Question

What mass (in g) of NH3 must be dissolved in 475 g of methanol to make a 0.250 m solution?

Answer 1

Answer:

We need 2.02 grams of NH3

Explanation:

Step 1: Data given

Mass of methanol = 475 grams

Molality of the solution = 0.250 M

Molar mass of NH3 =17.03 g/mol

Molar mass of = methanol = 32.04g/mol

Step 2: Calculate moles NH3

Molality = 0.250 m = mol NH3 / 0.475 kg

moles NH3 = 0.250 molal * 0.475 kg

Moles NH3 = 0.11875 moles

Step 3: Calculate the mass of NH3

Mass NH3 = moles NH3 * molar mass NH3

Mass NH3 = 0.11875 mol * 17.03 g/mol

Mass NH3 = 2.02 grams

We need 2.02 grams of NH3

Answer 2

The mass of ammonia needed to dissolve the methanol is 2.02 g.

The given parameters;

• mass of methanol, = 475 g
• concentration of the solution, = 0.25 m

The molar mass of the given compounds is calculated as follows;

NH₃ = (14) + (3 x 1) = 17 g/mol

CH₃OH  = (12) + (3 x 1) + (16) + (1) = 32 g/mol

The number of moles of the ammonia is calculated as follows;

$0.25 = \frac{ mole \ of \ NH_3}{kg \ of \ methanol} \\\\mole \ of \ NH_3 = 0.25 \times 0.475\\\\mole \ of \ NH_3 = 0.11875 \ mole$

The mass of the ammonia is calculated as follows;

mass of ammonia = 0.11875 x 17 g

mass of ammonia = 2.02 g

Thus, the mass of ammonia needed to dissolve the methanol is 2.02 g.

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