英语周报2018420答案

15.CKc(H+)·c(C2O)C(HC O),当c(H)=10-419时lgX=0,故c(C2 Oi)c(HC2 O1,故K2=10419,当c(H+)(C,O102时,则(HCO.)=10,所以gc(HCO.5==2.97=M,M=2.97,A错误;二元弱酸草酸的c(H)·c(HC2O)K>Kc(H)·c(C2O-)alc(H2 C2O)C(HC2 OA),当lgX=0时,pH=-lgc(H+)=-lgK,pH1=1.22 Ka2=1041,所以I表示的是(HC,Oc(H2 C2 O4与pH的变化关系,Ⅱ表示的是C2 O4c(HC2 OA与pH的变化关系,B错误;pH=4.19时,溶液中c(C2O)=c(HC2O),代入c(Na)+c(H)=c(HC2O)+2c(C2O-)+c(OH),得c(Na+)+c(H)=3c(C2O)+c(OH),又因为c(H+)c(OH),所以c(Na)<3c(C2O)),C正确;设pH=a,c(H)=10(C2O2-)K4.19C(HCON C(Hc(C2O-) c(H2C2O4)时,102-5.41>1,即2a-5.41>0,解得a>2.705,所以c(HC2O1)>c(C2O(H2C2O4)对应2.705

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

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