8.称取乙酰水杨酸试样0.5490g,加 .00mL0.1660mol/L NaOH, 加热煮-|||-沸,反应式为-|||--COOH +2NaOH= □ -COONa+C(H)_(3)COONa+(H)_(2)O-|||--O-C-C(H)_(3)-|||-O-|||-过量的碱用27.14mL HCl回滴。已知 https:/img.cdnjtzy.com/zyb_1f83a57b39e4ab59226a79b18baf02dd.jpg.000mL HCl=0.03814gNa2(B)_(4)(O)_(7)cdot (a)_(2)(O)_(4)cdot 10(H)_(2)O,-|||-计算试样的纯度(以%表示),滴定时用什么指示剂?为什么?(已知:乙酰水杨酸-|||-的摩尔质量为 .16g/mol, Na2B4 O7·10H2O的摩尔质量为 .37g/mol, 水杨-|||-酸的 (K)_({a)_(1)}=3.00, (K)_({w)_(2)}=13.40, HAc的 _(a)=1.80times (10)^-5