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**Solution Concentration**

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**What is different between the glasses of Kool-aid?**

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**Solution concentration can be described generally**

Dilute - reduced in strength, weak, watered down. Concentrated – stronger, pure. Has less water.

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

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**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

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**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?

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**Concentration can be represented by…**

Molarity Molality Percent by Mass We will learn about this calculation later on.

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**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

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**Molality Molality = moles of solute per kg solvent Moles of solute**

kilogram of Solvent Used for chemistry when volume of solvent is not constant

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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

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**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

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**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.

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**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

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**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.

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**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.

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**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

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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

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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

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Practice Problems

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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.

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

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

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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?

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

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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?

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