Answer:
1. Weigh 3.27 ×10⁻⁴ ng of NaOH in a special balance for weighing in nanograms
2. Measure a volume of 650 mL in a test tube
3. Make the solution by mixture
Explanation:
NaOH is a strong base. As every strong base, can be completely dissociated:
NaOH → Na⁺ + OH⁻
If pH is 13.90, we can calculate the [OH⁻], so we would know the molarity of NaOH.
1 mol of NaOH can generate 1 mol of OH⁻
[OH⁻] = 10⁻¹³'⁹ = 1.26×10⁻¹⁴ M
In conclussion, molarity of NaOH is 1.26×10⁻¹⁴ M
M = moles of NaOH / volume of solution
We convert the volume from mL to L
650 mL . 1 L /1000mL = 0.650 L
Moles of NaOH = 0.650 L . 1.26×10⁻¹⁴ M = 8.18×10⁻¹⁵ moles
We convert the moles to mass, to determine the grams:
8.18×10⁻¹⁵ moles . 40 g/mol = 3.27 ×10⁻¹³ g
We can convert the grams to ng = 3.27 ×10⁻⁴ ng
