Question

SALTS: For each of the following salt solutions, record the experimental pH, determine the theoretical pH (show your work) and then determine the percent error between the two (show your work). For errors of greater than 20%, provide an explanation for the deviation.

1) 0.15 M KCl Solution; experimental pH = 6.82

Acid | Ka |

HCL | >>1 |

Calculated pH: _____________ Actual pH: ______________ Percent error: ____________

2) 0.15 M Na2HPO4 Solution; experimental pH = 8.90

Acid | Ka |

H_{3}PO_{4} |
7.1 x 10^{-3} |

H_{2}PO_{4}^{-} |
6.3 x 10^{-8} |

HPO_{42-} |
4.5 x 10^{-13} |

Calculated pH: _____________ Actual pH: _______________ Percent error: _____________

3) 0.15 M NH_{4}NO_{3}; experimental pH =
6.90

Acid | Ka |

HNO_{3} |
>>1 |

NH_{4}^{+} |
5.6 x 10^{-10} |

Calculated pH: _____________ Actual pH: ______________ Percent error:____________

Please show calculations! I am very confused.

Answer #1

1) For KCl

salt of strong acid and strong base would have a theoretical pH = 7

Percent error = (7 - 6.82) x 100/7 = 2.60%

2) 0.15 M Na2HPO4

HPO4- + H2O <==> H2PO4- + OH-

1 x 10^-14/6.16 x 10^-8 = x^2/0.15

x = [OH-] = 1.56 x 10^-4 M

pOH = -log[OH-] = 3.80

pH = 14 - pOH = 10.19

Percent error = (10.19 - 8.90) x 100/8.90 = 14.50%

3) 0.15 M NH4NO3

NH4NO3 --> NH4+ + NO3-

NH4+ + H2O --> NH3 + H3O+

1 x 10^-14/1.8 x 10^-5 = x^2/0.15

x = [H3O+] = 9.13 x 10^-6 M

pH = -log[H3O+] = 5.04

Percent error = (6.9 - 5.04) x 100/6.9 = 26.96%

Acid Ka
H2PO4- 6.29 x 10-8
NH4+ 5.68 x 10 -10
HCl >> 1
Calculate the pH of a 0.150 M solution of Na2HPO4.
Calculate the pH of a 0.150 M solution of NH4NO3.
Calculate the pH of a 0.150 M solution of KCl.

Which of the following combinations would be best to buffer an
aqueous solution at a pH of 7.0?
a) H2PO4– and HPO42–, Ka2 = 6.2E-8
b) NH4+ and NH3, Ka = 5.7E-10
c) H3PO4 and H2PO4–, Ka1 = 7.5E-3
d) CH3CO2H and CH3COO–, Ka = 1.8E-5
e) HNO2 and NO2–, Ka = 4.5E-4

Determine the pH of a solution that is 0.15 M NaH2PO4 and 0.10 M
Na2HPO4 (the Ka for H2PO4- is 6.2 x10^-8). Include a chemical
equation showing the relevant equilibrium.
Please show me how you got the answer, I understand how to do
single pH calculations but not entirely sure how to do it with two
chemicals. Thanks!

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c. H3PO4 + H2O =
H2PO4- + H3O+
d. PO43- + H2O =
HPO42- + OH-
2. Tina has two aqueous solutions: 1.2 x 10-2
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Ka1 = 7.5 x 10^-3
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10-9

Determine the pH of a 0.0520 M solution of the following salts.
A table of pertinent K values is found to the right. a) NaHCO3 b)
NaH2PO4
acid
formula
K1
k2
k3
arsenic acid
H3AsO4
5.8e-3
1.1e-7
3.2e-12
carbonic acid
H2CO3
4.45e-7
4.69e-11
hydrogen sulfide
H2S
9.6e-8
1.3e-14
phosphoric acid
H3PO4
7.11e-3
6.32e-8
4.5e-13

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Determine the pH of the solution, if possible. (Ammonium: Ka =
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