19. Which of the following is the weakest acid? A. H3BO3 B. H3As04 C. HCI04 D. H

Question

19. Which of the following is the weakest acid? A. H3BO3 B. H3As04 C. HCI04 D. H2SO4 E. H2COs 20. What is the pH of a 4.30 x 10-3 M Ba(OH)2 solution? A. 2.07 B. 2.37 C.9.27 21. Which of the following substances is never a Bransted-Lowry base in an aqueous solution? A. potassium hydroxide, NaOH B. sodium dihydrogen phosphate, NaH PO C. sodium phosphate, NasPO D. ammonium chloride, NH.CI E. sodium bicarbonate, NaHCO 22. What is the HO, concentration in 5.8 x 104 M KOHaq) at 25 °C? (K-.0 x 1014) A. 5.8x101"M B. 1.7x101 M C. 5.8 x 10 M E. 5.8 x 10° M 23. An aqueous solution with a pH of 12.00 is diluted from 1.0L to 4.0L. What is the pH of the diluted solution? A. 3.00 B. 6.78 C. 7.22 D. 11.40 E. 19.93

Explanation / Answer

19. H3BO3 = pKa = 9.23

    H3AsO4 = pka1 = 2.3

    HClO4 = pka<1

    H2SO4 = pka<!

    H2CO3 = 6.37

increasing pka value, decreases the acidity.so that

weakest acid = H3BO3

answer: A
  

20. Ba(OH)2 is strong base,

   [OH-] = 2*4.3*10^-3 = 8.6*10^-3 M

pOH = -log(OH-)

     = -log(8.6*10^-3)

    = 2.06

pH = 14-2.06 = 11.94

answer: E

21. answer: D. NH4Cl

NH4Cl IS ACIDIC in aqueous solution.so that it can not accepts a proton,therefore it wont acts as bronsted-base.

22. answer: B

    KOH- stron base,

   [OH-] = 5.8*10^-4 M

   [H3O+] = KW/[OH-]

          = 1*10^-14/(5.8*10^-4)

   = 1.724*10^-11 M

23. pH = 12,
  
     pOH = 14-12 =2

pOH= -log[OH-]

    [[OH-] = 10^-pOH

            = 10^-2 M

M1V1 = M2V2

10^-2*1 = M2*4

M2 = concentration of [OH- diluted = 2.5*10^-3 M

poH = -log(2.5*10^-3) = 2.6

pH = 14-2.6 = 11.4

answer: D.

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