Tag: chemistry

Questions Related to chemistry

The number of protons is equal to ________ in a neutral atom.

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. atomic weight

  2. atomic number

  3. number of electrons

  4. both B and C

Show answer
Correct Option: D
Explanation:

The atomic number is the number of protons in an atom of an element. Atoms are electrically neutral. That means that there must be a balance between the positively charged protons and the negatively charged electrons.


Thus, atoms must have equal numbers of protons and electrons.


Hence, the correct option is $\text{D}$

The mass of electron, proton and neutron in grams are :

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $1.108\times 10^{-28}, 1.6726\times 10^{-24}, 1.675 \times 10^{-24}$

  2. $9.108\times 10^{28}, 1.6726\times 10^{24}, 1.675 \times 10^{24}$

  3. $9.108\times 10^{-24}, 1.6726\times 10^{-24}, 1.675 \times 10^{24}$

  4. $9.108\times 10^{-28}, 1.6726\times 10^{-24}, 1.675 \times 10^{-24}$

Show answer
Correct Option: D
Explanation:

An electron is a tiny particle with a mass of $9.108\times 10^{-28}$ g and a negative charge. All neutral atoms contain electrons. The mass of a proton is $1.6726\times 10^{-24}$ g, or about 1836 times the mass of an electron. The proton carries a positive electrical charge, that is equal in magnitude to the charge of the electron but opposite in sign. Mass of a neutron is $1.675 \times  10^{-24}$ g. It is very close to that of the proton. A neutron carries no charge.

Find the number of neutrons in silver having atomic mass of $107.86$.

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $65$

  2. $71$

  3. $61$

  4. $47$

Show answer
Correct Option: C
Explanation:

The atomic weight is basically a measurement of the total number of particles in an atom's nucleus. Mass number can be found by rounding off an elements atomic mass to the nearest whole number.
$Mass\ Number = (Number\ of\ protons) + (Number\ of\ neutrons)$
Number of neutrons $= mass\ number- number\ of\ protons$
Atomic mass of silver $= 107.86$
Mass number $= 108$
Number of protons $= 47$
Number of neutrons $= 108 - 47$
$= 61$
$\therefore$ Number of neutrons in a silver $=61$

 How many moles of electron weighs one kilogram?

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $6.023 \times 10^{23}$

  2. $\dfrac{1}{9.108} \times 10^{32}$

  3. $\dfrac{6.023}{9.108} \times 10^{54}$

  4. $\dfrac{1}{9.108 \times 6.023} \times 10^{8}$

Show answer
Correct Option: D
Explanation:
Mass of one electron $ \displaystyle =9.108 \times 10^{-31}$ kg.

Mass of one mole of electrons $ \displaystyle =9.108 \times 10^{-31} \times 6.023 \times 10^{23}=9.108   \times 6.023 \times 10^{-8}$ kg.

The number of moles of electrons that weigh one kilogram $ \displaystyle = \dfrac {1}{9.108   \times 6.023 \times 10^{-8}}= \dfrac {1}{9.108   \times 6.023}  \times 10^{8}$

Hence, the correct option is $D$

Positronium is the name given to an atom-like combination formed between_____________.

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. a positron and a proton

  2. a positron and a neutron

  3. a positron and an $\alpha$-particle

  4. a positron and an electron

Show answer
Correct Option: D
Explanation:

Positronium is the name given to an atom-like combination formed between a positron and an electron. Electron  and positron are particle and antiparticle.

If $N _A$ is the Avogadro's number then number of valence electrons in 4.8 g of $O^{2-} $ is:

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $2.4\, N _A$

  2. $4.2\, N _A$

  3. $1.6\, N _A$

  4. $3.2\, N _A$

Show answer
Correct Option: A
Explanation:
Number of mole in 4.8 gm of oxygen atom $=\dfrac{4.8}{16} = 0.3$ mole 

Number of the valence electron in one ion of $O^{2-} = 8$

Number of the valence electron in 0.3 mole of $O^{2-} = 8\times0.3\times N _A =2.4N _A$

Hence, the correct option is $(A)$.

Mass of 1 mole neutrons $(m _n= 1.675 \times 10^{-27}\, kg)$ is:

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $1.8 \times 10^{-3}\, kg$

  2. $1.008 \times 10^{-4}\, kg$

  3. $1.08 \times 10^{-3}\, kg$

  4. $1.008 \times 10^{-3}\, kg$

Show answer
Correct Option: D
Explanation:

Mass of one neutron $= 1.675 \times 10^{-27}$ kg


1 mole contains $6.02 \times 10^{23}$ neutrons

mass of 1 mole neutrons $= 1.675 \times 6.02 \times  10^{-27} \times 10^{23}$

                                         $=1.008 \times 10^{-3}$ kg

Select the correct statement?

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. An atom has equal number of electrons and protons.

  2. An atom has equal number of electrons and neutrons.

  3. An atom has equal number of protons and neutrons.

  4. An atom has equal number of electrons, protons and neutrons.

Show answer
Correct Option: A
Explanation:

An atom is electrically neutral as it has an equal number of electrons and protons, that is, an equal number of negative and positive charges. 


In order to become stable, atom loses or gains one or more electrons and forms an ion which carries a charge.

Hence the correct option is A.

What is the total number of electrons present in 1.6 g of methane?

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $6.023 \times 10^{23}$

  2. 16

  3. $12.04 \times 10^{23}$

  4. $6.023 \times 10^{24}$

Show answer
Correct Option: A
Explanation:
1 mole methane = 16 g
Electrons in 1 mole of methane are $=6+4 \times 1=10$
Mole of methane in 1.6 g=$\cfrac{mass}{molar\ mass}$
$=\cfrac{1.6}{16}=0.1$ mole
$\therefore$ 0.1 mol methane contains $0.1 \times 10$mol electron=1 mole of electron
1 mole electron=$6.023 \times 10^{23}$ electrons

The molar mass of an electron is:

chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

  1. $6.023\times10^{23}$ g/mol

  2. $5.486\times10^{-4}$ g/mol

  3. $9.108\times10^{-28}$ kg/mol

  4. $9.108\times10^{-24}$ g/mol

Show answer
Correct Option: B
Explanation:

Mass of an electron $=9.1\times 10^{-28}$g
1 mole $=6.02\times 10^{23}$ electrons
$\therefore$ molar mass of electron $=(9.1\times 10^{-28}) \times (6.02\times 10^{23}) = 5.48\times 10^{-4}$ g/mole