EQB12: Concentration of Solutions

In a coffee shop, the following coffee samples are prepared for customers. Based on the amount of sugar added, which sequence ranks the coffee from the sweetest coffee to the least-sweet coffee? i. 10 g of sugar added to 100 g of coffee ii. 10 g of sugar added to 200 g of coffee iii. 4 g of sugar added to 200 g of coffee iv. 4 g of sugar added to 100 g of coffee

• i, ii , iii, iv
• iii, iv, ii, i
• iv, i, ii, iii
• i, ii, iv, iii

Answer explanation

- **Explanation:** The sweetness of coffee depends on the sugar-to-coffee ratio. Sample i has 10 g of sugar per 100 g of coffee, which is the highest ratio, followed by sample ii (10 g of sugar per 200 g of coffee), making it less sweet than i. Sample iv (4 g of sugar per 100 g of coffee) is sweeter than iii (4 g of sugar per 200 g of coffee).

Given that the molar mass of NaCl is 58.44 g/mol, what is the molarity of a solution that contains 87.75 g of NaCl in 500. mL of solution? Use .

• 0.333 M
• 0.751 M
• 1.50 M
• 3.00 M

Answer explanation

- **Explanation:** Molarity is calculated using the formula M = moles of solute / liters of solution. First, convert 87.75 g of NaCl to moles by dividing by its molar mass (58.44 g/mol), and then divide by the volume in liters (0.500 L).

A 1.00 L volume of HCl reacted completely with 2.00 L of 1.50 M Ca(OH)2 according to the balanced chemical equation below. What was the molarity of the HCl solution? 2HCl + Ca(OH)2 CaCl2 + 2H2O

• 0.375 M
• 1.50 M
• 3.00 M
• 6.00 M

Answer explanation

- **Explanation:** From the stoichiometry of the reaction, 1 mole of Ca(OH)2 reacts with 2 moles of HCl. Calculating the total moles of Ca(OH)2 (2.00 L x 1.50 M) and then finding the necessary moles of HCl, we find the molarity by dividing the moles of HCl by the volume of the HCl solution used (1.00 L).

Tags

NGSS.HS-PS1-7

A number of beakers have different concentrations of a solution. Which statement best describes the most concentrated solution?

• It has the largest volume.
• It has the most solute for a given volume.
• It has the greatest amount of solute.
• It has the most volume for a given amount of solute.

Answer explanation

- **Explanation:** Concentration refers to the amount of solute in a given volume of solution. The most concentrated solution has the highest ratio of solute to solution volume.

The molar mass of NaOH is 40.00 g/mol. If 5.20 g NaOH are dissolved in 0.500 L of solution, what is the molarity of the solution? Use .

• 0.0125 M
• 0.260 M
• 3.85 M
• 7.69 M

Answer explanation

- **Explanation:** Using the formula M = moles of solute / liters of solution, first convert the mass of NaOH to moles (5.20 g ÷ 40.00 g/mol), then divide by the volume of the solution in liters.

A student requires 2.00 L of 0.100 M NH4NO3 from a 1.75 M NH4NO3 stock solution. What is the correct way to get the solution? Use .

• Measure 114 mL of the 1.75 M solution, and dilute it to 1.00 L.
• Measure 114 mL of the 1.75 M solution, and dilute it to 2.00 L.
• Measure 8.75 mL of the 1.75 M solution, and dilute it to 2.00 L.
• Measure 8.75 mL of the 0.100 M solution, and dilute it to 2.00 L.

Answer explanation

- **Explanation:** Using the dilution formula M1V1 = M2V2, where M1 and V1 are the molarity and volume of the concentrated solution, and M2 and V2 are the desired molarity and volume.

Tags

NGSS.HS-PS1-7

Which best defines concentration?

• ratio that describes the amount of solute divided by the amount of solvent or solution
• ratio that describes the amount of solvent or solution divided by the amount of solute
• ratio that describes the mass of solute divided by the mass of solvent
• ratio that describes the amount of solvent in a solution

Answer explanation

- **Explanation:** Concentration is fundamentally a ratio that indicates how much solute exists within a given volume of solvent or total solution.

Tags

NGSS.HS-PS1-5

Which solution is the most concentrated?

• 2.0 mL of 10 M H2SO4, where H2SO4 has a molar mass of 98 g/mol
• 5.0 mL of 1.0 M PbSO4, where PbSO4 has a molar mass of 303 g/mol
• 2.0 mL of 10.5 M H2O2, where H2O2 has a molar mass of 34 g/mol
• 100 mL of 10 M NaCl, where NaCl has a molar mass of 58 g/mol

Answer explanation

- **Explanation:** Among the options, the solution with the highest molarity is the most concentrated. Molarity directly indicates concentration level.

Which would be the best way to represent the concentration of a 1.75 M K2CrO4 solution?

• 0.0175
• [K2CrO4] = 1.75 M
• (K2CrO4)
• K2CrO4, [M]

Answer explanation

- **Explanation:** This notation clearly indicates that the concentration of K2CrO4 in the solution is 1.75 moles per liter, which is a direct expression of molarity.

Which is a way to express concentration of a solution?

• parts per billion
• moles
• molar mass
• force per square meter

Answer explanation

- **Explanation:** Parts per billion (ppb) is a unit used to express very low concentrations of a substance in a solution, particularly in water quality measurements.

Tags

NGSS.HS-PS1-5