## Atoms, Molecules and Chemical Arithmetic MCQs

This is continuous series of chemistry MCQs, so in this post we cover 20 MCQs of chapter Atoms, Molecules and Chemical Arithmetic.#### MCQ-1. What is SI unit of temperature :

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MCQ-2. Prefix 10^{18} is :

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#### MCQ-3. Derived SI Unit of Area is :

^{2}

^{3}

^{2}

^{3}

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#### MCQ-4. Which one of the following is a physical change :

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#### MCQ-5. Law of Multiple Proportions was proposed by which of the following scientist :

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#### MCQ-6. Which pair of compounds illustrate the law of multiple proportions :

_{2}S and SO

_{2}

_{2}and FeCl

_{3}

_{2}O

_{3}and NCl

_{3}

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#### MCQ-7. The ratio of the rates of the diffusion of a given element to that of helium is 4. what is the molecular weight of the element :

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#### MCQ-8. The Law of Reciprocal proportions can be used to determine :

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#### MCQ-9. The specific heat of a metal is 0.16 , its approximate atomic weight would be _____________ :

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#### MCQ-10. Atomic weight of a trivalent element of equivalent weight 9 is_____ :

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#### MCQ-11. Which property of element is always a whole number :

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#### MCQ-12. A metallic oxide contains 60% of the metal. The equivalent weight of the metal is ________ :

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#### MCQ-13. Equivalent weight of an acid is _______ whose basicity is 3 :

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#### MCQ-14. 90 gram of water contains how many moles :

^{23}

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#### MCQ-15. which one of the following has maximum number of atoms :

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#### MCQ-16. 18 gram of water contains :

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#### MCQ-17. volume of 4.4 gram of carbon di oxide at STP is________ :

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#### MCQ-18. Avogadro Number of Helium atom weighs ______ gram :

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#### MCQ-19. A hydrocarbon containing 86% carbon. 448 mL of the hydrocarbon weighs 1.68 gram at STP, Then hydrocarbon is an __________ :

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#### MCQ-20. The % of nitrogen in urea is about________ :

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## Chemistry formulas for Atoms, Molecules and Chemical Arithmetic Part I

##
__Atomic Weight related Chemical Formulas__

· Atomic Weight of an Element = Weight of an average Atom of that Element/ (1/12)x Mass of an element of C

^{12}
· 1 a.m.u. = 1.66x10

^{-24}g
· Atomic Weight = Gram Atomic Weight (GAW)

· 1 Gram Atomic Weight (GAW) of every element contains 6.023x10

^{23}atoms of that element.
· No. of gram of an element = weight of element in gram/ Gram Atomic Weight (GAW) of that element

### Methods of Determining Atomic Weight

#### i. Dulong and Pettits Method:

Applicable only for solid elements except Be, B, C, Si.

· Atomic Weight x Specific Heat = 6.4 (app.)

· Atomic Weight (app.) = 6.4/ Specific Heat (in Calories)

· Exact Atomic Weight = Equivalent Weight x Valency

· Valency = App. Atomic Weight / Equivalent Weight

#### ii. Vapour Density Method:

Applicable only for those elements whose chlorides are volatile.

· Valency of the Element = Molecular Weight of Chloride / Equivalent Weight of Chloride

· Valency of the Element = (2 x V.D. of Chloride) / (Equivalent Weight of Metal + 35.5)

Where, V.D. = Vapour Density

· Atomic Weight = Equivalent Weight of Metal x Valency

#### iii. Specific Heat Method:

Applicable only for Gases.

· Cp/Cv for monoatomic gases = 1.66

· Cp/Cv for diatomic gases = 1.40

· Cp/Cv for triatomic gases = 1.33

· Atomic Weight of Gaseous Element = Molecular Weight/ Atomicity

Where, Atomicity is number of atoms present in a molecule of a gaseous element. For example atomicity of Inert Gas is 1, atomicity of Ozone is 3, atomicity of H

_{2}N_{2}O_{2}X_{2}is 2, and atomicity of Sulphur is 8.#### iv. Volatile Chloride Formation Method:

· Atomic Weight of the Element = Equivalent Weight (Z) x Valency (x)

#### v. Isomorphism Method:

This method based on law of Isomorphism. According to law of Isomorphism, “Compounds having identical crystal structure have similar constitution and chemical formula”

· Atomic Weight = Equivalent Weight x Valency

· Weight of Element A that combines with certain weight of other elements/Weight of Element B that combines with the same weight of other elements = Atomic Weight of A / Atomic Weight of B

##
__Molecular Weight related Chemical Formulas__

· Molecular Weight = Weight of 1 Molecule of the Substance/ (1/12)x Weight of 1 atom of C

^{12}
· Actual Weight of 1 Molecule = Molecular Weight x 1.66x10

^{-24}g### Methods of Determining Atomic Weight

#### 1. Diffusion Method:

Applicable only for gases.

·

Where, r

_{1}& r_{2}is rate of diffusion of gases and M_{1 }& M_{2}is Molecular Weight.#### 2. Vapour Density Method:

Applicable only for gases.

· Molecular Weight = 2 x Vapour Density

#### 3. Victor Mayer Method:

Applicable only for volatile liquids and solids.

· Molecular Weight of a substance = 22400 ml of vapour of a substance at STP

##
__Equivalent Weight related Chemical Formulas__

· No. of Gram Equivalent Weight = Weight of the substance in gram/ Gram Equivalent Weight of the substance

· Equivalent Weight of an Element = Atomic Weight/ Valency

· Equivalent Weight of an Acid = Molecular Weight/ Basicity

· Equivalent Weight of an Base = Molecular Weight/ Acidity

· Equivalent Weight of a Salt = Formula Weight/ Total Positive or Negative Charge

· Equivalent Weight of a Reducing Agent = Formula Weight/ No. of electrons lost per molecule or Total change in Oxidation Number

· Equivalent Weight of an Oxidising Agent = Formula Weight/ No. of electrons gained per molecule or Total change in Oxidation Number

· Equivalent Weight of Radicals = Formula Weight of Radical/ No. of units of Charge.....