A beaker with 160 mL of an acetic acid buffer with a pH of 5.00 is sitting on a benchtop. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 5.30 mL of a 0.420 M HCl solution to the beaker. How much will the pH change? The pKa of acetic acid is 4.760.
Express your answer numerically to two decimal places. Use a minus (-) sign if the pH has decreased.