MLT 81 Chapter 7 Quiz A

What is the purpose of rounding off numbers in laboratory calculations?

• To increase accuracy

• To decrease accuracy

• To express precision

• To express accuracy

Answer explanation

The purpose of rounding off numbers in laboratory calculations is to express precision. Rounding helps to convey the level of uncertainty in the measurements and calculations, ensuring that the reported values are consistent with the limitations of the instruments and methods used. It does not increase or decrease accuracy, nor does it express accuracy directly.

What is the definition of density?

• The amount of matter per unit volume of a substance

• The weight of 1 mL of a solution

• The number of moles of solute per kilogram of solvent

• The number of osmoles of solute per liter of solution

Answer explanation

Density is defined as the amount of matter per unit volume of a substance. This means it measures how much mass is contained within a given volume. The other options refer to different concepts, such as weight, concentration, and osmolarity, which are not related to density.

How is molality defined?

• The amount of matter per unit volume of a substance

• The weight of 1 mL of a solution

• The number of moles of solute per kilogram of solvent

• The number of osmoles of solute per liter of solution

Answer explanation

Molality is defined as the number of moles of solute per kilogram of solvent. This measure is used to express the concentration of a solution and is independent of temperature and pressure. The other options refer to different concepts: matter per unit volume, weight of a solution, and osmoles per liter, which are not related to molality.

What is the formula for calculating molarity?

• Molarity = Grams of solute / Liters of solution

• Molarity = Moles of solute / Liters of solution

• Molarity = Grams of solute / Gram-molecular weight x Liters of solution

• Molarity = Moles of solute / Gram-molecular weight x Liters of solution

Answer explanation

The formula for calculating molarity is Molarity = Moles of solute / Liters of solution. This is because molarity is a measure of the concentration of a solute in a solution, and it is expressed as the number of moles of solute present in a given volume of solution (liters).

What is the purpose of a dilution factor?

• To increase the concentration of a solution

• To decrease the concentration of a solution

• To correct for using a diluted sample in a determination

• To calculate the amount of solute needed for a dilution

Answer explanation

The purpose of a dilution factor is to correct for using a diluted sample in a determination. It is not meant to increase or decrease the concentration of a solution, nor is it used to calculate the amount of solute needed for a dilution. The dilution factor helps in adjusting the results obtained from a diluted sample to represent the original, undiluted sample.

What is the formula for calculating the concentration of a single dilution?

• Concentration = Original concentration x Dilution

• Concentration = Original concentration / Dilution

• Concentration = Dilution / Original concentration

• Concentration = Dilution - Original concentration

Answer explanation

The correct formula for calculating the concentration of a single dilution is 'Concentration = Original concentration / Dilution'. This formula is used to determine the final concentration of a solution after it has been diluted by a specific factor. By dividing the original concentration by the dilution factor, you can find the new concentration of the solution.

What is the purpose of osmolality and osmolarity measurements?

• To determine the density of a substance

• To calculate the weight per unit volume of a solution

• To measure the concentration of particles in a solution

• To determine the molarity of a solution

Answer explanation

Osmolality and osmolarity measurements are used to measure the concentration of particles in a solution. They help in understanding the solute concentration and the osmotic pressure exerted by the solution, which is crucial in various fields like biology, chemistry, and medicine. The other options, such as determining density, calculating weight per unit volume, or determining molarity, are not the primary purposes of these measurements.

What is the difference between osmolality and osmolarity?

• Osmolality is the number of osmoles of solute per kilogram of solvent, while osmolarity is the number of osmoles of solute per liter of solution

• Osmolality is the number of osmoles of solute per liter of solution, while osmolarity is the number of osmoles of solute per kilogram of solvent

• Osmolality is the number of moles of solute per kilogram of solvent, while osmolarity is the number of moles of solute per liter of solution

• Osmolality is the number of moles of solute per liter of solution, while osmolarity is the number of moles of solute per kilogram of solvent

Answer explanation

The difference between osmolality and osmolarity lies in the units used to measure them. Osmolality is expressed as the number of osmoles of solute per kilogram of solvent, focusing on the concentration of solute particles in a mass of solvent. On the other hand, osmolarity is measured as the number of osmoles of solute per liter of solution, considering the concentration of solute particles in a volume of solution.

What is the purpose of a titer in laboratory analysis?

• To measure the concentration of antibody in a specimen

• To calculate the dilution factor of a solution

• To determine the density of a substance

• To express the precision of a measurement

Answer explanation

The purpose of a titer in laboratory analysis is to measure the concentration of antibody in a specimen. It is not used for calculating dilution factors, determining substance density, or expressing measurement precision. By measuring antibody concentration, titers help in assessing immune response and diagnosing various conditions.

What is the relationship between volume and concentration in a dilution?

• As volume increases, concentration increases

• As volume increases, concentration decreases

• As volume decreases, concentration increases

• As volume decreases, concentration decreases

Answer explanation

The question asks about the relationship between volume and concentration in a dilution. The correct answer is 'As volume increases, concentration decreases'. This is because in a dilution, when the volume of the solvent is increased, the solute particles are spread out more thinly, resulting in a lower concentration.