Answer:
Approximately [tex]1.92[/tex].
Explanation:
The [tex]{\rm pH}[/tex] of a solution is the opposite of the base-[tex]10[/tex] logarithm of that solution's [tex]{\rm H^{+}}[/tex] concentration measured in [tex]{\rm mol \cdot L^{-1}}[/tex]. In other words:
[tex]{\rm pH} = - \log_{10} ([{\rm H^{+}])[/tex].
Using properties of logarithms:
[tex]\begin{aligned}{\rm pH} &= - \log_{10} ([{\rm H^{+}]) \\ &= -\left(\frac{\ln([{\rm H^{+}]})}{\ln(10)}\right)\end{aligned}[/tex].
In this question, [tex][{\rm H^{+}}] = 1.2 \times 10^{-2}\; {\rm mol \cdot L^{-1}}[/tex]. Therefore:
[tex]\begin{aligned}{\rm pH} &= - \log_{10} ([{\rm H^{+}]) \\ &= -\left(\frac{\ln([{\rm H^{+}]})}{\ln(10)}\right) \\ &= - \frac{\ln(1.2 \times 10^{-2})}{\ln(10)} \\ &\approx 1.92\end{aligned}[/tex].
By convention, the number of decimal values in the [tex]{\rm pH}[/tex] should be equal to the number of significant figures in the [tex]{\rm H^{+}}[/tex] concentration of the solution.
In this question, there are two significant figures in the measurement[tex][{\rm H^{+}}] = 1.2 \times 10^{-2}\; {\rm mol \cdot L^{-1}}[/tex]. Thus, the [tex]{\rm pH}[/tex] result should be rounded to two decimal places.
Answer:
Magnesium Mg .)
Explanation:
In the Bohr Model of atoms, each "ring" denotes a non-empty main energy shell. The Bohr Model for this atom has three rings, meaning that three of the main energy shells of this atom contain electron(s).
Refer to a copy of the modern periodic table. Elements on the modern periodic table are arranged into rows ("periods") by the number of non-empty main energy shells in each atom.
There are three non-empty main energy shells in the atom in this question. Thus, the element of this atom would belong to the third period (third row) of the modern periodic table.
Examples of alkaline-earth metal elements include Beryllium, Magnesium, Calciums, and a few others. These elements are in IUPAC group 22 and are found in the second column from the left of a modern periodic table.
There is only one alkaline-earth metal in each period. The question implied that the element here includes three non-empty main energy shells per atom. That element would thus be in the third period. The alkaline-earth metal of the third period is magnesium. Therefore, the element in this question would be magnesium.
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