Question

The equation for the pH of a substance is pH = –log[H+], where H+ is the concentration of hydrogen ions. A basic solution has a pH of 11.2. An acidic solution has a pH of 2.4. What is the approximate difference in the concentration of hydrogen ions between the two solutions? a) 1.6*10^-9 b) 4.0*10^-3 c)6.7*10^-1 D)1.6*10^-1

Answer 1

PH=-log[H⁺]

First solution:
PH=11.2

11.2=-log[H⁺]

log[H⁺]=-11.2
[H⁺]=10⁻¹¹.²=6.0309⁻¹²


Second solution:
PH=2.4

2.4=-log[H⁺]
log[H⁺]=-2.4
[H⁺]=10⁻².⁴=3.98*10⁻³

Difference between the two solutions=3.98*10⁻³ - 6.03*10⁻¹²≈4.0*10⁻³.

Answer: b) 4.0*10⁻³

Answer 2

Answer:

The correct answer si option (b).

Explanation:

$pH = -\log[H+]$

Concentration of hydrogen ions when pH is 11.2.

$11.2=-\log[H^+]$

$[H^+]=6.309\times 10^{-12} M$

Concentration of hydrogen ions when pH is 12.4.

$2.4=-\log[H^+]$

$[H^+]'=0.0039810 M=3.9810\times 10^{-3} M$

Difference between the hydrogen ions:

$=[H^+]'-[H^+]$

$=0.00398 M-6.309\times 10^{-12} M=0.00397 M=3.97\times 10^{-3}\approx 4.0\times 10^{-3}M$

Hence, the correct answer si option (b).