Regents Chemistry Exam Explanations June 2002

Questions	Answer	Explanations
21 What is the oxidation number of chromium in K₂Cr₂O₇? (1) +12 (3) +3 (2) +2 (4) +6	4	K₂Cr₂O₇ K 2(+1) =+2 Cr 2(x)=+12 O 7(-2)=-14
22 Which process requires an external power source? (1) neutralization (3) fermentation (2) synthesis (4) electrolysis	4	EXAMPLE-Electricity is required to seperate water into hydrogen
23 A substance that conducts an electrical current when dissolved in water is called (1) a catalyst (3) a nonelectrolyte (2) a metalloid (4) an electrolyte	4	Definition Electrolyte
24 Which product of nuclear decay has mass but no charge? (1) alpha particles (3) gamma rays (2) neutrons (4) beta positrons	2	Definition-Gamma Ray Table O
25 Given the reaction: HCl(aq) + LiOH(aq) → HOH(ℓ) + LiCl(aq) The reaction is best described as (1) neutralization (2) synthesis (3) decomposition (4) oxidation-reduction	1	Neutraliztion-Acid (H+) reacts with a base (OH-) to produce salt and water (HOH)
26 Which ion is produced when an is dissolved in water? (1) H⁺, as the only positive ion in solution (2) H₃O⁺, as the only positive ion in solution (3) OH^-C, as the only negative ion in solution (4) H^- , as the only negative ion in solution	3	Definition- Arrhenius base
27 The change that is undergone by an atom of an element made radioactive by bombardment with high-energy protons is called (1) natural transmutation (2) artificial transmutation (3) natural decay (4) radioactive decay	2	Bombardment is artifical transmutation- changing the number of protons (changes teh element)
28 As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy (1) decreases (2) increases (3) remains the same	2	During a phase change potential energy changes
29 As a sample of the radioactive isotope ¹³¹I decays, its half-life (1) decreases (2) increases (3) remains the same	3	HALF LIFE NEVER CHANGES
30 As an atom becomes an ion, its mass number (1) decreases (2) increases (3) remains the same	3	IONS formed from a change in electrons no effect on mass number (P and N)