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Practice Test 3( Net Ionics, Ch # 6,ch8,ch11) KEY 1. The empirical formula of a compound is CH. The molar mass of this compound is 78.0, then the molecular formula is A) C2H2 B) C5H18 C) C6H6 ( 78.0/14=6)*** D) No correct answer given 2. A) B) C) D) The molar mass of MgCl2 is 95.21 g*** 59.76 g 119.5 g 125.8 g 3. A) B) C) D) How many moles are contained in 2.54 g Cu? 0.0400 mol (g/MM)*** 25.0 mol 161 mol no correct answer given 4. A) B) C) D) The number of oxygen atoms in 7.8 g of O2 is 2.93 x 1023 ( 78.0 g x1/32.00 g x 6.022 x1023 x 2 atoms/1 molecule) *** 1.47 x 1023 5.86 x 1023 0.488 5. A) B) C) D) Which one of the following could not be an empirical formula? CH2 CH4 C2H5 C2H6 ( It can be reduced further to CH3) *** 6. A) B) C) D) One mole of hydrogen atoms contains 2.0 g of hydrogen 6.022 x 1023 atoms of hydrogen *** 1 atom of hydrogen 12 g of carbon-12 1 7. A) B) C) D) For the reaction 2 H2 + O2 2 H2O + 572.4kJ, which of the following is not true? The reaction is exothermic. 572.4 kJ of heat are liberated for each mole of water formed.*** Two moles of hydrogen react with 1 mol of oxygen. 572.4 kJ of heat are liberated for each 2 mol of hydrogen reacted. 8. Choose the set of coefficients which balances the chemical equation given below. N2O5 + B2O3 + H2O B3N3H6 + O2 A) 6, 5, 5, 2, 15 B) 3, 3, 3, 5, 2 C) 3, 3, 6, 2, 15 *** D) 2, 1, 1, 5, 1 9. A) B) C) D) All of the following are endothermic except boiling water melting ice condensing water vapor *** reaction inside an ice pack 10. A) B) C) D) What is the mass in grams of 0.30 mol of BaSO4? 7.0 x 103 g 0.13 g 70. g ( mol x 233.37 (MM)) *** 700.20 g 11. A) B) C) D) The number of moles in 1.00 kg NaCl is 1000 1000 x 58.44 1.00/(58.44 x 1000) 1000/58.44 *** ( Convert kg to g) 2 12. How many moles of SO2 can be produced from 20.0 g of H2S? 2 H2S + 3 O2 2 SO2 + 2 H2O A) 0.312 B) 2.00 C) 20.0 D) 0.587 9 2.00 g x 1mol/34.07 x 2mol/2 mol) *** ********************************************************************* 13. What volume will 3.00 L of a gas occupy if the temperature is changed from 30°C to 90°C (P is constant)? A) 1.00 L B) 9.00 L C) 2.50 mL D) no correct answer given ( V1/T1= V2/T2) 14. A) B) C) D) The pressure exerted by a mixture of an ideal gas is given by Boyle's Law Charles's Law Gay-Lussac's Law Dalton's Law *** 15. Given 0.838 L of NH3 at 30.0°C. At what temperature will the NH3 have a volume of 2.00 L (P is constant)? 127 K 450°C ( T2= T1 V2/V1 , Subtract 273 from the answer you get to C) *** 71.6°C 12.6°C A) B) C) D) 16. A) B) C) D) What is the partial pressure of O2 collected over water at 25°C and 630 torr? (Vapor pressure of H2O at 25°C is 23.8 torr.) 654 torr 681 torr 606 torr ( 630- 23.8) *** 23.8 torr 16. Which of the following is not one of the principal assumptions of the Kinetic-Molecular Theory for an ideal gas? A) All collisions of gaseous molecules are perfectly elastic. B) A mole of any gas occupies 22.4 L at STP. *** C) Gas molecules have no attraction for one another. D) The average kinetic energy for molecules is the same for all gases at the same temperature. 3 17. If the pressure on 45 mL of gas is changed from 600. torr to 800. torr, the new volume will be A) 60 mL B) 34 mL( V2= P1 V1/P2) *** C) 0.045 mL D) 22.4 L 18. Which of the graphs below represents the relationship between temperature and pressure of an ideal gas, if volume and moles are held constant A) B) C) D) A *** b c d 19. A) B) C) D) Which of the following defines standard conditions for a gas? 0K and 1 atm 273oC and 760 torr 273K and 760 torr *** 25oC and 1 atm 20. A) B) C) D) Which pressure does not correspond to 1.25 atm? 950 torr 37.4 in. Hg 950 cm Hg *** ( it is given cms here) 1.27 kPa 21. At constant temperature the volume of a gas is inversely proportional to its pressure. Which statement correctly expresses this relationship? A) P1 P2 V1 V2 B) PV = constant *** C) P = constant V D) V= P 4 22. A) B) C) D) The combined gas law includes all of the following laws except Boyles's Law Gay-Lussac's Law Charles's Law Avogadro's Law *** *************************************************************************** 1. A compound called cadaverine is formed by action of bacteria on meat and fish. Analysis shows that the elemental composition is C 58.8% , H 13.8 % and N 27.4 %. Determine the empirical formula. Show all formulas and work to get full credit. – 6 points. C= 58.8/12.01= 4.89/1.96=2.5 x 2=5 H=13.8/1.008=13/7/1.96=6.9=7 x 2= 14 N=27.4/14.01=1.96/1.96=1 x 2=2 EF: C5H14N2 2. A sample of ethylene chloride was analyzed to contain 6.00 g of C, 1.00 g of H, and 17.75 g of Cl. Calculate the % composition of ethylene chloride. Show all formulas and work to get full credit. – 6 points. Total grams=24.75 g % C =6.00/24.75 x 100=24.2 % % H=1.00/24.75 x 100=4.04 % % Cl= 17.75 /24.75 x 100=71.72 % 3. How many grams of steam and iron must react to produce 375 g of magnetic iron oxide, Fe3 O4 ? 3Fe(s) + 4H2 O (g) →Fe3 O4 (s) +4H2 ( g) Show all formulas and work to get full credit. – 6 points. 375 g Fe3 O4 x 1mol/231.55 g Fe3 O4 x 3mol Fe/ 1mol Fe3 O4 x 55.85 g Fe/1 mol Fe= 271 g 375 g Fe3 O4 x 1mol/231.5 g Fe3 O4 x 4 mol H2O/1mol Fe3 O4 x 18.02 g H2O/ 1 mol H2O= 117 g 5 4. Change the following word equations into formula equations, balance it give its total ionic, net ionic equations.(6 points) nickel(II) phosphate + sulfuric acid_________ nickel(II) sulfate + phosphoric acid. Ni3(PO4)2 (aq) + 3 H2SO4 (aq) → 3 NiSO4 (s) + 2 H3PO4(aq) TIE: 3 Ni2+ (aq) + 2 PO43-(aq) + 6 H+ (aq) + 3 SO42- (aq) → 3 NiSO4 (s) + 6 H+ (aq) + 2 PO43(aq) NIE: 3 Ni2+ (aq) + 3 SO42- (aq) → 3 NiSO4 (s) NIE: Ni2+ (aq) + SO42- (aq) → NiSO4 (s) 5. Balance the following equation and calculate how many moles of Cu can be formed from 5.0 moles of Al and 10.0 moles of CuSO4 . What is the limiting reactant and how much of the excess reactant is left after the reaction? Al + CuSO4 → Cu + Al2(SO4)3 Show all formulas and work to get full credit. – 10 points. 2Al + 3CuSO4 → 3Cu + Al2(SO4)3 5.0 mol Al x 3 mol Cu/2 mol Al =7.5 mol Cu 10.0 mol CuSO4 x 3 mol Cu/ 3mol CuSO4= 10.0 mol Cu LR= Al , moles of Cu= 7.5 5.0 mol Al x 3 mol CuSO4/2 mol Al= 7.5 mol CuSO4 reacted 10.0 mol-7.5 mol=2.5 mol unreacted. 6. The volume of a gas filled balloon is 50.0L at 20.0 C and 742 torr. What volume will it occupy at STP?- 6 points. P1=742 torr, V1=50.0 L, T1=20 + 273= 293 K P2 = 760 torr, V2= ? , T2= 273 K P1V1/T1=P2V2/T2 V2= P1V1T2/ P2T1 = 48.9 L 6 7. When measured at 400 C and 630 torr, the mass of 691 mL of diethylether is 1.65 g. Calculate the molar mass of diethyl ether. Show all your working to get full credit.(5 points) T= 40 + 273=313 K P=630 torr/760= 0.829 atm V=691/1000=.691 L Mass= 1.65 g D= mass/V=2.39 g/L M=DRT/P=74.04 g 7