answer; ///(u-235); ///is the correct
ph = 4.63.explanation
nh₄cl is a soluble salt. it dissociates completely into its ions when dissolved in water.
nh₄cl → nh₄⁺ + cl⁻.
all nh₄cl in the 0.10 m solution dissociates. there's one mole of nh₄⁺ ions in each mole formula unit of nh₄cl. in the end, the concentration of nh₄⁺ will also be 0.10 m.
the nh₄cl salt comes from a weak base (nh₃) and a strong acid (hcl). it would undergo hydrolysis after dissolving. its solution will be slightly acidic.
the kb value of nh₃ (or nh₄oh as in water) is quite small. as a result, nh₄oh tend to act as a weak base. the conjugate acid of nh₄oh is nh₄⁺. nh₄⁺ will undergo hydrolysis to produce nh₄oh and h⁺. in other words, nh₄⁺ will combine with water to produce the weak base nh₄oh and make the solution slightly acidic.
nh₄⁺ + h₂o → nh₄oh + h⁺
the initial concentration of nh₄⁺ ions is the same as that of nh₄cl. how acidic is this solution? the acidity of this solution depends on the h⁺ concentration, which depends on the ka value of nh₄⁺. only the kb of nh₃ was given. luckily, the two species are conjugates acid and base of each other. the kb of nh₃ relates to the ka of nh₄⁺ by kw, the ionization constant of water. the value of kw under standard conditions is around 1.0 × 10⁻¹⁴.
therefore, ka(nh₄⁺) = 5.56 × 10⁻⁹.
now make a rice table for this reaction. let x be the increase in the concentration of with the unit m (the same as ).
ka of nh₄⁺ is so small that the reaction barely takes place. note the expression for ka.
x will be much smaller than 0.10. (0.10 - x) will be nearly the same as 0.10. however, the x² in the numerator is a standalone term. the same approximation shall not work for x². to simplify the calculation:
as a result
answer: 4.86 x 10⁻³ mole.
explanation:the number of moles can be calculated using the relation; n = mass / molar mass.n is the number of moles, mass is the mass of the substance in g (m = 0.5 g), and molar mass of nabr = 102.894 g/mole.n = mass / molar mass = (0.5 g) / (102.894 g/mole) = 4.86 x 10⁻³ mole.
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