用司盘20(HLB=8.6)和吐温60(HLB=14.9)组成的混合表面活性剂的HLB值为12.38，问二者混合量之比是
A．2:5
B．3:2
C．3:4
D．4:3
E．2:3
参考答案：E
解析：
掌握混合表面活性剂的HLB值的计算。
解：非离子型表面活性剂的HLB值具有加和性，其混合体系的HLB值可用下式计算：
HLBab=(HLBa·Wa+HLBb·Wb)/(Wa+Wb)
式中：HLBab为混合乳化剂的HLB值；
HLBa为乳化剂a的HLB值；Wa为乳化剂a的重量；
HLBb为乳化剂b的HLB值；Wb为乳化剂b的重量。
将数据代入公式：12.38=[8.6×Wa+14.9×(1-Wa)]
计算得：Wa：Wb=2:3
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