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# 2. Water

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## Ricardo Luna

on 26 October 2015

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#### Transcript of 2. Water

2. Water
Stoichiometry
Mole
602 200 000 000 000 000 000 000
602 hexillion

1 mole of an element,
means 6.022x10 of atoms.

1 mole of a compound,
means 6.022x10 molecules

Molar mass
Mole conversions
How many atoms are in 4 moles of Iron?

How many moles contains 3.01x10 molecules of CO ?

How many molecules of ammonia NH are in 1.75 moles?
Volume percent
Conclusion
Specific properties
Concepts MARKET
Examples
1.0 mole of NaCl in a 1.0 L of solution, this is a molarity of 1.0 M.

M = mole/L

1.0 mole NaCl = 1.0 M NaCl
1.0 solution

What is the molarity (M) of 60.0 g of NaOH in a 0.250 L solution?

What is the molarity of a solution that contains75.0 g of KNO disolved in 0.350 L of solution?

As a conversion factor...

How many liters of a solution of 2.00 M of NaCl are needed to have 67.3 g of NaCl?

How many mililiters of a 2.25 M of HCl will yield 4.12 g of HCl?
Water cycle
Mental map
Importance and availability of water
99.7% of water is not available for human consumption.

Only 0.3% is adequate for humans, most in underground.

Molarity
Solutions

Solute

Solvent

Molarity: number of moles in exaclty 1L of solution.

Molarity= moles of solute = mol solute
Molarity vs molality
Mass percent
In teams of 3 mates, research:
- heat of vaporization
- specific heat
- superficial tension
- capillarity
- density
- molecular structure
- polarity
- vapor presure
- fusion and boiling point
- water reactions
- ionic and covalent compounds solubility

After research, collect all the concepts with your classmates and build your own mental map
What is a mole?

dozen: 12 things

mole: 602 200 000 000 000 000 000 000 things
602 hexillion things
dozen of doughnuts

dozen of jellybeans
mole of doughnuts
mole of jellybeans
23
23
2
24
3
liters of solution
L solution
3
Molarity: number of moles of solute per liter of solution

Molality: number of moles of solute per kilogram of solvent
molality =
moles of solute
kg of solvent
mass of solute
mass of solution
x 100
For molality you just need a scale and any container.

Stays constant over a wide range of temperature, rather than molarity.

A solvent can expand or contract depending of temperature, changing the molarity in the solution.

4° C 60° C 98°C
1 mole 1 mole 1 mole
0.975 L 1.00 L 1.025
1.026
M
1.00 M
0.976
M
Instead, with molality, there will always be 1 kg of solvent
While mol
ar
ity change at different temperatures and/or pressures, mol
al
ity remains constant
Examples
Calculate the molal concentration of a solution that contains 36 g of glucose in 500 g of water.

Prepare a solution of 86.53 g Na CO in water, in a 1000 mL flask determine molality.

What is the molality of a solution of 29.22 g NaCl in 100 mL?

How many grams of AgNO are needed to prepare 200 mL of a 2.0 m solution?

What is the molality in 40 g C H O in 150 g of water?
2
3
12
22
11
3
What is the mass percent of a solution prepared with 30 g NaOH in 120 g of water?

What is the mass percent of NaCl in a solution made with 2 g NaCl and 56 g of water?
volume percent (%v/v) = x 100
volume of solute
volume of solution
There is a solution of 5 mL of ethanol (C H OH) in a final volume of 250 mL. What is the volume percent of the ethanol solution?

What is the volume percent of Br in a solution of 12 mL of bromine in enough carbon tetrachloride to make 250 mL of solution?
2
5
2
pH
Scale that specify acidity or alkalinity in an aqueous solution

Represents the concentration of H+, its the negative logarithm of the hydrogen ion concentration.

Scale 0-14, where 7 is neutral.
Chemical bonds
Ionic
Two or more electrons are transfered between two atoms in a compound (from metals to non metals).

= Metals (+) and No metals (-)

Covalent
In non metals, it occurs in atoms that share one or more valence electrons.

Polar: formed when electrons are shared unequally between two atoms in a compound/molecule.

Non polar: formed when electrons are shared equally between two atoms in a compound/molecule.

Coordinate: two electrons are shared but one member does not share, occurs between atoms or ions on non metal
Colligative properties
Vapor pressure depression

Boiling point elevation

Freezing point depression

Osmotic pressure
Lewis structures
1. Find the number of valence electrons

2. Put the least electronegative atom in the center
*Hydrogen always goes on the outside

3. Put two electrons between atoms to form a chemical bond

4. Complete octets on the outside atoms

5. If central atom does not have an octet, move electrons from outer atoms to form double or triple bonds
Intramolecular forces
Intramolecular forces: are forces that hold the atoms together in a compound or molecule

Metallic
Formed between atoms in a pure metal or metal alloy

This bond, forms a cloud of electrons surrounding the atoms
Electronegativity difference between two bonded atoms
0 - 0.4 non polar covalent

0.5 - 2.0 polar covalent (non metal + non metal)

Intermolecular forces.
Are forces of attraction or repulsion that exists between neighboring particles.

dipole-dipole
: force of attraction between two neighboring polar covalent molecules.

hydrogen bond
: IMF between polar covalent molecules containing H bonded to either N, O or F.

London dispersion forces
: a temporary attraction force caused when the electrons adjacent particles occupy positions that make the atoms form temporary dipoles.
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