An aqueous solution with a low pH is necessary for a certain industrial process.

Question

An aqueous solution with a low pH is necessary for a certain industrial process. Which of the following solutions would have the lowest pH? 2.0 M NaoH 0.5 M HCl 1.0 M acetic acid 1.0 M HCl All solutions would have the same pH. Which one of the following correctly represents a conjugate acid-base pair? H_2O, O^- H_3O^+, H_3CO_3, CO_3^2- HCl, Cl_2 H_2CO_3, HCO_3^- What is the pH of a 1.0 Times 10^-4 solution of KOH? 4.00 6.00 7.00 10.00 14.00 A solution containing a buffer has an initial pH of 8.78. If student adds 5 drops HCl to this solution, what would be a reasonable pH for the resulting solution? 5.22 7.00 8.64 8.78 8.89 Identify the oxidizing agent and reducing agent, respectively, in the reaction below. Cl_2(aq) + 2l^- (aq) rightarrow 2Cl^- (aq) + I_2(aq) Cl_2 and I^- For the reaction shown below, which of the following is a conjugate acid-base pair? C_3H_3N(aq) + H_2O(l) C_5H_5NH^+ (aq) + OH^- (aq) A buffer solution is prepared by placing twice the concentration of propanoic acid (C_2H_3COOH, K_a = 1.34 Times 10^-5) as the concentration of its conjugate base sodium propanoate into a flask. The pH of the resulting buffer solution is best described as which of the following? less than 4.87 4.87 between 4.87 and 9.00 greater than 11.00 Undeterminable; the concentrations of the acid and conjugate base must be given What is the pH of a 0.035 M HCl solution? 3.50 1.46 2.27 5.59 12.54 What is the [OH^-] of a solution which has a pH = 10.95? 1.03 M 1.1 Times 10^-11 M 8.9 Times 10^-4 3.05 M 7.4 Times 10^-5 M

Explanation / Answer

(34) We know that stronger is the acid, lower is the pH. in the given choices the stronger acid is HCl. There are two choices with HCl. So, let's calculate the pH for both of them,

Being a strong acid, there is complete dissociation for HCl and so H+ concentration is same as concentration of HCl.

for 0.5M HCl, pH = - log(0.5) = 0.301

for 1.0 M HCl, pH = log(1.0) = 0

So, correct choice is (D), 1.0 M HCl

(35) according to Bronsted -Lowry concept, an acid is a proton donor and a base is a proton acceptor.

So, would have one extra H atom than its conjugate base, and a base would have one less H atom then its conjugate acid.

(A) H2O and O- this is not the right pair since if one proton goes out from H2O then we would get OH- not O-.

(B) H3O+ and OH- This one is also not the right pair since if one proton goes out from H3O+ then we would get H2O not OH-

(C) H2CO3 and CO3-2 This is also not the correct pair since if one proton goes out from H2CO3 then we would get HCO3- and not CO3-2.

(D) HCl and Cl2 is also not a correct pair since if one proton goes out from HCl then we would get Cl- and not Cl2.

(E) H2CO3 and HCO3-1 This one is correct since if one proton goes out from H2CO3 then we get HCO3-1.

(36) KOH is a strong base so it dissociates completely and so the OH- would be 1.0 x 10-4 M

pOH = - log(1.0 x 10-4) = 4

pH = 14 - pOH = 14 - 4 = 10

So, the correct choice is (D), 10.00

(37) initial pH of buffer = 8.78

we know that a buffer solution resists a change to its pH if an acid or base is added to it. When a strong acid is added then a very slight decrease to its pH takes place since the added acid decreases the conjugate and increases the weak acid.

so, the reasonable value would be 8.64. so, choice (C) is correct.

(38) Cl2(aq) + 2I-(aq) ----------------> 2Cl-(aq) + I2(aq)

in this equation oxidation number of Cl is decreasing from 0 to -1 and that of I is increasing from -1 to 0. So, oxidation of iodine and reduction of chlorine is taking place.

An specis that undergoes oxidation acts as a reducing agent and an species that undergoes reducttion acts as oxidizing agent.

So, oxidizing agent is Cl2 and reducing agent is I-. So, the correct choice is (A).

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