Answer:
by changing the number of protons in the atom
Explanation:
Elements are defined by their number of protons. For example, an element with 1 proton is hydrogen, and an element with 2 protons is helium. Changing the number of neutrons or electrons in a preexisting element will not make a new element. Is is possible to create new elements, but it requires large amounts of heat and/or pressure.
First, we write out a balanced equation.
HA <--> H(+) + A(-)
Next, we create an ICE table
HA <--> H+ + A-
[]i 0.40M 0M 0M
Δ[] -x +x +x
[]f 0.40-x x x
Next, we write out the Ka expression.
Ka = [H+][A-]/[HA]
Ka = x*x/(0.40-x)
However, because Ka is less than 10^-3, we can assume the amount of dissociation is negligible. Thus,
Assume 0.40-x ≈ 0.40
Therefore, 1.2x10^-6 = x^2/0.40
Then we solve for the [H+] concentration, or x

x=6.93x10^-4
Next, to find pH we do
pH = -log[H+]
pH = -log[6.93x10^-4]
pH = 3.2
Answer:8
Everything after the decimal place is a significant figure here
The answer is option C 7.60 M