Question

156 grams of sodium sulfide, Na2S, is dissolved in

1000 mL of solution. Determine the molarity (M).

Answer 1

The molarity of the Na2S solution is 2.00 M

Step-by-step explanation:

Step 1: Data given

Sodium sulfide = Na2S

Mass of sodium sulfide = 156.0 grams

Molar mass of sodium sulfide (Na2S) = 78.0452 g/mol

Volume = 1000 mL = 1.0 L

Step 2: Calculate moles of sodium sulfide (Na2S)

Moles Na2S = mass Na2S / molar mass Na2S

Moles Na2S = 156.0 grams / 78.0452 g/mol

Moles Na2S = 1.999 moles

Step 3: Calculate molarity Na2S solution

Molarity Na2S solution = moles Na2S / volume solution

Molarity Na2S solution = 1.999 moles / 1.0 L

Molarity Na2S solution = 1.999 M ≈ 2.00 M

The molarity of the Na2S solution is 2.00 M

Answer 2

M Na2S = 2 M

Step-by-step explanation:

• molarity (M) [=] mol/L sln

∴ mass Na2S = 156 g

∴ molar mass Na2S = 78.0452 g/mol

⇒ mol Na2S = (156 g)*(mol/78.0452 g) = 1.9988 mol ≅ 2 mol

∴ volume sln = 1000 mL = 1 L

molarity (M):

⇒ M Na2S = 2 mol / 1 L

⇒ M Na2S = 2 M