Tag: atoms, molecules and radicals

Questions Related to atoms, molecules and radicals

Quantitatively, formula represents:

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. One molecule of the substance.

  2. The actual number of atoms of each element in one molecule of the substance.

  3. The number of parts by weight of the substance (molecular weight).

  4. The number of parts by weight of each element.

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Correct Option: A,B,C,D
Explanation:

(A) One molecule of the substance

$\longrightarrow$ example $NaCl,C _2H _5OH$

(B) The actual number of atoms of each element in one molecule of the substance.
$\longrightarrow$ example $H _2O$ [water]
It shows that water contains $2$ atoms of hydrogen and $1$ atom of oxygen.

(C) The number by parts by weight of the substance [molecular weight]
$\longrightarrow$ Molecular weight can be determined by chemical formula as shown below:-
$CO _2$
one atom of carbon $\times$ mass of carbon + $2$ atoms of oxygen $\times$ mass of oxygen
$=1\times 12+2\times 16$
$=12+32$
$=44g/mol$.

(D) The number of parts by weight of each element $\longrightarrow$ example (1) $C _2H _5OH$ [ethanol] Molecular mass= $46$
(i) Each mole of ethanol contains $2$ moles of carbon
$=12\times2$
$=24g$
(ii) $1$ mole of oxygen atom
$=16\times 1$
$=16g$
(iii) $6$ moles of hydrogen atom
$=1\times 6$
$=6g$
These are present in $46g$ of ethanol
$\therefore$ Percentage of carbon=$\cfrac {24}{46}\times 100=52.17$%
Percentage of oxygen=$\cfrac {16}{46}\times 100=34.78$%
Percentage of hydrogen=$\cfrac {6}{46}\times 100=13.05$%

The formula of iron (III) sulphate is:

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $Fe _3CO _4$

  2. $Fe _2(SO _4) _3$

  3. $Fe _2(CO _4) _3$

  4. $FeCO _4$

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Correct Option: B
Explanation:

It is given that the valency of iron in iron sulphate is $+3$ and we know that for sulphate $({SO _4}^{2-})$, it is $-2$. Therefore, the formula is $Fe _2(SO _4) _3$.


$2Fe^{+3} +3{SO _4}^{-2} \rightarrow Fe _2(SO _4) _3$
                                  Iron (III) sulphate

Hence, option B is correct.

Two oxides of a metal contain 30.0% and 27.6 % of oxygen respectively. If the formula of the first oxide is $M _3O _4$, the formula of the second oxide, is

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $M _2O _3$

  2. $M _4O _3$

  3. $M _3O _4$

  4. $M _3O _2$

Show answer
Correct Option: A
Explanation:

Formula of first oxide = $M _3O _4$ 
let mass of the metal be = x
percentage of metal in $\displaystyle M _3O _4 = \frac{3x}{ 3x+64}\times100$
but % age = (100-27.6) = 72.4 %
so, $\displaystyle \frac{3x}{ 3x+64}\times100$
or x = 56.
in 2nd oxide,
oxygen = 30%....so metal = 70%
so, ratio :--
M : O
70/56 : 30/16
1.25 : 1.875
2 : 3
so, 2nd oxide =$ M _2O _3$

The formula for potassium permanganate is:

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. ${ K } _{ 2 }{ MnO } _{ 4 }$

  2. ${ K }{ MnO } _{ 4 }$

  3. ${ K } _{ 2 }{ Mn } _{ 2 }{ O } _{ 4 }$

  4. ${ K }{ Mn } _{ 2 }{ O } _{ 4 }$

Show answer
Correct Option: B
Explanation:

Potassium permangnate is a strong oxidizing agent and an inorganic chemical compound which is used in titrations. It has formula ${ KMnO } _{ 4}\ consisting\ of\ { K }^{ + },{ MnO } _{ 4 }^{ - }\quad ions.$ In this compound manganese is in $+7$ oxidation state.

Chemical formula of few compounds are given.
(i) $Zn(PO _4) _2$ (ii) $Fe _2S _3$ (iii) $AlN$ (iv) $Ca(HCO _3)$ (v) $K _2SO _4$.

The wrong chemical formulas are :

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. (ii) and (iii)

  2. (i), (iv) and (v)

  3. (i) and (iv)

  4. (i), (ii), (iii), (iv), (v)

Show answer
Correct Option: C
Explanation:

Correct chemical formula's
(i) $Zn _3(PO _4) _2$ 
(ii) $Fe _2S _3$
(iii) $AlN$ 
(iv) $Ca(HCO _3) _2$ 
(v) $K _2SO _4$.

Which of the following chemical formulae of compounds given are wrong:


(i) $Zn(SO _4)$ (ii) $SFe$ (iii) $MgN _3$ (iv) $Ca(OH) _2$ (v) $KCl$.

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. (ii) and (iii)

  2. (i), (iv) and (v)

  3. (i) and (iv)

  4. (i), (ii), (iii), (iv), (v)

Show answer
Correct Option: A
Explanation:

Correct chemical formula's
(i) $ZnSO _4$ 
(ii) $Fe _2S _3$
(iii) $Mg _3N _2$ 
(iv) $Ca(HO) _2$ 
(v) $KCl$.

Electrovalencies of three metals $A, B, C $are $1, 2, 3$ respectively and those of non-metals $X, Y, Z$ and $3, 2, 1$ respectively. Which among the following couldn't be the formula of the various ionic compounds formed between the respective metals and non-metals?

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $A _3 X, BY, CZ _3$

  2. $AZ, B _3 X _2, C _2 Y _3$

  3. $AZ _3, B _2X, C _3Y _2$

  4. $A _2Y, BZ _2, CX$

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Correct Option: C
Explanation:

The incorrect formula's are; $AZ _{3}$, $B _{2}X$, $C _{3}Y _{2}$

The formula of calcium dihydrogen phosphate is :

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $Ca(H _2 PO _4) _2$

  2. $Ca(HPO _4) _2$

  3. $Ca _3HPO _4$

  4. $Ca _3(H _2 PO _4) _2$

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Correct Option: A
Explanation:

 $Ca^{2+}$ ion and $H _{2}PO _{4}^{-1}$ ion combine to form $Ca(H _{2}PO _{4}) _{2}$

The formula of hydrogen phosphate of a metal M is MHPO$ _4$. Give the formula of metal chloride.

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $MCl$

  2. $MCl _3$

  3. $MCl _2$

  4. $M _2$Cl

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Correct Option: C
Explanation:

$MHPO _4$ is derived from the acid $H _{3}PO _{4}$ . Thus the metal $M$ replaced two hydrogen atoms of hydrogen phosphate. So, its valency is $2.$ Hence the formula of the metal chloride is $MCl _{2}$ . (Because the valency of$ M$ is $2$ and the valency of$ Cl$ is $1$

Identify the incorrect formula among the following :

chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

  1. $(NH _4) _2 HPO _4$

  2. $PbO _2$

  3. $CaHSO _4$

  4. $BaO _2$

Show answer
Correct Option: C
Explanation:

Option(C) is incorrect. It can be $CaSO _{4}$ and not  $CaHSO _{4}$.