A 1.00 liter solution contains 0.46 M hydrocyanic acid and 0.35 M potassium cyan
ID: 635334 • Letter: A
Question
A 1.00 liter solution contains 0.46 M hydrocyanic acid and 0.35 M potassium cyanide. If 25.0 mL of water are added to this system, indicate whether the following statements are true or false. (Note the the volume MUST CHANGE upon the addition of water.)
A 1.00 liter solution contains 0.46 M hydrocyanic acid and 0.35 M potassium cyanide If 25.0 mL of water are added to this system, indicate whether the following statements are true or false. (Note the the volume MUST CHANGE upon the addition of water.) A. The concentration of HCN will increase. B. The concentration of CN" will decrease. C. The equilibrium concentration of Hy0 will remain the same 4 D. The pH will remain the same. E. The ratio of [HCN]/[CN] will decrease.Explanation / Answer
Moles of HCN = molarity x volume = 0.46 mol/L x 1L = 0.46 mol
Moles of KCN = molarity x volume = 0.35 mol/L x 1L = 0.35 mol
pH = pKa + log [base/acid]
= 9.31 + log (0.35/0.46)
= 9.19
After adding water
Total volume = 25 mL x 1L/1000 mL + 1 L
= 1.025 L
Concentration of HCN = 0.46/1.025 = 0.4489 M
Concentration of KCN = 0.35/1.025 = 0.3415 M
pH = pKa + log [base/acid]
= 9.31 + log (0.3415/0.4489)
= 9.19
A - concentration of HCN will decrease
B - concentration of KCN will decrease
C - equillibrium concentration of H3O+ will remain same
D - pH remain same
E - the ratio will remain same
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