现使用酸碱中和滴定法测定市售白醋的总酸量(g⼀100mL).Ⅰ.实验步骤:(1)用______(填仪器名称)量取

2025-03-24 20:29:28
推荐回答(1个)
回答1:

I.(1)用滴定管(或10mL移液管)(量取10.00mL食用白醋,在烧杯中用水稀释后转移到100mL 容量瓶中定容,摇匀即得待测白醋溶液,故答案为:滴定管(或10mL移液管);烧杯; 容量瓶;
(2)食醋与NaOH反应生成了强碱弱酸盐,溶液呈碱性,应选择碱性变色范围内的指示剂酚酞,故答案为:酚酞;(3)滴定管液面的读数0.60mL,故答案为:0.60;
(4)NaOH滴定食醋的终点为:溶液由无色恰好变为红色,并在半分钟内不褪色,
故答案为:溶液由无色恰好变为红色,并在半分钟内不褪色;
III.(1)第1次滴定误差明显大,属异常值,应舍去;3次消耗的NaOH溶液的体积为:15.00mL;15.05mL;14.95mL;则NaOH溶液的体积的平均值为15.00mL;
设10mL市售白醋样品含有 CH 3 COOOH Xg,则
         CH 3 COOOH~NaOH
         60                       40
        Xg×0.2          0.1000mol/L×0.015L×40g/mol
          X=0.450
c(市售白醋)=
0.450g
 60  g/mol      
0.01L
=0.75mol/L,样品总酸量4.50g/100mL,
故答案为:第1次滴定误差明显大,属异常值,应舍去; 0.75; 4.5;
(2)电离常数判断酸的强弱,依据电离常数的大小判断酸性强弱,进而判断反应能否发生,其他选项不能判断酸的强弱,故选:c;
(3)a.碱式滴定管在滴定时未用标准NaOH溶液润洗,标准液浓度降低,造成V(标准)偏大,根据C(待测)=
C(标准)×V(标准) 
V(待测)
分析可知C(待测)偏大,故a正确;
b.碱式滴定管的尖嘴在滴定前有气泡,滴定后气泡消失,造成V(标准)偏大,根据C(待测)=
C(标准)×V(标准) 
V(待测)
分析可知C(待测)偏大,故b正确;
c.锥形瓶中加入待测白醋溶液后,再加少量水,对V(标准)无影响,根据C(待测)=
C(标准)×V(标准) 
V(待测)
分析可知C(待测)不变,故c错误;
d.锥形瓶在滴定时剧烈摇动,有少量液体溅出,待测液物质的量偏小,造成V(标准)偏小,根据C(待测)=
C(标准)×V(标准) 
V(待测)
分析可知C(待测)偏小,故d正确;
故选:ab

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