Name: Class; ates Chemical Calculations @answer v rie: Go through the worked example. Use the tips to guide you in understanding and answering the questions. Step 41: Excess iron(II) oxide, Fe,03, was added to dilute hydrochloric acid, HCI. ironitl!) chloride, FeCl, and water were formed as products. The reaction mixture was filtered to remove unreacted ironittl) oxide and the filtrate was collected. Step 2: The filtrate obtained in step 1 was added in excess to 30 cm® of 2.0 mol/dm® sodium hydroxide solution, NaOH. A brown precipitate of ironitll) hydroxide, Fe(OH)s, was formed {@) Write an ionic equation, including state symbols, to show the reaction in step 1. ‘Thought Process «The first step in writing an ionic equation is to write the balanced chemical equation. Fe,0,(s) + 6HC{aq) > 2FeCi.(aq) + 3H20(0) ‘Then, rewrite an equation in terms of ions and cancel out the spectator ions. Fe,0,(s) + 6H*(aq) + SCHtaq) —> 2Fe*(aq) + BCA) + 3H,0(0) Answer Fe,0,(s) + 6H"(aq) —> 2Fe*(aq) + 3H,0(/) (b) (i) Write an ionic equation for the reaction in step 2. (ii) Calculate the mass of iron(tl) hydroxide precipitated in step 2. ‘Thought Process (i) Since iron(lll) chloride is in excess, sodium hydroxide solution is the limiting reactant. The amount of product(s) formed is determined by the amount of limiting reactant used.‘Answer (i) Fe*(aq) + 30H (aq) —> Fe(OH).(s) (il) Number of moles of NaOH = concentration in mol/dm® x volume in dm? 30 20x30, = 0.06 mol From the equation, 3 mol of OH" ions react to form 1 mol of Fe(OH). Number of moles of Fe(OH). produced = 3 x 0.08 0.02 mol 56 + (3 x16) + (3x1) =107 Relative formula mass (M) of Fe(OH) Mass of Fe(OH)s = number of moles x molar mass 0.02 x 107 244g When calculating relative molecular mass or relative formula mass, make sure that you use relative atomic masses and not atomic numbers. TEST IT! Section De acme) Choose the correct answer and write its letter in the brackets provided. 1. Which pair of standards is used to measure the relative molecular mass and the relative atomic mass of a substance? Relative molecular mass Relative atomic mass A 5 mass of a carbon-12 atom 5 mass of a carbon-2 atom B75 mass of a carbor-12 atom mass of a hydrogen-1 atom © mass of a hydrogen atom By mass of a carbon-2 atom D mass of a hydrogen. atom mass of a hydrogen-1 atom c 2. What is the mass of oxygen in 74 g of calcium hydroxide, Ca(OH)2? A 8g B 16g © 32g D 64g ca 3. Urea, CO(NH)2, is used as a fertiliser. What is the percentage by mass of nitrogen in urea? 12% 23% 40% 41% on) vom> 42 Workshoot 6 © 2014 Marshall Cavendish Education Pte td“8. Which of the following statements about ethanoic acid (CH,COOH) and methyl methanoate (HCOOCH,) are true? They contain the same percentage by mass of oxygen, They have the same empirical formula. They have the same relative molecular mass. dand2 and 3 2and 3 4,2and3 ) vomr onn One of the reactions that takes place during the manufacture of iron is as shown: 2CO{g) + 02(g) > 2C0.(8) Which statement about this reaction is true? 2. of carbon monoxide reacts with 1g of oxygen. 2 mol of carbon dioxide can be obtained from 2 mol of oxygen. 28 kg of carbon monoxide produces 44 kg of carbon dioxide. 88 kg of carbon dioxide can be obtained from 16 kg of oxygen. Cc vou When calcium carbonate is heated strongly, it decomposes into calcium oxide and carbon dioxide gas. CaC0,(s) > Ca0{s) + C0,(g) What is the volume of carbon dioxide gas produced at r-t.p. when 10 g of calcium carbonate is heated strongly? 0.40 dm? 0.24 dm? 1.00 dm? 2.40 dim? co) vou A student carried out titration of sodium hydroxide with an unknown acid. He found that 20.0 cm® of 1.5 mol/dm: of sodium hydroxide exactly reacted with 10.00 cm® of 1.0 mol/dm* of the acid. How many moles of sodium hydroxide would react with one mole of the acid? 2 pomp 3 4 5 Co) Tin occurs naturally as tin(IV) oxide, $nO,, in the ore cassiterite. It is extracted by heating the ore with carbon, The equation for the reaction is: $n0q(s) + C{s) > Sn{s) + CO.(g) 357 g of tin was obtained from 30.2 kg of cassiterite. What is the percentage yield of tin? 0.015% 0.15% 1.5% 15% 8) voor © 2014 Marshall Cavendish Education Pte Lid Workshoot 6Use the following information to answer Questions 9 and 10. A sample of seawater contains bromide ions with a concentration of 0.1 g/dm®. When chlorine gas is bubbled through the sample, bromine gas is obtained. The equation of the reaction is: 2Br (aq) + Cl,(g) > Br,{g) + 2CI"(aq) 9. What volume of chlorine gas is required to produce 0.008 tonne of bromine gas at room temperature and pressure? (1 tonne = 10° g) A 50am? B 100dm* © 4200 um® D 2400 dm? ce *10. What volume of seawater is required to produce 0.008 tonne of bromine gas? (1 tonne = 10° g) A 20.000 dm? B 40.000 dm? © 80.000 dm® D 160.000 dm? Gy aioe Structured Questions Answer the following questions in the spaces provided. 4. When aqueous sodium sulfate, Na,SO,, was added to aqueous leadil) nitrate, Pb(NO,)., lead(ll) sulfate was precipitated. (a) Write a chemical equation for the reaction. Include state symbols. (b) Hence, write the ionic equation for the reaction in (a). {e) 200 cm? of 0.1 mol/dm? lead(l) nitrate solution was mixed with 100 om? of 0.1 mol/dm? sodium suifate solution. (i) What is the limiting reactant in this reaction? AA Wornsheet 6 ‘© 2014 Marshall Cavendish Education Pte Lid(li) Calculate the mass of lead{l) sulfate precipitated. 2. A student was provided with the following solutions: ‘A: Unknown concentration of sodium hydroxide solution B: 0.25 mol/dm? of dilute sulfuric acid The student titrated 25.0 cm? portions of A in a conical flask against B in a burette, The results of the experiment are shown below. » 1 2 3 19.10 | 18.70 | 18.70 0.00 0.00 0.00 19.10 | 18.70 | 18.70 (a) Using suitable sets of the titration results, calculate the average volume of the acid used for complete neutralisation. (b) (i) Write a chemical equation for the reaction between sodium hydroxide solution and dilute sulfuric acid. (il) Hence, write the ionic equation for the reactio {e) Calculate the concentration, in mol/dm®, of the sodium hydroxide solution.3. Oxygen is the third most abundant element in the universe by mass. The relative atomic mass of oxygen is 16. The most stable form of oxygen is the diatomic form, known as dioxygen. The other form of oxygen, known as ozone, has a relative molecular mass of 48. Ozone at the ground level is harmful to the human respiratory system. In some countries, the recommended limit of concentration of ground-level ozone is 1.57 x 10 g/m’. (a) Define ‘relative atomic mass’ {b) Based on the relative molecular mass of ozone, suggest the molecular formula of ozone. (c) An environmental scientist found that there are 1 x 10" molecules of ozone in 1 m° of air. Has the limit of 1.57 x 10% g/m? been exceeded? Support your answer with relevant calculations. (One mole of a substance contains 6 x 10” particles.) *4, Hydrogen fluoride attacks glass and is used to draw on glass. It is prepared by adding concentrated sulfuric acid to calcium fluoride. The reaction takes place at room temperature. CaF,{s) + H»SO4(l) > 2HF(g) + CaSO,(s) (a) When 15.6 g of a sample of calcium fluoride was reacted with 12.5 cm? of 20.0 mol/dm® sulfuric acid at r.t.p., 7.68 dm® of hydrogen fluoride was formed. (i) What is the limiting reactant in this reaction? AB Worksheot 6 (© 2014 Marshall Cavendish education Pe id(il) Calculate the theoretical volume of hydrogen fluoride that was formed (b) Caloulate the percentage purity of calcium fluoride *5. The recommended dosage of paracetamol for a child weighing 10-16 kg is 160 mg. A brand of medicine contains 0.20 mol of paracetamol in 1 dm? of solution. What is the maximum number of 2.5 cm® spoonfuls of the medicine a parent can safely feed her child, if her child weighs 15 kg? (M,: paracetamol = 151) © 2014 Marshall Cavendish Education Pe td Worksheet 6 aTSection Answer the following questions. Eee 1. Hydrated compounds are compounds that contain water of crystallisation. The information of some hydrated compounds is given in the table below. hydrated magnesium sulfate MgS0,.7H0 51.2 hydrated sodium carbonate NagCO3.10H,0 62.9 hydrated zine nitrate Zn{NOs)oxH20 36.5 (a) Given that one mole of a substance contains 6 x 10” particles, calculate the number of water molecules present in 5.00 g of hydrated magnesium sulfate. {b) When solid hydrated sodium carbonate is heated, the water of crystallisation is given off as steam. Write a balanced chemical reaction, with state symbols, to represent this change. (c) Calculate the value of x in Zn(NO,)2-xH AB Wortahoot 6 {© 2014 Marshall Cavendish education Pte td+2, The following results were obtained in an experiment to determine the formula of an oxide of mercury. The oxide is a red solid. It decomposed into its elements when heated at r.t.p. (One mole of a gas occupies 24 dm® at rt.p.) Mass of empty test tube = 15.45 g Mass of test tube + oxide of mercury = 17.61 ¢ Volume of oxygen collected at r-t.p. = 120 om? (a) Draw a labelled diagram of the apparatus that can be used to perform this experiment. (b) State a precaution to take when performing this experiment. (e) What observation (other than colour change) indicates that the reaction is complete? (@)_ From the results of the experiment, determine the molecular formula of this oxide of mercury. (One mole of this oxide of mercury weighs 247 g.)In the table below, circle the question(s) that you have answered incorrectly. Revisit the relevant section(s) in the textbook to strengthen your understanding of the key concept(s). ‘Question number(s) Textbook ‘Leaming outcomes Mutiple- a section(s) Mines | Structured | igthonge | torevise (a) Interpret chemical equations with state - - symbols, 2 et (b) Wiite balanced chemical equations e ees 4a, 21040) (b) ea (€) Write ionic equations with state == a symbols, e tb), 20x) 82 (@)_Define relative atomic mass (A). i Stal - ea (©) Define relative molecular mass (™M). i = = 92 (8) Calculate relative molecular mass or - - relative formula mass of a substance. = oa (g) Convert number of particles into number of moles of particles and vice - - Ye) 93 (h) Perform calculations involving the ‘number of moles, mass and molar 2 3) - 93 mass of a substance. (i) Determine the percentage composition of compounds from given data. ) Determine the empirical and molecular formulae of a compound from given 4 3b) 1(6), 2 95 data, (k) Perform calculations involving molar {gas volume and the number of moles - (ay) - 96 ofa gas. (1) Perform calculations involving the, Concentration of a solution (g/d? or 10 - - 97 mol/dm*), (m) Calculate the masses of reactants and products by using the mole ratio in a 5 fot) = 10.4 chemical equation. {n) Calculate the volumes of gaseous reactants and products using the mole 69 - - 10.2 rato in a chemical equation. (0) Perform stoichiometric calculations involving the idea of limiting reactants. - Henn. A¢en - ce {p) Process the results of volumetric = . experiments, 2{a}, 2c) 10.4 (a) Perform stoichiometric calculations © - involving concentrations of solutions. a (0), 5 104: (1) Calculate the percentage yield and A a) - ae percentage purity of a substance. BO Workshost 6 {© 2014 Marshall Cavendish Education Pte Ltd