3Mg + N₂ → Mg₃N₂
n(Mg) = 12,2g÷24,4g/mol = 0,5mol - limiting reagente.
n(N₂) = 5,16g÷28g/mol = 0,18mol
n(Mg₃N₂):n(Mg) = 1:3, n(Mg₃N₂) = 0,166mol
m(Mg₃N₂) = 0,166mol·101,2g/mol = 16,8g.
%(N)= 2·Ar(N)÷Mr(Mg₃N₂) = 2·14÷101,2 = 27,66% = 0,2766
%(Mg) = 3·Ar(Mg)÷Mr(Mg₃N₂) = 3·24,4÷101,2 = 72,34%
or 100% - 27,66% = 72,34%.
1) Chemical reaction: HCN + H₂O → CN⁻ + H₃O⁺.
c(HCN) = 2,2 M = 2,2 mol/L.
pKa(HCN) = 9,21.
Ka = 6,16·10⁻¹⁰.
[CN⁻] = [H₃O⁺] = x.
[HCN<span>] = 2,2 M - x.
</span>Ka = [CN⁻] · [H₃O⁺] / [HCN].
6,16·10⁻¹⁰ = x² / 2,2 M -x.
Solve quadratic equation: [CN⁻] = [H₃O⁺] = 0,0000346 M.
[HCN] = 2,2 M - 0,0000346 M = 2,199 M.
2) pH = - log[H₃O⁺].
pH = -log( 0,0000346 M).
pH = 4,46.
Hydrocyanic acid and hydronium ion (H₃O⁺) are acids. Cyanide anion (CN⁻) is the strongest base in the system, cyanide anion accept protons in chemical reaction.
pKb = pKw - pKa.
pKb = 14 - 9,21 = 4,79.
The idea is to foretell the formation of a carbonyl compound by the reaction between alcohol and too much pyridinium chlorochromate. An oxidizing agent called pyridinium chlorochromate converts the alcohol group into the 1carbonyl group.
The carbonyl molecule that results from the reaction will depend on the reactant's OH group. Pyridinium chlorochromate [PCC] converts primary OH to aldehydes, whereas it converts secondary OH to ketones, and oxidation of tertiary OH has little effect. Alcohols and pyridinium chlorochromate [PCC] react to create a carbonyl molecule.
From primary alcohols to aldehydes and from secondary alcohols to ketones, pyridinium chlorochromate oxidizes alcohols one step up the oxidation ladder. pyridinium chlorochromate will not oxidize aldehydes to carboxylic acids, in contrast to chromic acid. Comparable to Pyridine (the Collins reagent) and CrO3 will both oxidize primary alcohols to aldehydes. Here are two instances of pyridinium chlorochromate being used.
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