Name _______KEY__________________ Period _____

CRHS Academic Chemistry

Unit 7 - Chemical Quantities

Practice Problems

Due Date Assignment On-Time (100) Late (70)

______ 7.1

______ 7.2

______ 7.3

______ 7.4

______ 7.5

______ 7.6

______ 7.7

______ Warm-Up

______ EC

Notes, Homework, Exam Reviews and Their KEYS located on CRHS Academic Chemistry Website: https://cincochem.pbworks.com

Page 2 of 16 Unit 7 HW

Day 1 Day 7

Day 2 Day 8

Day 3 Day 9

Day 4 Day 10

Day 5 Day 11

Day 6 Day 12

Unit 7 HW Page 3 of 16

HW 7.1 INTRODUCTION TO THE “MOLE”

Find the molar mass of the compound. Round average atomic mass to the hundredths place. Show work and

units.

1. NaCl 2. Ca(OH)2

Na = __22.900________ Ca = __1(40.078) = 40.078________

Cl = __35.453_________ O = __2(15.999) = 31.998________

NaCl = __58.443 g/mol________ H = ___2(1.008) = 2.016_______

Ca(OH)2 = ___74.092 g/mol________

3. Fe2O3 4. Ammonium phosphate (NH4)3PO4 Fe = N =

O = H =

159.69 g/mol P =

O =

149.09 g/mol

5. Al2(SO4)3 6. Dinitrogen trioxide N2O3

Al = N =

S = O =

O = 76.011 g/mol

342.15 g/mol

7. An alien visits earth. He brings with him an unknown substance. He says, “I believe this substance is like

an Earthly compound; it is either like nitrogen dioxide or nitrogen trioxide. I’m not sure which. All I know is that its molar mass is 62.01 g.” Which compound did the alien bring with him? Show your work to

receive credit.

NO3 is unknown gas

Page 4 of 16 Unit 7 HW

HW 7.2 MOLE TO MASS AND MASS TO MOLE CONVERSIONS

Complete the following conversions using dimensional analysis. Show work!

1. Convert 0.780 mol of calcium cyanide, Ca(CN)2, to mass. Ca = 1(40.078) = 40.078 C = 2(12.011) = 24.022 N = 2(14.007 = 28.014 92.11 g/mol

0.780 𝑚𝑜𝑙 𝐶𝑎(𝐶𝑁)2 𝑥92.11 𝑔 𝐶𝑎(𝐶𝑁)2

1 𝑚𝑜𝑙 𝐶𝑎(𝐶𝑁)2= 71.849 = 𝟕𝟏. 𝟖 𝒈 𝑪𝒂(𝑪𝑵)𝟐

2. How many grams are in 0.50 mol of copper (II) sulfate? CuSO4

Cu = S =

O = 159.608 g/mol

𝐴𝑛𝑠𝑤𝑒𝑟 = 𝟖.𝟎𝐱𝟏𝟎 𝐠 CuSO4

3. Convert 30 g of silicon dihydride to moles. SiH2 Si =

H = 30.102 g/mol

𝐴𝑛𝑠𝑤𝑒𝑟 = 𝟏 𝐦𝐨𝐥 𝐒𝐢𝐇𝟐

4. How many moles are in 100 grams of potassium sulfide? K2S K = 2(39.098) = 78.196

S = 1(32.066) = 32.066 110.262 g/mol

100 𝑔 𝑥1 𝑚𝑜𝑙

110.262 𝑔= 0.9069 𝑚𝑜𝑙 = 𝟎.𝟗 𝒎𝒐𝒍 𝑲𝟐𝑺

5. Your grandfather has to take 5 grams of aspirin (C8H8O4) daily for his arthritis. How many moles of aspirin

should he take?

C = 8(12.011) = 96.088 H = 8(1.008) = 8.064 O = 4(15.999) = 63.996 168.148 g/mol

5 g x1 mol

168 .148 g= 0.02973 mol = 𝟎. 𝟎𝟑 𝐦𝐨𝐥 𝐂𝟖𝐇𝟖𝐎𝟒

Unit 7 HW Page 5 of 16

6. You go to the pawn shop to buy your girlfriend some jewelry. The clerk offers to sell you a necklace that has 5 grams of gold in it for $300. How many moles of gold are in the necklace?

5 𝑔 𝑥1 𝑚𝑜𝑙 𝐴𝑢

196.967 𝑔 𝐴𝑢= 0.0253 𝑚𝑜𝑙 𝐴𝑢 = 𝟎.𝟎𝟑 𝐦𝐨𝐥 𝐀𝐮

7. You are conducting a lab experiment to evaluate the reaction between calcium hydroxide and hydrochloric

acid. Your teacher has told you how much of each reactant to use (in moles). You must convert to mass

before you can start. Complete the table and show work below the table.

Name of Compound

Formula of Compound

Molar Mass Moles Needed Mass Needed

calcium hydroxide Ca(OH)2 74.092 g 2.00 mol 148 g

hydrochloric acid HCl 36.461 g 4.00 mol 146 g

Ca(OH)2

Ca = 1(40.078) = 40.078 O = 2(15.999) = 31.998 H = 2(1.008) 2.016

74.092 g/mol 2.0 𝑚𝑜𝑙 𝑥74.092 𝑔

1 𝑚𝑜𝑙= 148.1 𝑔 = 𝟏𝟒𝟖 𝒈

HCl H = 1.008 Cl = 35.453

36.461 g/mol 4.0 𝑚𝑜𝑙 𝑥36.461 𝑔

1 𝑚𝑜𝑙= 145.844 𝑔 = 𝟏𝟒𝟔 𝒈

Page 6 of 16 Unit 7 HW

HW 7.3 REPRESENTATIVE PARTICLES

Complete the following conversions using dimensional analysis. Show work!

1. How many moles are in 1.50 x 1023 molecules of nitrogen trihydride?

1.50x1023molecules x1 mol

6.02x1023 molecules= 0.24916 mol = 𝟎. 𝟐𝟒𝟗 𝐦𝐨𝐥

2. Convert 4.8 moles of calcium carbonate to formula units.

4.8 mol x6.02x1023 formula units

1 mol= 2.8896x1024formula units = 𝟐. 𝟗𝐱𝟏𝟎𝟐𝟒𝐟𝐨𝐫𝐦𝐮𝐥𝐚 𝐮𝐧𝐢𝐭𝐬

3. How many molecules are in 4.80 x 10–3 mol bromine gas?

4.80x10−3mol x6.02x1023molecules

1 mol= 2.8896x1021molecules = 𝟐. 𝟖𝟗𝐱𝟏𝟎𝟐𝟏𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞𝐬 𝐁𝐫𝟐

4. There are ___ moles in 3.73 x 1022 formula units of barium chloride.

3.73x1022formula units x1 mol

6.02x1023 formula units= 0.06196 mol BaCl2 = 𝟎.𝟎𝟔𝟐𝟎 𝐦𝐨𝐥 𝐁𝐚𝐂𝐥𝟐

5. Your doctor prescribes you lithium carbonate for your bipolar disorder. Examine the prescription below.

How many formula units of lithium carbonate will you ingest each day?

5 mol x6.02x1023formula units

1 moll= 3.01x1024formula units = 𝟑𝐱𝟏𝟎𝟐𝟒𝐟𝐨𝐫𝐦𝐮𝐥𝐚 𝐮𝐧𝐢𝐭𝐬 𝐨𝐟 𝐋𝐢𝟐𝐂𝐎𝟑

Dr. Emilio Avogadro Date Oct

23, 2012

Patient: Kim Estudiante

℞: Take 5 mol Lithium

Carbonate

Once daily at bedtime

Signature E. Avogadro

Unit 7 HW Page 7 of 16

6. The same pawn shop clerk from HW 6.2 says, “Okay, you don’t like that necklace? How about these earrings? They have 1.00 x 1025 atoms of gold in them!” How many moles of gold is this?

Answer = 𝟏𝟔. 𝟔 𝐦𝐨𝐥 𝐀𝐮

7. A cold pack uses an endothermic reaction to cool its surroundings . Inside a cold pack are 5.33 x 1024 formula units of ammonium nitrate. How many moles of ammonium nitrate are in a cold pack?

Answer = = 𝟖. 𝟖𝟓 𝐦𝐨𝐥 𝐍𝐇𝟒𝐍𝐎𝟑

Page 8 of 16 Unit 7 HW

HW 7.4 MIXED MOLE CONVERSIONS

Complete the following conversions using dimensional analysis. Show work! 1. Convert 3.33 x 1024 atoms of sodium to grams.

3.33𝑥1024𝑁𝑎 𝑎𝑡𝑜𝑚𝑠 𝑥1 𝑚𝑜𝑙 𝑁𝑎

6.02𝑥 1023 𝑁𝑎 𝑎𝑡𝑜𝑚𝑠 𝑥

22.990 𝑔 𝑁𝑎

1 𝑚𝑜𝑙 𝑁𝑎= 127.17 𝑔 𝑁𝑎 = 𝟏𝟐𝟕 𝒈 𝑵𝒂

2. There are ____ moles in 187 g aluminum.

187 g Al x1 mol Al

26.982 g Al= 6.9305 mol Al = 𝟔. 𝟗𝟑 𝐦𝐨𝐥 𝐀𝐥

3. How many grams are in 40 moles of ammonium chloride NH4Cl

N = 14.007

H = 4(1.008) = 4.032

Cl = 35.453

53.492 g NH4Cl/1 mol NH4Cl

40 mol NH4Cl x53,492 g NH4Cl

1 mol NH4Cl= 2139 g NH4Cl = 𝟐𝟎𝟎𝟎 𝐠 𝐍𝐇𝟒𝐂𝐥

4. How many moles are in 333 g tin (II) fluoride? SnF2

Sn = 118.711

F = 2(18.998) = 37.996

156.707 g SnF2/1 mol SnF2

333 g SnF2 x1 mol SnF2

156.707 g SnF2

= 2.12498 mol SnF2 = 𝟐. 𝟏𝟐 𝐦𝐨𝐥 𝐒𝐧𝐅𝟐

5. Convert 5.00 x 1025 molecules hydrogen (H2) to grams.

H – 2(1.008) = 2.016 g H2/1 mol H2

5.00x1025molecules H2x1 mol H2

6.02x1023 molecules H2x

2.016 g H2

1 mol H2= 167.44 g H2 = 𝟏𝟔𝟕 𝐠 𝐇𝟐

Unit 7 HW Page 9 of 16

6. In 1970, Nobel Prize winning scientist Linus Pauling recommended taking “megadoses” of vitamin C to ward off the

common cold. He suggested taking up to 2.5 grams per day. How many molecules of vitamin C (C6H8O6) did he

recommend that you should take per day?

C =

H =

O =

176.124 g Vit C/ 1 mol Vit C

Answer = = 𝟖. 𝟓𝐱𝟏𝟎𝟐𝟏 𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞𝐬 𝐕𝐢𝐭 𝐂

7. Have you ever tried the energy drink Crunk!!!? It’s made by Lil’ Jon (the rapper) and it is so yummy! It even has 62.0

grams of amazing sugar (C12H22O11) per can! That’s like _________ molecules of sugar!

Answer = 𝟏. 𝟎𝟗𝐱𝟏𝟎𝟐𝟑 𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞𝐬 𝐂𝟏𝟐𝐇𝟐𝟐 𝐎𝟏𝟏

Page 10 of 16 Unit 7 HW

HW 7.5 PERCENT COMPOSITION

1. Write the formula for percent composition below. Use the formula and the information given in

subsequent questions to complete this assignment.

% composition = 𝑇𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡

𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐶𝑜𝑚𝑝𝑜𝑢𝑛𝑑𝑥 100%

2. Find the percent composition of hydrogen in each compound:

a) Ca(OH)2 % of H = ___2.721%_______

Ca = 40.078

O = 2(15.999)=31.998 Molar Mass = 74.092 g/mol %𝐻 =2.016

74.092𝑥 100 = 𝟐.𝟕𝟐𝟏%

H=2(1.008) = 2.016

b) C2H6 % of H = __20.11%___

c) Al (C2H3O2)3 % of H = _4.445%____

3. Find the percent composition of each element in these compounds:

a) NaCl molar mass = __58.443 g/mol__

% of Na = _39.34%___ %Na =22 .990

58.443x 100% = 39.34%

% of Cl = __60.66%___ %Cl =35 .45

58.443x 100% = 60.66%

Na molar mass = 22.990 g/mol

Cl molar mass = 35.45 g/mol

b) (NH4)2S molar mass = __ ________

% of N = ________

% of H = ________

% of S = __47.06%__

Unit 7 HW Page 11 of 16

4. A sample of liquid with a mass of 8.657 grams was decomposed into its elements and gave 5.217 grams of carbon, 0.9620 grams of hydrogen, and 2.478 grams of oxygen. What is the percent composition of this oxygen in this compound? (hint: you don’t need to calculate molar mass to solve this problem, just use the formula from question #1)

%O =2.478

8.657 x 100% = 𝟐𝟖.𝟔𝟐% 𝐎

5. A quantitative analysis of 0.4620 grams of an unknown solid found 0.1945 grams of carbon, 0.02977 grams of hydrogen and 0.2377 grams of oxygen. Calculate the percent composition of carbon in this compound. (hint: you don’t need to calculate molar mass to solve this problem, just use the formula from question #1)

Answer = 𝟒𝟐.𝟏𝟎% 𝑪

6. What is the percentage of Fe in FeCO3 ?

Answer = 𝟒𝟖. 𝟐𝟎% 𝐅𝐞

Page 12 of 16 Unit 7 HW

HW 7.6 EMPIRICAL FORMULA

Answer the following questions concerning empirical formulae. Use the steps outlined in your notes.

1. Determine the empirical formula for a compound containing 19.55 grams potassium and 4.00 grams

oxygen.

Step 1 – 19.55 g K x1 mol K

39.098 g K= 0.500 mol K

4.00 g O x1 mol O

15.999 g O= 0.25 mol O

Step 2 – 0.500 mol K

0.25 mol= 2 K

0.25 mol O

0.25 mol= 1.00 O

Step 3 - K2O

2. A compound contains 174.86 grams of iron and 74.14 grams of oxygen. Construct the empirical formula.

174.48 g Fe x1 mol Fe

55.845 g Fe= 3.12 mol Fe

3.12 mol Fe

3.12 mol= 1 mol Fe x 2 = 2 mol Fe

74.14 𝑔 𝑂 𝑥1 𝑚𝑜𝑙 𝑂

15.999 𝑔 𝑂= 4.63 𝑚𝑜𝑙 𝑂

4.63

3.12= 1.48 1.48 𝑥 2 = 3 𝑚𝑜𝑙 𝑂

3. Sodium sulfite is a meat preservative and sodium sulfate is a laxative. Your grandmother gives you a side of beef for your birthday and you’d like to keep it from rotting. You’ve found a sample of a compound of sodium that contains 36.5 grams of sodium, 25.4 grams of sulfur, and 38.1 grams of oxygen. Do you have a laxative or the meat preservative you so desperately need? Sodium Sulfite – Na2SO3 Sodium Sulfate = Na2SO4

Fe2O3

Na2SO3 = Sodium Sulfite =

Preservative

Unit 7 HW Page 13 of 16

4. As lead arson investigator with the Houston Fire Department you find a small sample of the accelerant (fuel) that caused a fire that took the lives of 11 people in an urban apartment complex. You run the sample through a mass spectrometer and find that it contains 37.5% carbon, 12.5% hydrogen, and 50.0% oxygen, by mass. Determine the empirical formula of this substance.

CH4O

Page 14 of 16 Unit 7 HW

HW 7.7 MOLECULAR FORMULA

Answer the following questions concerning molecular formulae. Use the steps outlined in your notes. Show

work

1. Find the molecular formula for a compound with a molar mass of 90.04 g/mol and an empirical formula of

CHO2.

Step 1: Mass of CH02 = 1 x 12.011 + 1 x 1.008 + 2 x 15.999 = 45.02

Step 2: Scale factor = Mass of Molecule / Mass of Empirical Formula = 90.04/45.02 = 2

Step 3: Scale Factor x Empirical Formula = 2 x CHO2 = C2H2O4 is molecular formula

2. Find the molecular formula for a compound with 46.68% nitrogen and 53.32% oxygen and a molar mass of

60.01 g/mol.

46.68 g N x1 mol N

14 .007 g N= 3.33 mol N

3.33 mol N

3.33 mol= 1 mol N

53.32 𝑔 𝑂 𝑥1 𝑚𝑜𝑙 𝑂

15.999 𝑔 𝑂= 3.33 𝑚𝑜𝑙 𝑂

3.33 𝑀𝑜𝑙 𝑂

3.33= 1 𝑚𝑜𝑙 𝑂

NO is Empirical Formula. Mass of NO = 14.007 + 15.999 = 30.01 g/mol

Scale = 60.01 /30.01 = 2 Molecular Formula is 2 x NO = N2O2

3. Elaidic acid is the primary trans fatty acid present in partially hydrogenated oils used in food production.

Calculate the molecular formula for elaidic acid given that it has an empirical formula of C 9H17O1 and a

mass of 282 g/mol.

4. Strychnine, a deadly poison, has a mass of 334 g/mol and a percentage composition of 75.42% carbon,

6.63% hydrogen, 8.38% nitrogen, and 9.57% oxygen. What is the molecular formula of strychnine?

C18H34O2

N2O2

C21H22N2O2

Unit 7 HW Page 15 of 16

Common Polyatomic Ions List

Name Ion Name Ion

acetate C2H3O2– or CH3COO– hypochlorite ClO–

ammonium NH4+ nitrate NO3

–

carbonate CO32– nitrite NO2

–

chlorate ClO3– perchlorate ClO4

–

chlorite ClO2– permanganate MnO4

–

chromate CrO42– phosphate PO4

3–

cyanide CN– phosphite PO33–

dichromate Cr2O72– silicate SiO3

2–

hydrogen carbonate HCO3– sulfate SO4

2–

hydroxide OH– sulfite SO32–

How to key scientific notation into a TI calculator:

Type in 6.02 x 1023:

Should display:

How to key molar mass into a TI calculator in ONE STEP!:

Example: Na2SO4

Roman Numerals for Transition Metals 1-6

1 = I 2 = II 3 = III 4 = IV 5 = V 6 = VI

20 Common Polyatomic Ions

Page 16 of 16 Unit 7 HW