11. If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.89,
ID: 635503 • Letter: 1
Question
11. If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.89, w following is TRUE? b. [HCI 1021-[NaCHO21 d. HCHO2INaCHO21 12. In which of these solutions would silver carbonate have the lowest molar solubility? a. 0.03 MHSO b. 0.1 MAgNO c. 0.01 M AgNO, d. 0.01 MNa CO e. pure water 13. Which of the following is not a spontancous process at 25 C and 1 atm pressure? a. salt dissolving b. ice melting c. water freezing d. iron rusting e. steam condensing 14. Which of the following is true for the melting of a solid substance? a. AS-0 and AH- its normal boiling poim, 61.2C normal boiling point? 15. The standard enthalpy of vaporization of chloroform is 29.2 kJ/mol at What is the standard change in entropy for the vaporization of chloroform at its a. 87.3 J(mol K) b. 29.2 J/(mol K) c. 0.477 J(mol K) d. 0.0873 J(mol K) e. 477 J/(mol K) Page 6 of 14Explanation / Answer
Q11
pH = pKa + log [NaCHO2]/[HCHO2]
pH = 3.89
pka = 3.74
When [NaCHO2]=[HCHO2] then pH = pKa .
When [HCHO2]< [NaCHO2] then pH>pKa
Answer : Option 'a' [HCHO2]< [NaCHO2]
Q12. Solubility of salt decreases in a solution that contains an ion in common with that salt.AgNO3 and Na2CO3 solution contain common ion with salt Ag2CO3 . But concetration of AgNO3 is 0.1M and Na2CO3 is 0.01M so answer is option 'b'
Answer : Option 'b' 0.1M AgNO3
Q13 At room temperature ice can not freez so answer is option'c' .
Answer :option'c' water freezing.
Q14. Entropy is measure of randomness. During melting solid is converted into liquid. Due to increase in randomness entropy increases. So deltaS >0
Also melting is endothermic process so enthalpy increases i.e. deltaH>0
Answer : Option ;d' deltaS>0 and deltaH>0
15.
deltaS = deltaH/T
deltaS = 29.2*103 J/mol /334.2K
deltaS = 87.3 J/mol*K
Answer : Option 'a'
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