Tag: chemistry

Questions Related to chemistry

Europium consists of $47.8$% Eu-$151$ and $52.2$% Eu-$153$. Calculate average atomic mass?

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. $152.2$

  2. $152.1$

  3. $151.9$

  4. $152$

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Correct Option: D
Explanation:

Average atomic mass is given by:


$M _{av}=\dfrac{151\times0.478+153\times0.522}{0.478+0.522}=152.044\ gm/mol$

 Rhenium (Re) consists of $37.1$% $185$ Re and $62.9$% $187$ Re. Calculate the relative atomic mass?

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. $185.6$

  2. $185.9$

  3. $186.3$

  4. $186.1$

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Correct Option: C

The relative abundance of two isotopes of atomic masses 85 and 87 are 75% and 25% respectively. The average atom mass of element is: 

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. 86

  2. 40

  3. 85.5

  4. 75.5

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Correct Option: C

Antimony (Sb) is $57.2$% Sb-$121$ and $42.8$% Sb-$123$. Calculate the average atomic mass?

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. $121.6$

  2. $120.8$

  3. $122.4$

  4. $121.9$

Show answer
Correct Option: D
Explanation:

Average Atomic mass is given as:


$M _{av}=\dfrac{121\times0.572+123\times0.428}{1}=121.856\ gm/mol$

The relative atomic mass of an atom is:

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. measured in atomic mass units (u)

  2. based on the mass of 1 atom of carbon-12

  3. different for different isotopes of an element

  4. all of the above are true

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Correct Option: D
Explanation:

Relative atomic mass is the mass of an atom measured relative to 1/12th the mass of 1 atom of C-12 isotope which is also known as atomic mass unit or amu(u).

Chromium has four stable isotopes.$4.31$% Cr-$50$, $83.76$% Cr-$52$, $9.55$% Cr-$53$ and $2.38$% Cr-$54$. Calculate the relative atomic mass?

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. $52.1$

  2. $52.4$

  3. $51.8$

  4. None

Show answer
Correct Option: A
Explanation:

Average atomic mass is given by:


$M _{av}=\dfrac{50\times0.0431+52\times0.8376+53\times0.0955+54\times0.0238}{1}=52.1\ gm/mol$

Consider a reversible isentropic expansion of $1$ mole of an ideal monoatomic gas from ${27}^{o}C$ to ${927}^{o}C$. If the initial pressure of gas was $1$ bar, the final pressure of gas becomes

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. $4$ bar

  2. $8$ bar

  3. $0.125$ bar

  4. $0.25$ bar

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Correct Option: B

Boron found in nature has an atomic weight of 10.811 and is made up of the isotopes $\displaystyle { B }^{ 10 }$ (mass 10.013 amu) and $\displaystyle { B }^{ 11 }$ (mass 11.0093). What percentage of naturally occurring boron is made up of $\displaystyle { B }^{ 10 }$ and $\displaystyle { B }^{ 11 }$, respectively?

determination of atomic and isotopic mass some basic concepts of chemistry chemistry

  1. 30 : 70

  2. 25 : 75

  3. 20 : 80

  4. 15 : 85

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Correct Option: C
Explanation:

Let the abundance of $B^{11}$ be $x$% and $B^{10}$ be $(100-x)$%

Average atomic mass= [Atomic mass of $B^{11} \times$ abundance + Atomic mass of $B^{10}\times$ abundance]$/100$ 
$\Rightarrow 10.811=\cfrac { 11.0093\times x(percent)+10.013\times (100-x)(percent) }{ 100 } $
$\Rightarrow 10.811\times 100= 11.0093x$%$+1001.3-10.013x$%
$\Rightarrow 1081.1=0.9963x$%$+1001.3$
$\Rightarrow 1081.1-1001.3=0.9963x$%
$\Rightarrow 79.8=0.9963x$%
$\Rightarrow x$%=$\cfrac {79.8}{0.9963}$
$\therefore x$%=$80$
$(100-x)$%=$20$
$\therefore$ Natural abundance of $B^{10}=20$
    Natural abundance of $B^{11}=80$
Ratio= $20:80$

Metallic bond is formed by sharing of electrons between ______.

bonding in metals metallic bonding chemical bonding and structure chemical bonding and molecular structure chemistry

  1. Two atoms

  2. Many atoms

  3. Three atoms

  4. Four atoms

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Correct Option: B
Explanation:

Metallic bond is formed by sharing of electrons between many atoms A metallic bond is pretty different from covalent and ionic bonds, but the goal is the same: to achieve a lower energy state. Instead of a bond between just two atoms, a metallic bond is a sharing of electrons between many atoms of a metal element. Hence option B is correct.

Iron is tougher than sodium because :

bonding in metals metallic bonding chemical bonding and structure chemical bonding and molecular structure chemistry

  1. iron atom is smaller

  2. iron atoms are more closely packed

  3. metallic bonds are stronger in iron

  4. none of these

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Correct Option: C
Explanation:
Iron is tougher than sodium because metallic bonds are stronger in iron.
Stronger is metallic bonding (FeFe has dd -subshell), more is hardness.

Hence, it is hard than Sodium like other alkali metals are soft.

So, the correct option is $C$