Question

53 mL of 0.65 M hydrocyanic acid (HCN) is added to 47 mL of 0.28 M calcium hydroxide (Ca(OH)_2). What is the pH of the resulting solution? Buffers are found extensively in nature, and particularly in the human body. Please explain how a buffer resists changes in pH when, for example, a strong acid is added to a buffered system.

Answer 1

Calculate the moles of HCN mol×53mL×1000ml 1 L 0.65-x5 Calculate the moles of Ca (OH) 0.28 ×47 mL×- 1 mol Ca(OH) requires 2 mol HCN fom neutralizati on Thus, moles of HCN required for 0.0132 mol Ca(OH) s as follows 0.0132 mol Ca (OH), x 2 mol HCN Moles of HCN left-0.0344-0.0264 0.008 mol mo 1000mL= 0.0132 mol HCN0.0264 mol 1 mol Ca (OH) 0.008 mol 1000 mL m0.0800 M (53+47) mL 1L K, value of HCNis 6.2x10-10 Dissociation of HCNis as follows HCN(aa) H'(aq) +CN(aq) I(M) 0.0800 C(M) E(M): 0.0800-r +x [HCN] 6.2×10-10-00800-X pH =-log =-log(7.04x10-6 pH- 5.15