Leaving Cert Chemistry Acids, Bases & PH: The concentration of an aqueous

The concentration of an aqueous solution of sodium hydroxide (NaOH) is 0.2 g per litre - Leaving Cert Chemistry - Question h - 2006

Question h

The concentration of an aqueous solution of sodium hydroxide (NaOH) is 0.2 g per litre. Calculate its pH.

Worked Solution & Example Answer:The concentration of an aqueous solution of sodium hydroxide (NaOH) is 0.2 g per litre - Leaving Cert Chemistry - Question h - 2006

Step 1

Calculate the concentration of NaOH in mol/L

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Answer

To find the concentration of NaOH in moles per liter (mol/L), we first need to determine the molar mass of NaOH. The molar mass is calculated as follows:

Na: 23 g/mol
O: 16 g/mol
H: 1 g/mol

So, the molar mass of NaOH is:

$ext{Molar Mass} = 23 + 16 + 1 = 40 ext{ g/mol}$

Now, using the formula for concentration:

$C = \frac{mass}{molar \ mass}$

We convert the mass given (0.2 g) into moles:

$C = \frac{0.2 ext{ g}}{40 ext{ g/mol}} = 0.005 ext{ mol/L}$

Step 2

Calculate pOH from [OH⁻]

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Answer

Since NaOH is a strong base, it completely dissociates in solution:

$ext{NaOH} \rightarrow ext{Na}^+ + ext{OH}^-$

Thus, the concentration of hydroxide ions, [OH⁻], is equal to the concentration of NaOH:

$[OH^-] = 0.005 ext{ mol/L}$

Next, we can find pOH using the formula:

$pOH = -\log[OH^-]$

Substituting in the concentration:

$pOH = -\log(0.005) ≈ 2.3$

Step 3

Calculate pH

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Answer

To find the pH from pOH, we can use the relationship:

$pH + pOH = 14$

Thus, substituting the previously calculated pOH:

$pH = 14 - pOH = 14 - 2.3 = 11.7$

Therefore, the pH of the solution is approximately 11.7.

The concentration of an aqueous solution of sodium hydroxide (NaOH) is 0.2 g per litre - Leaving Cert Chemistry - Question h - 2006

Worked Solution & Example Answer:The concentration of an aqueous solution of sodium hydroxide (NaOH) is 0.2 g per litre - Leaving Cert Chemistry - Question h - 2006

Calculate the concentration of NaOH in mol/L

Calculate pOH from [OH⁻]

Calculate pH

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