HF and HCN are both weak acids. Ka = 3.5 x 10-4 for HF Ka = 4.9 x 10-10 for HCN What is [CN-] in a mixture of 0.50 M HF and 0.30 M HCN. A. 1.2 × 10-5 M B. 7.4 × 10-6 M C. 2.4 × 10-10 M D. 1.1 × 10-8 M E. 3.7×10-6M