Some basic concepts of chemistry Flashcards
What is the definition of matter?
Matter is anything that has mass and occupies space.
What are the three physical states of matter and how are particles arranged in them?
- Solid - particles are close, strong forces of attraction and no intermolecular spaces
- Liquid - Particles are moderately apart. Forces of attraction weaker than sold, but has more intermolecular space
- Gas - Particles are far apart. They have very little forces of attraction and a large amount of intermolecular space.
How can matter be classified?
Into pure substances (elements and compounds) and mixtures (heterogenous and homogenous)
Differentiate between pure substances and mixtures
Pure substances have a fixed composition and definite properties (e.g., elements like O₂, compounds like H₂O). Mixtures consist of two or more substances physically combined, which can be separated by physical methods (e.g., air, saltwater).
Difference between homogenous mixture and heterogenous mixutre
A homogeneous mixture has uniform composition throughout, while a heterogeneous mixture has a non-uniform composition, with visible different components.
mass?
The mass of a substance is the amount of matter present in it and is constant.
How does weight differ from mass?
Weight is the force exerted by gravity on an object and may vary from one place to another, whereas mass remains constant.
Volume
Volume is the amount of space occupied by a substance, typically measured in cubic meters (m³), cubic centimeters (cm³), or liters (L).
What is density?
Density is mass per unit volume. It is the amount of matter present per unit volume in a substance.
Density = Mass/Volume
Law of conservation of mass
The law of conservation of mass states that mass can neither be created nor destroyed, it can only be transformed from one form to another.
Example: If 10g of hydrogen reacts with 80g of oxygen, the total mass of water formed is 90g.
Law of definite proportions
A given compound always contains a fixed/definite/constant proportion of elements by mass.
Irrespective of the source, a given compound consists of the same elements combined in the same proportions by mass.
Ex: ratio of H2O is always 1:8
Law of multiple proportions
When two elements combine to form more than one compound, the masses of one element, that combine with a fixed mass of the other element are in the ratio of small whole number.
Ex: Water and hydrogen peroxide both use only oxygen and hydrogen.
Number of hydrogen molecules remain same, but oxygen doesn’t. Ratio of mass of oxygen is 1:2 in water to hydrogen peroxide.
Gay Lussacs law of gaseous volume
When gasses combine and are produced, they do so in a simple ratio by volume provided all gasses are of same temperature and pressure.
2H2 + O2 = 2H2O
Two volumes of hydrogen combines with one and only one volume of hydrogen to form two volumes of water
Ratio of hydrogen to oxygen always same = 2:1
Two volume of water formed = 2:1:2
Avogadros law
Equal volume of all gasses at same temp and pressure should contain equal number of molecules
Ex: If 100mL of hydrogen has 10 molecules, 100mL of oxygen, at same temp and pressure, will also have 10 molecules.
Convert 1 angstrom (Å) to meters (m).
1 Å = 10⁻¹⁰ m
Define atomic mass unit (amu) or unified mass (u)
1 amu (u) is 1/12th the mass of a carbon-12 atom
Define a mole and state avogadros number
A mole is the amount of substance that contains 6.022 × 10²³ entities (atoms, molecules, or ions). This is called Avogadro’s number.
Calculate number of molecules in 9g of water
Moles of H₂O = (9g) / (18 g/mol) = 0.5 moles.
Molecules = 0.5 × 6.022 × 10²³ = 3.011 × 10²³ molecules.
what is the mass of one mole of CO2
1 mole CO₂ = (12) + 2(16) = 44 g.
A reaction has 20g of reactants but only 18g of products. Explain the missing mass
The missing 2g could be gas loss (e.g., CO₂, H₂ gas) or experimental errors like spillage or evaporation. The Law of Conservation of Mass still holds true if all mass is accounted for.
What is the gram atomic mass and gram molecular mass?
Gram atomic mass: Atomic mass of an element in grams (e.g., 1 mole of O = 16g).
Gram molecular mass: Molecular mass of a compound in grams (e.g., 1 mole of CO₂ = 44g).
What are ideal gas conditions, and how does Avogadro’s Law apply?
Ideal gases follow PV = nRT at low pressure & high temperature. Avogadro’s Law states that equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
Are there any exceptions to the Law of Definite Proportions? If so, give an example.
Non-stoichiometric compounds, e.g., iron oxides (FeO, Fe₃O₄), where Fe:O ratios vary.
