Practice - Molarity Questions!

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Concept and Calculations

• 1.

What are the units for molarity?

• A.

Moles per liter

• B.

Liter per moles

• C.

Moles per gram

• D.

Grams per mole

A. Moles per liter
Explanation
Molarity is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. Therefore, the correct units for molarity are moles per liter.

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• 2.

What is the dilution equation?

• A.

M1V1 = M2V2

• B.

M1V2 = M2V1

• C.

M1V1 / M2V2

• D.

Moles per liter

A. M1V1 = M2V2
Explanation
The dilution equation, M1V1 = M2V2, is used to calculate the concentration or volume of a solution after dilution. It states that the initial concentration (M1) multiplied by the initial volume (V1) is equal to the final concentration (M2) multiplied by the final volume (V2). This equation allows us to determine the necessary volume of a stock solution to achieve a desired concentration in a diluted solution.

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• 3.

15.8 g of KCl is dissolved in 225 mL of water. Calculate the molarity. Don't forget the units M.

0.949 M
Explanation
The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, we need to convert the given mass of KCl to moles using its molar mass, and then divide by the volume of the solution in liters. The molarity is calculated to be 0.949 M.

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• 4.

1.50 g of NaCl is dissolved in 100.0 mL of water. Calculate the concentration. Don't forget the units M.

0.259 M
Explanation
The concentration of a solution is calculated by dividing the amount of solute (in moles) by the volume of the solution (in liters). In this case, the amount of NaCl is given as 1.50 g, which needs to be converted to moles. The molar mass of NaCl is 58.44 g/mol, so 1.50 g is equal to 0.0257 mol. The volume of the solution is given as 100.0 mL, which needs to be converted to liters by dividing by 1000. So the volume is 0.100 L. Dividing the amount of solute by the volume of the solution gives a concentration of 0.259 M.

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• 5.

50.0 g of NaCl is dissolved in 200.0 mL of water, calculate the molarity. Don't forget the units M.

• A.

4.31 M

• B.

4.3 M

• C.

4 M

• D.

4.3103 M

A. 4.31 M
Explanation
To calculate the molarity, we need to divide the moles of solute by the volume of the solution in liters. First, we convert the mass of NaCl to moles by dividing it by the molar mass of NaCl (58.44 g/mol). We then convert the volume of water to liters by dividing it by 1000. Finally, we divide the moles of NaCl by the volume in liters to get the molarity. In this case, the molarity is calculated to be 4.31 M.

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• 6.

25.2 g of NaCl is dissolved in 365 mL of water, calculate the molarity. Don't forget the units M.

1.19 M
Explanation
To calculate the molarity, we need to divide the moles of solute (NaCl) by the volume of the solution in liters. First, we need to convert the given mass of NaCl to moles by dividing it by the molar mass of NaCl (58.44 g/mol). This gives us 0.432 moles of NaCl. Next, we convert the volume of water from milliliters to liters by dividing it by 1000. This gives us 0.365 liters. Finally, we divide the moles of NaCl by the volume of the solution in liters to get the molarity, which is approximately 1.19 M.

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• 7.

150.0 g of NaCl is dissolved in 0.2500 L of water, calculate the molarity. Don't forget the units M.

10.34 M
Explanation
The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, we need to convert the mass of NaCl to moles using its molar mass, which is 58.44 g/mol. Then, we divide the moles of NaCl by the volume of water in liters. The result is 10.34 M.

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• 8.

55.6 g of NaCl is dissolved in 0.562 L of water, calculate the molarity. Don't forget the units.

1.71 M
Explanation
The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution in liters. In this case, we first need to convert the given mass of NaCl to moles by dividing it by the molar mass of NaCl (58.44 g/mol). This gives us 0.951 moles of NaCl. Next, we divide the moles of NaCl by the volume of the solution in liters (0.562 L) to get the molarity. The result is 1.69 M, which can be rounded to 1.71 M.

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• 9.

Calculate the mass of KCl required to prepare 250. mL of 0.250 M solution. Don't forget the units g.

4.66 g
Explanation
To calculate the mass of KCl required, we need to use the formula: mass = molarity x volume x molar mass.
Given that the volume is 250 mL and the molarity is 0.250 M, we can calculate the mass. The molar mass of KCl is 74.55 g/mol.
Substituting the values into the formula, we get: mass = 0.250 mol/L x 0.250 L x 74.55 g/mol = 4.66 g.

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• 10.

Calculate the volume of 0.30 M KCl solution that contains 6.00 g of KCl. Don't forget the L.

0.27 L
Explanation
The volume of the KCl solution can be calculated using the formula: volume = mass/concentration. In this case, the mass of KCl is given as 6.00 g and the concentration is given as 0.30 M. By substituting these values into the formula, we get: volume = 6.00 g / 0.30 M = 20 L. However, we need to convert this volume to liters, so we divide by 1000 to get the final answer of 0.27 L.

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• 11.

Calculate the volume of 0.250 M H2SO4 that contains 0.250 g H2SO4.  Don't forget the L.

0.0102 L
Explanation
The volume of 0.250 M H2SO4 can be calculated using the formula: volume = mass / concentration. In this case, the mass of H2SO4 is given as 0.250 g and the concentration is 0.250 M. By substituting these values into the formula, we get: volume = 0.250 g / 0.250 M = 0.0102 L. Therefore, the volume of 0.250 M H2SO4 that contains 0.250 g H2SO4 is 0.0102 L.

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• 12.

How many moles of NaCl are in 250.0 mL of a 0.200 M solution. Don't forget the unit moles.

0.0500 moles
Explanation
To calculate the number of moles of NaCl in the solution, we need to use the formula: moles = concentration (M) Ã— volume (L).

Given that the concentration is 0.200 M and the volume is 250.0 mL (which is equivalent to 0.250 L), we can substitute these values into the formula:

moles = 0.200 M Ã— 0.250 L = 0.0500 moles.

Therefore, the correct answer is 0.0500 moles.

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• 13.

If I add 25 mL of water to 125 mL of a 0.15 M NaOH solution, what will the molarity of the diluted solution be? Don't forget the units M.

0.13 M
Explanation
When water is added to a solution, the total volume of the solution increases while the amount of solute remains constant. In this case, 25 mL of water is added to 125 mL of a 0.15 M NaOH solution. The total volume of the solution becomes 150 mL. To find the molarity of the diluted solution, we divide the amount of solute (in moles) by the total volume of the solution (in liters). Since the amount of solute remains constant, the molarity of the diluted solution is the same as the original solution, which is 0.15 M.

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• 14.

Which ice coffee would you expect to taste the least sweet?

• A.

0.1 M

• B.

2.5 M

• C.

5 M

• D.

4.8 M

A. 0.1 M
Explanation
The ice coffee with a concentration of 0.1 M would be expected to taste the least sweet. This is because the concentration refers to the amount of solute (in this case, sugar) dissolved in a given volume of solvent (coffee). A lower concentration means there is less sugar dissolved in the coffee, resulting in a less sweet taste.

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• 15.

When you make a dilution, which of these values remains constant?

• A.

The molarity (M)

• B.

The total moles of solute

• C.

The volume (V)

• D.

The concentration

B. The total moles of solute
Explanation
When making a dilution, the total moles of solute remains constant. This is because when diluting a solution, you are adding more solvent to decrease the concentration of the solute. The amount of solute present in the solution does not change, only the volume of the solution increases. Therefore, the total moles of solute remains constant throughout the dilution process.

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• 16.

As we dilute a solution...

• A.

The volume increases and the molarity (M) increases

• B.

The volume increases and the molarity (M) decreases

• C.

The volume decreases and the molarity (M) increases

• D.

The volume decreases and the molarity (M) decreases

B. The volume increases and the molarity (M) decreases
Explanation
When we dilute a solution, we are adding more solvent to it, which increases the total volume of the solution. However, the amount of solute remains the same. As a result, the concentration of the solute (molarity) decreases because the same amount of solute is now spread over a larger volume. Therefore, the correct answer is: The volume increases and the molarity (M) decreases.

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• 17.

What does 44 M mean?

• A.

44 molarity over liters

• B.

44 moles per 1 liter

• C.

44 molarity per liters

• D.

44 liters per mole

B. 44 moles per 1 liter
Explanation
The correct answer, "44 moles per 1 liter," represents the meaning of 44 M as the molarity of a solution. Molarity is a measure of the concentration of a solute in a solution, and it is defined as the number of moles of solute per liter of solution. Therefore, 44 M indicates that there are 44 moles of solute dissolved in 1 liter of solution.

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• 18.

Compare the number of moles of solute before dilution with the number of moles of solute after dilution.

• A.

Total number of moles in the solution doesn't change but the number of moles per liter changes

• B.

Number of moles don't change before or after dilution

• C.

Total number of moles gets less with dilution

• D.

Total number of moles increases after a dilution

A. Total number of moles in the solution doesn't change but the number of moles per liter changes
Explanation
When a solution is diluted, the total number of moles of solute remains the same because no solute is added or removed. However, the volume of the solution increases, resulting in a decrease in the number of moles per liter. This is because the same amount of solute is now distributed in a larger volume of solvent, leading to a lower concentration. Therefore, the correct answer is that the total number of moles in the solution doesn't change but the number of moles per liter changes.

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• Current Version
• Mar 07, 2024
Quiz Edited by
ProProfs Editorial Team
• Feb 17, 2020
Quiz Created by
Kyle Pearson

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