Aula 7 - Concentração das soluções (Partes por milhão, ppm e Partes por bilhão, ppb)

Summary

In this educational video, the concept of expressing solution concentration through parts per million (ppm) and parts per billion (ppb) is explored. The video covers the definitions and uses of ppm and ppb in mass and volume, providing clear examples to explain how to calculate concentration in solutions, especially those with very small amounts of solute. The lesson also includes step-by-step calculations using real-life examples, such as solutions of KBr and acetone. The content is aimed at helping viewers understand and apply these important concentration units in chemistry.

Takeaways

• 😀 Parts per million (ppm) is used to express the concentration of solutions with a very small amount of solute and a large volume of solvent.
• 😀 Ppm is particularly useful when dealing with very dilute solutions, avoiding the use of extremely small numbers in other concentration expressions.
• 😀 The concept of ppm can be applied in terms of mass or volume, depending on the context and the nature of the solute and solution.
• 😀 In mass, ppm indicates the number of milligrams of solute per one million milligrams of solution, or equivalently, grams of solute per one million grams of solution.
• 😀 A clear example: 2 milligrams of KBr in 2 kilograms of solution gives a concentration of 1 ppm.
• 😀 To calculate ppm, convert the mass of the solution and solute to the same units (milligrams, grams, or kilograms) and use the appropriate formula.
• 😀 If you know the concentration in ppm, you can calculate the amount of solute in a given volume of solution by applying the ppm ratio.
• 😀 An example of ppm in mass calculation: For a solution with 4 ppm of KOH, you can find the mass of KOH in 400 mL of solution by using unit conversions and cross-multiplying.
• 😀 The formula to calculate the mass of solute in a given volume of solution is derived from the relationship of ppm to the total volume or mass of solution.
• 😀 For volume-based ppm calculations, convert volume measurements to consistent units (such as milliliters or liters) and apply similar proportional reasoning to determine solute concentration.

Q & A

What is the purpose of expressing concentration in parts per million (ppm)?

Parts per million (ppm) is used to express concentrations in solutions where the solute is very small compared to the solvent, typically in extremely dilute solutions. This unit allows for easy representation of very low concentrations.

How is concentration expressed using ppm in mass?

In mass-based ppm, the concentration is expressed as the number of parts of the solute per one million parts of the solution. This can be represented by the formula: ppm = (Mass of solute in mg / Mass of solution in mg) * 10^6.

What is the significance of having a very large solution volume compared to the solute in ppm calculations?

Having a large solution volume compared to the solute allows for extremely dilute solutions, which is why units like ppm are used. These units help express the minuscule amount of solute in such large volumes without resorting to extremely small numbers.

How do you calculate the ppm concentration when given the mass of solute and solution mass?

To calculate ppm, divide the mass of the solute by the total mass of the solution, then multiply by one million. For example, if you have 2 mg of KBr in 2 kg of solution, the concentration is 1 ppm.

What is the conversion from kilograms to milligrams in ppm calculations?

In ppm calculations, 1 kilogram is equal to 1 million milligrams. This conversion allows you to work with consistent units when calculating the concentration of solute in solutions.

How would you calculate the mass of a solute if you are given the ppm concentration and volume of solution?

To calculate the mass of a solute, first convert the volume of solution to mass (if necessary), then apply the ppm concentration formula. For instance, if you are given 4 ppm of KCl in 400 ml of solution, and the solution's density is 1 g/ml, you can calculate the mass of KCl in the solution.

What is the difference between ppm expressed in mass and in volume?

The key difference is in the units used. In mass-based ppm, the concentration is expressed in terms of mass, while in volume-based ppm (ptb), it is expressed in terms of volume. Both methods reflect the relationship between solute and solution but use different units of measurement.

What is parts per billion (ptb) and how does it relate to ppm?

Parts per billion (ptb) is a similar concept to ppm but refers to even smaller concentrations, indicating one part of solute per one billion parts of solution. While ppm is used for concentrations on the scale of 10^6, ptb is used for more dilute solutions on the scale of 10^9.

How do you calculate ptb in a solution based on volume?

To calculate ptb in a solution based on volume, you first determine the volume of solute and solution, then apply the ratio. For example, if you have 0.01 ml of acetone in 3000 liters of solution, the ptb can be calculated as approximately 3.33 parts per billion.

Why is density important in ppm and ptb calculations?

Density is important because it allows for the conversion between volume and mass. When dealing with solutions, knowing the density helps you convert from milliliters to grams (or vice versa), which is crucial when applying ppm or ptb formulas.