1998 - U.S National Chemistry Olympiad 1998 National Test...

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U.S. National Chemistry Olympiad: 1998 National Test Go to the answers 1. Which pair of substances could be separated by mixing with water and filtering? (A) NaNO 3 and K 2 SO 4 (B) CH 3 OH and CH 3 COCH 3 (C) MgCO 3 and Fe(OH) 3 (D) KCl and CuS 2. Which gas produces an acidic solution when bubbled into water? (A) NH 3 (B) Cl 2 (C) H 2 (D) CH 4 3. A dilute HCl solution is to be prepared from a more concentrated solution. Which of pieces of glassware will give the highest level of precision? (A) graduated cylinder and volumetric flask (B) two graduated cylinders (C) pipet and graduated cylinder (D) pipet and volumetric flask 4. Which substance is likely to show the greatest change in mass when exposed to air? (A) Al (B) NaOH (C) CaCO 3 (D) SiO 2 5. Which is a yellow solid? (A) C (B) Na (C) S 8 (D) I 2 6. An alloy of gold and silver contains 38.5% silver by mass and has a density of 14.6 g mL¯ 1 . What is the molar concentration of silver in this alloy? (A) 52.1 mol L¯ 1
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(B) 45.6 mol L¯ 1 (C) 3.57 mol L¯ 1 (D) 2.64 mol L¯ 1 7. As 2 S 3 reacts with O 2 to give SO 2 and As 2 O 3 . What is the smallest whole number coefficient for O 2 when the equation for this reaction is balanced correctly? _As 2 S 3 (s) + _O 2 (g) ---> _As 2 O 3 (s) + _SO 2 (g) (A) 3 (B) 5 (C) 7 (D) 9 8. A 0.242 g sample of potassium is heated in oxygen. The result is 0.440 g of a crystalline compound. What is the formula of this compound? (A) KO (B) K 2 O (C) KO 2 (D) KO 3 9. What volume of 3.0 M Na 2 SO 4 must be added to 25 mL of 1.0 M BaCl 2 to produce 5.0 g of BaSO 4 ? (A) 7.2 mL (B) 8.3 mL (C) 10.0 mL (D) 14 mL 10. These three equations describe an oxidation-reduction method for determining dissolved oxygen in water. How many moles of S 2 O 3 2 ¯ are equivalent of each mole of O 2 ? 1) 2Mn 2+ (aq) + 4OH¯(aq) + O 2 (g) ---> 2MnO 2 (s) + 2H 2 O(l) 2) MnO 2 (s) + 2I¯(aq) + 4H + (aq) ---> Mn 2+ (aq) + I 2 (aq) + 2H 2 O(l) 3) 2S 2 O 3 2 ¯(aq) + I 2 (aq) ---> S 4 O 6 2 ¯(aq) + 2I¯(aq) (A) 0.5 (B) 1 (C) 2 (D) 4 11. A 15 mL sample of 0.20 M MgCl 2 is added to 45 mL of 0.40 M AlCl 3 . What is the molarity of Cl¯ ions in the final solution?
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(A) 1.0 M (B) 0.60 M (C) 0.35 (D) 0.30 M 12. How many electrons are present in 2.0 x 10¯ 3 moles of 18 8 O 2 ¯? (A) 1.2 x 10 21 (B) 9.6 x 10 21 (C) 1.2 x 10 22 (D) 1.9 x 10 22 13. In which change of state are covalent bonds broken? (A) evaporation of water (B) fusion of sodium chloride (C) vaporization of diamond (D) sublimation of dry ice 14. By what factor does the average velocity of a gaseous molecule increase when the absolute temperature is doubled? (A) 1.4 (B) 2.0 (C) 2.8 (D) 4.0 15. Which species is expected to have the highest boiling point at 1 am pressure? (A) O
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1998 - U.S National Chemistry Olympiad 1998 National Test...

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