Trick to Calculate Molarity | Molarity practice problems

Summary

This educational video script offers an easy method to calculate molarity, a measure of solute concentration in a solution. It explains the basic formula, m = n/V, where m is molarity, n is moles of solute, and V is volume in liters. The script provides step-by-step examples, including converting mass to moles and milliliters to liters, to find molarity for various solutions like HCl, NaCl, and HNO3. It also emphasizes the importance of understanding volume conversions and molar mass to solve complex molarity problems efficiently.

Takeaways

• 🧪 Molarity is defined as the number of moles of solute dissolved in 1 liter of solution.
• 📝 The formula for molarity is M = n/V, where M is molarity, n is moles of solute, and V is volume in liters.
• 🌟 An example given is dissolving 6 moles of HCL in 1 liter of water, resulting in a 6 M molar solution.
• 📏 Conversion of volume units is crucial; 1 liter is equal to 1000 cm³ or 1 dm³.
• 🔢 To convert from mL to liters, move the decimal point three places to the left.
• 🧪 For problems involving mass, first convert the mass of the solute to moles using its molar mass.
• 📐 The molar mass of a compound is the sum of the molar masses of its constituent elements.
• 🌡️ Example calculations include converting 2 grams of sodium hydroxide to moles and then calculating its molarity in a 600 cm³ solution.
• 📉 When given mass, always remember to perform the conversion to moles before applying the molarity formula.
• 💡 The script provides a step-by-step guide for calculating molarity, even when the solute's mass is provided instead of moles.
• 📚 Practice is encouraged with a final problem to calculate the molarity of a solution with a given mass of HCL.

Q & A

What is molarity and how is it defined?

Molarity is defined as the number of moles of solute dissolved in 1 liter of solution. It measures the concentration of a solute in a solution.

What is the formula used to calculate molarity?

The formula to calculate molarity is m = n/V, where 'm' stands for molarity, 'n' is the number of moles of solute, and 'V' is the volume of the solution in liters.

If 6 moles of HCL are dissolved in a solution that is marked to 1 liter, what is the molarity of the solution?

The molarity of the solution would be 6 M, as 6 moles of HCL are dissolved in 1 liter of solution.

What is the relationship between liters, cubic decimeters (dm³), and milliliters?

One liter is equal to 1 cubic decimeter (dm³), which is also equal to 1000 cubic centimeters (cm³) or 1000 milliliters.

How do you convert the volume of a solution from milliliters to liters?

To convert milliliters to liters, you move the decimal point three places to the left or divide the volume in milliliters by 1000.

What is the molarity of a solution if 0.5 moles of sodium chloride are dissolved in 400 ml of water?

The molarity of the solution would be 1.25 M, after converting 400 ml to 0.4 liters and using the molarity formula m = n/V.

How do you calculate the molarity of a solution when the volume is given in cubic centimeters?

First, convert the volume from cubic centimeters to liters by moving the decimal point three places to the left. Then, use the molarity formula m = n/V.

If the mass of a solute is given instead of moles, how do you find the number of moles?

To find the number of moles when the mass of a solute is given, you divide the mass by the molar mass of the solute.

What is the molar mass of sodium hydroxide (NaOH), and how do you calculate the number of moles from a given mass?

The molar mass of NaOH is 40 grams (23 for sodium + 16 for oxygen + 1 for hydrogen). To find the number of moles, divide the given mass of NaOH by 40.

How do you calculate the molarity of a solution when the mass of HNO3 is given as 4 grams and the volume of the solution is 80 milliliters?

First, find the molar mass of HNO3 (63 grams). Calculate the number of moles (4 grams / 63 grams/mole). Convert the volume to liters (80 ml / 1000 = 0.08 liters). Then, use the molarity formula m = n/V to find the molarity, which would be 0.75 M.

What is the molarity of a solution with 20 grams of HCL in a 0.5 DM³ volume?

First, find the molar mass of HCL (36.5 grams). Calculate the number of moles (20 grams / 36.5 grams/mole). Since 0.5 DM³ is equal to 0.5 liters, use the molarity formula m = n/V to find the molarity, which would be 1.1 M.