Pres x GINsystem xG how to find conc xBrooke Practices for Chapter 16 LOs Insert

Question

Pres x GINsystem xG how to find conc xBrooke Practices for Chapter 16 LOs Insert Design Layout References Mailings Review View ·Times New Ro...-120 A-Ar A- -r i-', A) 0.020 HC solution. A) 1Q Given twe of the three for a weak acid (or e means to solve for any of concentretions and pH, be able to solve for the missing one (l)A0.15 M aqueous solution ofthe weak acid HA at 250°Chas a pH of535. The value of for H A)3.0 x 10-, B) 1.8 × 10-5 c) 3.3 x 104 D) 1.3 x 10-" E) 7.1 x 10 (2) The & of bydrazsic acid (HNs) is 1.9 x 10- at 25.0°C. What is the pli of a 0.35 M aqueous solution of HNy? A)5.23 B) 259 C)2.41 D)-2.46 E)1.14 acids A) 1.70 (3) Find 1.8 x 10 .K of H A) 1.00 50 Min HCIO Kof HCHO, is E) 4.42 of 8 2011 Words nglish (us ok Air 1 F7

Explanation / Answer

2)

HN3 dissociates as:

HN3 -----> H+ + N3-

0.35 0 0

0.35-x x x

Ka = [H+][N3-]/[HN3]

Ka = x*x/(c-x)

Assuming x can be ignored as compared to c

So, above expression becomes

Ka = x*x/(c)

so, x = sqrt (Ka*c)

x = sqrt ((1.9*10^-5)*0.35) = 2.579*10^-3

since c is much greater than x, our assumption is correct

so, x = 2.579*10^-3 M

so.[H+] = x = 2.579*10^-3 M

use:

pH = -log [H+]

= -log (2.579*10^-3)

= 2.59

Answer: B

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