4n When a salt such as sodium uoride, moti. Nar, disolves wter tne pr of the res
ID: 698894 • Letter: 4
Question
4n When a salt such as sodium uoride, moti. Nar, disolves wter tne pr of the ressarg soktion is expected to ho- a pt that s a) less than ph 7 greater than pe The base oniation This cannot be predeted. folowing 4 expressed as which of the constant, k, for the cyanide anion, CN, can be b) 45) Benaoic acid, CHCO.Hf, has a Ki value of 63 x 10 whats the value of a for the benzoate ion, Gco, a) 5.6 x 10.0 b) 63x 10 e) 1.8×10, 1.6 x 1010 the OH in a dissoliertment Equiiborim or Sair Solutions an IL.C.E. chart was used to determine the concentration of OH] 1.26 x 10 M. What is the pH of the solution measure? a) 11.10 b) 1.26 c) 2.90 12.74 of Magnesium, the instructions indicate that this? 4) During the experimental setup for Determination of the Molar Mass the magnesium ribbon must be sanded with a piece of Emory cloth. What was the purpose for doing a To ensure the ribbon would b) To remove surface oxidation that can slow the reaction. properly col to avoid falling down the gas tube during the experiment. the ribbon would g To reduce the mass of the ribbon so it falls in the 0.7-0.8 g range. The reason was never stated. 48) In the analysis of the molar mass of pressure of magnesium, the pressure of the water vapor in the gas buret, P(H.O) was determined by a) b) Taking c) d) This information was provided by the instructor the atmospheric pressure from the pressure of the hydrogen gas collected. the height of the water column from mmH:O to mmHg. the temperature of the water and referring to the vapor pressure chart. 49) During the ewgeh ment to determine the molar mass of magnesium, the following reaction occurred in a ges buret. The source for the H' came from a) Water b) Electron transfer c) Hydrochloric acid d) A catalyst 50) For the experiment in Question 49, it was found experimentally that 1.51 x 103 mol of Hz was collected in the gas buret. What ) 0.0781 9 b) 0.0406 g ) 0.1562 g 0.0367 g mass of magnesium solid was reacted to produce this quantity of gas?Explanation / Answer
43).HF is a weak acid with pKa= 3.2, pKb for F-1 + H2O---->HF + OH-. pKb=Kw/Ka. So F- acts as a base and releases OH- by reacting with H2O. So pH >7. Thus answer is c).
44.)Liquid form like H2O are not included in equilibrium constant calculations as their concentrations are assumed to be unchanging. Thus answer is a).
45.)Kb= Kw/Ka=10-14/(6.3*10-5)=1.6*10-10. So answer is d).
46.)pH=14-pOH, pOH=-log[OH-]=-log(1.26*10-3)=2.9
pH=14-2.9=11.1. So answer is a).
47.)White coating of MgO that slows down the reaction is removed by rubbing with sand papers. So answer is b).
48.) Answer is b).
49.)HCl is reacted with Mg. So c).
50.) For one mole of H2 produced 1 mol of Mg reacts. So for 1.51*10-3 mol H2 produced 1.51*10-3 mol of Mg would react. Mass of 1.51*10-3 mol Mg = 1.51*10-3 mol*24.3g/mol=0.0367g. So answer is d).
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