<u>Answer:</u>
The correct answer option is a. Selenium (Se).
<u>Explanation:</u>
From the given answer options, Selenium (Se) is the only element which is a non metal.
It has the atomic number 34 with atomic weight 78.96. It is a member of the sulfur group of the non metallic elements and falls in period 4 of the Periodic table.
Selenium has non metallic properties which are intermediate between the elements that lie above and below it in the Periodic table.
Answer:
The correct answer is 0.61 ml
Explanation:
Nitric acid is a strong acid. That means that it dissociates completely in water as follows:
HNO₃ → H⁺ + NO₃⁻
As the dissociation is complete, the concentration of H⁺ ions is equal to the initial concentration of the acid (HNO₃). Thus, the pH can be calculated from the initial concentration of the acid:
pH= -log [H⁺] = -log [acid]
We want a nitric acid solution with a pH of 2.0. so we first calculate the concentration of acid we need:
2.0 = -log [acid]
10⁻²= [acid]
The chemist has a stock solution with C= 9.0 M and he/she wants a solution with C= 1 x 10⁻² M and V= 550 ml. We use the equation that relates the initial concentration and volume (Ci and Vi, respectively) of a solution with the final concentration and volume (Cf and Vf, respectively):
Ci x Vi = Cf x Vf
⇒ Vi= (Cf x Vf)/Ci = (1 x 10⁻² M x 550 ml)/9.0 M = 0.611 ml
Summarizing, the chemist must measure 0.611 ml of concentrated solution (9.0 M), add it to the flask and fill the flask to the mark until 550 ml in order to obtain a nitric acid solution with a pH of 2.0.
Answer:
to gain more confidence and to be more convincing.
Explanation:
A. Temperature is 273.15 K
There are about 118 elements on the periodic table. <span />
