Experiment #2

Which of the following instruments is used to measure the mass of calcium chloride in this experiment?

• Ion Selective Electrode

• Volumetric flask

• Balance

• Graduated cylinder

Answer explanation

The balance is the instrument used to measure mass. In this experiment, it accurately measures the mass of calcium chloride, while the other options serve different purposes such as volume measurement or ion concentration.

Why is it important to avoid leaving the vial of anhydrous calcium chloride open to the atmosphere for an extended time?

• It will evaporate

• It will absorb water from the air

• It will oxidize quickly

• It will lose calcium content

Answer explanation

Anhydrous calcium chloride is hygroscopic, meaning it readily absorbs moisture from the air. Leaving the vial open allows it to absorb water, which can compromise its effectiveness and alter its intended use.

What is the purpose of using a volumetric flask in this experiment?

• To measure the amount of chlorine

• To ensure the accurate dilution of the calcium chloride solution

• To store the calcium chloride for long-term use

• To heat the calcium chloride solution

Answer explanation

The volumetric flask is used to ensure the accurate dilution of the calcium chloride solution, providing precise measurements necessary for the experiment.

What is the primary function of an Ion Selective Electrode (ISE)?

• Measure mass

• Measure voltage and convert it into concentration

• Dissolve ionic compounds

• Determine the pH of a solution

Answer explanation

The primary function of an Ion Selective Electrode (ISE) is to measure voltage, which is then converted into the concentration of specific ions in a solution, making the second answer choice correct.

Why should a paper towel not be used to dry the Ion Selective Electrode?

• It will not dry the electrode thoroughly

• It can damage the sensitive tip

• It will alter the concentration of the solution

• It can cause the electrode to overheat

Answer explanation

Using a paper towel can damage the sensitive tip of the Ion Selective Electrode, which is crucial for accurate measurements. This risk outweighs any potential benefits of drying.

The formula for calcium chloride is CaCl₂. What does this formula tell you about the ratio of calcium to chlorine atoms?

• 1 calcium atom for every 2 chlorine atoms

• 2 calcium atoms for every 1 chlorine atom

• 1 calcium atom for every 3 chlorine atoms

• 3 calcium atoms for every 1 chlorine atom

Answer explanation

The formula CaCl₂ indicates that for every 1 calcium atom (Ca), there are 2 chlorine atoms (Cl). Therefore, the correct ratio is 1 calcium atom for every 2 chlorine atoms.

If your ISE reading gives a calcium concentration of 656 mg/L, how much calcium is present in 100 mL of solution?

• 6.56 mg

• 65.6 mg

• 656 mg

• 0.656 mg

Answer explanation

To find the amount of calcium in 100 mL, convert mg/L to mg/100 mL. Since 656 mg/L means 656 mg in 1 L (1000 mL), in 100 mL it is (656 mg/1000 mL) * 100 mL = 65.6 mg. Thus, the correct answer is 65.6 mg.

What does the empirical formula of a compound represent?

• The most accurate atomic weights

• The ratio of elements in a compound in their simplest form

• The molecular weight of the compound

• The specific atomic structure of the compound

Answer explanation

The empirical formula represents the simplest whole-number ratio of elements in a compound, not their exact weights or molecular structure. This is why the correct choice is the ratio of elements in a compound in their simplest form.

The concentration of calcium in your solution was 307 mg/L. If you made 100 mL of the solution, how many milligrams of calcium are present in the entire solution?

• 30.7 mg

• 307 mg

• 3.07 mg

• 30.70 mg

Answer explanation

To find the total calcium in 100 mL, use the concentration: 307 mg/L. Convert 100 mL to L (0.1 L) and multiply: 307 mg/L * 0.1 L = 30.7 mg. The correct answer is 30.70 mg.

How is the concentration of calcium in the solution converted into mass during the data analysis portion?

• By multiplying the concentration by the volume

• By multiplying the concentration by the weight of the solid

• By dividing the concentration by the solution volume

• By dividing the concentration by the weight of the solid

Answer explanation

The concentration of calcium in the solution is converted to mass by multiplying the concentration (usually in mol/L) by the volume of the solution (in L). This gives the total amount of calcium in grams.