Tag: chemistry

Questions Related to chemistry

Which of the following is a merit of Dalton's atomic theory?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. Laws of chemical combination

  2. Distinction between the fundamental particle of an element (atom) and that of a compound (molecule)

  3. Both A and B

  4. None of the above

Show answer
Correct Option: C
Explanation:

 Dalton's theory explains the laws of chemical combination.  Dalton was the first person to recognize a workable difference between the fundamental particle of an element (atom) and that of a compound (molecule).

Among the following, which one can not be further broken down by chemical means?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. Cation

  2. Inert Gas

  3. Crystal

  4. Anion

  5. Element

Show answer
Correct Option: E
Explanation:

An element can not be further broken down by chemical means.


An element is defined as a substance that cannot be decomposed by a simple chemical process into two or more different substances. 

Some of the examples of elements are gold, silver copper, carbon, sulphur and phosphorous.

Hence option E is correct.

Which one proposes the basic postulates concerning elements and atoms?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. Avogadro's number

  2. $P _1V _1=P _2V _2$

  3. $V _1T _2=V _2T _1$

  4. Dalton's theory

  5. Gay-Lussac's Law

Show answer
Correct Option: D
Explanation:

Dalton's theory proposes the basic postulates concerning elements and atoms.


All matter is made of atoms. Atoms are indivisible and indestructible. 

All atoms of a given element are identical in mass and properties.  

  Hence, the correct option is D.

Which of the following is not part of the Atomic Theory?

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. Compounds are made up of combinations of atoms

  2. All atoms of a given element are alike

  3. All matter is composed of atoms

  4. A chemical reaction involves the rearrangement of atoms

  5. The atom is mainly empty space

Show answer
Correct Option: E
Explanation:

Main Postulates of Dalton's Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms

option E is not a part of Atomic theory.

An important postulate of Dalton's atomic theory is: 

chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

  1. an atom contains electrons, protons and neutrons

  2. atom can neither be created nor destroyed nor divisible

  3. all the atoms of an element are not identical

  4. all the elements are available in nature in the form of atoms

Show answer
Correct Option: B
Explanation:

According to Dalton's theory, atoms can neither be created nor be destroyed.

The nucleus of the atom $\left( Z>1 \right) $ consists of:

chemistry inside the atom history of atomic model atomic theory of dalton daltons atomic theory

  1. Proton and neutron.

  2. Proton and electron.

  3. Neutron and electron.

  4. Proton, neutron and electrons

Show answer
Correct Option: A
Explanation:

The atomic nucleus is the central area of the atom. It is composed of two kinds of subatomic particles: protons and neutrons.The protons and neutrons held together to form the dense area of the nucleus.

For atoms havng $Z>1$ nucleus contains protons and neutrons.

Which of the following species has more number of protons than the number of electrons?

chemistry inside the atom history of atomic model atomic theory of dalton daltons atomic theory

  1. $F^-$

  2. $Na^+$

  3. $O^{2-}$

  4. $Ne$

Show answer
Correct Option: B
Explanation:

A positively charged species has more number of protons than the number of electrons.
No. of protons in $Na^+$ = Atomic number of $Na$ = $11$
No. of Electrons in $Na^+ = 10$

In pseudo unimolecule reactions:

pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

  1. both the reactants are present in low concentration

  2. Both the reactants are present in same concentration

  3. One of the reactant is present in excess

  4. One of the reactant is non-reactive

Show answer
Correct Option: C
Explanation:

Pseudo Unimolecular Reaction. The reactions having molecularity two but the order of reaction is one is called pseudo unimolecular reactions,in such type of reactions, one reagent is take in the excess amount so that the disappearance of that reagent is negligible and it does not determine the rate of reaction.

Example:
  • Hydrolysis of ester$CH _3COOC _2H _5$,
  • Hydrolysis of sucrose.

The value of rate of a pseudo first order reaction depends upon:

pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

  1. the concentration of both the reactants present in the reaction

  2. the concentration of the reactant present in small amount

  3. the concentration of the reactant present in excess

  4. the value of $\Delta H$ of the reaction

Show answer
Correct Option: B
Explanation:

$CH _3COOC _2H _5 + H _2O \rightarrow CH _3COOH + CH _3OH$
          0.01                    10                   0                      0

            0                      9.99              0.01               0.01 

The above reaction is a Pseudo first order reaction. As it can be seen from the above reaction that the concentration of water is not changing much. Thus the rate of the reaction is not much affacted by the change in concentration of  water. However rate of the reaction get significantly affacted by the concentration gradient of ethyl acetate. Hence, the rate of Pseudo first order reaction depends upon the concentration of the reactant present in small amount.

Option B is correct.

         

The value of rate constant of a pseudo first order reaction ________.

pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

  1. depends on the concentration of reactants present in small amount

  2. depends on the concentration of reactants present in excess

  3. is independent of the concentration of reactants

  4. depends only on temperature

Show answer
Correct Option: B
Explanation:

Pseudo first-order reaction is not the first-order reaction by nature. It is made the first order by adding something in excess.so, the rate constant depends on the concentration of reactants present in excess.