1. Some basic chemical reactions are given below. IIICALCULATIONS ON REACTIONS (a) Reactive metal + H 2 O (l)  metal hydroxide + H 2 (g) (Metals above Mg in reactivity series (Table 1) react with cold water.)Table 1 (b) Reactive metal + acid  salt + H 2 (g) (Metals above H 2 in reactivity series (Table 1) react with dilute acid.)Table 1 A.Reactions & Equations

(c) Metal hydroxide or metal oxide + acid  salt + H 2 O(l) (e) NH 4 + salt + base    salt + NH 3 (g) + H 2 O(l) (f) Pb(NO 3 ) 2 (aq) + 2 NaCl(aq)  PbCl 2 (s) + 2 NaNO 3 (aq) (Precipitation of insoluble compounds (Table 3).)Table 3 (g) Hydrocarbons like C x H y or C x H y O z + excess O 2 (g)  CO 2 (g) + H 2 O(g)Complete combustion (d) Metal carbonate or metal hydrogencarbonate + acid  salt + CO 2 (g) + H 2 O(l)

(h) Mg(s) + Zn 2+ (aq)  Mg 2+ (aq) + Zn (s) (Displacement reaction (Table 1))Table 1 (i) Cl 2 (aq) + 2I - (aq)  2Cl - (aq) + I 2 (aq) (Displacement reaction (Table 2))Table 2 (j) N 2 (g) + 3H 2 (g)  2NH 3 (g) (Haber Process: reversible reactions)

Reducing power of metal decreases from K Na Ca Mg Al Zn Fe Pb (H 2 ) Cu Ag Au Oxidising power of non-metal decreases from F 2 Cl 2 Br 2 I 2 Table 1 Reactivity of Some Metals Table 2 Reactivity of Some Non-metals

Reducing power of metal decreases from K Na Ca Mg Al Zn Fe Pb (H 2 ) Cu Ag Au Oxidising power of non-metal decreases from F 2 Cl 2 Br 2 I 2 Table 1 Reactivity of Some Metals Table 2 Reactivity of Some Non-metals

1. All Group I metal ions like Na +, K + and all NH 4 + are soluble. 2. All NO 3 -, HCO 3 - and CH 3 COO - are soluble. 3. All Cl - and Br - are soluble except Ag +, Pb All SO 4 2- are soluble except Ba 2+, Pb All CO 3 2-, OH - and O 2- are insoluble except Group I metal ions and NH 4 +. Table 3 Solubility of Some Ionic Compounds in Water Note: Tables 1,2, & 3 are NOT exhaustive; they are just a general guide.

(a) Chemical equations should always be balanced with all state symbols when written. (b) Ionic equations are chemical equations that show only the reacting species. Ions that are not included in a chemical reaction are called ______________. 2. Recap on Equations: spectator ions

Eg 3.1 Write a balanced chemical equation for each of the following reactions. (a) KOH(aq) + H 2 SO 4 (aq)  (b) solid sodium hydrogencarbonate + dil. aq. nitric acid (c) warming a mixture of aq ammonium sulphate and aq sodium hydroxide K 2 SO 4 (aq) + H 2 O(l) NaHCO 3 (s) + HNO 3 (aq)  NaNO 3 (aq) + CO 2 (g) + H 2 O(l) (NH 4 ) 2 SO 4 (aq) + NaOH(aq)  Na 2 SO 4 (aq) + NH 3 (g) + H 2 O(l) 

Eg 3.2 Write a balanced equation (chemical or ionic) for each of the following reactions, if any. (a) Ca(s) + HCl(aq)  (b) aq silver nitrate + aq calcium bromide (c) solid calcium carbonate + aq calcium chloride 2 CaCl 2 (aq) + H 2 (g) Ag + (aq) + Br - (aq)  AgBr(s) no reaction

1. For a reaction 2KOH(aq) + H 2 SO 4 (aq)  K 2 SO 4 (aq) + 2H 2 O(l), it means “2 mol of KOH(aq) reacts with 1 mol of H 2 SO 4 (aq) to give 1 mol of K 2 SO 4 (aq) and 2 mol of H 2 O.” In calculations, it can be simply expressed as Hence, ifno. of mol of H 2 SO 4 reacted = x no. of mol of KOH reacted = no. of mol of K 2 SO 4 formed = 2 mol KOH  1 mol H 2 SO 4 2x x B.Calculations See E.g. (a)–(c)

2. Limiting Reactant: For reactants that are not mixed according to the stoichiometric ratio, the reactant that reacts completely is called the _________________. After the reaction, the other unreacted reactants will be present together with the products of the reaction. limiting reactant See E.g.(a)-(b)

A) CO 2 and H 2 O are the only products provided complete combustion is ensured, i.e. in the presence of large excess of oxygen. B) H 2 O formed immediately after combustion exists as water vapour H 2 O(g). When the mixture is cooled and all volumes are measured at room temperature, H 2 O will condense as liquid H 2 O(l) which occupies negligible (very small) volume compared to the volume of vapour. 3. For combustion problems, note the following points: (E.g. (a) & (b))

D) If insufficient base is used, NaHCO 3 (aq) may be formed and not all CO 2 (g) will be absorbed. NaOH(aq) + CO 2 (g)  NaHCO 3 (aq) E) Note that “100 cm 3 decreases by 30 cm 3 ” is equivalent to “100 cm 3 decreases to 70 cm 3 ”. C) Since CO 2 is acidic, volume of the gaseous products will decrease when a base like NaOH(aq), KOH(aq) is added. Hence, all CO 2 is absorbed only if excess base is used. 2NaOH(aq) + CO 2 (g)  Na 2 CO 3 (aq) + H 2 O(l)

E.g. (a) 6NaOH(aq) + 3Cl 2 (g)  NaClO 3 (aq) + 5NaCl(aq) + 3H 2 O(l) 65.0 g of NaOH is reacted completely in the above reaction, cal. the (a) mass of NaClO 3 produced, (b) volume (measured at r.t.p.) of Cl 2 reacted.

E.g. (b) A sample containing silver has a mass of 1.40 g. When it dissolved in conc. nitric acid, all the Ag in the sample was converted to Ag + ions. Excess dil. HCl(aq) was then added, & g of precipitate were obtained. Calculate the % by mass of silver in the sample. State the assumption(s) in your calculations.

E.g. (c) When g of a metal hydride MH(s) reacted with excess water, the products were the metal hydroxide and hydrogen gas. The vol. of gas evolved at s.t.p. was 56.0 cm 3. Calculate the A r of the metal M.

E.g. (a) Mg(s) + 2AgNO 3 (aq)  Mg(NO 3 ) 2 (aq) + 2Ag(s) When 4.56 g of magnesium ribbon is added to 150 cm 3 of mol dm -3 silver nitrate, what is the mass of Ag obtained?

E.g. (b) 4NH 3 (g) + 5O 2 (g)  4NO(g) + 6H 2 O(g) When 12 dm 3 of NH 3 (g) and 15 dm 3 of O 2 are mixed, calculate the total vol. of the mixture after reaction at r.t.p.

E.g. (a) 10 cm 3 of a hydrocarbon, C x H y, were exploded with 100 cm 3 of oxygen. The total vol. after the explosion was 75.0 cm 3, which decreased to 25.0 cm 3 on shaking with excess sodium hydroxide solution. All volumes were measured at r.t.p. Calculate the molecular formula of the hydrocarbon. (i) Write a balanced equation for the combustion. (ii) Explain, with aid of balanced equation, the decrease in volume after treatment with NaOH(aq).

(iii) Deduce the molecular formula of the hydrocarbon.

E.g. (b) 10.0 cm 3 of a hydrocarbon, C a H b, were exploded with an excess of oxygen. A contraction of 25.0 cm 3 occurred. On treating the resulting mixture with excess aq. NaOH, a further contraction of 40.0 cm 3 occurred. All vol. were measured at r.t.p. (i) Why was excess oxygen required?

(ii) Deduce the molecular formula of the hydrocarbon. Before explosion After explosion vol. contracted by 25.0 cm 3 After passing through NaOH, contracted by 40.0 cm cm 3 of C a H b (V +x) cm 3 of O 2 V - Excess O 2 (g) x - O 2 (g) reacted. V cm 3 of O 2 CO 2 (g) produced, V cm 3 of O 2