with our expectations, around 0.04 g Ar.
Which contains the greatest mass of oxygen: 0.75 mol of ethanol (C2H5OH), 0.60 mol of formic acid (HCO2H), or 1.0 mol of water (H2O)? Explain why.
Formic acid. Its formula has twice as many oxygen atoms as the other two compounds (one each). Therefore, 0.60 mol of formic acid would be equivalent to 1.20 mol of a compound containing a single oxygen atom.
A tube of toothpaste contains 0.76 g of sodium monofluorophosphate (Na2PO3F) in 100 mL. (a) What mass of fluorine atoms in mg was present? (b) How many fluorine atoms were present?
Molar mass of Na2PO3F = 2(22.9898) + 1(18.9984) + 1(30.9738) + 3(15.9994) = 143.95 g/mol; (a) mol Na2PO3F =(0.76g/143.95g mol^-1) = 0.00528 mol Since there is only one F atom in the formula, the number of moles of fluorine is also 5.28 × 10^-3 mol. Mass F = 5.28 × 10^-3 mol × 18.9984 g/mol × 1000 mg/g = 1.0 × 10^2 mg; (b) atoms of F 100 mg F × (1g/1000 mg)×(1 mol F/18.9984 g F) × 6.022×10^23 atoms mol^-1=3.2×10^21 atoms F
Determine the mass of each of the following: (a) 0.0146 mol KOH (b) 10.2 mol ethane, C2H6 (c) 1.6 × 10−3 mol Na2 SO4 (d) 6.854 × 103 mol glucose, C6 H12 O6 (e) 2.86 mol Co(NH3)6Cl3
(a) 0.819 g; (b) 307 g; (c) 0.23 g; (d) 1.235 × 106 g (1235 kg); (e) 765 g
Use the Build a Molecule simulation to repeat Exercise, but build a molecule with three carbons, seven hydrogens, and one chlorine. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms to make a different molecule? If so, draw its structural formula and state its name. (c) How are the molecules drawn in (a) and (b) the same? How do they differ? What are they called (the type of relationship between these molecules, not their names)?
(a) 1-chloropropane H H H H-C-C-C-Cl H H H (b) 2-chloropropane H H H H-C-C-C-H H H H (c) These molecules have the same chemical composition (types and number of atoms) but different chemical structures. They are structural isomers.
Calculate the molar mass of each of the following: (a) the anesthetic halothane, C2HBrClF3 (b) the herbicide paraquat, C12H14N2Cl2 (c) caffeine, C8H10N4O2 (d) urea, CO(NH2)2 (e) a typical soap, C17H35CO2Na
(a) 197.382 g mol−1; (b) 257.163 g mol−1; (c) 194.193 g mol−1; (d) 60.056 g mol−1; (e) 306.464 g mol−1
Calculate the molar mass of each of the following compounds: (a) hydrogen fluoride, HF (b) ammonia, NH3 (c) nitric acid, HNO3 (d) silver sulfate, Ag2SO4 (e) boric acid, B(OH)3
(a) 20.00 g/mol (b) 17.04 g/mol (c) 62.99 g/mol (d) 311.76 g/mol (e) 61.81 g/mol
Calculate the molar mass of each of the following: (a) S8 (b) C5H12 (c) Sc2(SO4)3 (d) CH3COCH3 (acetone) (e) C6H12O6 (glucose)
(a) 256.528 g/mol; (b) 72.150 g mol−1; (c) 378.103 g mol−1; (d) 58.080 g mol−1; (e) 180.158 g mol−1
Determine the mass in grams of each of the following: (a) 0.600 mol of oxygen atoms (b) 0.600 mol of oxygen molecules, O2 (c) 0.600 mol of ozone molecules, O3
(a) 9.60 g; (b) 19.2 g; (c) 28.8 g
Determine the empirical formulas for the following compounds: (a) caffeine, C8H10N4O2 (b) fructose, C12H22O11 (c) hydrogen peroxide, H2O2 (d) glucose, C6H12O6 (e) ascorbic acid (vitamin C), C6H8O6
(a) C4H5N2O; (b) C12H22O11; (c) HO; (d) CH2O; (e) C3H4O3
Determine the empirical formulas for the following compounds: (a) acetic acid, C2H4O2 (b) citric acid, C6H8O7 (c) hydrazine, N2H4 (d) nicotine, C10H14N2 (e) butane, C4H10
(a) CH2O; (b) C6H8O7; (c) NH2; (d) C5H7N; (e) C2H5
Open the Build a Molecule simulation and select the "Larger Molecules" tab. Select an appropriate atoms "Kit" to build a molecule with two carbon and six hydrogen atoms. Drag atoms into the space above the "Kit" to make a molecule. A name will appear when you have made an actual molecule that exists (even if it is not the one you want). You can use the scissors tool to separate atoms if you would like to change the connections. Click on "3D" to see the molecule, and look at both the space-filling and ball-and-stick possibilities. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms in any way to make a different compound?
(a) ethane H H H-C-C-H H H (b) No, unless more than one molecule can be made, such as, C2H4 + H2. The carbon atoms have to be connected to each other, and then there is only one way to place the hydrogens
Use the Build a Molecule simulation to repeat Exercise, but build a molecule with two carbons, six hydrogens, and one oxygen. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms to make a different molecule? If so, draw its structural formula and state its name. (c) How are the molecules drawn in (a) and (b) the same? How do they differ? What are they called (the type of relationship between these molecules, not their names).
(a) ethanol H H H H-C-C-O H H (b) methoxymethane, more commonly known as dimethyl ether H H H-C-O-C-H H H (c) These molecules have the same chemical composition (types and number of atoms) but different chemical structures. They are structural isomers.
(a) O=C=O (b) H-C=C-H (c)H H C=C H H (d) O O-S-O-H O-H
(a) molecular CO2, empirical CO2; (b) molecular C2H2, empirical CH; (c) molecular C2H4, empirical CH2; (d) molecular H2SO4, empirical H2SO4
How many moles of sucrose, C12H22O11, are in a 25-g sample of sucrose?
0.073 mol 25g x 1mole/342.296g c 12 x 12.01= 144.12 H 22 x 1.008=22.176 o 11 x16= 176 342.296 0.073 mol
A certain nut crunch cereal contains 11.0 grams of sugar (sucrose, C12H22O11) per serving size of 60.0 grams. How many servings of this cereal must be eaten to consume 0.0278 moles of sugar?
0.865 servings, or about 1 serving.
Vitamin C is a covalent compound with the molecular formula C6H8O6. The recommended daily dietary allowance of vitamin C for children aged 4-8 years is 1.42 × 10^−4 mol. What is the mass of this allowance in grams?
1.42 × 10−4 mol x 176.124ggram/1 mole C6H8O6. figure out the formula mass for this = 176.124g .000142 .0250g 1.42×10^−4 mol vitamin C(176.124g/mol vitamin C)=0.0250g vitamin C
The Cullinan diamond was the largest natural diamond ever found (January 25, 1905). It weighed 3104 carats (1 carat = 200 mg). How many carbon atoms were present in the stone?
3104 carats × (2oo mg/1carat) × (1 g/1*10^3mg) × (1 mol/12.01g)×(6.02 × 10^23 atoms C/1mol) = 3.113 × 10^25 C atoms
What is the molar mass of iron(Fe)?
55.845g/mol
How many C4H10 molecules are contained in 9.213 g of this compound? How many hydrogen atoms?
Answer: 9.545 × 10^22 molecules C4 H10; 9.545 × 10^23 atoms H 9.213 g x 1mole/58.1 g x 6.022 x 10 23/1 mole 9.545 x 10 22 molecules 9.545 x 10 22 molecules x 10 H/molecules 9.545 X10 23 atoms H c4x12.01 H 10x1.008 58.1
According to nutritional guidelines from the US Department of Agriculture, the estimated average requirement for dietary potassium is 4.7 g. What is the estimated average requirement of potassium in moles?
The mass of K is provided, and the corresponding amount of K in moles is requested. Referring to the periodic table, the atomic mass of K is 39.10 amu, and so its molar mass is 39.10 g/mol. The given mass of K (4.7 g) is a bit more than one-tenth the molar mass (39.10 g), so a reasonable "ballpark" estimate of the number of moles would be slightly greater than 0.1 mol. The molar amount of a substance may be calculated by dividing its mass (g) by its molar mass (g/mol): 4.7gK(mol K/39.10g)=0.12mol K The calculated magnitude (0.12 mol K) is consistent with our ballpark expectation, since it is a bit greater than 0.1 mol.
Molecules of glucose (blood sugar) contain 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. What are the molecular and empirical formulas of glucose?
The molecular formula is C6H12O6 because one molecule actually contains 6 C, 12 H, and 6 O atoms. The simplest whole-number ratio of C to H to O atoms in glucose is 1:2:1, so the empirical formula is CH2O.
Copper is commonly used to fabricate electrical wire (Figure). How many copper atoms are in 5.00 g of copper wire?
The number of Cu atoms in the wire may be conveniently derived from its mass by a two-step computation: first calculating the molar amount of Cu, and then using Avogadro's number (NA) to convert this molar amount to number of Cu atoms: Considering that the provided sample mass (5.00 g) is a little less than one-tenth the mass of 1 mole of Cu (~64 g), a reasonable estimate for the number of atoms in the sample would be on the order of one-tenth NA, or approximately 1022 Cu atoms. Carrying out the two-step computation yields: 5.00gCu(molCu/63.55g)(6.022×1023atoms/mol)=4.74×1022atoms of copper The factor-label method yields the desired cancellation of units, and the computed result is on the order of 1022 as expected.
Explain why the symbol for an atom of the element oxygen and the formula for a molecule of oxygen differ.
The symbol for the element oxygen, O, represents both the element and one atom of oxygen. A molecule of oxygen, O2, contains two oxygen atoms; the subscript 2 in the formula must be used to distinguish the diatomic molecule from two single oxygen atoms.
Explain why the symbol for the element sulfur and the formula for a molecule of sulfur differ.
The symbol for the sulfur atom, S, represents the element and one atom of the element. The sulfur molecule (S8) consists of eight sulfur atoms linked in a ring. Thus, S without a subscript would be an inadequate representation of the molecule.
How are the molecular mass and the molar mass of a compound similar and how are they different?
The two masses have the same numerical value, but the units are different: The molecular mass is the mass of 1 molecule while the molar mass is the mass of 6.022 × 10^23 molecules.
Write a sentence that describes how to determine the number of moles of a compound in a known mass of the compound if we know its molecular formula.
Use the molecular formula to find the molar mass; to obtain the number of moles, divide the mass of compound by the molar mass of the compound expressed in grams.
