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Quantitative Chemistry Click to start Question 1 What is the mass in grams of one molecule of ethanoic acid CH3COOH? 0.1 1 x 10-22 3.6 x 1025 60 Wrong Answer! Molar mass of CH3COOH is 24 + 4 + 32 = 60 Question 2 Which is not a true statement? One mole of methane contains four moles of hydrogen atoms. One mole of 12C has a mass of 12.00g. One mole of hydrogen gas contains 6.02 x 1023 atoms of hydrogen. One mole of methane contains 75% of carbon by mass. Wrong Answer! 1 mole of hydrogen gas contain 6 x 1023 molecules of hydrogen gas. Since 1 mole of hydrogen is made up of 2 H atoms, 1 mole of hydrogen gas contains 2 x 6 x 1023 atoms. Question 3 Which sample has the greatest mass? 1.0 mol N2H4 2.0 mol N2 3.0 mol NH3 25.0 mol H2 Wrong Answer! A: 1 x (28+4) = 32g B: 2 x 28 = 56g C: 3 x (14+3) = 51g D: 25 x 2 = 50g Question 4 Which one of the following statements about SO2 is/are correct? I. One mole of SO2 contains 1.8 x 1024 atoms II. One mole of SO2 has a mass of 64g Both I and II Neither I nor II I only II only Wrong Answer! SO2 is made up of 3 atoms, hence 1 mole of SO2 contains 3 x 6 x 1023 atoms. Molar mass of SO2 = 32 + 32 = 64. Question 5 2Cl2 represents: two chlorine molecules two chloride ions two chlorine atoms four free chlorine atoms Wrong Answer! 2Cl2 represents two chlorine molecules : Cl-Cl and Cl-Cl Question 6 Which one of the following equations is not correctly balanced? Ca(s)+2H+(aq) Ca 2+(aq)+H2 (g) Mg(s)+ H2O(l) Mg(OH)2 (aq)+H2(g) Fe 2+(aq)+Ag+(aq) Fe3+(aq)+ 2Cl-(aq) Fe 2+(aq)+ Cl2 (g) Fe3+(aq)+ 2Cl-(aq) Wrong Answer! The charge is not balanced. Question 7 Sulfuric acid and sodium hydroxide react together according to the equation? H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) What volume of 0.250 moldm-3 NaOH is required to neutralise exactly 25.0 cm3 of 0.125 moldm-3 H2SO4 ? 6.25 cm3 50 cm3 12.5 cm3 25.0 cm3 Wrong Answer! Conc x Vol of NaOH = 2 x Conc x Vol of H2SO4 0.25 x Vol of NaOH = 2 x 0.125 x 25 Vol of NaOH = 25 cm3 Question 8 Which expression represents the density of a gas sample of relative molar mass, Mr, at temperature T, and pressure, P? PM r RT RM r PT RT PM r PM r T Wrong Answer! nRT PV m PV M r RT m PM r V RT Density = PM r RT Question 9 Separate samples of two gases, each containing a pure substance, are found to have the same density under the same conditions of temperature and pressure. Which statement about these two samples must be correct? They have the same volume. There are equal numbers of moles in the two samples. They have the same relative molecular mass. They condense at the same temperature. Wrong Answer! nRT PV Under the same pressure and temperature where R is a constant, they should have the same relative molecular mass. m PV M r RT m PM r V RT Density = PM r RT Question 10 A 250 cm3 sample of an unknown gas has a mass of 1.42g at 350C and 0.85 atmospheres. Which expression gives its molar mass, Mr? (R = 82.05 cm3 atm K-1 mol-1) 1.41 82.05 35 0.25 0.85 1.41 82.05 308 0.25 0.85 1.41 250 0.85 82.05 308 1.41 82.05 308 250 0.85 Wrong Answer! nRT PV mass RT PV Mr Mr massRT PV Question 11 What is the concentration of nitrate ions in 0.500cm3 of 0.60moldm-3 Fe(NO3)3 solution? 0.60 moldm-3 0.90 moldm-3 1.20 moldm-3 1.80 moldm-3 Wrong Answer! Fe(NO3)3 Fe3+(aq) + 3NO3-(aq) Nitrate ions concentration = (0.6 x 3) = 1.80 moldm-3 Question 12 32.0 grams of sulfur (atomic mass of 32.0) combine with a metal, M (atomic mass of 40.0) to give a product which weighs 52.0g. What is the empirical formula of the sulfide formed? MS MS2 M 2S M2S5 Wrong Answer! Amount of M atoms = (52-32)/40 = 0.50 mol Amount of S atoms = 32/32 = 1.0 mol Multiplying through by 2 gives MS2 Question 13 Under what conditions of temperature and pressure will a real gas behave most like an ideal gas? Temperature Pressure Low Low High Low High High Low High Wrong Answer! High pressure will bring the gas molecules very close together. This causes more collisions and also allows the weaker attractive forces to operate. With low temperatures, the gas molecules do not have enough kinetic energy to continue on theire path to avoid the attraction. Question 14 At stp (i.e. 00C and 1 atm pressure (101 kPa)), it was found that 1.15 dm3 of a gas weighed 3.96g. What is its molar mass? 77 gmol-1 47 gmol-1 39 gmol-1 4 gmol-1 Wrong Answer! PV 101000 Pa 1.15 103 m3 n 0.0512mol 1 1 RT 8.31Jmol K 273K 3.96g Molar mass = 77.34 gmol 1 0.0512mol Question 15 A sample of argon gas in a sealed container of fixed value is heated from 50 to 2500C. Which quantity will remain constant? Average speed of the atoms Pressure of the gas Average kinetic energy of the atoms Density of the argon Wrong Answer! All properties will increase in value except density which remain constant since the mass and volume of gas remain constant. Question 16 Nitrogen(II) oxide,NO, is made from the oxidation of NH3: 4NH3 + 5O2 4NO + 6H2O An 8.5g sample of NH3 gives 15.0g of NO. What is the percentage yield of NO? 40% 60% 80% 100% Wrong Answer! Amount of NH3 = 8.5/17 = 0.5 mol Amount of NO = 15/30 = 0.5 mol Percentage yield = 0.5/0.5 x 100% = 100% Question 17 A pure compound contains 24g of carbon, 4g of hydrogen and 32g of oxygen. No other elements are present. What is the empirical formula of the compound? C2H4O2 CH2O CH4O CHO Wrong Answer! No. of moles of C = 24/12 = 2 No. of moles of H = 4/1 = 4 No. of moles of O = 32/16 = 2 Dividing all by 2 gives a ratio of C:H:O = 1:2:1 The empircal formula is CH2O Question 18 1000cm3 of ammonia gas combines with 1250cm3 of oxygen to produce two gaseous compounds with a combined volume of 2500cm3, all volumes being measured at 2000C and 0.500 atm pressure. Which of the following equations fits the facts? 4NH3 + 7O2 4NO2 + 6H2O 4NH3 + 5O2 4NO + 6H2O 4NH3 + 5O2 4N2O2 + 6H2O 4NH3 + 3O2 2N2+ 6H2O Wrong Answer! 4 vol + 5 vol 10 vol Experimental data 1 vol + 1.25 vol 2.5 mol Multiplying throughout by 4 gives 4 vol + 5 vol 10 vol Question 19 Butane burns in oxygen according to the equation 2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) If 11.6g of butane is burned in 11.6g of oxygen which is the limiting reagent? Neither Butane Oxygen Oxygen and butane Wrong Answer! No. of moles of butane = 11.6/58 = 0.2 No. of moles of oxygen = 11.6/32 = 0.3625 2 mols of butane react with 13 mols of oxygen 0.2 mols of butane will react with 1.3 mols of oxygen. 0.3625 mols of oxygen will react with 0.05577 mols butane. The limiting reagent is oxygen since the no. of mols of butane produced by 0.3625 mols is smaller. Question 20 A 350cm3 sample of helium gas is collected at 22.00C and 99.3kPa. What volume would this gas occupy? 318cm3 450cm3 477cm3 220cm3 Wrong Answer! 350cm3 99.3kPa 273K V2 101.3kPa 295 K V2 317.5034cm3 318cm3 Question 21 When 250 cm3 of 3.00 moldm-3 HCl(aq) is added to 350 cm3 of 2.00 moldm-3 HCl(aq) the concentration of the solution of hydrochloric acid obtained in moldm-3 is: 1.45 2.90 2.50 2.42 Wrong Answer! (250+350)/1000 x Conc of HCl = 250/1000 x 3 + 350/1000 x 2 Conc of HCl = (0.25 x 3 + 0.35 x 2)/0.6 = 2.416moldm-3 Question 22 Magnesium reacts with hydrochloric acid according to the following equation: Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) What mass of hydrogen will be obtained if 100 cm3 of 2.00 moldm-3 HCl are added to 4.86g of magnesium? 2.0g 0.8g 0.4g 0.2g Wrong Answer! No. of moles of HCl = 100/1000 x 2 = 0.2 No. of moles of Mg = 4.86/24 = 0.2025 The limiting reagent is HCl Since 2 mols of HCl produces 1 mol H2, 0.2 mols of HCl produces 0.1 mol H2. Hence, 0.1 x 2g = 0.2g of H2 Question 23 12g of anhydrous magnesium sulfate combines with 12.6g of water to form hydrated manesium sulfate. What is the formula of the hydrated magnesium sulfate? MgSO4.9H2O MgSO4.7H2O MgSO4.5H2O MgSO4.3H2O Wrong Answer! No. of moles of MgSO4 = 12/122 = 0.09836 No. of moles of H2O = 12.6/18 = 0.7 Multiplying by 10 to both gives approximately 1 mole MgSO4 and 7 moles H2O Question 24 In order to dilute 40.0 cm3 of 0.600 moldm-3 HCl(aq) to 0.100 moldm-3, what volume of water must be added? 60 cm3 160 cm3 200 cm3 240 cm3 Wrong Answer! M1V1= M2V2 0.600moldm-3 x 40.0cm3 = 0.600moldm-3 x V2 V2 = 240cm3 V2 – V1 = 240 – 40 = 200 cm3 Congratulations!