Tag: masses of atoms and molecules

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Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The number of electrons in 1.8 ml of $H _{2}O$ will be:

  1. $0.1N _{A}$
  2. $0.2N _{A}$
  3. $0.3N _{A}$
  4. $N _{A}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
There is a total of 10 electrons in $ H _{2}O$ molecule.

moles of $H _{2}O(n)=\dfrac{mass\, of\, substance}{molar\, mass}$

Therefore, 1.8 ml of $H _{2}O$ means 0.1 mole
of $H _{2}O$

Number of atoms = $n\times $ Avogrdro Number

Number of atom = $0.1\times 6.022\times 10^{23}$

$= 0.6022\times 10^{23}$

Number of electron of $H _{2}O$ = $0.6022\times 10^{23}\times 10$

$= 6.022\times 10^{23}$ = Avogard's number

So, the correct option is $D$
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

In an ionic compound, mole ratio of cation to anion is $1:2$. If atomic masses of metal and non-metal respectively are 138 and 19, then correct statement is :

  1. molecular mass of compound is 176

  2. formula mass of compound is 176

  3. formula mass of compound is 157

  4. molecular mass of compound is 157
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

1 mole of ionic compound contains 1 mole of cations and 2 moles of anions.
The formula mass of the compound is $138+2(19)=176 \ g/mol$.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Which of the following statements are true?

  1. $1$ mole $H$ atoms $=6.02\times 10^{23}H$ atoms.
  2. $6.02\times 10^{23}H$ atoms have a mass of $1.008$ g.
  3. The formula mass of $O _2=32.00$ amu.

  4. All of the above are true.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(A) $ 1 $ mole of any substance contains Avogadro's number of atoms or molecules. Thus, $1$ mole of H atoms corresponds to $=6.02\times 10^{23}H$ atoms.
Hence, the option A is true.
(B) $6.02\times 10^{23}H$ atoms have mass equal to molar mass of H. it is equal to $1.008$ g.
 Hence, the option B is true.
(C) The formula mass of $O _2=32.00 amu$. Thus, $1$ oxygen molecule weighs $32$ amu and $1$ mole of oxygen molecules weighs $32$ g.
Hence, the option C is true.
As we know, 1 mole is the collection of $6.02\times 10^{23}$ entities. Here entities may represent atoms, ions, molecules.
And mass of one mole of H is $1.008$ g so $6.02\times 10^{23}H$ atoms have a mass of $1.008$ g.
The formula mass of $O _2= 2(8p+8n) = 2\times16 = 32.0$ amu.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The relative atomic mass of $N$ and relative molecular mass of $N _2$ are:

  1. $14, 28$
  2. $7, 14$
  3. $14, 14$
  4. $7, 28$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of an atom of carbon-12.

The relative atomic mass of N is 14  and relative molecular mass of $N _2$ is 28.

Hence, option A is correct.
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Find the relative molecular mass of methyl alcohol $(CH _3OH)$, if $160 gm$ of the alcohol on vaporization has a volume of $112$ litres at STP.

  1. $16 gm$
  2. $32 gm$
  3. $160 gm$
  4. $80 gm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As we know, one mole of a gaseous substance occupies $22.4$ litres volume.


Mole $= \dfrac{w}{M}$


$\dfrac{160}{M} = \dfrac{112}{22.4}$

$M = 32 gm$

Also, molar mass $=2\times vapour  density$
Therefore, vapour density $= 16 gm$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The element chlorine consists of mixture of 75.53% $ _{17}$Cl$^{35}$ and 24.47% $ _{17}$Cl$^{37}$ having a mass of 34.97 amu and 36.95 amu, respectively. The atomic weight of chloride is:

  1. 35.25

  2. 35.45

  3. 36.25

  4. 36.45
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given - $ _{17} Cl^{35} - 75.53$% and mass of $Cl$ 34.97 amu
$ _{17} C^{37} - 24.47$% and mass of $Cl$ 36.95 amu
$\therefore $ Atomic weight of chlorine
$= \displaystyle \frac{(75.53 \times 34.97)+(24.47 \times 36.95)}{100} = \frac{3545.45}{100}$
$=35.45$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

Two flasks A and B of equal volumes are kept under similar conditions of temperature and pressure. If flask A holds 16.2 g of gas X while flask B holds 1.012 g of hydrogen, calculate the relative molecular mass of gas X:

  1. 20 g

  2. 32 g

  3. 28 g

  4. 44 g
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A mole is equal to the relative molecular mass of a gas. As given, the number of moles of gas X and hydrogen are same in the two flasks.
Therefore no. of moles in 2g of hydrogen gas = 1
No. of moles in 1.01g of hydrogen gas = 1/2
Now the weight of gas X that contains 1/2 moles = 16.2g
Weight of gas X that contains 1mole = $\frac{16.2}{1/2}$ = 32g

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The amount in parts by weight of sulphur present in one sulphuric acid molecule:

  1. $16$
  2. $32$
  3. $64$
  4. $48$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$H _2SO _4$ is sulphuric acid. 
Molecular mass of $H _2SO _4= 2+32 + (4 \times 16)=38 \ g$
Weight of sulphur in it $= 32 \ g$
So, amount in parts by weight of sulphur in one sulphuric acid molecule is $32 \ g$
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The molecular mass of a salt of oxy acid of chlorine of a divalent metal which contains more number of oxygen atoms than its corresponding '-ic' acid is $239\ g/mole$.
What is the atomic mass of the metal?

  1. 24

  2. 39

  3. 40

  4. 30
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The formula of the salt with molecular weight 239 is $Ca(ClO _{4}) _{2}$ and thus the divalent metal is calcium with atomic weight 40.