Revision: Formulas and Mole Conversions

 

1.        What is a cation? Give an example.

2.        Where are the nonmetals located on the periodic table?

3.        Fill in the chart.

Symbol

Name

# of p+

# of no

# of e-

atomic #

atomic mass

 

aluminum ion

 

 

 

 

 

O-2

 

 

 

 

 

 

 

 

27

 

25

 

 

 

 

 

 

10

9

 

 

mercury

 

 

 

 

 

4.        Name the following compounds. State whether they are formula units or molecules.
a) Na2SO4 b) N2O4 c) MgCl2 d) KH2PO4 e) SiF4
f) HNO2 g) Fe(NO3)3 h) NO2 i) MnCrO4 j) Co3(PO4)2

5.        Write the formula for the following compounds.
a) carbonic acid b) barium chlorate c) tin (IV) nitride d) hydrochloric acid
e) cobalt (I) hydride f) nitrogen triiodide g) sulfur hexachloride h) silver carbonate

6.        State whether each of the compounds listed in #5 are molecular or ionic.

7.        List the three types of representative particles.

8.        Name the eight (seven for Mr. Koppel's class) diatomic molecules.

9.        How many atoms are in 0.455 moles of lead?

10.     Find the number of moles in 1.33 x 1021 molecules of oxygen.

11.     What is the mass of 1 molecule of carbon tetrachloride?

12.     How many formula units are in 14.22 grams of iron (III) oxide?

13.     What is the volume (in L) of 3.72 moles of hydrogen gas at STP?

14.     What is the mass of 370 L of nitrogen gas at STP?

15.     What is the density of methane (CH4, natural gas) at STP?

16.     Which compound contains the most copper, by weight: CuO, CuS, or Cu2S or Cu3PO4?

17.     A compound is found to be 53.0% aluminum and 47.0% oxygen. Find its empirical formula.

18.     A 1.338 gram sample of a compound contains 0.366 grams of Na and 0.220 grams of N. The rest is oxygen. Find the empirical formula.

19.     Find the molar masses of the compounds in questions #4 f-j.

20.     Vitamin C is an organic compound (and Mr. Koppel's favorite vitamin) which contains carbon, hydrogen, and oxygen. Analysis of a sample shows that it is 40.9 % C, 4.58 % H, and 54.5 % O. Its molar mass is about 180 g/mole. Find the molecular formula.

21.     What is the mass, in kg, of 5.00 x 1026 atoms of lead?

22.     How many atoms of carbon has a man given his fianceé if the engagement ring has a 0.500 carat diamond? There are 200.0 mg in a carat.

 

 

 

Answers to select problems:
9) 2.74 x 1023 atoms 10) 2.21 x 10-3 moles 11) 2.55 x 10-22 g 12) 5.360 x 1022 form. units. 13) 83.3 L
14) 460 g 15) .7165 g/L 16) CuO w/79.89% Cu 17) Al2O3 18) NaNO3 19) f) 47.02 g/mole
g) 241.88 g/mol h) 46.01 g/mol i) 170.94 g/mol j) 366.73 g/mol 20) C6H8O6 21) 172 kg
22) 5.01 x 1021 atoms

 


Avogadro's Number and Moles Exercise Sheet

1. What are the units of molar mass?

2. The mass of 2.5 X 104 grapes is 50 kilograms, and that of an equal number of oranges is
1.2 X 103 kg. What is the mass ratio of a single single grape to a single orange?

3. A mole of carbon atoms has a mass of 12 grams, and a mole of magnesium atoms, 24
grams. What is the mass ratio of a single carbon atom to a single magnesium atom?

4. Aluminum and oxygen combine in a mass ratio of 9.00 to 8.00. If a flashbulb contains
5.4 X 10-3 grams of aluminum, what mass of oxygen must be present for complete
combustion of the aluminum?

5. If there are 'x' atoms in 5 grams of carbon, how many atoms are there in 5 grams of silicon?

6. If 10 grams of iron contain 'y' atoms, how many grams of aluminum will contain 'y' atoms.

7. If 8 grams of oxygen contain 3.01 X 1023 atoms, calculate the number of atoms present
in 2 grams of oxygen.

8. Using Avogadro's number, calculate the number of atoms in 0.005 kilograms of carbon.

 

Grams, Moles and Molecular Mass Worksheet

1. What is the mass of 0.100 mol of each of the substances given below:
(a) Sodium carbonate, Na2CO3
(b) Ammonium tetraborate, (NH4)2B4O7
(c) Calcium cyclamate, Ca(C6H12NSO3)2

2. How many moles of sodium nitrate are in 1.70 grams of sodium nitrate, NaNO3, a
substance used in fertilizers and to make gunpowder.

3. Ammonium sulphate, (NH4)2SO4, is a fertilizer used to supply both nitrogen and sulphur.
How many grams of ammonium sulphate are in 35.8 moles of (NH4)2SO4.

4. A 0.500 mol sample of table sugar, C12H22O11, weighs how many grams?

5. A solution of zinc chloride, ZnCl2, in water is used to soak the ends of wooden fenceposts
to preserve them from rotting while they are stuck in the ground. One ratio used is 840 grams
ZnCl2 to 4 L water. How many moles of ZnCl2 are in 840 grams of ZnCl2?

6. In the early 1970s, thallium sulphate, Tl2SO4, a powerful poison, was illegally used in poison
baits to control predators such as coyotes on western rangelands. Hundreds of eagles died
after taking these baits. A 1.00 kilogram can of Tl2SO4 contains how many moles of this
compound?

7. Borazon, one crystalline form of boron nitride, BN, is very likely the hardest of all substances.
If one sample contains 3.02 X 1023 atoms of boron, how many atoms and how many grams
of nitrogen are also in this sample?

8. If iodine is not in a person's diet, a thyroid condition called goitre develops. Iodized salt is all
that it takes to prevent this disfiguring condition. Calcium iodate, Ca(IO3)2, is added to table
salt to make iodized salt. How many atoms of iodine are in 0.500 moles of Ca(IO3)2?
How many grams of calcium iodate are needed to supply this much iodine?

9. Ammonium carbonate,(NH4)2CO3, is used as a fertilizer and to manufacture explosives.
How many atoms of nitrogen are in 0.665 moles of this substance? How many grams of
ammonium nitrate supply this much nitrogen?

10. Sodium perborate, NaBO3, is present in "oxygen bleach". It acts by releasing oxygen,
which has bleaching ability. How many grams of sodium perborate are in 4.65 moles
of NaBO3?

11. Barium sulphate, BaSO4, is given to patients as a thick slurry in flavoured water before
X-rays are taken of the intestinal tract. The barium blocks the X-rays, and the tract
therefore casts a shadow that is seen on the x-ray film. How many grams are in 0.568
mole of barium sulphate.

12. Calculate the number of grams in 0.586 mole of each of the following substances?
(a) Water, H2O.    (b) Glucose, C6H12O6, a sugar in grape juice and honey.
(c) Iron, Fe.           (d) Methane, CH4.

13. Calculate the number of moles of each substance in 100.0 grams of each of the following samples:
(a) Ammonia, NH3               (b) Cholesterol, C27H46O
(c) Gold, Au                         (d) Ethyl alcohol, C2H6O

14. Why does 100.0 grams of ammonia, NH3, have so many more moles than 100.0 grams
of cholesterol, C27H46O?

15. A sample of a compound with a mass of 204 grams consists of 1.00 x 1023 molecules.
What is its formula weight?

 

 

 


A  problem set :

 

1.        Styrene is an organic molecule that is used as a building block for many polymers (like polystyrene). The molecular formula for styrene is C8H8.

a.        What is the molecular weight of styrene?

b.       What is the emperical formula of styrene?

c.        How much does 1.000 mole of styrene weigh?

d.       How much does 1.54 pmole of styrene weigh?

e.        How much many moles in 9.67 kg of styrene?

f.         How many moles in 84.6 mg of styrene?

g.       What is the mass percent of carbon in styrene?

h.       What is the mass percent of hydrogen in styrene?

i.         A barrel of an unknown material is recovered from the Delaware river near a plant that produces polystyrene. It has been suggested that the barrel contains styrene. Results from the elemental analysis of an unknown compound are shown below. Does this support the hypothesis that the barrel contains styrene?

Element

Abundance (%)

Carbon

92.26

Hydrogen

7.74

j.         Further experimentation determines that the molecular weight of this compound is 78.11 grams per mole. What is the molecular formula for the unknown compound?

 

 



Chemical Formulas and Composition Stoichiometry

1. Identify the compound below which is an ionic compound.

a) CH4
b) H2O2
c) Na2CO3
d) NH3
e) SO2

2. Identify the compound formula that is INCORRECT.

a) Ca3(PO4)2 for calcium phosphate
b) NaNO3 for sodium nitrate
c) K2CO3 for potassium carbonate
d) NH4SO4 for ammonium sulfate
e) KCl for potassium chloride

3. Identify the INCORRECT statement below:

a) The atomic weight is the number of atoms in one mole of the element.
b) The electron and proton have charges of equal magnitude and opposite sign.
c) The atomic number is the number of protons in the nucleus.
d) An atom is the smallest particle of an element that maintains the chemical identity of that element.
e) The number above the element symbol on the periodic chart is the atomic number.

4. Identify the INCORRECT statement below:

a) Atoms cannot be created, destroyed, or transformed into atoms of another element except by nuclear reactions.
b) Some elements exist in pure form as polyatomic molecules.
c) All atoms of a given element have identical properties, which differ from those of other elements.
d) Compounds form when masses of different elements combine in small whole-number ratios.
e) The relative numbers and kinds of atoms are constant in a given compound.

5. How many Hydrogen atoms are present in 27.0 g of H2O?

a) 1.80 x 1024
b) 9.03 x 1023
c) 6.02 x 1023
d) 27.0
e) 4.5 x 10-23

6. Calculate the formula weight of TNT, trinitrotoluene, which has a formula C6H2(CH3)(NO3)3.

a) 179
b) 263
c) 247
d) 307
e) 275

7. Calculate the % Oxygen in NaHCO3, sodium bicarbonate.

a) 57.1%
b) 43.3%
c) 19.0%
d) 0.57%
e) 21.7%

8. Determine the simplest empirical formula of a compound with the following composition by mass: 29.1% Na; 40.5% S; 30.4 % O.

a) NaSO2
b) Na2S2O3
c) NaSO3
d) Na2SO4
e) Na2SO3

9. An alkene hydrocarbon with an empirical formula of CH2 has a molecular weight of 98.2 amu. What is the true molecular formula for the compound?

a) CH2
b) C7H14
c) C8H2
d) C3H6
e) C5H10

 

 

10. How many grams of Nitrogen combine exactly with 6.0 grams of Hydrogen to produce NH3?

a) 7.0 g
b) 2.0 g
c) 14.0 g
d) 28.0 g
e) 1.28 g

11. Balance the following chemical equation with the smallest whole number coefficient.

___KOH + ___CO2 ---> ___K2CO3 + ___H2O

a) 2:1:1:4
b) 1:1:1:1
c) 2:1:1:2
d) 2:1:1:1
e) 2:2:1:4

12. Balance the following chemical equation with the smallest whole number coefficients. What is the value of the coefficient of the CO2 species?

___C4H10 + ___O2 ---> ___CO2 + ___H2O

a) 5
b) 4
c) 13
d) 10
e) 8

KEY

1)c 2)d 3)a 4)d 5)a 6)e 7)a 8)b 9)b 10)d 11)d 12)e

 

 


Chemical Formulas and Compound Stoichiometry

1. Identify the compound below which is a molecular compound:

a) CaF2
b) NaCl
c) Na2CO3
d) NH4NO3
e) SO3

2. Identify the compound formula that is INCORRECT.

a) AgCl = silver chloride
b) KNO3 = potassium nitrate
c) CuCO3 = copper(I) carbonate
d) NH4Cl = ammonium chloride
e) ZnBr2 = zinc bromide

3. Calculate the formula weight of iron(III) sulfate, Fe2(SO4)3.

a) 351.9
b) 489.8
c) 399.9
d) 344.0
e) 335.0

4. Calculate the % Oxygen by mass in glucose, C6H12O6.

a) 53.3%
b) 3.33%
c) 25.0%
d) 57.5%
e) 5.3 x 10-1%

5. Determine the simplest empirical formula of the drug methaqualone with the following composition by mass: 76.78% C; 5.64% H; 11.19% N; 6.39% O.

a) C12H10N2O
b) C6H6NO
c) C12H10NO
d) C16H14N2O
e) C13HN2O

6. An alkene hydrocarbon with an empirical formula of CH has a molecular weight of 26.0 amu. What is the true molecular formula for the compound?

a) CH
b) C2H2
c) CH2
d) C2H4
e) C3H3

7. Calculate the mass of a single molecule of water in grams.

a) 18.0 x 10-23 g
b) 18.0 g
c) 1.67 x 10-24 g
d) 3.0 x 10-23 g
e) 3.3 x 1022 g

8. How many moles of benzene (C6H6) are present in 7.81 grams of benzene?

a) 7.81 mol
b) 1.00 mol
c) 0.100 mol
d) 78.1 mol
e) 609.9 mol

9. Identify the INCORRECT statement:

a) One mole of water contains 6.022 x 1023 H2O molecules.
b) There are 16.0 g in 1.00 mole of O2.
c) 12.0 grams of Carbon have the same number of atoms as 14.0 grams of Nitrogen.
d) 28.0 grams of N2 have the same number of molecules as 32.0 grams of O2.
e) A mole is the amount of substance having the same number of particles as 12 grams of pure Carbon-12.

 

 

 

10. How many glucose molecules are present in 1.0 picogram (1 trillionth of a gram) of glucose, C6H12O6?

a) 6.02 x 1012 molecules
b) 3.34 x 10211 molecules
c) 6.02 x 1011 molecules
d) 33 molecules
e) 3.34 x 109 molecules

11. Which has a greater mass?

a) 1 atom of iron
b) 1 atom of Neon
c) 1 molecule of carbon dioxide
d) 1 molecule of water

12. In which sample are there more particles?

a) 1.0 gram of gold
b) 1.0 gram of carbon
c) 1.0 gram of helium
d) 1.0 gram of iron

13. The fact that water is always found to be 89% Oxygen and 11% Hydrogen by mass is an example of:

a) The Law of Conservation of Matter
b) The Law of Conservation of Energy
c) The Law of Multiple Proportions
d) The Law of Definite Proportions
e) Democritus' theory of atoms

14. Which of the following species DOES NOT represent an element in its most stable form?

a) H2
b) Br
c) S8
d) P4
e) Ne

15. The number of protons in a silicon atom is:

a) 28
b) 14
c) 32
d) 16
e) 47

KEY

1)e 2)c 3)c 4)a 5)d 6)b 7)d 8)c 9)b 10)e 11)a 12)c 13)d 14)b 15)b

Selected solutions:

Problem 5:
Divide the % composition of each element by that element's atomic weight. That converts a mass ratio to a mole ratio. Then convert that mole ratio to whole numbers by dividing each of the mole ratio numbers by the smallest of the numbers. That gives you 16:14:2:1

Problem 7:
Calculate the mass of a single molecule of water in grams.

18.0 grams of H2O make up 1 mole.
1 mole is 6.022 x 1023 molecules

So:

      18.0 grams/mol

-----------------------    = 3.0 x 10-23 grams/molecule

6.022 x 1023 molecules/mol

 


Chemical Formulas and Compound Stoichiometry

1. Which of the following statements are TRUE?

1) Under normal conditions nitrogen exists as a diatomic molecule.
2) Ca(NO)3 is an ionic solid.
3) An ionic solid always consists of cations and anions in equal numbers.

a) only 1
b) 2 and 3
c) 1 and 2
d) 1, 2, and 3

2. Which of the following ion/name combinations is NOT CORRECT?

a) NO3-/nitrate
b) SO42-/sulfate
c) NH4+/ammonia
d) PO43-/phosphate

3. How many moles of silver atoms are in 0.780 grams of silver?

a) 0.78 moles
b) 0.00723 moles
c) 84.2 moles
d) 0.522 moles

4. What is the formula weight of Mg(BrO4)2?

a) 312 amu
b) 232 amu
c) 168.2 amu
d) 477 amu

5. What mass of the compound FeWO4 contains 50.0 grams of tungsten (atomic symbol W, atomic number = 74)?

a) 30.0 g FeWO4
b) 304 g FeWO4
c) 82.6 g FeWO4
d) 188 g FeWO4

6. Which of the following is NOT an ionic compound?

a) LiF
b) CCl4
c) NH4Cl
d) FeSO4

7. A compound contains 20.2% magnesium, 39.8% titanium, and 40.0% oxygen by mass. What is the empirical formula of this compound?

a) MgTiO
b) MgTi2O3
c) Mg2TiO4
d) MgTiO3

8. Which of the following DOES NOT contain 4.00 moles of oxygen atoms?

a) 2.00 moles of CO2
b) 128.0 g of SO2
c) 0.40 moles of P4O10
d) 4.00 moles of KClO3

9. A compound has an empirical formula of C2HBr. If the molar mass of the compound is 314.7 g/mol, what is the molecular formula of the compound?

a) C2HBr
b) C4H2Br2
c) C6H3Br3
d) C8H4Br4

10. A doubly negative ion, symbolized by X2-, forms a compound with a metal M, of the formula M2X. What is the charge on the metal, M?

a) +1
b) +2
c) +3
d) +4

 

11. What is the mass percent of copper in the mineral bornite, Cu4FeS4?

a) 44.4%
b) 58.0%
c) 14.5%
d) 72.4%

12. Which of the following is the empirical formula for the compound iron(II) carbonate?

a) Fe(CO3)2
b) FeCO3
c) Fe2CO3
d) Fe2(CO3)2

13. A 0.2420 sample of an unknown containing C, O, and H is burned completely. Analysis shows that 0.2265 grams of water are produced. How many grams of hydrogen were present in the 0.2420 grams of sample?

a) 0.0253 grams
b) 0.2265 grams
c) 0.0127 grams
d) 0.1522 grams

14. What is the mass of 0.220 moles of AgNO3?

a) 169.9 g
b) 0.415 g
c) 0.220 g
d) 37.4 g

KEY

1)c 2)c 3)b 4)a 5)c 6)b 7)d 8)d 9)c 10)a 11)b 12)b 13)a 14)d


Chemical Formulas and Compound Stoichiometry

1. Which of the following statements is incorrect?

a) A molecule is the smallest part of a compound that can have a stable independent existence.
b) Molecules that consist of more than one atom are called polyatomic molecules.
c) The atomic number of an element is defined as the number of neutrons in the nucleus.
d) Molecules of compounds are composed of more than one kind of atom.
e) The charge on an electron is negative and the charge on a proton is positive.

2. Calculate the number of moles of nitrogen atoms in 20.9 grams of nitrogen.

a) 1.49 moles
b) 0.746 moles
c) 0.37 moles
d) 1.74 moles
e) 1.23 moles

3. Calculate the formula weight of K3PO4.

a) 173.2 amu
b) 134.1 amu
c) 212.3 amu
d) 228.3 amu
e) 185.1 amu

4. What is the mass of 2.50 moles of CH3CH2OH?

a) 100 g
b) 102 g
c) 46.0 g
d) 115 g
e) 239 g

5. What is the mass of 1.0 x 1012 molecules of O2?

a) 1.9 x 1013 g
b) 6.0 x 1011 g
c) 2.7 x 10-11 g
d) 5.3 x 10-11 g
e) 1.7 x 10-12 g

6. Suppose you have a 100 gram sample of each of the following compounds. Which sample contains the smallest number of moles of compound?

a) NH3
b) MgCl2
c) H3PO4
d) CrCl3
e) NaCl

7. Calculate the percent by mass of nitrogen in ammonium carbonate, (NH4)2CO3.

a) 14.5%
b) 27.8%
c) 29.2%
d) 33.3%
e) 17.1%

8. A 4.628 g sample of an oxide of iron was found to contain 3.348 g of iron and 1.280 g of oxygen. What is the simplest formula for this compound?

a) FeO
b) Fe2O3
c) Fe3O4
d) FeO2
e) none of these answers

9. Balance the following equation with the smallest whole number coefficients. Choose the answer that is the sum of the coefficients in the balanced equation. Do not forget coefficients of one. P4 + Cl2 --> PCl5

a) 7
b) 9
c) 11
d) 13
e) 15

 

 

10. Balance the following equation with the smallest whole number coefficients. Choose the answer that is the sum of the coefficients in the balanced equation. Do not forget coefficients of one. C7H16 + O2 --> CO2 + H2O

a) 23
b) 27
c) 29
d) 30
e) 32

11. How many moles of CO2 would be produced from 56 moles of O2 according to the following balanced equation? 2C2H6 + 7O2 --> CO2 + H2O

a) 16
b) 32
c) 224
d) 48
e) 8

12. The complete combustion of a hydrocarbon produced 352 mg of CO2 and 216 mg of H2O. What is the simplest formula of this hydrocarbon?

a) CH
b) CH2
c) C2H3
d) CH3
e) C3H2

13. Which of the following statements is not an idea from Daltonšs Atomic Theory?

a) An element is composed of extremely small indivisible particles called atoms.
b) All atoms of a given element have identical properties which differ from those of all other elements.
c) Atoms can only be transformed into atoms of another element by nuclear reactions.
d) Compounds are formed when atoms of different elements combine with each other in small whole-number ratios.
e) The relative numbers and kind of atoms are consistent in a given compound.

14. What is the molecular formula for ammonia?

a) HNO3
b) HNO2
c) NH3
d) CH4
e) N2H4

15. Consider the following balanced equation. 2H2 + O2 --> 2H2O Which one of the following statements is false?

a) One molecule of O2 will react with 2 molecules of H2.
b) One mole of O2 will react with 2 moles of H2.
c) The complete reaction of 32.0 g of O2 will produce 2 moles of H2O.
d) The complete reaction of 2.0 g of H2 will produce 36.0 g of H2O.
e) The amount of reaction that consumes 32.0 of g O2 produces of 36.0 g H2O.

KEY

1)c 2)a 3)c 4)d 5)d 6)d 7)c 8)c 9)e 10)b 11)b 12)d 13)c 14)c 15)d

 


 

Percent Composition

1.

What is the percentage composition of CaO?

2.

Calculate the mass percentage composition of each compound.

 

a) MgCl2 b) Na2SO4 c) Fe2O3 d) C7H5N3O6 e) AlBr3.6H2O

3.

Determine the percent composition of Ca3(PO4)2

4.

A sample of a 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 percentage composition of this compound?

5.

The drug known as LSD has the formula C20H25N3O. One suspected sample contained 74.07%C, 7.95%H, and 9.99% N. Are the percentages given in the question consistent for LSD within the allowed limits of error and rounding?

6.

Calculate the percentage of nitrogen in the two important nitrogen fertilizers, ammonia, NH3 and urea, CO(NH2)2

7.

A 27.0 g sample of a compound contains 7.20 g of C, 2.20 g of hydrogen and 17.6 g of oxygen. Calculate the percentage composition of the compound.

8.

Carbon will burn in sufficient oxygen to produce carbon dioxide. In an experiment 8.40 grams of C reacts with oxygen and 30.80 grams of carbon dioxide is produced.

 

a) What mass of oxygen reacted with the 8.40 grams of C?

 

b) Calculate the percentage composition of the carbon dioxide.

9.

In one sample of a compound of copper and oxygen, 3.12 g of the compound contains 2.50 g of copper and the remainder is oxygen. In another sample of a compound of copper and oxygen, 1.62 g of the compound contain 1.44 grams of copper and the remainder is oxygen.

 

a) Calculate the percentage composition of each compound.

 

b) Are the two samples the same compound? Justify your answer.

10.

Calculate the percentage by mass of the indicated elements in each of the following compounds.

 

a) sodium in sodium azide, NaN3(s); used in automobile air bags.

 

b) aluminum in aluminum oxide, Al2O3; the naturally occurring mineral corundum

 

c) nitrogen in dopamine, C8H11O2N; a neurotransmitter in the brain

11.

A forensic scientist analyzes a sample for sodium arsenate, Na2AsO4(s), a source of arsenic. Calculate the percentage composition of sodium arsenate.

12.

A cleaning solution has the acronym, TSP, which is short for trisodium phosphate, Na3PO4. Calculate the percentage composition of the compound. (P.S. TSP is not an official name for the compound.)