Analytical Chemistry Solution Preparation and Concentration Calculations – Step-by-Step Guidance

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Q1. Se ha preparado una solución disolviendo 15 g de sal en 60 g de agua. Calcular la concentración de la solución en porcentaje masa-masa.

Background

Topic: Solution Concentration – Mass Percent (w/w%)

This question tests your ability to calculate the mass percent concentration of a solution, a fundamental concept in analytical chemistry for expressing how much solute is present relative to the total mass of the solution.

Key Terms and Formula:

Solute: The substance dissolved (here, salt).
Solvent: The substance doing the dissolving (here, water).
Solution: The mixture of solute and solvent.

Key formula:

Step-by-Step Guidance

Identify the mass of the solute (salt) and the mass of the solvent (water).
Calculate the total mass of the solution by adding the mass of solute and solvent.
Set up the mass percent formula using the values you have found.
Plug the numbers into the formula, but do not perform the final calculation yet.

Try solving on your own before revealing the answer!

Final Answer: 20% w/w

This means the solution is 20% salt by mass.

Q2. ¿Qué cantidades de soluto y de solvente se necesitarán para preparar 400 g de solución al 25% en m/m?

Background

Topic: Solution Preparation – Mass Percent (w/w%)

This question asks you to determine the masses of solute and solvent required to prepare a solution of a given total mass and specified mass percent concentration.

Key Terms and Formula:

Solute: The substance to be dissolved.
Solvent: The substance in which the solute is dissolved.
Solution: The total mixture (solute + solvent).

Key formula:

Step-by-Step Guidance

Write down the total mass of the solution and the desired mass percent of solute.
Convert the percent to a decimal for calculation (e.g., 25% = 0.25).
Multiply the total mass of the solution by the decimal percent to find the mass of solute needed.
Subtract the mass of solute from the total mass to find the mass of solvent required.

Try solving on your own before revealing the answer!

Final Answer: 100 g solute, 300 g solvent

You need 100 g of solute and 300 g of solvent to prepare 400 g of a 25% w/w solution.

Q3. Calcule la masa en gramos de soluto presente en 478 mg de solución al 12,5% en m/m.

Background

Topic: Solution Concentration – Mass Percent (w/w%)

This question tests your ability to use mass percent to determine the mass of solute in a given mass of solution. Pay attention to units (mg vs g).

Key Terms and Formula:

Mass percent (w/w%): The mass of solute per 100 mass units of solution.

Key formula:

Step-by-Step Guidance

Write down the mass of the solution (convert mg to g if needed).
Convert the percent to a decimal (12.5% = 0.125).
Multiply the mass of the solution by the decimal percent to find the mass of solute.
Be careful with units in your final answer (grams).

Try solving on your own before revealing the answer!

Final Answer: 0.0598 g

There are approximately 0.0598 g of solute in 478 mg of a 12.5% w/w solution.

Q4. Determine la concentración de una solución que ha sido preparada añadiendo 80 ml de agua a 320 ml de una solución alcohólica al 20% v/v.

Background

Topic: Solution Dilution – Volume Percent (v/v%)

This question tests your understanding of how dilution affects the concentration of a solution, specifically when using volume/volume percent.

Key Terms and Formula:

Volume percent (v/v%): Volume of solute per 100 units of solution volume.
Dilution: Adding solvent to decrease concentration.

Key formula:

Where: = initial concentration = initial volume = final concentration = final total volume

Step-by-Step Guidance

Write down the initial concentration () and volume () of the alcoholic solution.
Calculate the final total volume after adding water ( mL).
Set up the dilution equation to solve for the new concentration .
Plug in the known values, but do not solve for yet.

Try solving on your own before revealing the answer!

Final Answer: 16% v/v

The new concentration after dilution is 16% v/v.

Q5. La etiqueta de una botella de 0,750 L de vino indica “11,5 % de alcohol por volumen”. ¿Cuántos litros de alcohol contiene el vino?

Background

Topic: Solution Concentration – Volume Percent (v/v%)

This question tests your ability to use volume percent to calculate the actual volume of solute (alcohol) in a given volume of solution (wine).

Key Terms and Formula:

Volume percent (v/v%): Volume of solute per 100 units of solution volume.

Key formula:

Step-by-Step Guidance

Write down the total volume of wine and the percent alcohol by volume.
Convert the percent to a decimal (11.5% = 0.115).
Multiply the total volume by the decimal percent to find the volume of alcohol.

Try solving on your own before revealing the answer!

Final Answer: 0.0863 L

The bottle contains approximately 0.0863 L of alcohol.