Question

A solution is prepared by dissolving 0.4g of NaOH in 500ml. calculate the pH of the solution​

Answer 1

Answer:

0.4 grams in 500 ml means 0.8 grams in one litre.

Molecular mass of NaOH is 40.

No of moles per litre is 0.8/40=0.02

0.02 molar NaOH in aqueous solution gives 0.02 molar hydroxide ions.

in aqueous solutions [H+].[OH- ] = 10^-14

[H+] = 10^-14/[OH-]= 10^-14/0.02

pH= -log [H+]= -log 10^-14 + log 0.02 = 14–1.6989=12.30

Explanation:

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Answer 2

Answer:

When a solution is prepared by dissolving 0.4g of NaOH in 500ml pH of the solution = 12.30

Explanation:

It is given that 0.4g of NaOH is dissolving in 500ml. That means 0.8g in one liter.

We know that,

         The molar mass of NaOH = 40$g/mol$

   Number of moles of NaOH= $\frac{0.8}{40}$ = 0.02 moles

Volume of solution = 1$l$

Molarity of NaOH = $\frac{0.02}{1}$ = 0.02$M$

Since NaOH is a strong electrolyte it completely dissociates in water to produce OH⁻ and Na⁺ ions.

Here [OH⁻] = 0.02 = 2×10⁻²$M$

since,

     [OH⁻][H⁺] = 1×10⁻¹⁴

    2×10⁻²×[H⁺] = 1×10⁻¹⁴

                 [H⁺]=  1×10⁻¹⁴÷ 2×10⁻²

                        = ($\frac{1}{2}$) × 10⁻¹²

                        = 0.5 × 10⁻¹²

  pH = -log( [H⁺]) = -log (0.5 × 10⁻¹²)

                            = -(log 0.5 + log(10⁻¹²))

                            = -( -0.301+-12)

                            = -( -12.301)

                             = 12.301 = 12.30