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pH

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Určte pH a pOH roztoku, ktory vznikne doplenim 20 g 0,02% roztoku NaOH do objemu
1000 ml.

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Zelmira B.
Zelmira B. Contact
NaOH - máš 20 g roztoku 0,02 %
0,02 % znamená, že máš 0,02 g NaOH v 100 g roztoku
Ty máš len 20 g roztoku, preto budeš mať v 20 g roztoku len 0,004 g NaOH
K 20 g roztoku pridáš 980 ml H2O a získaš 1000 ml roztoku NaOH, v ktorom sú 0,004 g NaOH. Vypočítaš látkové množstvo NaOH: n = m/Mr Mr(NaOH) = 40
n = 0,004/40 = 0,0001 mol NaOH = 1 . 10-4 mol NaOH (-4 je exponent)
vypočítaš koncentráciu NaOH: c = n/V V = 1 l c (NaOH) = 1 . 10-4 mol/l
pOH = - log c(OH)- = - log 1 . 10-4 pH + pOH = 14
pOH = 4 pH = 14 - pOH = 14 - 4 = 10
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