Calculate the mass of urea $\left( NH _{2} CONH _{2}\right)$ required in making $2.5 \,kg$ of $0.25$ molal aqueous solution.
- 37.5 g
- 73.5 g
- 53.7 g
- 75.3 g
The Correct Option is A
Solution and Explanation
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.
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Concepts Used:
Stoichiometry
Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated.
Stoichiometry helps us determine how much substance is needed or is present. Things that can be measured are;
- Reactants and Products mass
- Molecular weight
- Chemical equations
- Formulas
Stoichiometric Coefficient
The Stoichiometric coefficient of any given component is the number of molecules and/or formula units that participate in the reaction as written.
Mole Ratios
The mass of one mole of a substance in grams is called molar mass. The molar mass of one mole of a substance is numerically equal to the atomic/molecular formula mass.