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No. 2 (è£)
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ã§ã¯ãããŸããŸãªååç©ã®ç·©è¡äœçšã«ãã,pHãäžæ§ä»è¿ã«ä¿ãããŠããããªã³é
žäºæ°ŽçŽ å¡©ãšãªã³é
ž
æ°ŽçŽ å¡©ã®çµã¿åããããã®äžäŸã§ããã以äžã§ã¯ããããã®ãªã³é
žå¡©ã®25âã«ãããé»é¢å¹³è¡¡ãšç·©è¡äœçšã«ã€ããŠ
èãããããªã³é
žã¯æ°Žäžã§æ¬¡ã®ããã«3段éã§é»é¢ããã
HsPOH+ + H2PO4 (1)
H2PO4H+ + HPO
HPO H+ + PO (3)
(2)
Ki = 7.5Ã10mol/L
K = 6.2Ã10mol/L
K's = 2.1Ã10-13mol/L
K. K, K ã¯ãããã (1) (2) (3) åŒã®å¹³è¡¡å®æ°ã§ããã ãŸããæ°Žã®ã€ãªã³ç©ã K(=1.0Ã10-14mol/L2 ) ãšããã
ã¯ããã«, 0.10mol/Lã®NaH2PO4 氎溶液ã®å¹³è¡¡ã«ã€ããŠèããã ãã®å¡©ã¯æ°Žäžã§å®å
šã«é»é¢ããã çããH2P
O ã€ãªã³ã«é¢ããŠã¯, (2) åŒã®å¹³è¡¡ã®ä»ã«æ¬¡ã®å¹³è¡¡ãååšããã
.(4)
H2PO4 + H2O H3PO4 + OH-
ãã®å¹³è¡¡ã«ãããŠãæ°Žã®ã¢ã«æ¿åºŠ [H2O][mol/L]ã¯äžå®ãšã¿ãªãããã, (4) åŒã®å¹³è¡¡å®æ° Ka 㯠H2PO4 HsPO4,
OH-ã®ã¢ã«æ¿åºŠãçšããŠã
[H3PO4] [OH-1
Kâ =
A
[H2PO4]
ãšè¡šããããããšã®å€ã®æ¯èŒããããã®æ°Žæº¶æ¶²ã¯ãŠæ§ã瀺ãããšããããã
次ã«, 0.10mol/Lã®Na2HPO 氎溶液ã®å¹³è¡¡ã«ã€ããŠèããã ãã®å¡©ãæ°Žäžã§å®å
šã«é»é¢ããã ããã§çããHP
042 ã€ãªã³ã«é¢ããŠãã (3) åŒã®å¹³è¡¡ã®ä»ã«æ¬¡ã®å¹³è¡¡ãååšããã
HPO42 + H2O HPO + OH-
(5)åŒã®å¹³è¡¡å®æ°ã¯,
K5 =
[H2PO4][OH-]
[HPO2]
B
ãšè¡šããããé¢ãšã®å€ã®æ¯èŒãã,ãã®æ°Žæº¶æ¶²ã¯ãšæ§ã瀺ãããšããããã
(5)
ããã«ããã® NaHPO4 æ°Žæº¶æ¶²ã®æ°ŽçŽ ã€ãªã³æ¿åºŠ[H+] [mol/L] ã衚ãåŒãå°ããŠã¿ããã ãã®ããã«, (2) åŒãš(3)åŒ
ãçµã¿åãããæ¬¡ã®å¹³è¡¡ãèããã
2HPO H2PO4 + POã-.
ã»(6)
(6)åŒã®å¹³è¡¡å®æ°ã¯,次åŒã§è¡šãããã
[H2PO4][PO4]
K6 =
C
[HPO42-J2
ãªã³é
žäžæ°ŽçŽ å¡©ã®æ¿åºŠã0.10mol/Lã®å Žå, (3) (5) (6) åŒã®ãã¡, (6) åŒã®å¹³è¡¡ãæã倧ãã峿¹åã«åãã ãŸã,
(3) åŒãš (5) åŒã®å¹³è¡¡å®æ°ãæ¯èŒãããš,åæ®µã®èå¯ãããªåŒã®å¹³è¡¡å®æ°ã®æ¹ãååã«å€§ãããããããäžæ¹ã®
åŒã®å¹³è¡¡ã¯ç¡èŠã§ããã ãããã£ãŠ, [H+] ãæ±ããããã«ã¯,ãªåŒãš(6)åŒã®2ã€ã®å¹³è¡¡ãèæ
®ããã°ããã
ãªåŒãš(6)åŒã®å¹³è¡¡åå¿ã«ãã£ãŠæ¶è²»ããã HPO4 ã€ãªã³ã®æ¿åºŠãã ãããã [mol/L] ãš [mol/L] ãšãããšã
HPOPOã®åã€ãªã³ã®ã¢ã«æ¿åºŠã¯æ¬¡ã®ããã«è¡šãããã
H2PO4
[H2PO4] = I
[HPO42] = 0.10-x-y
[PO-] = II
ããã§ãªåŒãš (6) åŒã®å¹³è¡¡å®æ°ã¯éåžžã«å°ããã®ã§, 0.10-x-yâ0.10 ãšè¿äŒŒã§ããã ãã£ãŠ, x, y, 平衡
宿°ãå«ã2ã€ã®é¢ä¿åŒãã,[H+] [mol/L] ã¯,
[H+] = K2Ks+ D
ãšå°ãããã
å4
å5
å6
ãŠãªã«ããŠã¯ãŸãèªå¥ãŸãã¯æ°åãèšå
¥ããã
I
II ã«ããŠã¯ãŸãæ°åŒã, x, y ãçšããŠèšãã
A~Dã«ããŠã¯ãŸãæ°åŒã K, K, K, Kw ãçšããŠèšãã
7 0.10mol/Lã®NaH2PO4 氎溶液10mL ãš 0.10mol/Lã®Na2HPO4 氎溶液10mL ãæ··åããŠç·©è¡æ¶²ã調補ããã
ãã®ç·©è¡æ¶²ã«é¢ããŠã次ã®(i), (ii)ã®åã«çããã ãã ãããã®ç·©è¡æ¶²ã«ã€ããŠã¯ã(2)åŒã®é»é¢å¹³è¡¡ã®ã¿ãèæ
®ã
ãã°ããã æ°å€ã¯æå¹æ°å2ããã§çããã
(i) ãã®ç·©è¡æ¶²ã®æ°ŽçŽ ã€ãªã³æ¿åºŠ [mol/L] ãæ±ããã
ãã®ç·©è¡æ¶²ã« 0.10mol/Lã®å¡©é
žãpHã7.0ã«ãªããŸã§å ãããå ããå¡©é
žã®äœç© [mL] ãæ±ããã ãŸãããã®
å€ãçšããŠãå¡©é
žã®æ·»å ã«ããæ°ŽçŽ ã€ãªã³æ¿åºŠã®å¢å é (AD [H+]) ãšå¡©åç©ã€ãªã³æ¿åºŠã®å¢å é(4[CI-I)ã®æ¯
A[H+1
A[CI-]
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