Find the hydroxide ion concentration [OH-] of an HCl solution with a pH of 6.93.

[OH-] = 1.8 x 10^-7

Explanation:

pH + pOH = 14 --> 6.93 + pOH = 14 *subtract 6.93 from both sides

pOH = 7.07

-->

10^pH => 10^-6.93 => 1e - 6.93 [H+]

-->

H+ x OH- = 1 x 10^-6.93 *divide H+ from both sides

-->

[OH-] = 1.17 x 10^-7 or 1.8 x 10^-7

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.