# Solution Concentration

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Solution Concentration

What is different between the glasses of Kool-aid?

Solution concentration can be described generally
Dilute - reduced in strength, weak, watered down. Concentrated – stronger, pure. Has less water.

What is the problem with just using dilute and concentrated as descriptions of the solution concentration?

Is solution B dilute or concentrated?
The terms dilute and concentrated are relative. Scientists need a more precise way of referring to the concentration of a solution. Concentrated Dilute Solution A Solution B Solution C

Solution concentration can be described specifically
Do you remember the “mole” from Stoichiometry? What is a mole? How might you use it to describe the concentration of a solution?

Concentration can be represented by…

The ratio of the moles of solute to the volume of solution in liters.
Molarity The ratio of the moles of solute to the volume of solution in liters. Moles of solute Molarity (M) = Volume in Liters of solution Used for most chemistry calculations of concentration

Molality Molality = moles of solute per kg solvent Moles of solute
kilogram of Solvent Used for chemistry when volume of solvent is not constant

Percent by Mass Percent by Mass = mass of solute divided by mass of total solution Mass (g) of solute % by mass = Mass of Solvent + Mass of Solute Used for food, medicine, household cleaners and chemicals

How to Calculate Dilutions
Using molarity to calculate dilutions is EASY. Moles stays the same Volume changes Molarity changes M1V1 = M2V2 Re-arrange to solve for the requested information

How to read Molarity 6.0 M NaCl Read: “6 molar solution of NaCl”
Can be abbreviated 6M solution You must be careful to label the molarity with a capital M so that it is not confused with m for molality.

How to make a solution using molarity (6M NaCl)
(a) Add 6 moles NaCl to the volumetric flask. How would you measure that? 6moles NaCl g NaCl 1 mole NaCl = 351 g NaCl

How to make a solution using molarity (6M NaCl)
(b) Add dH2O to dissolve and mix the NaCl (c) Fill the flask with dH2O until you reach the 1000mL line.

Types of Calculations with Molarity:
1. Finding concentration of a solution. 2. Finding the mass of solute needed. 3. Finding the volume of solution made.

Finding Concentration
Antifreeze is a solution of ethylene glycol, C2H6O2 in water. If 4.50 L of antifreeze contains 27.5 g of ethylene glycol, what is the concentration of the solution? 27.5 g C2H6O2 1 mol C2H6O2 62.08 g C2H6O2 4.5 L = mol/L or M C2H6O2

Finding Mass What mass of sodium carbonate, Na2CO3, is present in 50 ml of a 0.750M solution? Conversion Factor 50 ml 1 L 0.750 mol g Na2CO3 1000 mL 1 L 1 mol Na2CO3 = 3.97 g Na2CO3

Finding Volume Conversion Factor What volume of 1.50 mol/L HCl solution contains 10.0 g of hydrogen chloride? 10.0 g HCl 1 mol HCl 1 L 36.46 g HCl 1.50 mol = L or 183 mL

Practice Problems

Practice Problems 1. A L aqueous solution contains 90.0 g of ethanol, C2H5OH. Calculate the molar concentration of the solution in mol·L-1.

Practice Problem 2. What mass of NaCl are dissolved in 152 mL of a solution if the concentration of the solution is M?

Practice Problem 3. What mass of dextrose, C6H12O6 is dissolved in 325 mL of M solution?

Practice Problem 4. A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a M solution. What is the volume of the solution?

Practice Problem 5. A solution of sodium carbonate, Na2CO3, contains 53.0 g of solute in 215 mL of solution. What is its molarity?

Practice Problem 6. What is the molarity of a solution of HNO3 that contains 12.6 g of solute in 5.00 L of solution?