Water and Solutions (Chapter 15 and 16) Date: _______________ Name: _________________________________________ Formative Points: __/10

TOPICS:Vocabulary1. Properties of water2. Molarity and calculations3. Dilution and calculations4. Solubility curves

Vocabulary

1. Solute: the substance that is dissolved in a solvent (Ex: Salt crystals)2. Solvent: the liquid in which a solute is dissolved (Ex: Water)3. Solution: a homogeneous mixture of one or more solutes that has dissolved in a solvent (Ex: Salt

water)4. Suspensions: A heterogeneous mixture of a solvent and large sized solute where the solute settles

at the bottom (Sand and water mixture)5. Colloid: A homogeneous mixture of a solvent and large sized solute where the solute does not

settle at the bottom (Ex: Milk and water mixture/ Gelatin and Water)6. Electrolyte: Remember that Ionic substances are made up of a metal and a non metal. Solutions

made up of Ionic compounds and water. All electrolytes conduct electricity. (Ex: NaCl or table salt solution)

1. Properties of water (H 2O)

Water is made up of a central oxygen atom that is covalently bonded to two hydrogen atoms at either side. In covalent bonds atoms share Electrons to complete the octet (8) in their outermost electron shells. Because oxygen atom very electronegative, compared to hydrogen these shared electrons are pulled close to the Oxygen atom in a water molecule.

So, the Oxygen is negatively charged and Hydrogen becomes positively charged making the water molecule a POLAR.

This polarity makes is a great solvent for either positively charged or negatively charged compounds. This is why water is the solvent of life and so may chemicals can dissolve in water. Non-polar solutes do not dissolve in water.

Water molecules make hydrogen bonds (H-bonds) with each other as shown in this diagram: H of one molecule is attracted to the Oxygen of another due to opposite charge attractions. H- bonds are very strong inter-molecular bonds.

Water has a high boiling point (100C) because of the large amount of energy required to break H-bonds

Water has high surface tension because of the strength of H-bonds on the molecules on the surface creating a film-like state. This is why pond skaters can walk on water!

There are two unpaired-electrons in the oxygen molecules of water that repel the covalently bonded H-atoms away from oxygen giving the water molecules a BENT shape.

Diagram of ice and water showing the arrangement of Molecules:

This shape in important for understanding why ice floats on water.

As the temperature decreases the water molecules move farther away from each other and form a crystal structure when Ice is formed. Since water molecules are less tightly packed that water, Ice is less dense and floats on water!

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2. Molarity and calculations

Molarity: The concentration of solute in a solution

Molarity formula: Molarity = moles of Solute Liters of Solution

Unit: M or Moles/Liters (mol L-1)Examples:

o 2.2M KOH is read as “2.2 Molar Potassium hydroxide.” This is a base because of OH- ions This means there are 2.2 mole of KOH in 1 Liter

o 4.4M HBr is read as “4.4 Molar Hydrogen bromide or hydrobromic acid.” This is a an acid of H+ ions This means there are 4.4 mole of HBr in 1 Liter.

Calculation steps:1. Find the moles of solute (Mass of Solute/Molar mass of solute)2. Apply to Molarity formula

Calculations:

Q1: What is the molarity of a Sodium Hydroxide (NaOH) solution if 40g of NaOH pellets are dissolved in 2.0 L of water? Identify the Solute:_____________________ and Solvent:________________

Q2: What is the molarity of a 0.5 L solution made with 60g of NaOH?

Q3: How many grams of NaCl are required to make 500ml of a 3.0M solution?

Q4: How many liters of water are needed to make a 0.5 M NH4NO3 solution with 100g of the solute?

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Name: __________________________________ Period:_______ Date: 4-9-2018 Formative Points: /50

Chapter 15 and 16 continued3. Dilutions and calculations

Adding more solvent into a given solution is called dilution. When you dilute something, its concentration is reduced. For example, if you have a 100ml of 2.0 M NaCl solution and you add 100 mL of water to this solution, its final (new) volume is: 200 ml. And the concentration (Molarity) of NaCl is: 1.0M (Since the volume doubled, the concentration is decreased 2-fold). So, there is a relationship between the molarity, and volume before and after dilution.

In chemistry, we use a formula given below to calculate the Molarity before (M1) and Molarity after (M2) dilution as well as the volume before (V1) and volume after (V2) dilution.

Molarity & concentration formula: M1 x V1 = M2 x V2

Units: Molarity =M (moles per liter), Volume= Liters(L) or milliliters (mL)

Note: 1L = 1000ml, 1M =1000mM (millimoles)

Ex-1: If 75ml of water is added to a 150ml of 2.0 M LiOH, what is the concentration of this solution now?

Step 1: Find the following from the problem: M1=2.0, M2=?(unknown), V1= .150L, V2= .75+ .150 = .225LStep 2: Apply the data to the molarity and concentration formula and solve for the unknown.

M1 x V1 = M2 x V2

2.0 x .150 = M2 x .225M2 = 2.0 x .150 = 1.5M

.225

Problems:

1. 500 ml of 0.5M NaCl is combined with 40 ml of water. What is the new volume?____________ What is the new concentration of NaCl in this solution? (10 points)

2. Sam adds 100 ml of HCl to a 150ml of 2.0 M NaOH. What is the concentration of this solution? (10 points)

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3. You are given a 3.5M acid solution. How much of this solution must be added to make a 300 ml solution that has a final concentration of 1M? (10 points)

4. If you had 110ml of 0.75M Sucrose (table sugar) and you needed to make this into a 0.25 M solution, how much water needs to be added into the original solution? (10 points)

5. There is a 1.23L solution of NaOH which has a concentration of 0.3M. If 200ml of water was added to this solution, what is the final concentration now? (10 points)

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