August 2008 Chemistry Regents #31-40
Highlight to reveal answers and explanations
Questions 1-10 Questions 11-20 Questions 21-30 Questions 31-40 Questions 41-50 |
Questions | Answer | Explanations |
| 31 What is the total number of protons in an atom with the electron configuration 2-8-18-32-18-1? (1) 69 (3) 118 (2) 79 (4) 197 | 2 | add them up protons = electrons when it say "atom" |
| 32 Which two elements have the most similar chemical properties? (1) Be and Mg (3) Cl and Ar (2) Ca and Br (4) Na and P | 1 | same group |
| 33 In the ground state, each atom of an element has two valence electrons. This element has a lower first ionization energy than calcium. Where is this element located on the Periodic Table? (1) Group 1, Period 4 (3) Group 2, Period 3 (2) Group 2, Period 5 (4) Group 3, Period 4 | 2 | 2 valence electrons Group 2 Lower first ionization energy is lower on the PT or Table S |
| 34 Which equation shows conservation of mass and charge? (1) NH4Br ==> NH3 + Br2 (2) 2Mg + Fe3+ ==>Mg2+ + 3Fe (3) H2SO4 + LiOH ==> Li2SO4 + H2O (4) Cu + 2Ag+ ==> Cu2+ + 2Ag | 4 | atoms in equal atoms out Charges in equal charges out |
| 35 What is the percent composition by mass of hydrogen in NH4HCO3 (gram-formula mass = 79 grams/mole)? (1) 5.1% (3) 10.% (2) 6.3% (4) 50.% | 2 | 5/79 x 100% |
| 36 What is the total number of valence electrons in a sulfide ion in the ground state? (1) 8 (3) 16 (2) 2 (4) 18 | 1 | sulfide has 8 valence electrons (it is an ion of sulfur) |
| 37 A temperature of 37C is equivalent to a temperature of (1) 98.6 K (3) 310. K (2) 236 K (4) 371 K | 3 | add 273 (table T) |
| 38 Which balanced equation represents a chemical change? (1) H2O(l) + energy → H2O(g) (2) 2H2O(l) + energy → 2H2(g) + O2(g) (3) H2O(l) → H2O(s) + energy (4) H2O(g) → H2O(l) + energy | 2 | chemical changes create new compounds or elements |
| 39 When 5 grams of KCl are dissolved in 50. grams of water at 25C, the resulting mixture can be described as (1) heterogeneous and unsaturated (2) heterogeneous and supersaturated (3) homogeneous and unsaturated (4) homogeneous and supersaturated | 3 | dissolving (aq) = homogeneous mixture using table G (double 5g because of the 50mL of water) 10 grams at 25C is below the line=unsaturated |
| 40 Which aqueous solution of KI freezes at the lowest temperature? (1) 1 mol of KI in 500. g of water (2) 2 mol of KI in 500. g of water (3) 1 mol of KI in 1000. g of water (4) 2 mol of KI in 1000. g of water | 2 | The most concentrated mol/liters |