A chemistry graduate student is given 300.mL of a 0.50M nitrous acid HNO2 solution. Nitrous acid is a weak acid with =Ka×4.510−4 . What mass of KNO2 should the student dissolve in the HNO2 solution to turn it into a buffer with pH =2.80 ? You may assume that the volume of the solution doesn't change when the KNO2 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.