Review Questions for 1st-Year Chemistry: Solve for Mass, Energy, Equations, Electrons, and More

1. Review Questions for 1st year chemistry

2. If gold has a density of 20 g/cm3, what is the mass of a cube of gold with sides of 2 cm? • 160 g • 40 g • 20 g • 10 g Answer: A Use density = mass/volume 20 = mass/(2×2×2) 20 = mass/8 so mass = 160

3. 100. grams of water is heated from 30 degrees Celsius to 60 degrees Celsius, calculate the amount of energy added. • 10,000 J • 12,500 J • 16,300 J • 40 kJ • Answer: B • 100 g x 4.18 x 30 = 12540 J

4. Balance the following equation: __Al + __H3PO4 __AlPO4 + __H2 2,2,2,3 1,2,2,4 2,1,4,1 3,1,3,3 Answer: A Balance H’s so both sides are 6 Balance PO4’s as a group Then balance Al’s last

5. How many electrons are in the VALENCE shell of oxygen? • 16 • 10 • 8 • 6 Answer: D Oxygen has 8 electrons total but two of them are in the first shell of the Bohr Model. The six remaining electrons are found in the outer shell of the model.

6. Which of the following statements is true about the nucleus? A. It is positively charged. B. It contains only neutrons. C. It is negatively charged. D. It contains electrons and neutrons. Answer: A The nucleus has a positive charge because it contains positively charged protons to attract the electrons surrounding it.

7. What group on the periodic table contains elements that are very malleable, are good conductors, and are ductile? • Halogens • Alkaline-Earth Metals • Noble Gases • Metalloids Answer: B The structure of metals includes a sea of electrons which allows heat to more easily flow through the substance. It also allows metals to bend without breaking easily.

8. Which of the following statements is true? The reaction presented by the graph is endothermic. The reaction presented by the graph is exothermic. The reaction above has a negative delta H. The reaction above has a catalyst. • Answer: A • The reaction presented by the graph is endothermic because it is absorbing energy instead of releasing it, shown by the positive change in delta H (difference between products and reactants).

9. How many moles of O2 are in 64 grams of O2? • 2.5 • 4 • 128 • 2 Answer: D 64 g O2 1 mol O2 = 2 mol O232 g O2

10. What is the formula mass of ? • 83.19 g/mol • 122.29 g/mol • 120 g/mol • 244.58 g/mol • Answer: B • (39.098*2)+(28.085)+(16) = 122.29

11. If the wavelength of light is 5.8x10-7 m, what color is the light? • Yellow • Orange • Blue • Green Answer: A Check reference table page 8. Yellow is correct because the wavelength falls between 5.7x10-7 m and 5.9x10-7 m.

12. Which of the following changes would increase the pressure of a gas in a closed container? • Increased volume of container • Increased number of particles in the container • Decreased temperature • Decreased number of particles in the container Answer: B The more particles there are in a container, the more collisions that occur which raises the pressure.

13. Which element has the highest electronegativity? • Chlorine • Iodine • Fluorine • Bromine • Answer: C • Electronegativity decreases as you move down the periodic table because as you move down, there are more valence shells which shield the pull of the protons in the nucleus. Fluorine is the first element in its group and therefore has the highest electronegativity.

14. For an atom that is neutral, which of the following statements is FALSE? The number of protons is equal to the number of neutrons. The atomic number is equal to the number of protons. The number of protons is equal to the number of electrons. The atomic mass is equal to the sum of protons and neutrons in the atom. Answer: A

15. Which of the following has the highest boiling point? • CH4 • CO2 • SO2 • HF Answer: D An H-F bond is a type of hydrogen bond. This bond has a stronger intermolecular force, so it will have the higher boiling point.

16. The molecular geometric shape of H2S is: • Bent • Linear • Trigonal Planar • Trigonal Pyramidal • Answer: A • Since the lone pairs want to repel each other, it causes the bond pairs to bend towards each other, causing the molecular form of the compound to be bent.

17. If an electron drops from the 6th energy level to the 2nd, what type of light is released? • Visible • Infra-red • Ultraviolet • X rays Answer: A Visible is correct because the wavelength of light released based on the Bohr model falls in the visible light range. Use page 8 of the reference tables.

18. Which image shows a representation of a compound? • A • B • C • None of the images Answer: B The molecules are made of two kinds of atoms bonded together. All particles are the same.

19. 19 grams of water are heated from ice at 0 degrees Celsius to 15 degrees Celsius, calculate the amount of energy added. • 9,000 J • 7,500 J • 17 kJ • 1,900 J • Answer: B • (19 x 4.18 x 15) + (19 x 334) = 7537.3

20. What is the percent composition of hydrogen in ethylene glycol ()? • 1.62% • 10.00% • 4.87% • 9.74% • Answer: D • (1.008 × 6)/62.068 × 100 = 9.74%

21. What type of bonding is found between carbon and hydrogen in CH4? • Metallic • Covalent • Ionic Answer: B A bond between two nonmetals is covalent. Both Carbon and Hydrogen are nonmetals so the bond between them is Covalent.

22. The volume of a gas at 99.0 kPa is 300 mL. If the pressure increases to 188 kPa, what is the final volume? • 569 mL • 52.1 mL • 158 mL • None of the above Answer: C Using Boyle’s Law P1V1=P2V2, to find the final volume. 99.0 × 300 = 188 × V2

23. What does T represent on the graph? The products of the reaction. The reverse activation energy. The effects of a catalyst. The heat of reaction. • Answer: D • T displays the energy absorbed during the reaction, which is the positive difference between Y (reactants) and X (products) in this case.

24. How many moles are in 25 grams of water? • 1.6 moles • 1.39 moles • 1.48 moles • 11.39 moles Answer: B 25 g H2O 1 mol H2O = 1.39 mol H2O 18.02 g H2O

25. What type of reaction is this? • PbCl2+ AgNO3 —-> Pb(NO3)2 + AgCl • combustion • decomposition • synthesis • double replacement Answer: D Because two compounds traded ions.

26. Which element matchesthe following Bohr model? A. Boron B. Magnesium C. Neon D. Sodium Answer: D Sodium has 11 electrons and needs 3 electron shells. The Bohr model represents the electrons by the 11 dots.

27. As you move across the periodic table • Atomic radii increases • Atomic radii decreases • Atomic radii stay the same size Answer: B As you move across the periodic table, elements have more protons. Their increasingly stronger pull on the outer shell draws the outer shell closer to the nucleus, decreasing the size of the element.

28. Which of the following elements will NOT be surrounded by an octet of electrons in a correctly drawn Lewis structure? • Hydrogen • Oxygen • Chlorine • Carbon Answer: A The hydrogen atom only has one valence electron in the outermost shell. Its outer shell (its only shell) is the 1s orbital, which only needs two electrons.

29. 1s22s22p63s2 is what element? • magnesium • manganese • sodium • silicon Answer: A Magnesium has 12 electrons. It is located in the 3rd row, 2nd column.

30. An ice cube is placed in a cup of hot tea. What is the nature of the change that occurs? • The ice becomes liquid water, chemical change • The ice becomes tea, chemical change • The ice becomes liquid water, physical change • The ice becomes tea, physical change Answer: C Ice melting is a physical change from solid to liquid.

31. What is it called when a solid proceeds directly to the gas state skipping the liquid state? • Sublimation • Deposition • Vaporization • Freezing Answer: A

32. What is the empirical formula of propanedinitrile(C8H4N2 ) ? • C8H4N2 • C16H8N4 • C4H2N • CHN Answer: C Simplify the subscripts. Empirical formula has the most simplified ratio.

33. At what temperature will 0.654 moles of neon gas occupy 12.30 L at 1.95 atm? • 447 K • 18 K • 273 K • None of the above Answer: A Using the ideal gas law, PV=nRT, T=PV/nR, plug in all the given information and solve for the temperature. 1.95 × 12.30 = 0.654 × 0.0821 × T

34. Different isotopes of an element have different numbers of _____________? • neutrons • protons • voltrons • electrons • Answer: A • Different numbers of neutrons result in different masses.

35. What is the molar mass of Ca3 N2 ? • 150.00 g/mol • 148.25 g/mol • 54.09 g/mol • 100.0 g/mol • Answer: B • (40.078 × 3) + (14.01 × 2) = 148.25

36. Which of the following does not form hydrogen bonds? • H2S • H2O • NH3 • HF Answer: A Hydrogen bonds can occur when a hydrogen atom is attracted to either a nitrogen atom, a fluorine atom, or an oxygen atom.

37. What does U represent on the graph? The activation energy for the forward reaction. The activation energy for the reverse reaction. The heat of reaction. The effect of a catalyst. • Answer: B • U represents the energy required to undergo the reverse reaction from X back to Y.

38. If an atom’s outermost electron is in a • d-orbital then the atom is a(n) • alkali metal. • alkaline-earth metal. • halogen. • transition metal. Answer: D Transition metal because only transition metals have an outermost electron in the d-orbital.

39. What happens to water as it boils? • The hydrogen and oxygen atoms separate and become gases. • The water molecules move slower. • Nothing • Hydrogen bonds between molecules break. Answer: D Water’s molecules remain intact, but bonds between molecules are weakened.

40. What is the point at which a substance coexists in solid, liquid, and gaseous forms? • equivalence point • equilibrium point • triple point • physical point Answer: C

41. What kind of compound is Ca3N2? • Covalent • Ionic • Metallic • Other • Answer: B • It is composed of a metal and a nonmetal.

42. Which of the following is a part of Dalton’s Atomic Theory? • All matter is made up of atoms. • Atoms cannot be subdivided, created, or destroyed. • Atoms of different elements can combine in whole-number ratios to form chemical compounds. • All of the above Answer: D Dalton’s Atomic Theory states all of these.

43. The half-life of beryllium-14 is 4.84 seconds. How much of a 16 gram sample of beryllium-14 is left after 14.52 seconds? • 4 g • 8 g • 20 g • 2 g • Answer: D • 14.52/4.84 = 3 half-lives • 16/2/2/2 = 2 g (cut 16 in half 3 times)

44. Identify the correct products: Na + CaF2 • NaF + Ca • Ca2F + Na • No reaction • NaF2 + Ca Answer: C Na is below Ca on the activity series. Always check the activity series for single replacement reactions.

45. What is FALSE about the relationship between 147N and 167N? These are two different isotopes of nitrogen. Both atoms have 7 protons. The atoms have different atomic masses. Both atoms have 7 neutrons. Answer: D These isotopes have different masses (14 and 16), but the same number of protons (7). To find the neutrons, calculate mass minus protons.

46. Which of the following is the best example of a trigonalplanar molecule? • CO2 • BF3 • NH3 • H2O Answer: B This molecule does not have enough valence electrons to follow the octet rule because it only needs six valence electrons. The fluorine atoms repel each other at 120 degree angles.

47. The wavelength of light released when an electron drops from n=4 to n=3 is • 1282 nm • 656 nm • 1875 nm • 97 nm Answer: C According to the Bohr model on page 8 of the reference tables, the wavelength is 1875 nm when the electron makes that transition from ring 4 to ring 3.

48. A + B ↔ C • What is the equilibrium constant for this reaction? • [A][B] Answer: D Keq = products divided by reactants

49. In what state is water at extremely low pressure and high temperature according to a phase diagram? • Liquid • Gas • Solid • Solid and Liquid Answer: B

50. What is the formula of lithium phosphate? • Li2PO4 • Li3 PO3 • Li2PO2 • Li3PO4 • Answer: D • Lithium has a +1 charge, and phosphate has a -3 charge. You can look up phosphate on the list of polyatomic ions. When you cross charges, your subscripts will be 3 and 1, respectively.