Question

Calculate the mass of urea $\left( NH _{2} CONH _{2}\right)$ required in making $2.5 \,kg$ of $0.25$ molal aqueous solution.

• A. 37.5 g
• B. 73.5 g
• C. 53.7 g
• D. 75.3 g

Answer 1

Answer: (A)

37.5 g

Answer 2

We know that, Molality $=\frac{\text { moles of solute }}{\text { mass of solvent }(\text { in } kg )}$ $\because$ mass of solvent $=\frac{\text { mass }}{\text { molar mass }}$ So, Molality $=\frac{\frac{\text { mass }}{\text { molar mass }}}{\text { mass of solvent }(\text { in } kg )}$ $0.25=\frac{60}{2.5}$ ( $\because$ Molar mass of urea $=60$ ) or Mass $=0.25 \times 2.5 \times 60$ $=37.5 \,g$

The total mass of all the atoms in one mole of a chemical compound is known as its molar mass, expressed in grammes. Its simplest definition is "mass per mole."

The amount of the material contained in one mole of the substance is measured by its molar mass.

According to Avogadro's Number, a mole contains 6.023 x 1023 molecules.

Molar mass is stated in its standard unit, g/mol, even though the SI unit is kg/mol.

The Molar Mass Formula is the product of the mass of an element and its molecular weight. It represents the total atomic mass of the molecule's atoms. The Molar Mass Formula is as follows:

Molar Mass = Mass of Given Substance/Amount of Substance

'Mass per Mole' is the definition of 'Molar Mass'. A mole of a certain molecule consists of grammes worth of the sum of all the atoms. The usual unit of measurement is grammes per mole (g/mol). The molar mass unit in the SI is kg/mol.

For both elements and molecules, a molar mass is determined.

The molar mass of an element is the element's mass expressed in atomic mass units.

It implies that an atom's atomic mass and molar mass are equivalent.

The molar mass of a molecule is the sum of the masses of all the atoms

By summing the atomic masses of a particular chemical, one may derive the molar mass. The mass of a particular substance divided by the amount being delivered is the basic definition of the molar mass formula.

The Molar Mass Formula is as follows:

M = m/n

Molar Mass is denoted by M.

The mass of the specified material is denoted by m.

N is the quantity of the substance.