3)Which substance has aqueous solution with ph less than 7? a) Hydrochloric acid (b) sodium hydroxide (c) hydrosulfuric acid , (d) Acetic acid

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Answer 1 · 2018-04-18T18:42:15

All the substances EXCEPT $(b)$ have $pH<7$ .........

By definition, $pH=-log_10[H_3O^+]$ ...and thus the LOWER (or more negative) the $pH$ the GREATER the concentration of $H_3O^+$ .

In aqueous solution, in which we ASSUME all these solvents are dissolved, the following equilibrium operates:

$2H_2Orightleftharpoons H_3O^+ + HO^-$

And, by careful measurement, the following equilibrium is established and quantified....

$K_w=10^-14=[H_3O^+][HO^-]$ ...under standard conditions...

And we take $log_10$ of BOTH sides...

$underbrace(log_(10)10^-14)_(-14)=log_10([H_3O^+][HO^-])=log_10[H_3O^+]+log_10[HO^-]$

And so $-14=underbrace(log_10[H_3O^+])_(-pH)+underbrace(log_10[HO^-])_(-pOH)$ ... or...

$14=pH+pOH$ ...

And thus THE GREATER $[H_3O^+]$ the LOWER the $pH$ . Acetic acid and $H_2S$ are weak acids, however, the extent of equilibrium reduces the $pH<7$ ...

What are $pH$ for $1.0*mol*L^-1$ $HCl$ , and for $10*mol*L^-1$ $HCl$ ?

On the other hand, were we to have $1.0*mol*L^-1$ $NaOH$ .. $[HO^-]=1.0*mol*L^-1$ ...and $pOH=-log_(10)1=0$ ...i.e. $pH=14$ . Capisce?

3)Which substance has aqueous solution with ph *less than* 7? a) Hydrochloric acid (b) sodium hydroxide (c) hydrosulfuric acid , (d) Acetic acid