Chemical reactions in aqueous solution Fundamentals of Chemistry Dr HNIMIR Chemical reactions in aqueous solution

Solution terminology Solubility: the amount of solute required to give a saturated solution. Saturated solution: a solution that contains as much dissolved solute as it can hold while in contact with undissolved solute. E.g.: sugar has a solubility of 211g per 100ml of water at 25 ºC. A solution containing 215g of sugar is: concentrated, dilute, unsaturated, Supersaturated Or saturated. Dissociation: the separation of the ions of the compound as it dissolves. Unsaturated solution: A solution that is capable of dissolving more solute. Supersaturated solution: a solution in which there is more dissolved solute than could normally exist when in contact with excess solute. Electrolyte: A substance that give ions in an aqueous solution and that conduct electricity.

Reactions between ions Double replacement (metathesis): these are ionic reactions between two salts in which the positive ions and negative ions exchange partners. e.g. reaction between sodium sulfate and barium nitrate. Write the ionic and net ionic equations for the following reactions: 1. NaI+AgNO3→AgI +NaNO3 2. lead nitrate + barium hydroxide → lead hydroxide + barium nitrate. page87

Acid-base reactions Acids and bases have certain characteristic properties, two of which are: Acids taste sour; bases taste bitter. Acids and bases affect the colors of indicators such as litmus and phenolphthalein. Definitions: Arrehenius definition: Acids produce H3O+ when dissolved in water; Bases produce OH- when dissolved in water. Lowry-Bronested definition: acids are proton donor and bases are proton acceptors. Lewis definition: acids are electron acceptor [electron deficient centers] , while bases are electron donors[electron rich centers].

solutions also called alkaline solution . Weak bases Strong acids dissociate fully into ions in their solutions e.g. HCl, H2SO4, HNO3. Weak acids dissociates partially in solution e.g organic acids, CH3COOH Metal oxides are known as acid anhydride. They give acid when react with water. CO2 + H2O → H2CO3 Bases includes: hydroxides of the S-block elements e.g. NaOH, KOH, Ca(OH)2 their solutions also called alkaline solution . Weak bases Like Na2CO3, NH4OH. Metal oxides are known as basic anhydrides. When react with water they give metal hydroxides, because of the reaction: O2- + H2O → 2OH- Acids and bases react with each other to produce a salt and water. Salt is a general term That is used to refer to any ionic compound except metal oxides and hydroxides(bases) Tutorial: Write the chemical equation for the reaction of each of the following with water: HBr, H2SO4, N2H4, and the oxide ion O2-. 2. Identify the following as acidic or basic anhydrides? CaO, SO2, CO2, Li2O, N2O3, P4O6. 3. Write a chemical equation of the reaction for following oxides with water? SO3, P4O10, BaO, N2O3. 4. What is the net ionic equation for the neutralization reaction between a strong acid and strong soluble base in aqueous solution? H+ + OH- → H2O 5. Write formulas for salts formed between Ca(OH)2 and each of the following: H2C2O4, H2CO3, H3AsO4, HBr.

Concentration of solution New Terms: Precipitate: a solid that is formed in a solution, usually as the result of a chemical reaction. E. g. Solute: a substance dissolved in a solvent. Solvent: generally, the substance in a solution that is present in largest amount. If one substance is a liquid, it is normally considered to be the solvent. When water is present, it is taken to be the solvent. Concentrated solution: a solution contains a large proportion of solute to solvent ratio. Dilute: very little solute dissolved in a solution. A low ratio of solute to solvent. Concentration: a quantitative statement of the proportion of solute to solvent, or of solute to the total amount of solution. Molar concentration(Molarity): a ratio of moles of solute to liters of solution. It is the number of moles per liter of solution.

The concentration of a solution(see part1) could be expressed in many different ways: Molarity, M, normality N, (pph) or percent concentration %w/w, %w/v, %v/v, mg%, ppm, ppb …etc The proportions of solute and solvent are specified by giving the solution’s Concentration. Molar concentration, or molarity, is a convenient concentration unit for measuring small amounts of solute that are dissolved in a solution. Molarity = moles of solute/liter of solution A label such as 2.50M sulfuric acid could be translated into the following factors: 2.50mol H2SO4/1.00 L solution or 1.00L solution/2.50mol H2SO4 Tutorials 1. What is the molarity of the following solutions: 0.350 mol sodium hydrogen carbonate in 0.400 L of solution. 0.250mol KCl in 200 ml of solution. 15.6g of magnesium chloride in 300ml of solution. 1.85g of silver nitrate in 75 ml of solution

2. How many moles of calcium chloride are in? 1.15L of 0.840M calcium chloride solution? 325ml of 0.150M calcium chloride solution? 3. What volume in ml of 3M ammonia solution contains 1.35mol of NH3? 21.4g of NH3? 4. How many grams of potassium nitrate are needed to prepare 750ml of 0.200M KNO3 solution? 5. How much water must be added to 50ml of 1M sodium hydroxide to prepare 0.100M NaOH?

The stoichiometry of reactions in solution: Here amounts of reactants or products is specified as volumes of solutions Of known concentration (in molarity). See some relations and memorize them Consider the following reaction that takes place in solution: calcium chloride + silver nitrate → calcium nitrate + silver chloride Suppose that we began with 200ml 0f a 0.200M solution of CaCl2. How many moles of CaCl2 are in this solution? 0.04 mol How many moles of AgNO3 would be required to react completely with this amount of CaCl2?0.08 mol How many milliliters of 0.500M AgNO3 solution would be needed to contain this number of moles of AgNO3? 160ml 2. Consider the reaction described above. Suppose that 200ml of 0.15M CaCl2 Solution are mixed with 180 ml of 0.220M AgNO3 solution? How many moles of CaCl2 are in the first solution?0.030 mol How many moles of AgNO3 are in the second solution?0.0396mol When the solutions are mixed, which is the limiting reactant? AgNO3 limiting reactant; How many moles of AgCl are formed in the reaction? 0.0396mol

e. How many moles of the reactant in excess are left over after the reaction Has stopped? 0.0102 mol of CaCl2 left over. f. What is the molar concentration of the excess reactant in the reaction mixture after the reaction has stopped? 0.0268M CaCl2

Percentage composition Is the percentages by mass (weight) of the elements in a compound. The weight percent: The weight percent of an element in a compound is calculated by dividing the mass Of the element in the compound by the molecular (Mr) and then multiplying by 100. e.g. the percentage of Cl in CCl4 % Cl = total mass of Cl in CCl4/Mr CCl4X100 = (4X35.5)/(12+4X35.5)X100 = 142/154X100 = 92.2% Calculations of the mass of an element in a given mass of its compound: Suppose we wish to calculate the mass of Cl in 85g of CCl4? The first step is to calculate Mr of CCl4 4 Cl 4X35.5 = 142 1C 1X12.0 = 12 Mr = 154 Wt of Cl in 85.0 g CCl4 = 85gX142gCl/154gCCl4 = 78.4 g Cl

H.W: 1. Calculate the percentage compositions of each of the following NaNO3. Answer[27.1% Na, 16.5%N, 56.5%O] Ca(HCO3)2. Answer[24.7% Ca, 1.24%H, 14.8%C, 59.2%O] NiCl2. Answer [ 45.3%Ni, 54.7%Cl] 2. Calculate the mass of Ag in 22.0g of AgCl? Answer 16.6g of Ag. 3. Calculate the mass of sulfate in, SO4. in 12.3g of BaSO4? Ans. 5.06g SO4. 4. In a chemical analysis a 3.14g sample known to contain a mixture of CuSO4 And CuCl2 was dissolved in water and treated with Ba(NO3)2. solid BaSO4 was Formed, which was filtered from the solution, dried and weighed. The BaSO4 weighed 2.58g. What mass of SO4 was in the BaSO4? Ans. 1.06g SO4. What was the weight percent SO4 in the original sample? Ans. 33.8%

Redox reactions in solution; balancing equation by the ion-electron method Divide the reaction into two half-reactions. Balance atoms other than H and O. Balance O and H (O first then H) using H2O and H+, respectively. Determine the net charge on both sides of each half-reaction. For each half-reaction, add electrons to the more positive (least negative) side to make the net charge on both sides of the arrow the same. Multiply the half-reactions by appropriate factors to make the electron gain equal the electron loss. Add the half-reactions. Cancel anything that appears the same on both sides of the equation. Common oxidizing and reducing agents: Oxidizing agents: potassium permanganate KMnO4. the permanganate ion MnO4-,is purple in solution. In acidic solution it is reduced to the nearly colourless Mn2+ ion. In basic or neutral solutions the dark-brown precipitate MnO2 is formed.

Chromate ion, CrO4(2-), and the dichromate ion Cr2O7(2-), usually as their sodium or potassium salts. The ions can be converted from one to the other by changing the pH of the solution. In acidic solution, the oxidizing agent is Cr2O7(2-), ; in basic Solution it is CrO4(2-), . Both ions contain Cr(VI). The products of the reduction depend On the acidity of the reaction mixture. In acidic solution, the product is Cr(III)[green]; in Slightly basic solution, the product is insoluble Cr(OH)3 [green precipitate]; in strongly Basic solution the product is CrO2(-) 2. Reducing agent: metals are strong reducing agents. Sulfite and bisulfite salts. The actual reactant in solution depends on the pH. If the strongly acidic, he active reducing agent is H2SO3; if slightly acidic, HSO3- is the Reducing agent; if basic, SO3(2-) is the reducing agent. The product of oxidation is sulfate ion SO4(2-). thiosulfate ion, usually as Na2S2O3. when reacted with strong oxidizing agents it produce, sulfate ion and yellow precipitate of S. reaction of Iodine with S2O3(2-) give tetrathionate ion, S4O6(2-) H.W: Balance he following by the ion-electron method. [All reactions in acidic solution] HNO2 + I- → I2 + NO ClO3(- )+H2S → Cl- + S S2O8(2-) + P → SO4(2-) + H3PO4