Lavoisier’s Law (Conservation of Mass): In a chemical reaction, total mass of reactants = total mass of products. No net gain or loss of matter.

Proust’s Law (Constant Proportion): A pure compound always contains the same elements in the same fixed mass ratio (e.g., water H:O = \(1:8\)).

Chemical Symbols: IUPAC symbols—first letter capital, second (if any) small (Na, Cl, Fe, Hg, etc.).

Atomic Mass Unit: Unified atomic mass unit \(1\ \text{u}=1.66053904\times10^{-27}\ \text{kg}\). Carbon-12 scale: \(^{12}C=12\ \text{u}\).

Molecular Mass: Sum of atomic masses in the molecule. Example (via MathJax): \(M(H_2O)=2(1)+16=18\ \text{u}\).

Mole Concept: \(1\ \text{mol}\) contains \(N_A=6.022\times 10^{23}\) entities. \(n=\dfrac{m}{M}\), molecules \(=nN_A\).

Valency (electronic view): Number of electrons lost/gained/shared to achieve octet/duet. Na (2,8,1) → valency 1; O (2,6) → valency 2.

Radicals: Basic (cations, e.g., \(Na^+, NH_4^+\)) and acidic (anions, e.g., \(Cl^-, SO_4^{2-}\)). Charge magnitude = valency.

Writing Ionic Formulae: Write cation left, anion right, cross-multiply valencies → subscripts; reduce to simplest whole numbers (e.g., \(Na^+\) & \(SO_4^{2-}\) → \(Na_2SO_4\)).

1) Unit of atomic mass?

Unified atomic mass unit, Dalton (u).

2) Value of Avogadro’s number?

\(\displaystyle N_A=6.022\times10^{23}\ \text{mol}^{-1}\).

3) Mass of 1 mole of water?

\(18\ \text{g}\) (\(M=18\ \text{u}\)).

4) Molecules in 1 mole of any gas?

\(\displaystyle 6.022\times10^{23}\) molecules.

5) Law relating mass of reactants & products?

Law of conservation of mass (Lavoisier).

6) Law about fixed mass ratio in a compound?

Law of constant proportion (Proust).

7) Symbol of sodium & its common ion?

Na; ion \(Na^+\).

8) Charge on sulphate radical?

\(-2\) on \(SO_4^{2-}\).

9) What is valency of Mg?

2 (gives \(Mg^{2+}\)).

10) Formula of calcium hydroxide?

\(\mathrm{Ca(OH)_2}\).

11) Molecular mass of \(CO_2\)?

\(12+2\times16=44\ \text{u}\).

12) Name of \(NH_4^+\)?

Ammonium (basic radical).

13) Name of \(NO_3^-\)?

Nitrate (acidic radical).

14) Ion with variable valency of iron?

\(\mathrm{Fe^{2+}}\) (ferrous) & \(\mathrm{Fe^{3+}}\) (ferric).

15) Define mole in one line.

Amount containing Avogadro’s number of entities.

16) Unit of amount of substance?

mole (mol).

17) Composite radical example.

\(SO_4^{2-}, CO_3^{2-}, NH_4^+\).

18) Simple radical example.

\(Na^+, Cl^-, O^{2-}\).

19) Formula of sodium carbonate.

\(\mathrm{Na_2CO_3}\).

20) Define ‘u’ in words.

\(1\ \text{u}\) is \(1/12\) the mass of a carbon-12 atom.

1) State conservation of mass with an example.

Mass is conserved; e.g., \(CaO+H_2O\to Ca(OH)_2\): total mass same before/after.

2) Why does water always show H:O = 1:8 by mass?

Fixed composition; \(M(H_2O)=2(1)+16\Rightarrow\) ratio \(2:16=1:8\).

3) Write \(n=\dfrac{m}{M}\) and meaning of symbols.

\(n\) moles, \(m\) mass (g), \(M\) molar mass (g/mol).

4) Give symbols: antimony, iron, gold, silver, mercury, lead, sodium.

Sb, Fe, Au, Ag, Hg, Pb, Na.

5) What is variable valency? Example.

Element shows more than one valency: Fe(II), Fe(III).

6) Molecules in 36 g water.

\(n=36/18=2\) mol ⇒ \(2N_A\) molecules.

7) Define radical.

Charged atom/group acting as a single ion (\(Na^+\), \(SO_4^{2-}\)).

8) Name two acidic radicals.

Chloride \(Cl^-\), sulphate \(SO_4^{2-}\).

9) Name two basic radicals.

Sodium \(Na^+\), ammonium \(NH_4^+\).

10) What are nucleons?

Protons + neutrons in nucleus.

11) Which is heavier: proton or electron?

Proton is much heavier than electron.

12) Define atomic number in words.

Number of protons in nucleus (=\# electrons in neutral atom).

13) Give formula of aluminium hydroxide.

\(\mathrm{Al(OH)_3}\).

14) Give formula of ferric phosphate.

\(\mathrm{FePO_4}\).

15) What is the charge on phosphate?

\(-3\) on \(PO_4^{3-}\).

16) What is meant by monoatomic and diatomic molecule?

Single-atom molecule (He), two-atom molecule (O\(_2\)).

17) Molecular mass of \(NaOH\)?

\(23+16+1=40\ \text{u}\).

18) Why cross-multiply valencies?

To balance total positive and negative charges to zero.

19) Define ‘chemical formula’ briefly.

Symbolic representation showing element types and simplest whole-number ratio.

20) Write formula of calcium oxide via valencies.

\(Ca^{2+}\) & \(O^{2-}\) → cross → \(CaO\).

1) State and verify law of constant proportion using \(CuO\).

Different \(CuO\) samples give the same mass ratio \(Cu:O\approx4:1\), matching formula \(CuO\) (63.5:16 ≈ 3.97:1).

2) Why was a reference atom needed for atomic masses?

Absolute atomic masses are tiny; relative scale simplifies comparison—now based on \(^{12}C=12\ \text{u}\).

3) Define molecular mass with two examples.

Sum of atomic masses: \(H_2SO_4=2(1)+32+4(16)=98\ \text{u}\); \(NaCl=23+35.5=58.5\ \text{u}\).

4) Write steps to form \(Na_2SO_4\).

\(Na^+\) (1+), \(SO_4^{2-}\) (2−) → cross valencies → \(Na_2SO_4\); already simplest.

5) Distinguish simple & composite radicals with examples.

Simple: single atom \(Na^+, Cl^-\). Composite: group \(NH_4^+, CO_3^{2-}\).

6) Define mole and relate to mass and particles.

\(n=m/M\); particles \(=nN_A\). One mole corresponds to molar mass in grams.

7) What is variable valency? Give two elements.

Element shows multiple stable ionic states: Fe(II/III), Cu(I/II), Hg(I/II).

8) Why do ionic names have two words?

First cation, second anion (e.g., sodium chloride); reflects ionic constituents.

9) Compute molecules in 66 g \(CO_2\).

\(n=66/44=1.5\ \text{mol}\Rightarrow 1.5N_A=9.033\times10^{23}\) molecules.

10) Show water ratio \(1:8\) by mass.

\(H_2O\): \(2\times1:16 \Rightarrow 2:16 = 1:8\).

11) Write formula of magnesium oxide by cross method.

\(Mg^{2+}\) and \(O^{2-}\) → \(MgO\).

12) What are nucleons and mass number?

Protons+neutrons; mass number \(A=p+n\).

13) How to deduce formula of aluminium hydroxide?

\(Al^{3+}\), \(OH^-\) → cross \(3:1\) → \(Al(OH)_3\).

14) Give reason: 1 mol of different substances have different masses.

Because molar mass \(M\) differs; mole fixes number of entities, not mass.

15) Define atomic radius in brief.

Distance from nucleus to outermost electron shell (≈ nm scale).

16) Write names for \(FeCl_2\) and \(FeCl_3\).

Iron(II) chloride (ferrous); Iron(III) chloride (ferric).

17) Derive formula of calcium phosphate.

\(Ca^{2+}\), \(PO_4^{3-}\) → cross → \(Ca_3(PO_4)_2\) (simplest 3:2).

18) Why does \(Na\) show valency 1?

Configuration (2,8,1): loses one electron to achieve octet → \(Na^+\).

19) Why are fractional atomic masses seen?

Because masses are relative to \(^{12}C\) and reflect isotopic averages.

20) Write the steps to compute molecular mass of \(KNO_3\).

Add atomic masses: \(39+14+3\times16=101\ \text{u}\).

a) Positive radicals

\(Na^+, K^+, Ca^{2+}, NH_4^+, Cu^{2+}\).

b) Basic radicals

Same as positive radicals (cations): \(Na^+, NH_4^+, Mg^{2+}, Al^{3+}\).

c) Composite radicals

\(SO_4^{2-}, CO_3^{2-}, NO_3^{-}, NH_4^+\).

d) Metals with variable valency

Fe(II/III), Cu(I/II), Hg(I/II), Sn(II/IV).

e) Bivalent acidic radicals

\(SO_4^{2-}, CO_3^{2-}, SO_3^{2-}, CrO_4^{2-}, Cr_2O_7^{2-}\).

f) Trivalent basic radicals

\(Al^{3+}, Fe^{3+}, Cr^{3+}\).

Elements: Mercury, Potassium, Nitrogen, Copper, Sulphur, Carbon, Chlorine, Oxygen

Mercury: Hg → \(Hg^+\), \(Hg^{2+}\).
Potassium: K → \(K^+\).
Nitrogen: N → \(N^{3-}\) (nitride).
Copper: Cu → \(Cu^+\), \(Cu^{2+}\).
Sulphur: S → \(S^{2-}\) (sulphide).
Carbon: C → \(C^{4-}\) (carbide; rare), common composite \(CO_3^{2-}\).
Chlorine: Cl → \(Cl^-\).
Oxygen: O → \(O^{2-}\) (oxide).

Sodium sulphate (\(Na^+, SO_4^{2-}\))

Cross valencies \(1 \leftrightarrow 2\) → \(Na_2SO_4\).

Potassium nitrate (\(K^+, NO_3^-\))

Valencies 1 & 1 → \(KNO_3\).

Ferric phosphate (\(Fe^{3+}, PO_4^{3-}\))

3 & 3 → \(FePO_4\).

Calcium oxide (\(Ca^{2+}, O^{2-}\))

2 & 2 → simplify to \(CaO\).

Aluminium hydroxide (\(Al^{3+}, OH^-\))

3 & 1 → \(Al(OH)_3\).

a) Explain how sodium is monovalent.

Na has (2,8,1); loses one electron to form \(Na^+\) → valency 1.

b) M is bivalent. Write steps to get formulae with sulphate and phosphate.

With \(SO_4^{2-}\): \(M^{2+}\) & \(SO_4^{2-}\) → \(MSO_4\).
With \(PO_4^{3-}\): Cross \(2\) & \(3\) → \(M_3(PO_4)_2\).

c) Need for a reference atom; two reference atoms.

Atomic masses are tiny; relative scale needed. Early: H = 1; modern: \(^{12}C=12\ \text{u}\).

d) What is Unified Atomic Mass?

Unit of atomic mass (u): \(1\ \text{u}=1/12\) of mass of a \(^{12}C\) atom.

e) Explain ‘mole’ with examples.

Amount containing \(N_A\) entities; \(18\ \text{g}\ H_2O=1\ \text{mol}\), \(44\ \text{g}\ CO_2=1\ \text{mol}\).

Name and compute molecular mass for: \(Na_2SO_4, K_2CO_3, CO_2, MgCl_2, NaOH, AlPO_4, NaHCO_3\).

\(Na_2SO_4\) (Sodium sulphate): \(2\times23+32+4\times16=142\ \text{u}\).
\(K_2CO_3\) (Potassium carbonate): \(2\times39+12+3\times16=138\ \text{u}\).
\(CO_2\) (Carbon dioxide): \(12+2\times16=44\ \text{u}\).
\(MgCl_2\) (Magnesium chloride): \(24+2\times35.5=95\ \text{u}\).
\(NaOH\) (Sodium hydroxide): \(23+16+1=40\ \text{u}\).
\(AlPO_4\) (Aluminium phosphate): \(27+31+4\times16=122\ \text{u}\).
\(NaHCO_3\) (Sodium bicarbonate): \(23+1+12+3\times16=84\ \text{u}\).

Which law is proved by given data and how?

Law of constant proportion. For m: \(Ca:O=5:2=2.5\). For n: \(1.0:0.4=2.5\). Same fixed mass ratio in both samples ⇒ constant composition of the compound.

Find molecules in: 32 g \(O_2\); 90 g water; 8.8 g \(CO_2\); 7.1 g chlorine (\(Cl_2\)).

\(O_2\): \(M=32\Rightarrow n=32/32=1\) ⇒ molecules \(=N_A\).
\(H_2O\): \(M=18\Rightarrow n=90/18=5\) ⇒ molecules \(=5N_A\).
\(CO_2\): \(M=44\Rightarrow n=8.8/44=0.2\) ⇒ molecules \(=0.2N_A=1.2044\times10^{23}\).
\(Cl_2\): \(M\approx71\Rightarrow n=7.1/71=0.1\) ⇒ molecules \(=0.1N_A=6.022\times10^{22}\).

If \(0.2\ \text{mol}\) is required, how many grams of each?

\(NaCl\) (\(M=58.5\)): \(m=nM=0.2\times58.5=11.7\ \text{g}\).
\(MgO\) (\(M=24+16=40\)): \(m=0.2\times40=8\ \text{g}\).
\(CaCO_3\) (\(M=40+12+48=100\)): \(m=0.2\times100=20\ \text{g}\).

Compute molecular mass of \(HNO_3\) and \(Ca(OH)_2\).

\(HNO_3: 1+14+3\times16=63\ \text{u}\).
\(Ca(OH)_2: 40+2(16+1)=74\ \text{u}\).

Molecules in \(36\ \text{g}\) water (show steps).

\(\displaystyle n=\frac{m}{M}=\frac{36}{18}=2\ \text{mol};\quad N=2N_A=1.2044\times10^{24}\ \text{molecules}.\)