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some basic concepts of chemistry Flashcards

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1
Q

Define the atomic mass unit (amu).

A

One atomic mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom.

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2
Q

What is a molecule?

A

A molecule is a group of two or more atoms bonded together, representing the smallest fundamental unit of a chemical compound.

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3
Q

What is an empirical formula?

A

The empirical formula gives the simplest whole-number ratio of atoms in a compound.
Example: The empirical formula of hydrogen peroxide (H₂O₂) is HO.

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4
Q

What is molecular mass?

A

Molecular mass is the sum of the atomic masses of all atoms in a molecule.

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5
Q

NIOS Board Question
Question: What is the empirical formula of a compound containing 53.1% carbon and 46.9% oxygen?

A

Step 1: Convert percentages to moles.
Carbon:
53.1/12=4.425mol
Oxygen:
46.9/16=2.931mol
Step 2: Simplify the ratio:
4.425/2.931≈1.51:1, or approximately 3:2.
Empirical Formula: C₃O₂.

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6
Q

What is the SI unit of mass?

A

The SI unit of mass is the kilogram (kg).

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7
Q

What is the law of constant proportions?

A

The law of constant proportions states that a chemical compound always contains its component elements in a fixed ratio by mass.

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8
Q

NIOS Board Question: Define atomic mass unit (amu).

A

One atomic mass unit (amu) is defined as 1/12th the mass of one carbon-12 atom.
Explanation: This unit provides a standard for measuring atomic and molecular masses.

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9
Q

Question: What is the role of chemistry in health and medicine?

A

Chemistry plays a crucial role in health and medicine. Advances such as the introduction of vaccines, antibiotics, gene therapy, and anesthesia have revolutionized disease prevention and treatment. Chemists develop drugs with fewer side effects and study the molecular components of diseases for better cures.
Explanation: Knowledge of chemical processes allows the development of life-saving treatments, improved surgeries, and solutions for genetic diseases.

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10
Q

NIOS Board Question
Question: What are isotopes?

A

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

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11
Q

NIOS Board Question
Question: What is the molecular mass of water?

A

H₂O:
H = 1 g/mol, O = 16 g/mol.
Molecular mass of H₂O = 2×1+16=18g/mol.

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12
Q

NEET Question
Question: Calculate the mass of 0.5 mol of NaOH.

A

Molar mass of NaOH =
23+16+1=40g/mol.
Mass of 0.5 mol =
0.5×40=20g.

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13
Q

What is the significance of balancing a chemical equation?

A

A balanced chemical equation ensures the law of conservation of mass, meaning the number of atoms of each element is the same on both sides of the equation.

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14
Q

JEE Main Question
Question: What is the molar mass of NaCl?

A

Na = 23 g/mol, Cl = 35.5g/mol.Molar mass of NaCl = 23+35.5=58.5g/mol.

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15
Q

Define excess reagent.

A

The excess reagent is the reactant that remains after the reaction has finished, meaning there was more of this reactant than required to react with the limiting reagent.

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16
Q

Define molar volume of a gas

A

The molar volume of a gas is the volume occupied by one mole of a gas at STP (Standard Temperature and Pressure), typically 22.7 liters.

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17
Q

How is the atomic mass of an element calculated?

A

Atomic mass is the weighted average mass of an element’s isotopes based on their natural abundance.

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18
Q

JEE Main Question
Question: Calculate the number of atoms in 4 grams of helium.

A

Molar mass of helium = 4 g/mol.
Number of moles = 4/4=1mol.
Number of atoms =
1×6.022×10^23

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19
Q

What is the volume of 1 mole of a gas at STP?

A

At standard temperature and pressure (STP), 1 mole of any gas occupies 22.7 liters.
Explanation: This is true for ideal gases at 0°C and 1 bar pressure.

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20
Q

How are molecules formed?

A

Molecules are formed when two or more atoms share or transfer electrons through covalent or ionic bonds.

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21
Q

What are cations and anions?

A

Cation: A positively charged ion.
Anion: A negatively charged ion.

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22
Q

What is an empirical formula?

A

The empirical formula represents the simplest whole-number ratio of elements in a compound.

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23
Q

Explain the law of conservation of mass with an example.

A

The law of conservation of mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products.
Example: When mercury (II) oxide is heated, it decomposes into mercury and oxygen. The mass of mercury and oxygen produced equals the original mass of mercury (II) oxide.

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24
Q

NEET Question
Question: Calculate the mass of 0.25 moles of CO₂.

A

Molar mass of CO₂ = 44 g/mol. Mass = 0.25×44=11g.

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25
Q

How is a chemical equation balanced?

A

A chemical equation is balanced by adjusting the coefficients so that the number of atoms of each element is the same on both sides of the equation.

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26
Q

What is empirical formula and molecular formula? Provide an example.

A

Empirical formula: The simplest whole-number ratio of atoms in a compound.
Molecular formula: The actual number of atoms of each element in a molecule.
Example: The empirical formula of glucose is CH₂O, while its molecular formula is C₆H₁₂O₆.
Explanation: Empirical formulas give the ratio of elements, while molecular formulas represent the actual composition of molecules.

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27
Q

Define Avogadro’s Constant.

A

Avogadro’s constant,
6.022×10
^23, represents the number of atoms or molecules in one mole of a substance.
Explanation: It is used to relate the amount of a substance to the number of its atoms or molecules.

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28
Q

What is a molecular formula?

A

The molecular formula shows the actual number of atoms of each element in a compound.
Example: The molecular formula of glucose is C₆H₁₂O₆.

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29
Q

What is a diatomic molecule?

A

A diatomic molecule contains two atoms of the same or different elements.
Example: Oxygen (O₂), Nitrogen (N₂), Hydrogen (H₂).

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30
Q

Calculate the mass of 0.5 mol of water

A

Molar mass of water (H₂O) = 18 g/mol.
Mass of 0.5 mol of water = 0.5×18=9g
explanation: The molar mass helps convert moles to grams using the relation
mass=moles×
molarmass

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31
Q

What is a reactant in a chemical reaction?

A

Reactants are the starting materials in a chemical reaction that undergo changes to form products.

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32
Q

JEE Main Question
Question: Calculate the number of moles in 90 g of water.

A

Molar mass of water = 18 g/mol.
Number of moles = 90/18=5mol.

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33
Q

How do you balance chemical equations?

A

To balance an equation, adjust the coefficients of the reactants and products to have the same number of atoms of each element on both sides.

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34
Q

Define Avogadro’s Law.

A

Avogadro’s Law states that equal volumes of gases at the same temperature and pressure contain an equal number of molecules.

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35
Q

What is the formula for Avogadro’s Law?

A

V∝n(atconstanttemperatureandpressure)
Where
𝑉 is volume and
𝑛 is the number of moles.

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36
Q

Define limiting reagent with an example.

A

The limiting reagent is the reactant that is completely used up in a chemical reaction, determining the amount of product formed.
Example: In the reaction 2𝐻2+𝑂2→2𝐻2𝑂2, if
𝑂2O2 is limited, it will stop the reaction even if
𝐻2 is present in excess.

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37
Q

What is an ion?

A

An ion is an atom or molecule that has gained or lost one or more electrons, giving it a net charge.

38
Q

What is a chemical reaction?

A

A chemical reaction involves the rearrangement of atoms to form new substances, often accompanied by the release or absorption of energy.

39
Q

What volume will 3 moles of oxygen gas occupy at STP?

A

At STP, 1 mole of gas occupies 22.7 L.
Volume of 3 moles =
3×22.7=68.1L

40
Q

Give an example of isotopes.

A

Hydrogen has three isotopes:

Protium (¹H)
Deuterium (²H)
Tritium (³H)

41
Q

What is the Law of Conservation of Mass?

A

The law states that mass is neither created nor destroyed in a chemical reaction.
Explanation: The total mass of the reactants equals the total mass of the products in any chemical reaction.

42
Q

Define product in a chemical reaction.

A

Products are the substances formed as a result of a chemical reaction between reactants.

43
Q

What is a limiting reagent?

A

The limiting reagent is the reactant that is completely consumed in a reaction, thus limiting the amount of product formed.

44
Q

What is the Law of Definite Proportions?

A

A chemical compound always contains its elements in a fixed ratio by mass.
Example: In water (H₂O), the mass ratio of hydrogen to oxygen is always 1:8.

45
Q

What volume of hydrogen gas is produced at STP when 2.5 moles of H₂ gas are released?

A

At STP, 1 mole of gas occupies 22.7 L.
Volume of 2.5 moles =
2.5×22.7=56.75L.
Explanation: The molar volume of a gas at STP allows the conversion of moles of gas to volume.

46
Q

How many grams of CO₂ are produced from the combustion of 12 g of carbon?

A

Step 1: Write the balanced equation:
C+O2→CO2
Step 2: Find the molar masses: C = 12 g/mol
CO₂ = 44 g/mol
Step 3: Use stoichiometry:
1 mole of C produces 1 mole of CO₂.
Mass of CO₂ produced = 44 g.

47
Q

Define atom.

A

An atom is the smallest unit of an element that retains the properties of that element.

48
Q

Calculate the number of molecules in 88 g of CO₂.

A

Molar mass of CO₂ = 44 g/mol.
Number of moles =88/44 =2mol.
Number of molecules= 2×6.022×10 ^23 = 1.2044×10 ^24 molecules.

49
Q

What is Chemistry?

A

Chemistry is the study of matter and the changes it undergoes.
Explanation: Chemistry helps explain the properties and behaviors of different substances and is often called the “central science” because it connects to biology, physics, and other sciences.

50
Q

JEE Main Question
Question: How many grams of O₂ are required to react with 12 g of carbon?

A

Balanced equation:
2C+O2→CO2 Moles of carbon = 12/12 =1mol.
1 mole of O₂ (32 g) reacts with 1 mole of C, so 32 g of O₂ is required.

51
Q

What is the difference between atomic mass and molecular mass?

A

Atomic mass: The mass of a single atom, measured in atomic mass units (amu).
Molecular mass: The sum of the atomic masses of all atoms in a molecule

52
Q

Write the balanced equation for the combustion of methane.

A

CH 4 +2O2 →CO2+2H2
Explanation: In the combustion of methane, methane reacts with oxygen to produce carbon dioxide and water.

53
Q

NEET Question
Question: If 0.5 mol of oxygen gas (O₂) is at STP, what is the volume occupied by the gas?

A

At STP, 1 mole of gas = 22.7 L.
0.5 mol of O₂ will occupy:
0.5×22.7=11.35L

54
Q

What is meant by molarity?

A

Molarity is the number of moles of solute per liter of solution, expressed as mol/L or M.

55
Q

What is the Law of Multiple Proportions?

A

When two elements combine to form more than one compound, the ratios of the masses of one element that combine with a fixed mass of the other element are simple whole numbers.
Example: Carbon monoxide (CO) and carbon dioxide (CO₂) both contain carbon and oxygen in different mass ratios.

56
Q

What is the SI unit of amount of substance?

A

The SI unit of amount of substance is the mole (mol).

57
Q

Define molar mass.

A

Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol).

58
Q

What is the difference between empirical and molecular formulas?

A

Empirical formula: Shows the simplest ratio of elements in a compound.
Molecular formula: Shows the actual number of atoms of each element in a molecule.

59
Q

What is the significance of the molecular formula?

A

The molecular formula shows the exact number of atoms of each element in a molecule and helps to understand the compound’s chemical properties.

60
Q

JEE Main/NEET Question
Question: The molar mass of water (H₂O) is 18 g/mol. How many molecules of water are present in 36 g of water?

A

The number of moles in 36 g of water =
36g/18g/mol=2moles
Since 1 mole contains
6.022×10^23molecule the total number of water molecules = 2×6.022×10^23=1.204×10^24 molecules

61
Q

NEET Question
Question: How many moles of Cl₂ gas are present in 71 g of Cl₂?

A

Molar mass of Cl₂ = 71 g/mol. Number of moles = 71/71=1mol.

62
Q

Question: What is Dalton’s atomic theory?

A

Dalton’s atomic theory includes the following postulates:

All matter is composed of indivisible atoms.
Atoms of a given element are identical in mass and properties.
Atoms combine in simple whole-number ratios to form compounds.
Atoms cannot be created or destroyed in chemical reactions.
Explanation: This theory laid the foundation for modern chemistry and explained laws such as conservation of mass and constant proportions.

63
Q

What are valence electrons?

A

Valence electrons are the outermost electrons of an atom that are involved in chemical bonding.

64
Q

How do you calculate molar mass?

A

The molar mass is the mass of one mole of a substance. It is calculated by adding the atomic masses of all atoms in a molecule.
Example: Molar mass of H₂O = 2×1+16=18g/mol.

65
Q

JEE Advanced Question
Question: Calculate the mass of 0.2 moles of NaCl.

A

Molar mass of NaCl = 58.5 g/mol.
Mass = 0.2×58.5=11.7g.

66
Q

Question: Define stoichiometry and its significance.

A

Stoichiometry is the branch of chemistry that deals with the quantitative relationships among reactants and products in chemical reactions.
Explanation: It helps in determining the correct proportions of reactants to use in order to avoid excess waste in industrial and laboratory chemical reactions.

67
Q

What is the significance of Avogadro’s constant?

A

Avogadro’s constant is 6.022×10^23 , representing the number of particles (atoms, molecules, ions) in one mole of any substance.
Explanation: It helps relate the amount of substance in moles to the actual number of atoms or molecules, making it essential for stoichiometry calculations.

68
Q

What is the Mole Concept?

A

The mole is a unit that represents a collection of 6.022×10 ^23
atoms, molecules, or particles of a substance.
Explanation: It helps in relating the mass of a substance to the number of particles it contains.

69
Q

Concept: Atomic Mass Unit
Question: What is the value of one atomic mass unit (amu) in grams?

A

Answer: 1 amu =
1.660539×10
^(−24)
grams.

70
Q

Concept: Mole Concept
Question: How many particles are there in 1 mole of any substance?

A

Answer:
6.022×10
^23
particles (Avogadro’s number).

71
Q

Concept: Mole Concept
Question: How many particles are there in 1 mole of any substance?

A

Answer:
6.022×10
^23
particles (Avogadro’s number)

72
Q

JEE Mains PYQ: Atomic Mass
Question: Calculate the molar mass of water (H₂O).

A

Answer: Molar mass of water = 18.02 g/mol

73
Q

NEET PYQ: Mole Concept
Question: How many molecules are present in 0.1 mole of oxygen gas (O₂)?

A

Answer:
6.022×10
^22
molecules

74
Q

Concept: Law of Conservation of Mass
Question: State the law of conservation of mass.

A

Answer: Mass is neither created nor destroyed in a chemical reaction

75
Q

KCET PYQ: Avogadro’s Law
Question: How many moles are in 4.22 × 10²³ molecules of nitrogen gas?

A

Answer: 0.70 moles.

76
Q

NIOS Question: Empirical Formula
Question: How do you determine the empirical formula of a compound?

A

Answer: By calculating the simplest whole-number ratio of atoms in the compound.

77
Q

Concept: Molecular Mass
Question: How do you calculate the molecular mass of a compound?

A

Answer: Add the atomic masses of all the atoms in the molecule

78
Q

CBSE Board Question: Significant Figures
Question: How many significant figures are in the measurement 0.0450 mL?

A

Answer: Three significant figures

79
Q

JEE Mains PYQ: Stoichiometry
Question: What is the stoichiometric coefficient for oxygen in the balanced reaction of methane combustion?

A

Answer: The stoichiometric coefficient for O₂ is 2

80
Q

Concept: Limiting Reagent
Question: How is the limiting reagent determined in a chemical reaction?

A

Answer: The reactant that is completely consumed and limits the formation of products

81
Q

NEET PYQ: Percentage Composition
Question: Calculate the percentage composition of hydrogen in water (H₂O

A

Answer: Hydrogen’s percentage in H₂O is 11.19%

82
Q

KCET PYQ: Atomic Mass Calculation
Question: What is the atomic mass of oxygen (O-16)

A

Answer: 16 amu

83
Q

NIOS Board Question: Empirical vs. Molecular Formula
Question: What is the difference between empirical and molecular formulas?

A

Answer: The empirical formula shows the simplest ratio of atoms, while the molecular formula shows the actual number of atoms

84
Q

Concept: Avogadro’s Constant
Question: What is Avogadro’s constant, and why is it important?

A

Answer: Avogadro’s constant is
6.022×10
^23 mol⁻¹, representing the number of particles in one mole

85
Q

JEE Mains PYQ: Molar Mass
Question: Calculate the molar mass of glucose (C₆H₁₂O₆).

A

Answer: Molar mass of glucose = 180.16 g/mol

86
Q

CBSE Board Question: Stoichiometric Calculations
Question: How many grams of CO₂ are produced from the complete combustion of 16 g of CH₄?

A

Answer: 44 g of CO₂

87
Q

Concept: Atomic, Molecular, and Formula Masses
Question: Define atomic mass, molecular mass, and formula mass.

A

Answer: Atomic mass refers to the mass of an atom, molecular mass is the sum of atomic masses in a molecule, and formula mass applies to ionic compounds

88
Q

NEET PYQ: Molar Volume of Gases
Question: What is the molar volume of an ideal gas at STP?

A

Answer: 22.4 L/mol at STP.

89
Q
A
90
Q
A

chemistry (1 decks)

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