18 Questions
Define molality and how is it calculated?
Molality is the number of moles of solute dissolved in 1000 g of solvent. It is calculated as molality = (Number of moles of solute) / (Weight of solvent in kg).
What is the difference between molality and molarity?
Molality is the number of moles of solute per 1000 g of solvent, while molarity is the number of moles of solute per litre of solution.
How is a decimolar solution different from a normal solution?
A decimolar solution contains 1/10th of a mole of solute per 1000 g of solvent, while a normal solution contains 1 equivalent weight of solute per litre of solution.
What is normality and how is it calculated?
Normality is the strength of solute in grams per litre. It is calculated as Normality = (Number of gram equivalent weight) / (Volume in litres).
Explain what a sub-normal solution is.
A sub-normal solution is one whose normality is less than one.
What is the mole fraction of a solute in a solution?
The mole fraction of a solute is the ratio of the number of moles of the solute to the total number of moles of all components in the solution.
How is molarity mathematically calculated?
Molarity = Strength of solute in gm / litre / Gram molecular weight of solute
What is the definition of molarity?
Molarity expresses the number of gram molecular weight (moles) of the solute dissolved per litre of solution.
What is a molar solution?
A molar solution contains one gram molecular weight (1 mole) of the solute per litre of the solution.
Explain how to calculate the molarity of HCl solution.
For HCl, with a molecular weight of 36.5 g, 36.5 g of HCl dissolved per liter equals 1 M HCl.
What does it mean if a solution is labeled as M/2 HCl?
18.25 g of HCl dissolved per liter represents a solution labeled as M/2 HCl.
Explain how to convert grams of solute to molarity.
To calculate molarity, divide the strength of solute in grams per liter by the gram molecular weight of the solute.
What is the formula for calculating the mole fraction of a solute in a solution?
$\frac{n}{n+N}$
How do you calculate the mole fraction of a solute in an aqueous solution?
$0.00358$
In a sample of rectified spirit containing 95% ethanol by weight, what is the mole fraction of ethanol?
$0.88$
What is the formula for calculating the mole fraction of a solvent in a solution?
$\frac{N}{n+N}$
How do you calculate the mole fraction of water in a sample of rectified spirit?
$0.12$
What is the relationship between mole fraction and weight percentage in a solution?
Mole fraction and weight percentage are related through the number of moles of each component in the solution.
Study Notes
Concentration of Solutions
- Molality: The number of moles of solute per kilogram of solvent, denoted by m and calculated as moles of solute per kilogram of solvent (m = moles of solute / mass of solvent in kg).
- Molarity vs Molality: Molarity is the number of moles of solute per liter of solution, whereas molality is the number of moles of solute per kilogram of solvent.
- Decimolar Solution: A solution with a molarity of 0.1 M (moles per liter).
Normality
- Normality: The number of equivalents of solute per liter of solution, where equivalent is the amount of substance that reacts with one mole of hydrogen ions (H+).
- Calculation of Normality: Normality is calculated as the number of equivalents of solute divided by the volume of the solution in liters.
Mole Fraction
- Mole Fraction of a Solute: The ratio of the number of moles of solute to the total number of moles in the solution, denoted by x (mole fraction = moles of solute / total moles).
- Mole Fraction Formula: x = (moles of solute) / (moles of solute + moles of solvent).
- Calculating Mole Fraction of a Solute: Calculate the number of moles of solute and solvent, then substitute into the formula.
Molarity
- Molarity: The number of moles of solute per liter of solution, denoted by M (M = moles of solute / volume of solution in liters).
- Molarity Calculation: M = moles of solute / volume of solution in liters.
- Molar Solution: A solution with a molarity of 1 M (one mole of solute per liter of solution).
HCl Solution
- Molarity of HCl Solution: Calculate the number of moles of HCl, then divide by the volume of the solution in liters.
- Labeled as M/2 HCl: The solution is diluted to half the original concentration.
Conversions
- Converting Grams to Molarity: Calculate the number of moles from the mass of solute, then divide by the volume of the solution in liters.
- Mole Fraction of Solvent: Calculate the number of moles of solvent and substitute into the mole fraction formula.
Rectified Spirit
- Mole Fraction of Ethanol: Calculate the number of moles of ethanol and water, then substitute into the mole fraction formula.
- Mole Fraction of Water: Calculate the number of moles of water and ethanol, then substitute into the mole fraction formula.
- Relationship between Mole Fraction and Weight Percentage: The mole fraction of a component in a solution is proportional to its weight percentage.
This quiz covers the concept of molality in chemistry, including the formula to calculate molality and examples of its application. Test your understanding of how to determine the molality of a solution based on the amount of solute and solvent present.
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