EN | ES | DE | NL | RU

Buy Printed or E-Book Version

Matters and Properties of Matters
Atomic Structure with Examples
Periodic Table
The Mole Concept with Examples
Gases with Examples
Chemical Reactions with Examples
Nuclear Chemistry (Radioactivity)
Acids and Bases
Rates of Reactions (Chemical Kinetics)
Chemical Equilibrium
Chemical Bonds
Exams and Problem Solutions
--Matters and Properties of Matters Exams and Problem Solutions
--Atomic Structure Exams and Problem Solutions
--Periodic Table Exams and Problem Solutions
--The Mole Concept Exams and Problem Solutions
--Gases Exams and Problem Solutions
--Chemical Reactions Exams and Problem Solutions
--Chemical Reactions Exam1 and Problem Solutions
--Chemical Reactions Exam2 and Problem Solutions
--Nuclear Chemistry (Radioactivity) Exams and Problem Solutions
--Solutions Exams and Problem Solutions
--Acids and Bases Exams and Problem Solutions
--Thermochemistry Exams and Problem Solutions
--Rates of Reaction Exams and Problem Solutions
--Chemical Equilibrium Exams and Problem Solutions
--Chemical Bonds Exams and Problem Solutions
Old Version


Chemical Reactions Exam2 and Problem Solutions

Chemical Reactions Exam2 and  Problem Solutions

1. In which one of the following compounds, X has different oxidation state?

I. HXO4-

II. X2O7-2

III. XO4-2


V. XO2


Oxidation states of H is +1 and O is -2. Using them we find oxidation state of X in given compounds.

I. In HXO4- compound, sum of oxidation states is -1. So,


X=+6 (Or X=-2)

II. In X2O7-2 compound, sum of oxidation states is -2. So,

2X + 7.(-2)=-2

X=+6 (Or X=-2)

III. In XO4-2 compound, sum of oxidation states is -2. So,

X + 4.(-2)=-2

X=+6 (Or X=-2)

IV. In XO3 compound, sum of oxidation states is 0. So,

X + 3.(-2)=0

X=+6 (Or X=-2)

V. In XO2 compound, sum of oxidation states is 0. So,

X + 2.(-2)=0

X=+4 V is different from others.

2. In which one of the following reactions, N is oxidized?

I. 3Cu + 2NO3- + 8H+ → 3Cu+2 + 2NO + 4H2O

II. Cl2O + 4NO2 + 3H2O → 2Cl-+ 4NO3- + 6H+

III. 2Ag+ + 2NH3 + H2O2 → 2Ag + 2NH4+ + O2

IV. 2N2O5 → 4NO2 + O2

V. 2NO2 → 2NO + O2


Elements which give electrons are reduced and which gain electrons are oxidized. Thus, we must find choice in which N lose electron.

I. NO3- → NO We find oxidation state of N in both sides. (Oxidation state of O is -2)

x + 3(-2) = -1, x=+5 in reactants

x + (-2) = 0, x=+2 So, N is reduced

II. NO2 → NO3-

x + 2(-2) = 0, x=+4 in reactants

x + 3(-2) = -1, x=+5 So, N is oxidized

III. NH3 → NH4+1

x + 3(1)=0, x=-3 in reactants

x + 4(1)=+1, x=-3 so oxidation state of N does not change

IV. N2O5 → NO2

2x + 5.(-2)=0, x=+5 in reactants

x + 2.(-2) =0, x=+4, So, N is reduced

V. NO2 → NO

x + 2(-2)=0, x=+4 in reactants

x + (-2)=0, x=+2 Thus, N is reduced.

3. Using 40 g Fe2O3 and 1,5mol CO following reactşons occur in closed container with 100% efficiency.

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

Which ones of the following statements are true for this reactşon?(Fe=56, O=16 and C=12)

I. All CO is used

II. 28g Fe is formed

III. Total mass in the container is 82g


Molar mass of;

Fe2O3=2.(56) + 3(16)=160g/mol


mole of Fe2O3 is;


I. If we assume all CO is used;

3 mol CO requires 1mol Fe2O3

1,5mol CO requires ?mol Fe2O3


?=0,5mol Fe2O3, however we have only 0,25mol Fe2O3 so, all CO is not used in this reaction.I is false.

II. All Fe2O3 is used in this reaction.

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

1mol         3mol          2mol      3mol  (for 1 mole Fe2O3)

0,25mol    1,5mol        ?            ?     (We have)

-0,25mol   -0,75mol    +0,50mol +0,75mol (used and formed)


Thus, 0,75mol CO is used and 0,50mol Fe and 0,75mol CO2 are formed.

Mass of Fe=0,5.(56)=28g II is true.

III. Conservation of mass law states that, amount of matter stays constant before and after reaction. So,

Mass of CO before reaction=42g

Mass of Fe2O3 before reaction=40

Total mass of matters=42 + 40=82g III is true.

4. Find types of given reactşons below.

I. H2(g) + 1/2O2(g) → H2O(l)

II. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

III. CaCO3(s) → CaO(s) + CO2(g)


I. It is combustion and formation reaction.

II. It is acid-base reaction or neutralization reaction.

III. It is analysis or decomposition reaction.

5. Which one of the following statements is false for following reactions,

KClO3(s) + Heat → KCl(s) + 3/2O2(g)

N2(g) + 3H2(g) → 2NH3(g) + Heat

C(s) + O2(g) → CO2(g) + Heat

I. First reaction is analysis and others are synthesis reactşons.

II. First one is endothermic and others are exothermic reactions

III. First and third reactions are heterogeneous.

IV. In second reaction volume increases after reaction.


I is true first one is analysis reaction and second and third are formation reaction.

II. Since first one takes  heat it is endothermic reaction and others give heat, so they are exothermic reactions.II is true.

III. There are different phases of matters in first and third reactions, they are heterogeneous reactions. III is true.

IV. We write volumes of matters and see whether it increases or decreases;

N2(g) + 3H2(g) → 2NH3(g)

V         3V              2V

Volume of reactants= V + 3V =4V

Volume of products=2V

So, IV is false, volume does not increases.On the contrary, it decreases.

The Original Author:

Tags: Chemical Reactions Cheat Sheet |  Chemical Reactions Exam1 and Problem Solutions | 

© Copyright www.ChemistryTutorials.org, Reproduction in electronic and written form is expressly forbidden without written permission of www.ChemistryTutorials.org. Privacy Policy