Redox Reactions Test

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Redox Reactions Test - 30

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Weekly Quiz Competition

Question 1
1 / -0

Statement I : The oxidation state of Cr in $$Al_2(Cr_2O_7)_3$$ is +3.
Statement II : as a neutral compound, the sum of oxidation numbers of all the atoms must equal zero.

A
Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

B
Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1

C
Statement 1 is correct but Statement 2 is not correct

D
Statement 1 is not correct but Statement 2 is correct

E
Both the Statement 1 and Statement 2 are not correct.

Solution

Oxidation state of $$Al$$ is $$+3$$. And oxidation number of $$O$$ is $$-2$$. Thus, oxidation state of $$Cr$$ can be calculated by considering it as $$X$$. Thus-
($$2$$$$*$$$$3$$) $$+$$ $$6X$$ $$+$$ [$$21$$$$*$$($$-2$$)] $$=$$ $$0$$
The value of $$X$$ obtained is $$+6$$. Oxidation state of $$Cr$$ in the above mentioned molecule is $$+6$$.
In a neutral compound, the sum of oxidation numbers of all the atoms must be equal to zero. If it's not zero, it can't be neutral.
Thus, statement 1 is not correct. Statement 2 is correct.
Option $$D$$ is the correct answer.
Question 2
1 / -0

In which of the following does sulphur has the lowest oxidation state?

A
$${ H }_{ 2 }{ SO }_{ 4 }$$

B
$$S{ O }_{ 3 }$$

C
$${ H }_{ 2 }{ SO }_{ 3 }$$

D
$${ H }_{ 2 }S$$

Solution

Sulphur has the lowest oxidation state in $$\displaystyle H_2S$$. The oxidation state of
$$\displaystyle S$$ in $$\displaystyle H_2S $$ is $$-2$$. The oxidation state of $$\displaystyle S$$ in $$\displaystyle H_2SO_4$$, $$\displaystyle SO_2$$ and $$\displaystyle H_2SO_3$$ are $$\displaystyle +6$$, $$\displaystyle +4$$ and $$\displaystyle +4$$ respectively.
Question 3
1 / -0

What is the oxidation number of $$Mn$$ in $$Mn{O}_{2}$$?

A
$$+2$$

B
$$+4$$

C
$$-2$$

D
$$-4$$

Solution

The oxidation number of simple ions is equal to the charge on the ion. The oxidation number of $$Mn$$ in $$MnO_2$$ is $$Mn^+4$$.
Hence option $$ B$$.
Question 4
1 / -0

What is the oxidation number of $$Si$$ in the compound $$CaSi{O}_{3}$$?

A
$$-4$$

B
$$+2$$

C
$$-2$$

D
$$+4$$

Solution

$$CaSiO_3$$
Total charge present $$=0$$.
Oxidation no. of Oxygen is $$-2$$.
Oxidation no. od Calcium is $$+2.$$
Let, oxidation no. of Slilicon be $$X$$.
So, $$[+2]+x+3[-2]=0 \\ 2+x-6=0\\x=4$$
So, oxidation number of silicon in $$CaSiO_3$$ is $$+4$$.
Question 5
1 / -0

What is the oxidation number of lead in $$Pb{F}_{2}$$?

A
$$0$$

B
$$+2$$

C
$$+1$$

D
$$-1$$

Solution

$$PbF_2$$
The total charge present is $$0$$.
Oxidation no. of Fluorine is $$-1$$.
Oxidation no. of lead be $$x$$.
So, $$x+2(-1)=0\\x-2=0\\x=2 $$
So, oxidation no. of lead in $$PbF_2$$ is $$+2$$.
Question 6
1 / -0

In which substance does manganese have the highest oxidation number?

A
$$LiMnO_{4}$$

B
$$K_{2}MnO_{4}$$

C
$$MnO_{2}$$

D
$$Mn(NO_{3})_{2}$$

Solution

In $$LiMnO_4\\+1+x+4(-2)=0,\\x-7=0,\\x=7.$$ $$K_2MnO_4\\2(1)+x+4(-2)=0,\\x-6=0,\\x=6.$$ $$MnO_2\\x+2(-2)=0,\\x+4.$$ $$Mn{(NO_3)}_2\\x+2(-1)=0,\\x=2.\\$$
Out of $$4$$, Manganese in $$LiMnO_4$$ has the highest oxidation number.
Question 7
1 / -0

Which of the following are redox reactions?
I. $$PCl_{3} + Cl_{2}\rightarrow PCl_{5}$$
II. $$Cu + 2AgNO_{3} \rightarrow Cu(NO_{3})_{2} + 2Ag$$
III. $$CO_{2} + 2LiOH \rightarrow Li_{2}CO_{3} + H_{2}O$$
IV. $$FeCl_{2} + 2NaOH \rightarrow Fe(OH)_{2} + 2NaCl$$

A
II

B
I and II

C
I, II, and III

D
I, II, III and IV

Solution

If in a reaction both, oxidation and reduction occurs, then it is called redox reaction.
In $$Cu+2AgNO_3\longrightarrow Cu{(NO_3)}_2+2Ag\\{\text{ }} \downarrow \quad \quad\downarrow\quad\quad\quad\quad\quad\quad \downarrow \quad\quad\quad\quad\downarrow$$
$$0$$ $$x-1=0\\x=1$$ $$x+2(-1)=0\\x=+2 $$ $$0$$
Oxidation state of $$Cu$$ changes from $$0$$ to $$+$$, it is oxidation.
$$Ag$$ reduced from $$+1$$ to $$0$$ , it is reduction.
So, all total it is a redox reaction.
Question 8
1 / -0

The oxidation number of chromium in $$K_{2}CrO_{4}$$ is?

A
$$2+$$

B
$$3+$$

C
$$6+$$

D
$$8+$$

Solution

In $$K_2CrO_4$$ ,
Oxidation no. of $$K$$ is $$+1.$$
Oxidation no. of $$O$$ is $$-2.$$
Oxidation no. of $$Cr$$ be $$x$$.
$$2(1)+x+4(-2)=0,\\ 2+x-8=0,\\ x-6=0,\\ x=6.$$
So, Oxidation no. of $$Chromium$$ in $$K_2Cr_2O_4$$ is $$+6$$.
Question 9
1 / -0

What is one of the spectator ions in the following reaction?
$$Pb(NO_{3})_{2} (aq) + 2KI(aq) \rightarrow PbI_{2} (s) + 2KNO_{3}(aq)$$

A
$$NO_{3}{^-}$$

B
$$I^{-}$$

C
$$PbI_{2}$$

D
$$Pb^{+2}$$

Solution

A precipitation reaction occurs when two ionic compounds react to produce a precipitate and an insoluble substance which stays in solution as spectator ion.
$$\longrightarrow$$ Ions that are not involved in the actual chemical reaction are called spectator ions.
$$\longrightarrow$$ Net ionic equation of given reaction is
$$Pb^{+2}+2I^-\longrightarrow PbI_2$$ It shows only the ions which involves in the chemical reaction,
Spectator ions:- $$K^+$$ and $${NO_3}^-$$ .
Question 10
1 / -0

Which of the following reactions represents an oxidation-reduction reaction?

A
$$2NaCl_{(aq)} + K_{2}CO_{3(aq)} \rightarrow Na_{2}CO_{3(aq)} + 2KCl_{(aq)}$$

B
$$CaCO_{3(aq)} \xrightarrow {\Delta} CaO_{(s)} + CO_{2(g)}$$

C
$$2Mg_{(s} + O_{2(g)} \rightarrow 2MgO_{(s)}$$

D
$$3FeCl_{2(aq)} + 2Cu_{3}PO_{4(aq)} \rightarrow Fe_{3}(PO_{4})_{2(aq)} + 6CuCl_{(aq)}$$

Solution

In a single reaction $$Sodium(I)$$ in $$NaCl$$ was changed to $$Sodium(II)$$ in $$Na_2CO_3$$ means it is oxidised and $$Potassium(II)$$ in $$K_2CO_3$$ is reduced to $$K(I)$$ in $$KCl$$. It is reduced. These two occur in a single reaction. So, it represents oxidation-reduction reaction.

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Redox Reactions Test - 30

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Question 1

Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1

Statement 1 is correct but Statement 2 is not correct

Statement 1 is not correct but Statement 2 is correct

Both the Statement 1 and Statement 2 are not correct.

Solution

Question 2

$${ H }_{ 2 }{ SO }_{ 4 }$$

$$S{ O }_{ 3 }$$

$${ H }_{ 2 }{ SO }_{ 3 }$$

$${ H }_{ 2 }S$$

Solution

Question 3

$$+2$$

$$+4$$

$$-2$$

$$-4$$

Solution

Question 4

$$-4$$

$$+2$$

$$-2$$

$$+4$$

Solution

Question 5

$$0$$

$$+2$$

$$+1$$

$$-1$$

Solution

Question 6

$$LiMnO_{4}$$

$$K_{2}MnO_{4}$$

$$MnO_{2}$$

$$Mn(NO_{3})_{2}$$

Solution

Question 7

II

I and II

I, II, and III

I, II, III and IV

Solution

Question 8

$$2+$$

$$3+$$

$$6+$$

$$8+$$

Solution

Question 9

$$NO_{3}{^-}$$

$$I^{-}$$

$$PbI_{2}$$

$$Pb^{+2}$$

Solution

Question 10

$$2NaCl_{(aq)} + K_{2}CO_{3(aq)} \rightarrow Na_{2}CO_{3(aq)} + 2KCl_{(aq)}$$

$$CaCO_{3(aq)} \xrightarrow {\Delta} CaO_{(s)} + CO_{2(g)}$$

$$2Mg_{(s} + O_{2(g)} \rightarrow 2MgO_{(s)}$$

$$3FeCl_{2(aq)} + 2Cu_{3}PO_{4(aq)} \rightarrow Fe_{3}(PO_{4})_{2(aq)} + 6CuCl_{(aq)}$$

Solution

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