Q: Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

The postulate of Dalton’s atomic theory resulting from the law of conservation of mass is ‘The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor be destroyed in a chemical reaction’.

Q: (i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

The number of electrons which will weigh 1 g is \$\displaystyle \frac {10^{-3}}{9.11 \times 10^{-31}} = 1.098 \times 10^{27} \$ .Mass of one mole of electrons is \$\displaystyle 9.11 \times 10^{-31} \times 6.023 \times 10^{23}= 5.486 \times 10^{-7} \$kg.Charge of 1 mole of electrons is \$\displaystyle 1.602 \times 10^{-19} \times 6.023\times 10^{23} = 9.647\times 10^{4}\ C\$.

Q: The increasing order for the values of \$e/m\$ (charge/mass) for electron (\$e\$), proton (\$p\$), neutron (\$n\$) and alpha particle (\$\alpha\$) is:

For neutron \$(n), \dfrac em=0\$For proton \$(p)= \dfrac em \times = \dfrac 11=1\$\$ For electron, \left( { e }^{ - } \right) , \dfrac em=\cfrac { 1 }{ 1/1837 } =1837\$For alpha particle \$\left( \alpha \right) , \dfrac em = \dfrac 24=0.5\$The increasing order for the values of \$\dfrac em\$ is \$n,α,p,e\$.Hence, the correct option is \$\text{D}\$.

Q: Which of the following statements about the electron is incorrect?

Explanation: Electrons have the following characteristics: 1. They are negatively charged particles. 2. The mass of the electron is \$200\$ times that of the neutron. The electron has a mass of \$9.1 \times {{10}^{-31}}\$ Kg and the neutron has a mass of \$1.67 \times {{10}^{-27}}\$ Kg. 3. They are the fundamental building blocks of all atoms. 4. Cathode rays are beams of electrons. Final Answer: The correct answer is option \$(B).\$

Q: An oil drop of 12 excess electrons is held stationary under a constant electric field of \$2.55\times10^{4} NC^{-1}\$ in Millikans oil drop experiment. The density of the oil is \$1.26\ g\ cm^{-3}\$. Estimate the radius of the drop. [g = \$9.8\ ms^{-2};\ \ \ \ e = \$1.60\$\times\,10^{-19}\$ C].

Excess electrons on an oil drop, \$n = 12\$Electric field intensity, \$E=2.55\times 10^4NC^{-1}\$Density of oil, \$\rho=1.26\,gm/cm^3=1.26\times 10^3kg/m^3\$Acceleration due to gravity, \$g=9.81\,m\,s^{-2}\$Charge on an electron, \$e=1.6\times 10^{-19}C\$Radius of the oil drop \$= r\$Force (F) due to electric field E is equal to the weight of the oil drop (W).\$F = W\$\$Eq = mg\$\$\displaystyle E_{ne}=\frac{4}{3}\pi r^3\times \rho \times g\$Where, \$q =\$ Net charge on the oil drop = ne\$m =\$ Mass of the oil drop \$=\$ Volume of the oil drop × Density of oil \$=\displaystyle \frac{4}{3}\pi r^3\times \rho\$\$\therefore r =\displaystyle \sqrt[3]{\frac{3\,E_{ne}}{4\pi\rho g}}\$\$\displaystyle =\sqrt[3]{\frac{3\times 2.55\times 10^4\times 12\times 1.6\times 10^{-19}}{4\times 3.14\times 1.26\times 10^3\times 9.81}}\$\$\displaystyle =\sqrt[3]{946.09\times 10^{-21}}\$\$=9.82\times 10^{-7}m\$\$=9.82\times 10^{-4}mm\$Therefore, the radius of the oil drop is \$9.82\times 10^{-4}mm\$.

Question 1

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

Accepted Answer

The postulate of Dalton&#8217;s atomic theory resulting from the law of conservation of mass is &#8216;The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor be destroyed in a chemical reaction&#8217;.

Question 2

What are canal rays?

Accepted Answer

E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. The beam of rays which travel in a direction away from anode towards cathode when gas is taken in a discharge tube is subjected to the action of high voltage under low pressure is known as canal rays. These rays were positively charged radiations which ultimately led to the discovery of another sub-atomic particle.Hence, the correct option is $A$

Question 3

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

Accepted Answer

Hint: Thomson atomic model is the first atomic model. It is also called the plum pudding model.Explanation : 1) According to the Thomson model, an atom consists of a positively charged sphere and the negatively charged electron are embedded in it.2) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.

Question 4

(i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

Accepted Answer

The number of electrons which will weigh 1 g is $\displaystyle \frac {10^{-3}}{9.11 \times 10^{-31}} = 1.098 \times 10^{27} $ .Mass of one mole of electrons is $\displaystyle 9.11 \times 10^{-31} \times 6.023 \times 10^{23}= 5.486 \times 10^{-7}   $kg.Charge of 1 mole of electrons is $\displaystyle 1.602 \times 10^{-19} \times 6.023\times 10^{23} = 9.647\times 10^{4}\ C$.

Question 5

Which of the following statements is not correct about the characteristics of cathode rays?

Accepted Answer

Characteristics of cathode rays are:(i) The cathode rays start from cathode and move towards the anode.(ii) These rays themselves are not visible but their behaviour can be observed with the help of phosphor materials such as $ZnS$.(iii) In the absence of electrical or magnetic field, these rays travel in straight lines.(iv) In the presence of electrical or magnetic field, the behaviour of cathode rays are similar to that expected from negatively charged particles, suggesting that the cathode rays consist of negatively charged particles, called electrons.(v) The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.Option D provides a wrong statement.

Question 6

Which of the following is not a postulate of Dalton's atomic theory?

Accepted Answer

Postulates of Dalton's atomic theory:All matter consists of indivisible particles called atoms.Atoms of the same elements are similar in shape and mass but differ from the atoms of other elements.Atoms cannot be created or destroyed.Atoms of different elements may combine with each other in fixed, simple, whole-number ratios to form elements and compounds.The atom is the smallest unit of matter that can take part in a chemical reaction.'Atoms of a single element can have different masses' is not present in postulates of Dalton's atomic theory. It is in fact a limitation of Dalton's atomic theory. Hence, option D is the correct choice.

Question 7

The increasing order for the values of $e/m$ (charge/mass) for electron ($e$), proton ($p$), neutron ($n$) and alpha particle ($\alpha$) is:

Accepted Answer

For neutron $(n), \dfrac em=0$For proton $(p)= \dfrac em \times = \dfrac 11=1$$ For electron, \left( { e }^{ - } \right) , \dfrac em=\cfrac { 1 }{ 1/1837 } =1837$For alpha particle $\left( \alpha  \right) , \dfrac em = \dfrac 24=0.5$The increasing order for the values of $\dfrac em$ is $n,&#945;,p,e$.Hence, the correct option is $\text{D}$.

Question 8

Fill in the blanks in the following statements:
(a) The number of protons in the nucleus of an atom is called its .
(b) The total number of protons and neutrons in the nucleus of an atom is called .
(c) An atom has atomic mass number 23 and atomic number 11. The atom has electrons.
(d) An atom of an element has 11 protons, 11 electrons and 12 neutrons. The atomic mass of the atom is _.
(e) If the nucleus of an atom has atomic number 17 , mass number 37 and there are 17 electrons outside the nucleus, the number of neutrons in it is .
(f) Almost all the mass of an atom is concentrated in a small region of space called the .
(g) Cathode rays are a beam of fast moving .
(h) The anode rays obtained from hydrogen gas consist of particles called .
(i) The maximum number of electrons that can be accommodated in L shell are .
(j) The maximum number of electrons that can go into the M shell is .
(k) The subatomic particle not present in a hydrogen atom is .
(l) The electron has charge, the proton has charge, and the neutron has ____ charge.

Accepted Answer

(a) Atomic number(b) Mass number(c) 11 (d) 23(e) 20(f) Nucleus(g) Electrons(h) Protons(i) 8(j) 18(k) Neutron(l) Negative; Positive; No

Question 9

Which of the following statements about the electron is incorrect?

Accepted Answer

Explanation:&#10;&#10;Electrons have the&#10;following characteristics:&#10;&#10;1. They are&#10;negatively charged particles.&#10;&#10;2. The mass of the&#10;electron is $200$ times that of the neutron.&#10;&#10;The electron has a&#10;mass of  $9.1 \times {{10}^{-31}}$ Kg&#10;and the neutron has a mass of $1.67 \times {{10}^{-27}}$ Kg.&#10;&#10;3. They are the&#10;fundamental building blocks of all atoms.&#10;&#10;4. Cathode rays&#10;are beams of electrons.&#10;&#10;Final Answer:&#10;&#10;The correct answer&#10;is option $(B).$

Question 10

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55\times10^{4} NC^{-1}$ in Millikans oil drop experiment. The density of the oil is $1.26\ g\ cm^{-3}$. Estimate the radius of the drop. [g = $9.8\ ms^{-2};\ \ \ \  e = $1.60$\times\,10^{-19}$ C].

Accepted Answer

Excess electrons on an oil drop, $n = 12$Electric field intensity, $E=2.55\times 10^4NC^{-1}$Density of oil, $\rho=1.26\,gm/cm^3=1.26\times 10^3kg/m^3$Acceleration due to gravity, $g=9.81\,m\,s^{-2}$Charge on an electron, $e=1.6\times 10^{-19}C$Radius of the oil drop $= r$Force (F) due to electric field E is equal to the weight of the oil drop (W).$F = W$$Eq = mg$$\displaystyle E_{ne}=\frac{4}{3}\pi r^3\times \rho \times g$Where, $q =$ Net charge on the oil drop = ne$m =$ Mass of the oil drop     $=$ Volume of the oil drop &#215; Density of oil     $=\displaystyle \frac{4}{3}\pi r^3\times \rho$$\therefore r =\displaystyle \sqrt[3]{\frac{3\,E_{ne}}{4\pi\rho g}}$$\displaystyle =\sqrt[3]{\frac{3\times 2.55\times 10^4\times 12\times 1.6\times 10^{-19}}{4\times 3.14\times 1.26\times 10^3\times 9.81}}$$\displaystyle =\sqrt[3]{946.09\times 10^{-21}}$$=9.82\times 10^{-7}m$$=9.82\times 10^{-4}mm$Therefore, the radius of the oil drop is $9.82\times 10^{-4}mm$.

Revise with Concepts

Subatomic Particles - Electron

Subatomic Particles - Protons

Subatomic Particles - Neutrons

Atomic Theory of Matter

Learn with Videos

Quick Summary With Stories

History of Atoms and Molecules

Dalton's Atomic Theory

Cathode Rays

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

What are canal rays?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

(i) Calculate the number of electrons which will together weighs one gram.
(ii) Calculate the mass and charge of one mole of electrons.

Which of the following statements is not correct about the characteristics of cathode rays?

Which of the following is not a postulate of Dalton's atomic theory?

The increasing order for the values of $e / m$ (charge/mass) for electron ( $e$ ), proton ( $p$ ), neutron ( $n$ ) and alpha particle ( $α$ ) is:

Which of the following statements about the electron is incorrect?

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55 \times 1 0^{4} N C^{- 1}$ in Millikans oil drop experiment. The density of the oil is $1.26 g c m^{- 3}$ . Estimate the radius of the drop. [g = $9.8 m s^{- 2}; e =$ 1.60 $\times 1 0^{- 19}$ C].

Revise with Concepts

Subatomic Particles - Electron

Subatomic Particles - Protons

Subatomic Particles - Neutrons

Atomic Theory of Matter

Learn with Videos

Quick Summary With Stories

History of Atoms and Molecules

Dalton's Atomic Theory

Cathode Rays

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

What are canal rays?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

(i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

Which of the following statements is not correct about the characteristics of cathode rays?

Which of the following is not a postulate of Dalton's atomic theory?

The increasing order for the values of e/m (charge/mass) for electron (e), proton (p), neutron (n) and alpha particle (α) is:

Which of the following statements about the electron is incorrect?

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55×104NC−1 in Millikans oil drop experiment. The density of the oil is 1.26 g cm−3. Estimate the radius of the drop. [g = 9.8 ms−2; e=1.60×10−19 C].

(i) Calculate the number of electrons which will together weighs one gram.
(ii) Calculate the mass and charge of one mole of electrons.

The increasing order for the values of $e / m$ (charge/mass) for electron ( $e$ ), proton ( $p$ ), neutron ( $n$ ) and alpha particle ( $α$ ) is:

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55 \times 1 0^{4} N C^{- 1}$ in Millikans oil drop experiment. The density of the oil is $1.26 g c m^{- 3}$ . Estimate the radius of the drop. [g = $9.8 m s^{- 2}; e =$ 1.60 $\times 1 0^{- 19}$ C].