Siobhan wants to measure the mass of a bag of flour. What should she do?

g/cm^3

To answer directly its g/cm with the little three on top.

:)

Answer:

• The third chice: 0.0750 M Na₂SO₄

Explanation:

Assume 100% ionization:

1) 0.100 M solution K₂SO₄

• K₂SO4 (aq) → 2K⁺ (aq) + SO₄²⁻ (aq)

• Mole ratios: 1 mol K₂SO4 : 2 mol K⁺  + 1 mol SO₄²⁻ (aq) : 3 mol ions. This is 1 : 3

• At constant volume, the mole ratios are equal to the concentration ratios (M).

• 1  M K₂SO₄: 3 M ions = 0.100 M K₂SO₄ / x ⇒ x = 0.300 M ions

This means, that you have to find which of the choices is a solution that contains the same 0.300 M ion concentration.

2) 0.0800 M Na₂CO₃

• Na₂CO₃ (aq) → 2 Na⁺ + CO₃⁻

• 1 M Na₂CO₃ / 3 M ions = 0.0800M / x ⇒ x = 0.0267 M ions

This is not equal to 0.300 M, so this solution would not contain the same total concentration as a 0.100 M solution of K₂SO₄, and is not the right answer.

3)  0.100 M NaCl

• NaCl → Na⁺ + Cl⁻

• 1 M NaCl / 2 M ions = 0.100 M NaCl / x ⇒ x = 0.200 M ions

This is not equal to 0.300 M ion, so not a correct option.

4) 0.0750 M Na₃PO₄

• Na₃PO₄ → 3Na⁺ + PO₄³⁻

• 1 M Na₃PO₄ / 4 M ions = 0.0750 M Na₃PO₄ / x ⇒ x = 0.300 M ions

Hence, this ion concentration is equal to the ion concentration of a 0.100 M solution of K₂SO₄, and is the correct choice.

5)  0.0500 M NaOH

• NaOH → Na⁺ + OH⁻

• 1 M NaOH / 2 mol ions = 0.0500 M NaOH / x ⇒ x = 0.100 M ions

Not equal to 0.300 M, so wrong choice.