CHEM 120 Week 3 Balancing Chemical Equations Questions and Answers- Chamberlain College Atlanta
Balancing Chemical Equations
WEEK 3
1. Sodium bromide
... [Show More] reacts with calcium chloride to form sodium chloride and calcium
bromide. Which of these chemical reactions represents the balanced reaction?
a. NaBr + CaCl2 → NaCl + CaBr2
b. 2 NaBr + CaCl2 → 2 NaCl + CaBr2
c. NaBr + 2 CaCl2 → NaCl + 2 CaBr2
d. NaBr + CaCl → NaCl + CaBr
Balanced chemical equations have the same number of each atom
on each side of the arrow. This equation is correct: 2 NaBr + CaCl2 2 →
NaCl + CaBr2
2. The small number 2 in H2O is called a(n):
a. Atomic number
b. Superscript
c. Coefficient
d. Subscript
Subscripts tell you how many of an atom you have in a chemical formula.
3. Which of the following chemical equations violates the Law of
Conservation of Mass?
a. 2 H2 + N2 → 2 NH3
b. HCl + KOH → H2O + KCl
c. NaCl + KBr → NaBr + KCl
d. 2 H2 + O2 → 2 H2O
Check each chemical reaction to determine the one that does not have the same
number of each atom on each side of the chemical reaction. If a chemical
equation violates the Law of Conservation of Mass, the atoms will not equal out
on both sides. The correct answer is 2 H2 + N2 → 2 NH3. There are four atoms of
H on the left, or reactant side while there are six atoms of H on the right, or
products side. As matter cannot be create or destroyed in a chemical reaction,
these are not this choice violates the Law of Conservation of Mass.
4. The Coefficients represent the number of molecules in a balanced chemical
equation. The subscripts represent the number of atoms in a chemical
formula.
atomic numbers, Coefficients, subscripts, superscripts
atomic numbers, coefficients, subscripts, superscripts
The coefficients represent the number of molecules. The subscripts in a formula
represent the number of atoms.
5. 4 Fe(s) + 3 O2(g) > 2 Fe2O3(s)
In the equation, how many molecules of O2 are in the chemical equation?
a. 1
b. 4
c. 2
d. 3
Coefficients show us how many molecules of a given compound are in a chemical
equation. In this case there are 3 O2 molecules.
6. 4 Fe(s) + 3 O2(g) > 2 Fe2O3(s)
How many total atoms of O are on the left side of the equation?
a. 6
b. 5
c. 3
d. 2
The subscripts tell us how many of a molecule we have, and subscripts show how
many atoms are in each molecule. This means that by multiplying the coefficient
by the number of atoms of a given element in a molecule, we can determine how
many atoms of that element. In this case there are 3 x 2 = 6 oxygen atoms.
The coefficients show the number of molecules of a given compound. This equation is 2
H2(g) + 1 O2(g) > 2 H2O(g)
1 Ca 1
2 O 2
4 H 4
2 Br 2
3 Mg 3
3 S 3
3
0
O 30
2 Al 2
6 N 6
2 H2 + 1 O2 → 2 H2O
1 FeCl2(s) + 1 H2O(l) → 1 FeO(s) + 2 HCl(aq)
1 C4H8(g) + 6 O2(g) → 4 CO2(g) + 4 H2O(l)
2 NaHCO3(s)→ 1 Na2CO3 + 1 CO2(g) + 1 H2O(g)
2 NaOH(aq) + 1 MgCl2(aq)→ 2 NaCl(aq) + 1 Mg(OH)2(s)
6. Are these equations balanced or unbalanced?
H2 + O2 > H2O
Balanced
Unbalanced
H2 + O2 > H2O2
Balanced
Unbalanced
K + O2 > K2O
Balanced
Unbalanced
Na + Cl > NaCl
Balanced
Unbalanced
Balanced as written
H2 + O2 > H2O2
Na + Cl > NaCl
Not balanced as written
H2 + O2 > H2O
K + O2 > K2O
8. In the following chemical equation, which of the compounds are dissolved in
water? Select all that apply
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
a. NaNO3
b. NaCl
c. AgNO3
d. AgCl
The symbols after the molecule indicate the state of matter. (aq) indicates
aqueous compounds, so AgNO3, NaCl, and NaNO3 are all dissolved in water.
9. Balance the unbalanced chemical equation:
----S8(g) + ------ O2(g) → ---- SO3(g)
1, 2, 3, 4, 5, 6, 7, 8, 9
10, 11, 12, 13, 14, 15
1, 2, 3, 4, 5, 6, 7, 8, 9
Be sure to count up every atom on both the product and reactant side. A
balanced equation is 1 S8(g) + 12 O2(g) → 8 SO3(g)
10. In the unbalanced chemical equation Fe2O3(s) + HNO3(aq) → Fe(NO3)3(aq)
+ H2O(l), how many oxygen atoms are on the product side of the reaction?
a. 10
b. 7
c. 4
d. 6
e. 9
The first step of balancing a chemical equation is to find how many atoms of each
element are on each side of a chemical reaction. Be sure to count up all atoms in
each term for both products and reactants separately. Oxygen has 10 atoms on
the product side of this equation.
11. Select all examples where the Law of Conservation of Mass is not being
followed.
a. H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
b. Mg3N2(s) + 3 H2O(l) → NH3(g) + 3 Mg(OH)2(s)
c. 2 NaCl + MgBr2 → 2 NaBr + MgCl2
d. S8(g) + Ag(s) → 8 AgS
When both sides of a chemical equation have the same number of each atom, the
Law of conservation of mass is followed and the equation is balanced. Otherwise,
the equation is unbalanced. The equations S8(g) + Ag(s) → 8 AgS and Mg3N2(s)
+ 3 H2O(l) → NH3(g) + 3 Mg(OH)2(s) are both unbalanced.
12. Balance the chemical equation:
------ C5H12 + ----- O2 → ----- H2O + ---- CO2.
1, 2, 3, 4, 5, 6, 7, 8, 9
1, 2, 3, 4, 5, 6, 7, 8, 9
1, 2, 3, 4, 5, 6, 7, 8, 9
1, 2, 3, 4, 5, 6, 7, 8, 9
Be sure to count all atoms on each side every time you change a coefficient. The
balanced equation would be 1 C5H12 + 8 O2 → 6 H2O + 5 CO2
Stoichiometry
Atomic mass is the lower left number on the periodic table and has units of
g/mole.
13. If the balanced chemical reaction for the formation of Li2O is 4 Li(s) + O2(g)
→ 2 Li2O(s), how many molecules of Li2O(s) would you produce if you used up 6
atoms of Li(s)?
a. 6
b. 12
c. 3
d. 2
Just like following a recipe, we can know how many of an ingredient (reactant)
we need to make a specified amount of product according to a recipe (balanced
chemical equation). You produce 3 molecules of Li2O(s) by using 6 atoms of
Li(s).
Use g/mol as the unit for molecular mass and make sure to count up
all atoms in each molecule.
MgCl2
Number of Mg atoms 1
Number of Cl atoms 2
Molecular Mass of
MgCl2
95.21
g/mole
Ca(OH)2
Number of Ca atoms 1
Number of O atoms 2
Number of H atoms 2
Molecular Mass of
Ca(OH)2
74.1 g/mol
(NH4)2S
Number of N atoms 2
Number of H atoms 8
Number of S atoms 1
Molecular Mass of
(NH4)2S
68.17
g/mol
Complete the formula for the correct molecular weights:
32.00 g O2 / 1 mole O2
82.98 g Na3N / 1 mole Na3N
132.1 g Ca(NO2)2 / 1 mole Ca(NO2)2
157.9 g P2O6/ 1 mole P2O6
Use the method you learned previously to convert the following:
Convert 3.8 grams of H2O into moles
(Molar mass of H2O is 18.02 g/mol)
3.8 g H2O 1 mol H2O 0.21 moles H2O
18.02 g H2O
Convert 9.6 moles of NaOH into grams
(Molar mass of NaOH is 40.0 g/mol)
9.6 mol NaOH 40.0 g NaOH 384 g NaOH
1 mol NaOH
The molar mass from the periodic table has units of grams per mole (g/mol). The
units of mass are grams, which can be measured easily in a lab or similar. The
units of moles are used in balanced chemical equations. Therefore, the molar
mass from the periodic table can be used to relate what is measured in lab to
what is written in balanced chemical equations.
14. My water bottle contains 500 grams of water, H2O. How many moles of water
is this?
a. 500 moles
b. 18.00 moles
c. 27.8 moles
d. 9000 moles
500 grams of water, divided by 18.0 g/mol is 27.8 moles of water.
42 moles H2O 1 mole O2 21 moles O2
2 moles H2O
Using the chemical formula CaO + 2 NaCl → Na2O + CaCl2, calculate how
many moles of CaCl2 you would produce if you used up 5.4 moles of CaO?
5.4 moles CaO 1 mole CaCl2 5.4 mol CaCl2
1 mole CaO
15. What is the molecular mass of Ca3(PO4)2?
a. 310.2 g
b. 110.98 g
c. 110.98 g/mol
d. 310.2 g/mol
The molecular mass of Ca3(PO4)2 is 310.2 g/mol.
16. If you have 9 moles of CaCl2 and all the Na3PO4 I needed, how many moles
of NaCl could you produce?
a. 9 moles
b. 6 moles
c. 18 moles
d. 2 moles
You could produce 18 moles of NaCl.
17. If you produced 5 moles of Ca3(PO4)2, how many moles of NaCl did you also
produce?
a. 30 moles
b. 1/6 mole
c. 1 mole
d. 6 moles
You would produce 30 moles of NaCl.
18. If you have 17 grams of NaCl, how many moles of NaCl do you have?
a. 58.44 moles
b. 2.83 moles
c. 0.29 moles
d. 17 moles
You would have 0.29 moles of NaCl.
19. What is the molecular mass of Mg(NO2)2?
a. 102.32 g/mol
b. 116.31 g
c. 116.31 g/mol
d. 102.32 g
Remember, molecular mass always has units of g/mole and we want to be sure to
count every atom. The molecular mass of Mg(NO2)2 is 116.31 g/mol.
20. If you have 0.5 moles of NaCl, how many molecules of NaCl do you have?
a. 6.022 x 1023
b. 3.011 x 1023
c. 1.204 x 1024
d. 58.44
Just as 12 makes a dozen, Avogadro’s number (6.022 x 1023) makes a mole. So,
just like half of a dozen is 6, half of a mole is half of Avogadro’s number, 3.011 x
1023
21. Use the reaction below to determine how many moles of Al2S3 you would
produce from fully reacting 15 moles of Ag2S:
3 Ag2S + 2 Al → 6 Ag + Al2S3
a. 15 moles
b. 5 moles
c. 1 mole
d. 3 moles
e. 6 moles
You can perform mole to mole conversions using the ratios from a balanced
chemical equation. Make sure that your units cancel. In this reaction you would
produce 5 moles of Al2S3
22. If the molecular mass of methanol is 32.04 g/mol, what would be the mass of a
56.6 mole sample?
a. 0.57 g
b. 1813.46 g
c. 32.04 g
d. 1.77 g
You can use molecular mass to convert from grams to moles. A 56.6 mole sample
of methanol would have a molecular mass of 1813.46 g.
Molecular weight has units of g/mol. Mass has units of grams. The balanced
chemical equation has units of moles.
One mole of C2H8 will react with 4 moles of O2 to yield 2 moles of CO2 and 4
moles of H2O.
23. After completing a certain chemical reaction, you should have 56 moles of
water. What is the mass of this amount of water?
a. 1008 g
b. 18.0 g
c. 3.1 g
d. 2016 g
Starting with 56 moles H2O and multiplying by 18.0 g H2O/mol H2O will give
1008 grams.
24. Given the following balanced equation, determine how many moles of O2 are
needed to completely react with 8 moles of K:
4K + O2 > 2K2O
a. 3.0 moles
b. 4.0 moles
c. 1.0 moles
d. 2.0 moles
The mole-mole ratio between O2 and K is 1 mol O2 = 4 moles K, so starting with
8.0 moles of K will yield 2 moles of O2.
25. Given the following balanced equation, determine how many moles of HCl
will be produced from 4.2 moles of HOCl?
3 HOCl → HClO3 + 2 HCl
a. 2.8 moles
b. 1.5 moles
c. 2.0 moles
d. 6.3 moles
Given 4.2 moles of HOCl and the mole-mole ratio from the balanced equation of
3 moles of HOCl = 2 moles HCl, multiply 4.2 moles HOCL by 2 moles HCl and
divide by 3 moles HOCl to determine the answer: 2.8 moles HCl.
Types of Solutions
26. Which of the following would be considered a solution?
a. Mustard
b. Soda water
c. Table sugar dissolved in water
d. Milk
A solution consists of substances fully dissolved in other substances. Solutions
also tend to be transparent. Table sugar in water is a solution.
27. If you were to dissolve 2.5 grams of NaCl in 150 g of water, You would call the
NaCl the:
a. solution
b. solvent
c. solute
d. mixture
In a solution, the solute is the small part that is dissolved and the solvent is what
the solute is dissolved in.
28. Mix two liquids together and shake them up. You see that you have
microscopic droplets of one liquid suspended in the other. You would call this:
a. emulsion
b. solution
c. solvent
d. solute
An emulsion is a type of suspension where microscopic droplets of one liquid are
dispersed within another liquid.
29. Think back to the cup of tea. Remove the teabag from the cup of tea. Do you
think that this cup of tea is a homogenous solution or a heterogenous mixture?
Assume when the teabag is removed, no tea leaves remain in the cup.
a. Heterogenous
b. Homogenous
Assuming the tea leaves were removed, the composition of the tea in the cup
would be uniform. This tea would therefore be considered a homogenous
mixture we call a solution.
Solution= Gas canister of oxygen and neon, Salt water, Bleach. Suspension=
Urine sample with visible particles. Colloid= Whole blood, Proteins in blood.
Emulsion= Butter, Homogenized milk.
29. Which of the following would you expect to have the greatest concentration?
a. 5 grams of solute in 2 liters of solvent
b. 6 grams of solute in 2 liters of solvent
c. 4 grams of solute in 2 liters of solvent
d. 3 grams of solute in 2 liters of solvent
The more solute in a given amount of solvent, the more concentrated the solution.
In this case, the greatest concentration would have 6 grams of solute in 2 liters of
solvent.
30. If 20 ml of ethanol is mixed with 100 ml of water, the ethanol would be
considered the:
a. solution
b. solvent
c. solute
d. suspension
The solute is the small portion and the solvent is the major portion of the
solution. Therefore, ethanol would be considered the solute.
31. Match each of the following with the term that best describes the mixture:
Air --- Solution
Blood --- Colloid
Cream --- Emulsion
Flour in water --- Suspension
Each of these terms describes a mixture based on factors such as particle size,
composition, dispersal, and transparency. Air= solution. Blood= colloid. Cream=
emulsion. Flour in water= suspension.
32. I dissolve 1 gram of salt in 400 ml of hot water. I would call the resulting
mixture a:
a. Colloid
b. Solute
c. Solution
d. Colloid
Solutions are typically transparent and have solutions have a solute completely
dissolved in a solvent. Dissolving salt in water results in a solution.
Solution Chemistry
33. What is the mass/volume % concentration of a solution that consists of 5
grams of sugar dissolved in a solution with a volume of 140 ml?
a. 0.28%
b. 28%
c. 3.57%
d. 0.0357%
Calculating mass/volume % is similar to how we determine our % grade on a
test. The answer is 5 grams / 140 ml = 0.0357 = 3.57%.
34. I took 20 ml of a 7 % NaCl solution and added water to bring the total
volume of the solution to 100 ml. The resulting solution has a concentration of
1.4 %. This process is known as:
a. dilution
b. solution
c. condensation
d. concentration
The process of taking a concentrated solution and making the solution less
concentrated is known as dilution.
35. The osmolarity of a 1 M NaCl solution would be:
a. 3 Osm/L
b. 2 Osm/L
c. 1 Osm/L
d. 4 Osm/L
Osmolarity is molarity multiplied by the number of ions the dissolved solute
breaks into in solution. Since each NaCl breaks down into a Na+ and a Cl-, we
multiply 1 M by 2 ions to get 2 Osm/L.
36. Compute the following blood alcohol levels and classify as not impaired or
impaired:
0.003 grams of alcohol in a 15 ml sample of blood
0.006 grams of alcohol in a 5 ml sample of blood
0.01 grams of alcohol in a 12 ml sample of blood
0.006 grams of alcohol in a 20 ml sample of blood
Not significantly impaired (≤ 0.03% m/v) ---
Impaired (≥ 0.08% m/v) ---
0.006 grams of alcohol in a 20 ml sample of blood, 0.003 grams of alcohol in a 15 ml
sample of blood, 0.006 grams of alcohol in a 5 ml sample of blood, 0.01 grams of
alcohol in a 12 ml sample of blood
Both the volume of the solution and solvent mass have a large effect on
the % mass/volume concentration. Use the formula
mass of solute in gramssolution
volume in ml×100%
0.003 grams in 15 ml & 0.006 grams in 20 ml are not significantly
impaired, 0.01 grams in 12 ml & 0.006 grams in 5 ml are impaired.
37. Determine the % mass/mass concentration for a solution of 61 g of salt
dissolved in 970 g of water.
a. 6.3%
b. 0.0063%
c. 5.9%
d. 0.0059%
Always remember to add up the total grams on the bottom for mass/mass % and
be sure to multiply by 100% in the last step. The answer is 5.9%.
38. A particular solution for administering glucose to patients with low glucose
levels is 10% mass/volume glucose in water. Which of the following preparations
would give a glucose solution with this concentration? Select all that apply.
a. 5 g of glucose mixed with 50 grams of water
b. 10 g of glucose mixed with 90 grams of water
c. 5 g of glucose mixed with 45 grams of water
d. 10 g of glucose mixed with 100 grams of water
Be sure to take the total mass of the solution into account. The correct answers
are 10 g of glucose mixed with 100 grams of water and 5 g of glucose mixed with
50 grams of water; % mass by volume is determined by: mass (g) / volume (ml) x
100%.
39. What would be the molarity of a solution made by dissolving 4.1 grams of
NaCl (molecular mass: 58.44 g/mole) in water to a total volume of 0.4 liters
a. 7.3 M
b. 0.4 M
c. 0.18 M
d. 141.6 M
Be sure to convert from grams to moles using the molecular mass. A common
error is to use the molecular mass as the mole value, so be sure to avoid that. The
answer is 0.18 M.
40. What is the % mass/volume concentration of a solution consisting of 36
grams of K2SO4 with a total solution volume of 0.6 L?
a. 0.06%
b. 1.6%
c. 60%
d. 6%
e. 21.6%
Be sure that your mass is in grams and your volume in in ml for % mass/volume.
Also, be sure to always multiply by 100 % as a final step. The answer is 6%.
41. If I have 82 ml of a solution with a molarity of 5.3 M NaBr, how many ml of a
1.1 M NaBr solution can I prepare?
a. 0.07 ml
b. 17.0 ml
478.1 ml
395.1 ml
Be sure to use the dilution equation when the situation calls for dilution. You can
tell that dilution is needed here because we are going from a more concentrated
solution to a less concentrated solution. The answer is 395.1 ml.
42. What is the % mass/mass of a methanol solution prepared by mixing 70
grams of ethanol and 800 grams of water?
a. 0.08%
b. 0.09%
c. 8.05%
d. 8.75%
When determinizing solution concentration by looking at % by mass/mass, be
sure that you add up the total mass of solution on the bottom. Also, be sure to
always multiply by 100 %. The answer is 8.05%.
43. What is the Osmolarity of a 0.7 M KNO3 solution
a. 3.5 Osm/L
b. 1.4 Osm/L
c. 0.35 Osm/L
d. 0.7 Osm/L
Be sure to review our polyatomic ions. Since we know that each KNO3 molecule
will break down into K+ and NO3-, we see that each molecule breaks down into
two ions. By multiplying number of ions with our molarity, we find our
osmolarity. The answer is 1.4 Osm/L.
44. What is the molarity of a solution prepared by dissolving 6.0 grams of NaOH
(molecular mass = 40.0 g/mol) to a total volume of 300 ml.
a. 20.0 M NaOH
b. 0.5 M NaOH
c. 133.3 M NaOH
d. 2.0 M NaOH
We must always be sure that our amount of compound is in moles and our
volume is in liters to calculate molarity. The way to convert from grams to moles
is to use the molar mass from the periodic table. Be sure also to convert your
volume to liters. The answer is 0.5 M NaOH.
45. What is the molarity of a solution that consists of 8.50 moles of HCl dissolved
in 670.0 ml of solution?
a. 78.8 M
b. 0.127 M
c. 12.7 M
d. 5.7 M
Molarity is a way to express the amount of moles of a substance per liter. The
answer is 12.7 M. [Show Less]