4．
乙二酸\(\rm{(HOOC-COOH}\)，可简写为\(\rm{H_{2}C_{2}O_{4})}\)俗称草酸，在\(\rm{100℃}\)开始升华，\(\rm{157℃}\)时开始分解．
\(\rm{(1)}\)探究草酸的酸性
\(\rm{①}\)已知：\(\rm{25℃H_{2}C_{2}O_{4}}\) 的电离常数 \(\rm{K_{1}=5.4×10^{2}}\)，\(\rm{K_{2}=5.4×10^{5}}\)；\(\rm{H_{2}CO_{3}}\)的电离常数 \(\rm{K_{1}=4.5×10^{7}}\)，\(\rm{K_{2}=4.7×10^{11}}\)则下列化学方程式正确的是 ______ \(\rm{(}\)填选项序号，下同\(\rm{)}\)
A.\(\rm{H_{2}C_{2}O_{4}+CO_{3}^{2}=HCO_{3}^{}+HC_{2}O_{4}^{}}\)
B.\(\rm{HC_{2}O_{4}^{}+CO_{3}^{2}=HCO_{3}^{}+C_{2}O_{4}^{2}}\)
C.\(\rm{H_{2}O+CO_{2}+C_{2}O_{4}^{2}=HC_{2}O_{4}^{}+HCO_{3}^{}}\)
D.\(\rm{C_{2}O_{4}^{2}+CO_{2}+H_{2}O=H_{2}C_{2}O_{4}+CO_{3}^{2}}\)
\(\rm{②}\)向\(\rm{1L}\) \(\rm{0.02mol/L}\) \(\rm{H_{2}C_{2}O_{4}}\)溶液中滴加\(\rm{1L}\) \(\rm{0.01mol/L}\) \(\rm{NaOH}\)溶液\(\rm{.}\)混合溶液中\(\rm{c(H^{+}) > c(OH^{-})}\)，下列说法中正确的是 ______ ．
A.\(\rm{c(H_{2}C_{2}O_{4}) > c(HC_{2}O_{4}^{})}\)
B.\(\rm{c(Na^{+})+c(H^{+})=2c(C_{2}O_{4}^{2})+c(HC_{2}O_{4}^{})+c(OH^{-})}\)
C.\(\rm{c(OH^{-})=c(H^{+})+2c(H_{2}C_{2}O_{4})+c(HC_{2}O_{4}^{})}\)
D.\(\rm{c(H_{2}C_{2}O_{4})+c(C_{2}O_{4}^{2})+c(HC_{2}O_{4}^{})=0.02mol/L}\)
\(\rm{(2)}\)用酸性\(\rm{KMnO_{4}}\)溶液滴定含杂质的\(\rm{Na_{2}C_{2}O_{4}}\)样品\(\rm{(}\)已知杂质不与\(\rm{KMnO_{4}}\)和\(\rm{H_{2}SO_{4}}\)溶液反应\(\rm{)}\)．
实验步骤：
准确称取\(\rm{1g}\)样品\(\rm{Na_{2}C_{2}O_{4}}\)固体，配成\(\rm{100mL}\)溶液，取出\(\rm{20.00mL}\)于锥形瓶中\(\rm{.}\)再向瓶中加入足量稀\(\rm{H_{2}SO_{4}}\)溶液，用\(\rm{0.016mol/L}\)高锰酸钾溶液滴定，滴定至终点时消耗高锰酸钾溶液\(\rm{25.00mL}\)．
\(\rm{(}\)已知：\(\rm{5H_{2}C_{2}O_{4}+2KMnO_{4}+3H_{2}SO_{4}=10CO_{2}↑+2MnSO_{4}+K_{2}SO_{4}+8H_{2}O)}\)
\(\rm{①}\)高锰酸钾溶液应装在 ______ 滴定管中\(\rm{.(}\)填“酸式”或“碱式”\(\rm{)}\)
\(\rm{②}\)滴定至终点时的实验现象是： ______ ．
\(\rm{③}\)下列操作可能使测量结果偏高的是 ______ ；
A.盛装的\(\rm{Na_{2}C_{2}O_{4}}\)的滴定管没润洗
B.盛装高锰酸钾溶液的滴定管滴定前尖嘴处有气泡，滴定后气泡消失
C.读数时滴定前仰视，滴定后俯视
D.锥形瓶中残留少量水
\(\rm{④}\)计算样品中\(\rm{Na_{2}C_{2}O_{4}}\)的纯度 ______ ．