If the Tris buffer was exactly at pH = 9, then calculate the expected pH values for tube 7 (undiluted), tube 8 (1/2 dilution), and tube 9 (1/10 dilution) after the addition of 1 ml of 0.05 M NaOH.
Test tube 7: 4 ml of 0.1 M Tris pH 9, + 1 ml 0.05 M NaOH
Test tube 8: 4 ml of 0.050 M Tris pH 9, + 1 ml 0.05 M NaOH
Test tube 9: 4 ml of 0.010 M Tris pH 9, + 1 ml 0.05 M NaOH