1) HBr is a strong acid meaning it ionizes 100% so H^+ from HBr is 0.115M. To this can be added the H^+ from HCHO2 but remember that the strong acid is a common ion to the HCHO2 so the ionization of HCHO2 will be suppressed.
It may be suppressed so much that the amount HT+ added is not significant but you will need to calculate it to know.
2) This is done the same way; however, both are weak acids. Caculate H^+ from acetic acid (the stronger one) and proceed as in 1 above.
Post your work if you get stuck.
Find the pH of each mixture of acids
1) 0.115M in HBr + 0.125M in HCHO2
2) 0.050M in acetic acid + 0.050M in hydrocyanic acid
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