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【单选题】
Gram-negative bacteria differ from gram-positive bacteria because of the fact ( ).A.
That in Gram-negative bacteria the peptidoglycan cell wall is only 1 or 2 layers thick, whereas in gram-positive bacteria it is many layers thick.
B.
That in gram-negative bacteria basic dyes and detergents are much more harmful than for gram-positive bacteria.
C.
That in gram-negative bacteria lipoprotein—which is not found in gram-negative bacteria—anchors the outer membrane to the capsule.
D.
That in gram-positive bacteria porin proteins are invariably found, and are not found in gram-negative bacteia.
E.
All of the above are ture.
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【单选题】欲用 H 3 PO 4 与 NaOH 来配制 pH = 7.20 的缓冲溶液,则 H 3 PO 4 与 NaOH 物质的量之比 n (H 3 PO 4 ) : n (NaOH) 应为 ( ) (已知 pK a ( H 3 PO 4 ): 2.12 7.20 12.36 )
A.
1:1
B.
1:2
C.
2:1
D.
2:3
【单选题】NaOH滴定H3PO4以酚酞为指示剂．终点时生成( )。（已知H3PO4的各级离解常数：Kal=6.9×10-3，Ka2 =6.2×10-8，Ka3=4.8×10-13） A．NaH2PO4 B．Na2HPO4 C．Na3PO4 D．NaH2PO4+Na2HPO4
A.
NaH2PO4
B.
Na2HPO4
C.
Na3PO4
D.
NaH2PO4+Na2HPO4
【单选题】已知H 3 PO 4 浓度为HCl浓度的1/2，以酚酞为指示剂，用同一NaOH溶液滴定H 3 PO 4 和HCl溶液，消耗的NaOH体积分别为V 1 与V 2 ，则V 1 与V 2 的关系为( )。
A.
V 1 =V 2
B.
V 1 ＞V 2
C.
V 1 ＜V 2
D.
V 1 =2V 2
E.
V 2 =2V 1
【单选题】已知C H3 PO4 =C NaOH =0.1mol·L -1 ,由H 3 PO 4 与NaOH配制pH=2.16的缓冲溶液,则其体积比为(已知H 3 PO 4 的pKa 1 =2.16,pKa 2 =7.21,pKa 3 =12.32)
A.
2:1
B.
1:1
C.
1:2
D.
1:3
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