试题与答案

实验室常用邻苯二甲酸氢钾(KHC8H4O4)来标定氢氧化钠溶液的浓度,反应如下:

题型:实验题

题目:

实验室常用邻苯二甲酸氢钾(KHC8H4O4)来标定氢氧化钠溶液的浓度,反应如下:

KHC8H4O4+NaOH=KNaC8H4O4+H2O。邻苯二甲酸氢钾溶液呈酸性,滴定到达终点时,溶液的pH约为9.1。

(1)为标定NaOH溶液的浓度,准确称取一定质量的邻苯二甲酸氢钾(KHC8H4O4)加入250mL锥形瓶中,加入适量蒸馏水溶解,应选用_____________作指示剂,到达终点时溶液由______色变为_______色,且半分钟不褪色。(提示:指示剂变色范围与滴定终点pH越接近误差越小。)

(2)在测定NaOH溶液浓度时,有下列操作:

①向溶液中加入1~2滴指示剂;

②向锥形瓶中加20mL~30mL蒸馏水溶解;

③用NaOH溶液滴定到终点,半分钟不褪色;

④重复以上操作;

⑤准确称量0.4000g~ 0.6000g邻苯二甲酸氢钾加入250mL锥形瓶中;

⑥根据两次实验数据计算NaOH的物质的量浓度。

以上各步操作中,正确的操作顺序是________________________________。

(3)上述操作中,将邻苯二甲酸氢钾直接放在锥形瓶中溶解,对实验是否有影响? ______________。(填“有影响”或“无影响”)

(4)滴定前,用蒸馏水洗净碱式滴定管,然后加待测定的NaOH溶液滴定,此操作使实验结果________。(填“偏大”“偏小”或“无影响”)

(5)现准确称取KHC8H4O4(相对分子质量为204.2)晶体两份各为0.5105g,分别溶于水后加入指示剂,用NaOH溶液滴定至终点,消耗NaOH溶液体积平均为20.00mL,则NaOH溶液的物质的量浓度为___________。(结果保留四位有效数字)

答案:

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参考答案:国家专利局如果认为必要,可以自行对申请实质审查。《专利法》第35条第2款规定:"国务院专利行政部门认为必要的时候,可以自行对发明专利申请进行实质审查。"

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