# WBBSE Class 10 Physical Science Notes Chapter 3 Chemical Calculations

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 3 Chemical Calculations can help students make connections between concepts.

## Chemical Calculations Class 10 WBBSE Notes

Accuracy: It refers to how close a measurement is to the true value.

Precision : It refers to how close one measurement is to another.

Scientific notation: The measurements of quantities in chemistry are spread over a wide range of 10-31 to 10+23. Hence, a convenient system of expressing the numbers in scientific notation is used.

Types of chemical reactions:

• Combination: e.g. Fe + S → FeS
• Decomposition: e.g. 2 KClO3 → 2 KCl + 3 O2
• Double Decomposition: e.g. AgNO3 + NaCl → AgCl + NaNO3
• Rearrangement or Isomerisation: e.g NH4 CNO → NH2 CONH2 (Urea)
• Displacement: e.g. Zn + CuSO4 → ZnSO4 + Cu
• Polymerisation: e.g. n(CH2 = CH2) →(-CH2-CH2-)n
• Neutralisation: e.g. HCl(aq) + NaOH(aq) → NaCl(aq) + H2 O
• Redox Reactions : e.g. H2 S + Br2 → 2 HBr + S
• Catalytic Reactions: e.g. N2 + 3 H2 $$\stackrel{\mathrm{Fe} / \mathrm{Mo}}{\rightleftharpoons}$$ = 2 NH3
• Plastic catalytic Reactions: Which require light as well as a catalyst to take place e.g. manufacture of starch and sugar by plants from CO2 and H2O in presence of light and chlorophyll (catalyst)

Laws of chemical combination:

• Law of conservation of Mass: (A. Lavoisier, 1774)
• Law of Definite proportions: (Louis Proust, 1799)
• Law of Multiple proportions: (John Dalton, 1804)
• Law of Reciprocal proporticns: (Richter, 1792)
• Gay Lussac’s Law of Gaseous volumes: (Gay Lussac, 1809)
• Dalton’s Atomic Theory: (John Dalton, 1803)

Atomic mass: It is the average relative mass of an atom of an element as compared to the mass of a carbon atom (12c) taken as 12.

Atomic mass unit: It is the quantity of mass equal to $$\frac{1}{12}$$ th of the mass of a carbon atom ( 12C). 1 amu = 1.6605 × 10-24 g

Carbon atomic mass: It is the atomic mass of an element expressed in gram.

Kelation among atomic mass, equivalent weight and valency:

Atomic mass = Equivalent weight × Valency

Avogadro constant: The number of atoms or any other particles present in a given system is expressed in the terms of Avogadro constant. (6.022 × 1023)

Molar volume: The volume of gaseous substance (element or compound) under a fixed temperature and pressure is known as volume of the gas.

Mole (SI system): A mole is the amount of substance which contains as many entities (atoms, molecules, ions or any other particle) as there are atoms in exactly 0.012 Kg (or 12 g) of the carbon -12 isotope.

Empirical formula: It is the formula of a compound which gives the simple whole number of ratio of the atoms of various elements present in one molecule of compound.

Molecular formula; It is the formula of a compound which gives the actual number of atoms of various elements present in one molecule of the compound.

Structural formula: A formula which gives the actual arrangement of the different atoms in the molecule are linked together is called a structural formula of the compound.

Percentage of an element: Percentage of an element in a chemical compound is the number of parts by weight of it present in 100 parts by weight of the compound.

Mass-mass relationship problems: In this type of problems mass of one of the reactants/products is to be calculated if that of the other reactants/products are given.

Limiting reactant: The reactant which is completely used and determines the amount of product formed is known as limiting reactant.

Theoretical yield: The theoretical yield of a product is the maximum yield obtainable as calculated on the basis of the amount of limiting reactant used.

Percent yield: Percent yield which is the ratio of the actual yield to the theoretical yield multiplied by 100.

Stoichiometry: The quantitative study of the reactants required or the products formed is called stoichiometry.

Dulong and Petit’s Law: It states that ‘the product of atomic weight and specific heat of an element is approximately equal to 6.4.

Isomorphism: Substances having same crystalline structure are said to isomorphous. e.g. ZnSO4.7 H2O and FeSO4.7 H2O

Vapour density: It is the ratio of the mass of a certain volume of the gas to the mass of same volume of hydrogen under similar conditions of temperature and pressure.

Relation between molecular weight and vapour density :
Molecular weight = 2 × Vapour density

Relation between empirical formula and molecular formula.
Molecular formula = n × Empirical formula
(n = a simple whole number and
may have values 1,2,3,…)

Equivalent weight: It is the number of parts of a substance which combine with or displace directly or indirectly 1.008 parts by weight of hydrogen or 8 parts by weight of oxygen or 35.5 parts by weight of chlorine.

Atomicity of a gas: It is the number of atoms present in one molecule of a gaseous element.

Solubility: The amount of solute in grams that can be dissolved in 100 grams of a solvent to form a saturated solution at a definite temperature is called the solubility.

Percentage by weight [%(w/w)]: It is the amount of solute in grams present in 100 grams of the solution.

Weight/volume percentage [%(w/v)]: It is the amount of solute in grams present in 100 mL of the solution.

Volume/volume percentage [%(v/v)]: It is the volume in mL of the solute percentage in 100 mL of the solution.

Normality (N): It is the number of gram equivalents of solite dissolved per litre of a solution.

Molarity (M): It is the number of moles of solute dissolved per litre of the solution.

Formality (F): It is the number of gram formula weight of the ionic solute dissolved per litre of the solution.

Molality (m): It is the number of moles of solute dissolved in 1000 g of the solvent.

Mole fraction: It is the ratio of the number of moles of one component to the total number of moles of substances in the solution.

Parts per million (ppm.): It is defined as the number of parts of a component per million parts of the solution.

The following equations are generally used for weight-weight calculation.

2 KClO3 = 2 KCl + 3 O2
Zn + H2 SO4 = ZnSO4 + H2
CaCO3 = CaO + CO2
2 NH4 Cl + CaO = 2 NH3 + CaCl2 + H2O
Mg + H2 SO4 = MgSO4 + H2
CaCO3 + 2 HCl = CaCl2 + H2O + CO2
2 H2 + O2 = 2 H2O