• Atomic 1 0 4 Percent Equals
• 1 Atomic Number
• Calculating Atomic Percent

Revision: Formulas and Mole Conversions

1.What is a cation? Give an example.

1. 1) Find the average atomic mass of the element, given the isotopic percentage of 75.0% for Cl-35 and 25.0% for Cl-37. 2) The part of an element that never changes is. Electric charge. Oxidation number. 3) The positively charged particle in the nucleus.
2. Determine the atomic mass of sulfur given the following naturally occurring isotopes: 32 / 16 S (31.972 amu, 94.99%), 33 / 16 S (32.971 amu, 0.75%), 34 / 16 S (33.968 amu, 4.25%) 36 / 16 S (35.967 amu, 0.01%) (33.968 amu, 4.25%),.
3. Cementite: consider cementite. Calculate the amount of carbon in Cementite (1) as atomic% (2) as weight% atomic weights Fe 56, c 12. Place cementite on the Fe-C phase diagram; explain the nature of its appearance on the diagram, and comment on the nature and properties of cementite.

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

Rubidium has two naturally occurring isotopes, 85Rb (relative mass 84.9118 amu) and 87Rb (relative mass 86.9092 amu). If rubidium has an average atomic mass of 85.47 amu, what is the abundance of. This is a table of the elemental composition of the human body by mass for a 70 kg (154 lb) person. The values for any particular person may be different, especially for the trace elements.

3.Fill in the chart.

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?

Aproblem 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?

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.

Atomic 1 0 4 Percent Equals

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) SO₄^2-/sulfate
c) NH₄⁺/ammonia
d) PO₄^3-/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 X^2-, 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 Dalton¹s 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

1 Atomic Number

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

Calculating Atomic Percent

Percent Composition