Tag: valency and chemical formulae

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

Quantitatively, formula represents:

  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.
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
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=$\cfrac {6}{46}\times 100=13.05$%

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

The formula of iron (III) sulphate is:

  1. $Fe _3CO _4$
  2. $Fe _2(SO _4) _3$
  3. $Fe _2(CO _4) _3$
  4. $FeCO _4$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. $M _2O _3$
  2. $M _4O _3$
  3. $M _3O _4$
  4. $M _3O _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
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$

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

The formula for potassium permanganate is:

  1. ${ K } _{ 2 }{ MnO } _{ 4 }$
  2. ${ K }{ MnO } _{ 4 }$
  3. ${ K } _{ 2 }{ Mn } _{ 2 }{ O } _{ 4 }$
  4. ${ K }{ Mn } _{ 2 }{ O } _{ 4 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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 :

  1. (ii) and (iii)

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

  3. (i) and (iv)

  4. (i), (ii), (iii), (iv), (v)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

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) $KCl$.

  1. (ii) and (iii)

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

  3. (i) and (iv)

  4. (i), (ii), (iii), (iv), (v)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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?

  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. $A _2Y, BZ _2, CX$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

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

  1. $MCl$
  2. $MCl _3$
  3. $MCl _2$
  4. $M _2$Cl
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $1$