1) REACTIONs: a) Al4C3(s) + H2O (l)=> Al(OH)3 (s) + CH4 (g) Solution : Al4C3(s) + 12 H2O (l)=> 4Al(OH)3 (s) + 3CH4 (g)

Size: px

Start display at page:

Download "1) REACTIONs: a) Al4C3(s) + H2O (l)=> Al(OH)3 (s) + CH4 (g) Solution : Al4C3(s) + 12 H2O (l)=> 4Al(OH)3 (s) + 3CH4 (g)"

Valentine Fisher
5 years ago
Views:

1 1) REACTIONs: a) Al4C3(s) + H2O (l)=> Al(OH)3 (s) + CH4 (g) Balance the reaction. Describe the chemical process represented by this reaction. Write the name of each single reactant and product. First, the oxidation number of each atom have to be calculated and check if any of them changed. None of the oxidation numbers changes. It is not a redox reaction. The aluminium carbide reacts with water to form the aluminium hydroxide and methane. Then we can balance by an intuitive method. It is an heterogeneous phase reaction, as the carbide is a solid, the aluminium hydroxide is not soluble in water and methane is gaseous then it evolves as formed. Al 4 C 3 (s) + 12 H 2 O (l)=> 4Al(OH) 3 (s) + 3CH 4 (g) Al 4 C 3 = aluminium carbide H 2 O = hydrogen oxide Al(OH) 3 = aluminium hydroxide CH 4 = methane. b) CaO(s) + NH4Cl(s) NH3(g) + H2O(g) + CaCl2 (s) Balance the reaction, describe which type of reaction is. First, the oxidation number of each atom have to be calculated and check if any of them changed. None of the oxidation numbers changes. CaO is a basic oxide as well as NH 4 + is the protonated ammonia, then it can deliver H + as an acid, then this reaction might be an acid base reaction. It occurs in heterogeneous phases, mostly in the solid phase with the formation of two gases, NH 3 and water. We can assume that high temperature can be reached as the water is a gas and not a liquid as normally is. We can suppose that the reaction is exothermic. We can observe that the balancing is through an intuitive method. CaO(s) + 2NH 4 Cl(s) 2NH 3 (g) + H 2 O(g) + CaCl 2 (s)

2 c) Na2SO4 (aq) + BaCl2 (aq) => BaSO4(s) + NaCl(aq) Balance the reaction. Describe to which class of compounds (oxide, hydride, acid, base, salt) the reactants and the products belong. Write the ionic and net ionic equation. First, the oxidation number of each atom have to be calculated and check if any of them changed. None of the oxidation numbers changes. It is a double exchange reaction where the driving force is the formation of an insoluble product as the BaSO 4. Checking the table of the solubility (if it is available) we observe that the sulfate salts of earth alkaline metals are always insoluble. The balancing is based on the intuitive method. Na 2 SO 4 (aq) + BaCl 2 (aq) => BaSO 4 (s) + 2NaCl(aq) Describe to which class of compounds (oxide, hydride, acid, base, salt) the reactants and the products belong Na 2 SO 4 = sodium sulfate (salt) BaCl 2 = barium chloride (salt) BaSO 4 = barium sulfate (salt) NaCl= sodium chloride (salt) d) Depict with a x, which one of the following reactions occurs as they are written or they do not occur: Zn + 2HCl => ZnCl2 + H2 2Na + 2H2O = 2NaOH + H2 2Au + 6HNO3 => 2Au(NO3)3 + 3H2 Ni + 2H2O => Ni(OH)2 + H2 Be + 2H2O => Be(OH)2 + H2 First, these reaction are single exchange reactions and they are redox processes because the formation of molecular hydrogen in observed for all of them. By checking the oxidation numbers it is clear that the metals are oxidized and the hydrogen reduced. To answer to these questions we need to recall the concepts of hydrogen displacement by the metals.

3 Now we can answer: Zn + 2HCl => ZnCl 2 + H 2 2Na + 2H 2 O = 2NaOH + H 2 2Au + 6HNO 3 => 2Au(NO 3 ) 3 + 3H 2 Ni + 2H 2 O => Ni(OH) 2 + H 2 Mg + 2H 2 O =>Mg(OH) 2 + H 2 x x x (if water is heated to steam) 2) Analysis of a gaseous chlorofluorocarbon, CClxFy, shows that it contains 9.93 % of C and % of Cl. In another experiment you find that g of the compound fills a 458 ml flask at 25 C with a pressure of 21.3 mmhg. what is the molecular formula of the compound? First, according the definite proportion law we have to calculate the empirical formula = 31.43% of fluorine 9.93 /12.01 = /35.45 = /18.99 = / = 2

4 Empyrical formula = CCl 2 F g of the compound fills a 458 ml flask at 25 C with a pressure of 21.3 mmhg 21.3 mmhg /760 mmhg /atm = atm = 298 K 458 ml = L Pv = nrt = MM = grt PV g MM RT MM = L atm g 298K mol K atm 0.458L = g/mol The molar mass of the empirical formula is : x x 2= The empirical formula represents the molecular formula: CCl 2 F 2 3) According to the following reaction: CaO(s) + NH4Cl(s) => NH3 (g)+ H2O + CaCl2(s) If 112g of CaO and 224 g of NH4Cl are mixed we obtain 16.3 g of gaseous ammonia. What is the yield of the reaction? The gas was collected in a 2L flask filled with water. How many moles of ammonia will be in 200 ml of this solution? First, according to the reaction equation we balance the reaction. The oxidation numbers do not change. It is an acid (NH 4+ ) and base (CaO) reaction. We balance by an intuitive method. CaO(s) + 2NH 4 Cl(s) => 2NH 3 (g)+ H 2 O + CaCl 2 (s) If 112g of CaO and 224 g of NH4Cl are mixed we obtain 16.3 g of gaseous ammonia. What is the yield of the reaction?

5 Being CaO and NH 4 Cl reactants we have to check if they are in the right molar ratio. 112 g /MM CaO = 112 g / g/mol = mol 224 g/mm NH 4 Cl = 224 / g/mol = mol From the reaction the mole ratio between CaO and NH 4 Cl is 1 : 2 and we have almost 1 : 4. It is clear that CaO is the limiting reactant. Then the mole ratio between CaO and NH 3 in the reaction is 1:2 then when it reacts mol of CaO mol x 2 are the mole of NH mol x 2 = mol mol x MM NH 3 = = mol x g/mol = g theoretical mass of NH 3. To calculate the yield the proportion can be set up: 16.3 : = x : 100 X = % yield of the reaction 4) A mixture of CuCl2 and CuCl2. 2H2O has a mass of g. After heating to drive off all the water, the mass is only g. What is the mass percent of CuCl2. 2H2O in the mixture? First, we have to consider the relationship between the two salts; one contains water and the other is dry and they are mixed in a proportrion which is unknown = g of H 2 O g / MM CuCl 2 = g/ g/mol = 0,01034 moles of dry CuCl g / MM H 2 O = g / g/mol = moles of water

6 If are the moles of H 2 O, the mole ratio in the formula CuCl 2. 2 H 2 O between CuCl 2 and H 2 O is 1 : 2, respectively. Hence, / 2 = are the moles of CuCl 2 in the formula CuCl 2. 2 H 2 O moles x MM CuCl 2 = moles x g/mol = g Mass of CuCl 2 due to CuCl 2 x 2 H 2 O Mass of CuCl 2 x 2 H 2 O = g (CuCl2) g (H2O)= g What is the mass percent of CuCl2. 2H2O in the1.565 g of the mixture? : = y = 100 Y = 52.64%

AP Chemistry Semester 1 Practice Problems

AP Chemistry Semester 1 Practice Problems 1. Adipic Acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula? a) C 3 H 5 O 2 b) C 3 H 3 O 4 c) C 2 HO 3 d) C 2 H 5 O 4 e) C 3