· web viewread book sections 7.1, 7.2, and 7.3. quiz and test questions will come from the...

Honors Chemistry 1 Chapter 7 Study Guide Wilmington High School

Read book sections 7.1, 7.2, and 7.3. Quiz and test questions will come from the material covered in these sections, as well as the problems/concepts covered in this packet.

Section 7.1: Avogadro’s Number & Molar ConversionsThe Mole:

The MOLE is a counting unit used in chemistryo Just like a dozen is defined as 12 things, or a gross is defined as 144 things, the mole is defined

to represent a fixed quantity of things! Defined as the number of atoms in a 12 gram sample of carbon-12. 1 mol = 6.022 x 1023 units (THIS IS A VERY IMPORTANT CONVERSION FACTOR!!!!) The mol is a helpful unit of measure in chemistry (atoms are really small, so we need a unit of measure

that makes counting them easier!!)

Using Conversion Factors:

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Example Set 1: Particles to moles, and moles to particles

1) How many molecules of water are present in a 2.96 mol sample of H2O?

2) Find the number of molecules in 2.50 moles of sulfur dioxide.

3) A sample contains 2.77 x 1024 molecules of carbon tetrachloride. How many moles of CCl4 are present in the sample?

4) How many particles are present in a 0.447 mol sample of potassium cyanide?

5) How many carbon monoxide molecules are present in a 0.6709 mol sample of CO?

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Molar Mass:

The mass (measured in grams) of 1 mol of an element or compound The units for molar mass are always g/mol Molar mass is necessary to convert between MASS and AMOUNT of substance You can easily locate the molar masses of every element on your periodic table (it is the MASS

NUMBER)

Molar Mass Calculation Examples:

1) Calculate the molar mass of barium nitrate

2) Calculate the molar mass of calcium phosphate

Example Set 2: Mass to moles, and moles to mass

1) A chunk of copper wire has a mass of 3.913 grams. How many mols of copper atoms are present in the copper wire?

2) A balloon contains 0.35 mols of oxygen gas. What is the mass of oxygen gas present in the balloon?

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3) If a sample of Lead (II) Nitrate contains 2.11 mols, what is the mass of the sample?

4) A lab procedure requires you to create a 125.0 gram sample of glycerol, C3H8O3. How many mols of glycerol are present in the sample?

5) You breathe in 0.200 mols of sulfur hexafluoride to make your voice sound like Darth Vader. How many grams of sulfur hexafluoride did you breathe?

Example Set 3: Two-Step Conversions & Mixed Review

1) Calculate the mass of 500. atoms of iron (Fe).

2) Find the mass, in grams, of 2.79 x 1022 carbon atoms present in a diamond.

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3) Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is 92.11 g/mol.

4) Americium is an element that does not occur naturally. It can be produced in very small amounts in particle accelerators. Calculate the mass (in grams) of an Americium sample that contains 6 atoms.

5) Aluminum is a metal with an extremely high strength-to-mass ratio and a high resistance to corrosion, thus making it useful for structural purposes. Calculate the atoms present in a 10.0 gram sample of pure aluminum.

6) A silicon chip is used in an integrated circuit of a computer. If a silicon chip has a mass of 5.68 milligrams, how many silicon atoms are present in the computer chip?

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7) Cobalt is a metal that is added to steel to improve its resistance to corrosion. Calculate the mass of a cobalt sample that contains 5.00 x 1020 cobalt atoms.

8) Juglone, a dye that’s been used by civilizations for centuries, is produced from the husks of black walnuts. It is also a natural herbicide (weed killer) that kills off competitive plants around walnut trees but does not affect grasses or other noncompetitive plant life. The formula for the juglone molecule is C10H6O3.

a. What is the molar mass of juglone?

b. A 0.0156 gram sample of juglone is extracted from a sample of black walnuts. How many moles of juglone were extracted?

9) Calcium carbonate, also known as calcite, is a mineral found in limestone, marble, chalk, pearls, and the shells of many marine animals. A sample of calcite contains 4.86 moles. What is the mass of the sample?

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10) Isotentyl acetate (C7H14O2) is the compound responsible for the scent of bananas. Interestingly bees release about 1.0 µg (micrograms, or 1.0 x 10-6 g) of this compound when they sting. The resulting scent attracts other bees to join the attack. How many molecules of isopentyl acetate are released in a typical bee sting?

11) Freon-12 (CCl2F2) is used as a refrigerant in air conditioners and as a propellant in aerosol cans. Calculate the number of Freon-12 molecules in a 5.56 mg sample.

12) Ascorbic acid, or “Vitamin C” (C6H8O6), is an essential vitamin. It cannot be stored by our bodies and must be present in our diets.

a. What is the molar mass of ascorbic acid?

b. If a typical multivitamin contains 500.0 mg of vitamin C, how many moles of ascorbic acid does the multivitamin contain?

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13) Acetylsalicylic acid (aspirin) is a common pain reliever. Is molecular formula is C9H8O4. a. What is the molar mass of aspirin?

b. A typical dose of aspirin contains 500.0 mg of acetylsalicylic acid. How many aspirin molecules does the dose contain?

c. If a sample of pure aspirin contains 2.171 moles of compound, what is the mass of the sample, in grams?

14) A cup of coffee at Starbucks contains 400.0 milligrams of caffeine (C8H10N4O2). How many caffeine molecules are present in the cup of coffee?

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Section 7.2: Relative Atomic Mass & Chemical Formulas

Isotopes: Atoms that have different numbers of neutrons than other atoms of the same element.

Average Atomic Mass: A weighted average of the atomic mass of an element’s isotopes.

Calculating Average Atomic Mass Examples:

1) The mass of a Cu-63 atom is 62.94 amu, and that of a Cu-65 atom is 64.93 amu. Using the data below, find the average atomic mass of copper. The abundance of Cu-63 = 69.17%, and the abundance of Cu-65 = 30.83%

2) An element consists of 1.40% of an isotope with a mass of 203.973 amu, 24.10% of an isotope with a mass of 205.9745 amu, 22.10% of an isotope with a mass of 206.9759 amu, and 52.40% of an isotope with a mass of 207.9766 amu. Calculate the average atomic mass, and identify the element.

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A chemical formula tells you the ratio of the atoms or ions in a substance:

Understanding the formulas for polyatomic ionic compounds

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Section 7.3: Formulas and Percent Composition• Percent Composition: The percentage composition is the percentage by mass of each element in a

compound.

• Percent composition helps to verify the identity of a substance.

• Empirical Formula : An empirical formula is a chemical formula that shows the simplest ratio for the relative numbers and kinds of atoms in a compound.

How to find empirical formula

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• Actual Formula: An actual formula shows the actual ratio of elements or ions in a single unit of a compound. For instance, the ACTUAL FORMULA of glucose is C6H12O6, but the EMPIRICAL FORMULA for glucose is CH2O (a “carbohydrate”)

Solving Problems using Percent Composition, Empirical Formulas, and Actual Formulas:

How to determine an empirical formula:

IMPORTANT NOTES:

1) When you calculate mole ratios, be sure you round the number of atoms of each substance to the nearest whole number. This should be common sense, but you can’t have 1/3 of an atom!!

2) Try to carry at least 4 significant figures throughout your calculation to make sure you aren’t losing precision.

3) Here’s an easy way to remember the flow chart shown above: Just think “Percent to mass, mass to moles, divide by small, multiply until whole”

To find the actual formula once you know the empirical formula:

1) Determine the molar mass of the empirical formula.2) Divide the molar mass of the actual formula by the empirical formula.3) Multiply all subscripts and quantities in the empirical formula by this value to obtain the actual formula

(use only whole numbers!)4) Please keep in mind that the subscripts of the actual formula MUST BE WHOLE NUMBER

MULTIPLES OF THE EMPIRICAL FORMULA!

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Examples:

1) Chemical analysis of a liquid shows that it is 60.0% C, 13.4% H, and 26.6% O by mass. Calculate the empirical formula of this substance.

2) Calculate the empirical formula of the compound that contains 1.0 g S for each 1.5 g O.

3) A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the empirical formula of the compound?

4) Determine the empirical formula of the compound containing 37.5% C, 12.5% H, and 50.0% O by weight.

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5) What is the empirical formula of a compound containing 60.0% sulfur and 40.0% oxygen by mass?

6) A compound is found to contain 23.3% magnesium, 30.7% sulfur and 46.0% oxygen. What is the empirical formula of this compound?

7) What is the empirical formula for a compound containing 26.57% potassium, 35.36% chromium, and 38.07% oxygen?

8) What is the empirical formula of a compound containing 47.37% carbon, 10.59% hydrogen and 42.04% oxygen?

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9) Find the empirical formula for a compound containing 40.6% carbon, 5.1% hydrogen, and 54.2% oxygen.

10) Determine the empirical formula of the compound containing 38.7% C, 16.1% H, and 45.2% N by weight.

11) Ascorbic acid (vitamin C) contains 40.92% Carbon, 4.58% Hydrogen, and 54.50% Oxygen by mass. What is the empirical formula of ascorbic acid?

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12) A 5.325 gram sample of methyl benzoate—a compound used in the manufacture of perfumes—is found to contain 3.758 grams of carbon, 0.316 grams of hydrogen, and 1.251 grams of oxygen. What is the empirical formula of methyl benzoate?

13) What is the empirical formula of a compound if a 50.0 g sample of it contains 9.1 g Na, 20.6 g Cr, and 22.2 g O?

14) Determine the empirical formulas of the compounds with the following compositions by mass:a. 32.79% Na, 13.02% Al, and 54.19% F

b. 62.1% C, 5.21% H, 12.1% N, and 20.7% O

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15) Determine the empirical formulas of the compounds listed if a sample contains:a. 0.104 mol K, 0.052 mol C, and 0.156 mol O

b. 5.28 g Sn and 3.37 g F

c. 87.5% N and 12.5% H by mass

16) The empirical formula for a compound is P2O5. Its experimental molar mass is 284 g/mol. Determine the molecular formula (aka the “actual formula”) of the compound.

17) Determine the molecular formula given the following information: Empirical formula C3H7, molecular weight 86 g/mole

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18) Mesitylene, a hydrocarbon that occurs in crude oil, has an empirical formula of C3H4. The experimentally determined molecular weight of this substance is 121 amu. What is the molecular formula for mesitylene?

19) Ethylene glycol, a substance used in car antifreeze, is composed of 38.7% carbon, 9.7% hydrogen, and 51.6% oxygen by mass. Its molar mass is 62.1 g/mol.

a. What is the empirical formula of ethylene glycol?

b. What is the molecular formula of ethylene glycol?

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20) Ibuprofen, a headache remedy and pain reliever, contains 75.69% C, 8.80% H, and 15.51% O by mass. It has a molar mass of approximately 206 g/mol.

a. What is the empirical formula for ibuprofen?

b. What is the molecular formula for ibuprofen?

21) A compound contains 18.8% sodium, 29.0% chlorine, and 52.2% oxygen, by mass. If the molar mass of the compound is 122.44 g/mol, determine the:

a. empirical formula

b. molecular formula

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22) A 4.99 gram sample of a compound contains 1.52 grams of nitrogen atoms and 3.47 grams of oxygen atoms. The molar mass of the compound is between 90.0 g and 95.0 g. Determine the empirical and molecular formulas. Also, calculate the actual molar mass of this compound.

23) NutraSweet is an artificial flavor used in a variety of diet foods and drinks. NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O.

a. Calculate the empirical formula of NutraSweet.

b. Find the molecular formula of NutraSweet (The molar mass of NutraSweet is 294.30 g/mol)

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24) Epinephrine is also known as the hormone adrenaline. It is secreted into your bloodstream in times of danger or stress. If a sample of adrenaline is determined to be 59.0% C, 7.1% H, 26.2% O, and 7.7% N by mass, and the adrenaline molecule has a molar mass of 180 amu:

a. What is the empirical formula for adrenaline?

b. What is the molecular formula for adrenaline?

25) What is the molecular formula of each of the following compounds?a. Empirical formula = CH2, molar mass = 84 g/mol

b. Empirical formula = NH2Cl, molar mass = 51.5 g/mol

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Additional practice for your exams

1) Calculate the molar mass for each of the following substances:a. CF4

b. C3H6O2

c. Ag2SO4

d. (NH4)3PO4

e. Sn(CO3)2

2) Perform the following conversions:a. 13.2 g of Fe(NO3)3 to molesb. 8.5 g of CaSO4 to molesc. 5.20 moles of C2H4O2 to gramsd. 3.4 moles of HCl to gramse. 0.744 moles of glucose to moleculesf. 9.4 x 1021 molecules of H2O to molesg. 1.90 x 1025 molecules of BF3 to gramsh. 97.75 grams of SF6 to moleculesi. 3.11 x 1022 particles of NaC2H3O2 to gramsj. 54.22 grams of KCN to particles k. 20.0 kg of iron to atoms of ironl. 6.37 x 1028 atoms of iron to kilograms

3) Nitrogen dioxide is a major contributor to air pollution in urban areas. From a sample containing 4.000 grams of NO2, calculate:

a. The chemical amount (the number of moles in the sample)b. The number of NO2 molecules present in the sample

4) Cryolite (Na3AlF6) is used in the production of aluminum from its ores. If you obtain a cryolite sample that contains 8.17 x 1024 cryolite particles, how many grams of cryolite are present in the sample?

5) Potassium nitrate is used as a fertilizer for certain crops. If a fertilizer sample contains 5.309 moles of potassium nitrate:

a. What is the mass (in grams) of the potassium nitrate in the sample?b. How many particles of potassium nitrate are in the fertilizer sample?

6) Determine the percent composition of C4H6O2, which is the molecule used to make plexiglass. Don’t make this problem harder than it has to be.

7) Human parathormone is an important polypeptide protein that regulates the amount of calcium ion in the bloodstream. It has an impressive molecular formula of C691H898O164S11. (It is that big because it is made up of 84 amino acids, hence “polypeptide”). Compute the mass percentages of all four atoms present in human parathormone.

8) A 60.0 g sample of a dry-cleaning fluid was analyzed and found to contain 10.80 grams C, 1.36 grams H, and 47.84 grams Cl. What is the empirical formula of the substance?

9) Find the empirical formula for a compound that contains 38.7% chlorine and 61.3% fluorine, by mass.

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Honors Chemistry 1 Chapter 7 Study Guide Wilmington High School10) Find the empirical formula for the compounds described below (percent by mass):

a. 40% carbon; 6.7% hydrogen; 53.3% oxygenb. 88.8% copper; 11.2% oxygenc. 70.0% iron; 30.0% oxygend. 30.4% nitrogen; 69.6% oxygen

11) A dental cement ingredient contains 16.58 mg of O, 8.02 mg of P, and 25.40 mg of Zn. Determine the empirical formula of this substance.

12) Bromoform is 94.85% Br, 0.40% H, and 4.75% C by mass. What is the empirical formula for bromoform?

13) Fulgurites are products formed when lightning strikes the rocky earth. Microscopic examination of sand that had been struck by lightning shows that fulgurites in the mixture have a definite chemical composition of 46.01% Fe and 53.99% Si by mass. Determine the empirical formula of these fulgurite grains.

14) The most common form of nylon (nylon-6) is 63.68% C, 12.38% N, 9.80% H, and 14.14% O. Calculate the empirical formula of nylon-6.

15) A urine sample shows that the urea (an ingredient in urine) present contains 1.121 g N, 0.161 g H, 0.480 g C, and 0.640 g O. Determine the empirical formula of urea.

16) A compound contains 26.7% P, 12.1% N, and 61.2% Cl by mass. If it has a molar mass of 580 g/mol:a. What is the empirical formula of the compound?b. What is the molecular formula of the compound?

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· web viewread book sections 7.1, 7.2, and 7.3. quiz and test questions will come from the...

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