# CHE 110 work sheets.

Chapter 3: Mass Relationships in Chemical ReactionsDate:___________________________
Atomic Mass
Atomic mass – mass of an atom in atomic mass units (amu)
– mass of protons + neutrons
Originally defined using 12C (6 protons + 6 neutrons = 12 amu)
We have to consider the natural abundance of each isotope.
The atomic mass displayed on periodic table is actually the:
Average atomic mass – the a weighted average of all the naturally occurring isotopes
A student obtained 87% in the lecture and 72% in the lab.
Gallium has two naturally occurring isotopes, calculate the average atomic mass of gallium
69Ga
= 68.9256 amu, natural abundance of 60.11%
71Ga
= 70.9247 amu, natural abundance of 39.89%.
Chromium has four naturally occurring isotopes, calculate the average atomic mass of chromium
50Cr = 49.95 amu, natural abundance of 4.31%
52Cr = 51.941 amu, natural abundance of 83.76%
53Cr = 52.941 amu, natural abundance of 9.55%
54Cr = 53.939 amu, natural abundance of 2.38%
The Mole (mol): A unit to count numbers of particles
In chemistry:
1 mole = 6.022 x 1023 atoms, molecules, compounds, or particles
(eg. 1 mole of eggs is 6.022 x 1023; 1 mole of pencils is 6.022 x 1023)
Definition of a Mole
1 mole = the number of atoms in exactly 12 g of carbon-12
atoms
Molar mass is the mass of 1 mole of:
molecules
salt
in grams
eggs
pencils
1 mole of B atoms
1 mole of Ca atoms
1 mole of V atoms
1 mole of As atoms
=
=
=
=
6.022×1023 atoms
6.022×1023 atoms
6.022×1023 atoms
6.022×1023 atoms
1 mole of 12C atoms = 6.022×1023 atoms = 12.00g
1 mole of C atoms = 6.022×1023 atoms = 12.01g
= 10.81g
= ___________
= ___________
= ___________
For any element
atomic mass (amu) = molar mass (grams/mol)
How many atoms of helium are there in 3.5 moles of helium?
A silver ring contains 1.1 x 1022 silver atoms. How many moles of silver are in the ring?
How many atoms of carbon are in 3.48 g of graphite (pure carbon)?
A solid aluminum sphere contains 8.55 x 1022 aluminum atoms.
What is the sphere’s radius in centimeters? (d = 2.70 g/cm3)
Molecular mass (aka molecular weight) is the sum of the atomic masses (in amu) in a molecule.
1S
32.07 amu
2O
+2 ´ 16.00 amu
SO2
64.07 amu
1 molecule SO2 = 64.07 amu
1 mole SO2 = 64.07 g SO2
Molecular mass of SO2 = 64.07 g/mol
For any molecule
molecular mass (amu) = molar mass (gram)
Calculate the molecular mass of the following: 1) CH4, 2) CS2, 3) C10H12O
How many molecules of water are in 25.0 grams of water?
Formula mass is the sum of the atomic masses (in amu) in a formula unit of an ionic compound.
1Na
1Cl
22.99 amu
1 molecule NaCl = 58.44 amu
+35.45 amu
1 mole NaCl = 58.44 g NaCl
Molecular mass = 58.44 NaCl g/mol
58.44 amu
NaCl
For any ionic compound
formula mass (amu) = molar mass (gram/mol)
Calculate the formula mass of the following: 1) Li2CO3, K2CO4, Ca3(PO4)2
Percent Composition
Percent composition – is the % of each element in a compound
If you had 1 mole of ethanol (6.022×1023 ethanol molecules)
What % would be C, what % would be H, and what % would be O?
C 2H6 O = n ´ molar mass of element ´ 100% n is the number of each element in the compound
molar mass of compound
%C =
2 ´ (12.01 g )
´ 100% = 52.14%
46.07 g
%H =
6 ´ (1.008 g )
´ 100% = 13.13%
46.07 g
1´ (16.00 g )
´ 100% = 34.73%
46.07 g
52.14% + 13.13% + 34.73% = 100.0%
Calculate the % composition of each element in glucose (sugar).
%O =
C6H12O6
How many grams of oxygen, carbon, and hydrogen are in 23.6 grams of glucose (C6H12O6)?
Percent Composition and Empirical Formulas
Hydrogen Peroxide
Molecular formula = H2O2
Empirical formula = HO
Benzene
Molecular formula = C6H6
Empirical formula = CH
Glucose
Molecular formula = C6H12O6
Empirical formula = CH2O
You Can Use Percent Composition to Determine Empirical Formula
A compound containing nitrogen and oxygen is decomposed in the laboratory and produces
24.5g of nitrogen and 70.0g of oxygen. Calculate the empirical formula of the compound.
A laboratory analysis of aspirin determined the following mass percent composition:
C 60.00%; H 4.48%; O 35.53%. Find the empirical formula
Empirical Formulas and Molecular Formulas
If you know:
1)
the empirical formula and
2)
the molecular mass of the molecule
Then you can determine the molecular formula
Naphthalene is a compound containing carbon and hydrogen that is often used in mothballs.
Its empirical formula is C5H4 and its molar mass is 128.16g/mol. Find its molecular formula.
A sample of a compound contains 30.46 % nitrogen and 69.54 % oxygen by mass. The molar
mass of the compound is found to be between 90 g and 95 g. Determine the molecular formula
and the accurate molar mass of the compound
Chemical Reactions and Equations
chemical reaction – A process in which one or more substance(s) is changed into one or more
new substance(s) is a.
chemical equation – uses chemical symbols to show what happens during a chemical reaction:
reactants ® products
Two hydrogen molecules + One oxygen molecule ® Two water molecules
2H2
+ O2
®
2H2O
2 moles H2
+ 1 mole O2
®
2 moles H2O
2 ( 2.02 g ) = 4.04 g H2
+ 32.00 g O
!””””””””#””””””””\$2
®
36.04 g reactants
2 (18.02 g ) = 36.04 g H2O
!””””
“#”””””
\$
36.04 g product
36.04 g reactants ® 36.04 g product
2Mg + O2 ® 2MgO
_____ atoms Mg + _____ molecule O2 makes _____ formula units MgO
_____ moles Mg + _____ mole O2 makes _____ moles MgO
___ grams Mg + _____ grams O2 makes _____ grams of MgO
Balancing Chemical Equations
CH4(g) +
O2(g)
CO2(g) +
Reactants
(Starting Materials)
H2O(l)
Products
Balancing the equations below.
Na (s)
SiO2(s) +
KI(aq)
®
Cl2(g)
Pb(NO3)2(aq)
+
H3PO4
+
O2(g)
NaCl (s)
®
C(s)
+
KOH
C8H18(l)
+
®
®
SiC(s)
®
+
KNO3(aq)
H2O
+
CO2(g)
CO(g)
+
PbI2(s)
K3PO4
+
H2O(g)
Stoichiometery
Stoichiometery – the quantitative study of reactants and products in chemical reactions.
MOLE TO MOLE COMPARISON
N2(g)
+
3H2(g) ®
2NH3(g)
You Can Convert Amounts of Products to Amounts of Reactants and Vice Vera
How many moles of NaCl can you make from 2.7 moles of Cl2 if there is an excess of Na?
2Na(s) + Cl2(g) → 2NaCl (s)
How many grams of water are produced in the combustion of 5.00g of glucose, C6H12O6?
C6H12O6(s) + 6 O2(g) → 6CO2(g) + 6H2O(l)
Lithium hydroxide can be used to remove the carbon dioxide from the atmosphere. The solid
reacts with gaseous to form solid lithium carbonate and liquid water. How many grams of
carbon dioxide can be absorbed by 1.00g of lithium hydroxide?
Limiting Reagent
Limiting reagent – reagent used up first in a reaction
CO + 2H2 ® CH3OH
H2 is the limiting reagent
CO is the excess reagent
You have 10 frames & 10 wheels, how many bikes can you build?
How many moles of water can we produce with 10 moles of hydrogen gas and 7 moles of oxygen gas?
In a fuel cell, hydrogen gas and oxygen gas react to form water vapor. Suppose a fuel cell is set up with
1.5 x 102 g of hydrogen gas and 1.5×103 g of oxygen gas. How many grams of water vapor can be
formed?
A strip of zinc metal with a mass of 2.00g is placed in an aqueous solution containing 2.50g of silver
nitrate forming silver metal and zinc nitrate. How many grams of each reactant and product will be left at
the end of the reaction?
Theoretical Yield
Theoretical Yield – the amount of product that would result if all the limiting reagent reacted.
-This is the amount of product that should form in theory.
Actual Yield – is the amount of product actually obtained from a reaction.
Adipic acid, H2C6H8O4, is used to produce nylon. The acid is made commercially by a
controlled reaction between cyclohexane (C6H12) and oxygen gas, which also produces water
vapor. If you carry out the reaction with 25.0g of cyclohexane and excess oxygen gas, what is
the theoretical yield? If you actually obtain 33.5g of adipic acid from your reaction, what is your
the percent yield?
Name the polyatomic ions below:
Chapter 4 Worksheet
CHE 110
Net Ionic Equations
Show the total ionic and net ionic forms of the following equations. If all species are spectator ions,
please indicate that no reaction takes place. Note! You need to make sure the original equation is
balanced before proceeding!
1. ______ AgNO3(aq) + ______ KCl(aq) → ______ AgCl(s) + ______ KNO3(aq)
2. manganese(II)chloride(aq) + ammonium carbonate(aq) → manganese(II)carbonate(s) +
ammonium chloride(aq)
Please complete the following reactions and show the total ionic and net ionic forms of the equation:
3. K3PO4(aq) + Al(NO3)3(aq) →
4. BeI2(aq) + Cu2SO4(aq) →
5. barium nitrate + ammonium phosphate →
Chapter 4 Worksheet
CHE 110
Neutralization Reactions
Write the balanced chemical equations for the neutralization reactions between:
a) HI and NaOH
b) Ca(OH)2 and H3PO4
c) hydrobromic acid and barium hydroxide
d) aluminum hydroxide and hydrochloric acid
Give the name and the formula of the ionic compound produced by neutralization reactions between the
following acids and bases:
Acid and Base reactants
a) nitric acid
and sodium hydroxide
b) magnesium hydroxide
and sulfuric acid
c) chloric acid
and rubidium hydroxide
d) calcium hydroxide
and perchloric acid
Name of ionic compound
Formula
Chapter 4 Worksheet
CHE 110
For each of the following ionic compounds, identify the acid and base that reacted to form them.
Salt
Acid
a)
Ca3(PO4)2
b)
Zn(NO3)2
c)
Al(ClO)3
d)
NH4I
Base
Redox Reactions
1. Determine the oxidation number of the elements in each of the following compounds:
a. H2CO3
b. N2
c. Zn(OH)42-
d. NO2-
2. Identify the species being oxidized and reduced in each of the following reactions:
a. Cr+ + Sn4+
Cr3+ + Sn2+
b. 3 Hg2+ + 2 Fe (s)
c. 2 As (s) + 3 Cl2 (g)
3 Hg2 + 2 Fe3+
2 AsCl3
Chapter 4 Worksheet
CHE 110
3. Would you use an oxidizing agent or reducing agent in order for the following reactions to
occur?
a. ClO3-
d. Zn
ClO2
ZnCl2
4. Write half-reactions for the oxidation and reduction process for each of the following:
a. Fe2+ + MnO4-
b. Sn2+ + IO3-
c. S2- + NO3-
Fe3+ + Mn2+
Sn4+ + I-
S + NO
Molarity and Dilutions
Part 1: Molarity – calculate the molarities of the following solutions
1. 12 moles of calcium carbonate in 1.22 liters solution.
2. 120 grams of calcium nitrate in 240 mL of solution.
Chapter 4 Worksheet
CHE 110
3. 98 grams of barium hydroxide in 2.2 liters of solution.
3b. What is the concentration of OH-?
Part 2: Dilutions
4. If I have 340 mL of a 0.500 M NaBr solution, what will the concentration be if I add 560 mL more
water to it?
5. If I dilute 250 mL of 0.10 M lithium acetate solution to a volume of 750 mL, what will the
concentration of this solution be?
6. If I leave 750 mL of 0.50 M sodium chloride solution uncovered on a windowsill and 150 mL of
the solvent evaporates, what will the new concentration of the sodium chloride solution be?
Chapter 4 Worksheet
CHE 110
Acid-Base Titrations
1. If it takes 54 mL of 0.1 M NaOH to neutralize 125 mL of an HCl solution, what is the
concentration of the HCl? (0.0432 M)
2. If it takes 50 mL of 0.5 M Ca(OH)2 solution to completely neutralize 125 mL of sulfuric acid
solution (H2SO4), what is the concentration of the H2SO4 solution? (0.2 M)
3. How many milliliters of 0.360 M H2SO4 are required to neutralize 25.0 mL of 0.100 M Ba(OH)2?
(6.9 mL)
4. It takes 38 mL of 0.75 M NaOH solution to completely neutralize 155 mL of a sulfuric acid
solution (H2SO4). What is the concentration of the H2SO4 solution? (0.092 M)

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