D- It requires heat as a reactant
Answer:
A
Explanation:
Remember the number of valence electrons represent the group number. As shown in figure, there is only one electron in the valence shell. Therefore, this element belongs to group 1 elements also called as Alkali metals.
Furthermore, the number of electrons in a neutral atom equals number of protons. Hence, there are 11 protons in this element.
Also, number of protons equal atomic number therefore, the atomic number of this element is 11. And, by checking periodic table, the element having atomic number 11 is Sodium (Na).
Answer:
0.200M H₃PO₄
0.600N H₃PO₄
pH = 1.46
Explanation:
The acid-base reaction of phosphoric acid (H₃PO₄) with LiOH is:
3 LiOH + H₃PO₄ → Li₃PO₄ + 3H₂O
<em>Where 3 moles of LiOH reacts per mole of H₃PO₄</em>
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Moles of LiOH are:
0.030L× (0.5mol / L) = 0.0150 moles of LiOH
Moles of acid neutralized are:
0.0150 moles of LiOH × (1 mole H₃PO₄ / 3 moles LiOH) = 0.005 moles H₃PO₄
As volume of acid was 25mL, molarity is:
0.005mol H₃PO₄ / 0.025L =<em> 0.200M H₃PO₄</em>
Normality is:
0.200M × (3N H⁺ / 1M H₃PO₄) = <em>0.600N H₃PO₄</em>
H₃PO₄ dissolves in water thus:
H₃PO₄ ⇄ H₂PO₄⁻ + H⁺
Ka = 7.1x10⁻³ = [H₂PO₄⁻] [H⁺] / [H₃PO₄]
Where molar concentrations in equilibrium will be:
[H₂PO₄⁻] = X
[H⁺] = X
[H₃PO₄] = 0.200M - X
Replacing in Ka formula:
7.1x10⁻³ = [X] [X] / [0.200 - X]
1.42x10⁻³ - 7.1x10⁻³X = X²
0 = X² + 7.1x10⁻³X - 1.42x10⁻³
Solving for X:
X = -0.04M →False answer, there is no negative concentrations.
X = 0.0343M
As, [H⁺] = 0.0343M
pH = - log [H⁺],
<em>pH = 1.46</em>
