Motekaitis - Test 1 Solutions

Test 1 Solutions
Fall 1997
Chemistry 101 - Sections 450-461
Dr. Ramunas J. Motekaitis

Test #1 50 minutes 1. Two grams of hydrogen were chemically combined with sixteen grams of oxygen to form water. How much net matter was created in this process? A) sixteen grams B) eighteen grams C) zero grams Matter is neither created nor destroyed in a chemical reaction. D) thirty six grams E) fourteen grams 2. Which of the following examples of quantities of matter possesses the greatest mass? A) one gram water B) one gram ice C) one gram steam D) one gram snow E) two grams styrofoam This has the most matter even if the density is small 3. The correct sum of 252 g + 1.001 g is A) 252 g B) 253 g A) is wrong and C) - E) have too many significant digits. C) 253.001 g D) 253.00 g E) 253.0 g 4. The density of a 52.00% sulfuric acid H₂SO₄ solution at 20.00 ^oC is 1.4174 g/mL. What is the density of 100.00 mL of this solution? A) 0.014174 g/mL B) 1.4174 g/mL The density of matter is independent of the quantity. C) 141.74 g/mL D) 0.70552 g/mL E) 0.0070552 g/mL 5. Characteristics that describe samples of matter in terms of their chemical reactions with other samples of matter are aptly called: A) chemical densities B) chemical symbols C) chemical synonyms D) chemical properties E) chemical colors 6. In one molecule of cadmium nitrate Cd(NO₃)₂ the ratio of O atoms to Cd atoms is 6:1. What is this ratio in a cluster of 10 cadmium nitrate molecules? A) 60:1 B) 6:10 C) 120:1 D) 6:5 E) 6:1 The ratio of atoms is independent of quantity of matter in pure substances. 60:10 is same as 6:1 7. Pick out Avogadro's Number: A) 6.02 x 10²³ particles/mole correct number and units B) 6.02 x 10^-23 particles/mole C) 6.02 x 10²³ g/atom D) 6.02 x 10^-23 g/atom E) 6.02 x 10²³ g/mole 8. The formula for ammonium sulfate is (NH₄)₂SO₄. Count all the atoms in 10 molecules of ammonium sulfate. A) 14 B) 140 C) 15 D) 150 10 x [ 2 + 8 +1 + 4] E) 180 9. A compund mixture contains only C, H, O, and Br. Precise chemical determination provided the following percentages by weight: C 12.01%, H 1.01%, and Br 79.90%. What is the percentage by weight of the O in this mixture. A) 7.08 % O 12.01+1.01+79.90= 92.92 ; %O = 100 - 92.92 B) 16.00 % O C) 92.92 % O D) 100.00 % O E) 0.00 % O 10. A representation how atoms are connected in a compound is A) a molecule B) Law of Multiple Proportions C) simplest formula D) the molecular weight E) a structural formula 11. Find the chemical equation that has either a compositional or reaction stoichiometric error. A) 2Al + 6HCl -> 2AlCl₃ + 3H₂ B) CH₄ + 2O₂ -> CO₂ + 2H₂O C) NiCl₂ + 2NaOH -> Ni(OH)₂ + 2NaCl D) P₄ + 5O₂ -> P₄O₁₀ E) CaCl + Na₂CO₃ -> CaCO₃ + 2NaCl Should be CaCl₂ 12. Elemental calcium becomes oxidized in air according to 2Ca + O₂ ->2CaO If 40.1 grams of calcium is burned in the presence of excess oxygen and 40.1 grams of calcium oxide is recovered in this process, what can be said of the % yield? A) Yield of CaO is 100.% B) Yield of CaO is 50.% C) Yield of CaO is cannot be determined. D) Yield of CaO is 28.75 E) Yield of CaO is <100.0 % Theoretical yield is > 40.1 because Mol Wt of CaO > Ca 13. A 10.00 mL aliquot (sample) of a concentrated solution of potassium hydroxide KOH is diluted to make 50.00 mL of 0.1000 M solution. What is the molarity of KOH in the original concentrated solution? A) 0.500 mol KOH/L mmol solute taken = mmol solute after dilution (10.00 mL) (MKOH) = (50.00 mL)(0.1000 M) B) 1.000 mol KOH/L C) 2.000 mol KOH/L D) 10.00 mol KOH/L E) 50.00 mol KOH/L 14. A hypothetical reaction occurs: Ca + HBr + HCl -> CaBrCl + H₂(g) What is the limiting reactant if 2 moles of calcium are treated with 1 mole HBr and 3 moles HCl? A) Ca B) HBr least moles C) HCl D) CaBrCl E) H₂(g) 15. A 10.0% medicinal grade saline (salt) solution (density = 1.073 g/mL) can be described as: A) 10.0 grams water per 100.0 grams salt B) 10.0 grams salt per 100.0 grams solvent C) 10.0 grams solution per 100.0 grams salt D) 10.0 grams salt per 90.0 grams solvent or 10.0 g solute/ (10.00 g solute+90.00 g solvent) E) 10.0 grams salt per 100.0 mL solution 16. Look at the periodic table. Find and describe the element Ca A) 4th period metal| in the same family as K and Sc| forms 2+ ion B) 2nd period metal| in the same family as K and Sc| forms 2+ ion C) 4th period metal| in the same family as Mg and Sr| forms 2+ ion Periods are rows; families columns D) 2nd period metal| in the same family as Mg and Sr| forms 2+ ion E) 4th period metal| in the same family as K and Sc| forms 1+ ion 17. Which compound is expected to be soluble? A) silver chloride AgCl B) barium sulfate BaSO₄ C) calcium oxide CaO D) ammonium sulfate (NH₄)₂SO₄ All common ammonium salts are soluble. E) calcium phosphate Ca₃(PO₄)₂ 18. What is the oxidation number of Cl in Ca(ClO₄)₂? A) -1 B) +1 C) +3 D) +5 E) +7 Ca²⁺ is +2; O^2- is -2; therefore Cl is +7 to give a net charge of zero. 19. The following reaction is shown to occur: Zn(s) + Cu²⁺(aq) ->Zn²⁺ +Cu(s) The correct explanation is: A) Zinc metal is above copper metal in the activity series B) Copper metal is above zinc metal in the activity series C) Copper metal and zinc metal are at the same reactivity level D) Copper metal is above hydrogen in the activity series E) Hydrogen is above zinc metal in the activity series. 20. A substance that conducts electricity poorly in aqueous solution: A) a negative electrolyte B) a strong electrolyte C) a weak electrolyte definition of weak electrolyte; undergoes partial dissociation in aqueous solution D) a nonelectrolyte E) a positive electrolyte 21. The approximate relative masses of proton to neutron are: A) 0.0000:1 B) 0.0005:1 C) 1:1 Protons each possess ~1.00 amu while the electron has insignificant mass D) 1:0.0005 E) 1:0.0000 22. Find carbon in the periodic table. The isotope carbon-13 has A) 5 neutrons B) 6 neutrons C) 7 neutrons 13 total - 6 protons = 7 D) 12 neutrons E) 13 neutrons 23. Uranium-232 and uranium-235 have the same chemical symbol U, however they differ by 3 mass units. How are they related? A) Uranium-232 and uranium-235 are sisters B) Uranium-232 and uranium-235 are isotopes Same element, differ by mass (# neutrons present) C) Uranium-232 and uranium-235 are fundamental particles D) Uranium-232 is reduced and uranium-235 is oxidized E) Uranium-232 and uranium-235 cannot be distinguished by mass spectrometry 24. Given the ground state electronic configuration 1s²2s²2p⁴, what element are we talking about? A) oxygen 8 electrons makes it Element with Atomic Number 8. B) sulfur C) fluorine D) nitrogen E) selenium 25. "Beginning with the second energy level, the set of three degenerate mutually perpendicular, equal-arm, dumbell-shaped atomic orbitals per energy level" describes: A) s orbitals B) p orbitals 3 mutually perpendicular orbitals C) d orbitals D) e orbitals E) f orbitals When sure of your answers to questions 1-25, transfer to scantron sheet. 26. Compute the mass per cent of hydrogen in a sample of pure ammonium sulfate. Formula: (NH₄)₂SO₄ AtWt = 2 x 14.01 + 8 x 1.008 + 1 x 32.07 + 4 x 16.00 = 132.15 amu H mass = 8 x 1.008 = 8.064 amu %H in sample = 8.064 amu H x 100 = 6.10 % H in sample 132.15 amu 27. Write and balance the equation for the neutralization of hydrochloric acid with sodium hydroxide as a help in answering this question. How many mL of 0.1111 M sodium hydroxide solution is required to exactly neutralize 11.11 mL of 0.1000 M hydrochloric acid solution? NaOH + HCl ( NaCl + H₂O observe that 1 NaOH = 1 HCl (mL NaOH)x(0.1111 M NaOH)=(11.11 mL HCl)x(0.1000 mL HCl) (mL NaOH) = 10.00 mL NaOH 28. Write the correct chemical formula and indicate the oxidation numbers for each atom in the formula by writing small signed numbers above each atom. +1 -1 - sodium chloride ___NaCl______ +1 -2 - sodium oxide __Na₂O_______ +1 +1 -2 - sodium hypochlorite _NaClO____ +3 +7 -2 - aluminum perchlorate _Al(ClO₄)₃ ____ +7 -2 - dichlorine heptoxide _Cl₂O₇_ 29. Re: atomic structure. - 17Cl has ___17____ electrons and __17__ protons in the atom - 37Cl has ___20____ neutrons and an atomic mass of _37 amu___ - Please complete the electronic configuration of 11Na: 1s²2s²2p⁶ 3s¹_ - All of the alkali metals have a s¹ electronic ground state. For Rb, what is the principal quantum number n for this s orbital? __5___ - Briefly describe an atom in terms of protons neutrons and electrons. An atom consists of positive protons and neutral neutrons in the nucleus and negative electrons some distance from the nucleus. The number of protons and electrons match. The mass of the atoms is mostly the combined mass of the protons and neutrons in the nucleus. 30. Briefly describe the "Solubility Rules" for the common ionic compounds of NH₄⁺ ,Na⁺,and K⁺ in water. All common ionic compouds of these ions are soluble.