Ch 15/16 Water and its Properties

Ch 15/16 Water and its Properties

1mL = 0.001L

• Vocabulary (tested-star these terms)• • solute, solvent, pressure

• temperature, agitation, concentration• saturated, unsaturated, % composition– *** Molarity ***

Surface tension – hydrogen bonds create an inward pull that minimizes surface area. Mr. B:: Creates a solid shell on top of water that can support light weight items (small bugs, pepper flakes). Createsraindrops.

Hydrogen bonds between water molecules.

All atoms like to have 8 electrons in valance shell (2 s and 6 p’s.) They are in 4 pairs of two. 2 pairs grab H. 2 pairs grab other H20 molecules. Discuss Ice in rivers and circle of life.Show water / oil bottles with 2 dyes

Aqueous solution – water w/ dissolved particles (aq)

Solvent – water (dissolver)

Solute – salt (dissolvee)(NEW WORD?)

Surfactants • Stop or break down the hydrogen bonding

• Teacher Notes and You tube Video link:

• http://www.youtube.com/watch?v=hKoB0MHVBvM

• When you pair carbonated soda and Mentos candies, you can create an overflow of fun. Perform your experiments outside, in an open area, and use protective eye gear. The nature of the reaction between the soda and candy is a matter of debate among scientists. The effect may be due to a physical or chemical cause. Most believe that ingredients in the candies cause a break in surface tension in the liquid, allowing new bubbles to more easily form, while carbon dioxide bubbles form well on the pitted surface of the candies

Read more: Mentos and Soda Experiments | eHow.com http://www.ehow.com/list_7487590_mentos-soda-experiments.html#ixzz2Ow8u7tmr

http://www.youtube.com/watch?v=hKoB0MHVBvM

http://www.youtube.com/watch?v=hKoB0MHVBvM

http://www.ehow.com/list_7487590_mentos-soda-experiments.html





Solvation: a solute dissolves or dissociates into ions(happens with most soluble ionic compounds and acids)Electrolyte: will conduct electricity when dissolved in a liquid.

3 ways to speed up solvation HeatingStirringIncreasing surface area of the solute (powder)

A solution does not have to contain a liquid

Air is a solution 78% nitrogen

14karat gold is a solution58% gold 42% Copper

Solid Hydrate:A crystal with big spaces that water can easily move into.

Demo: Na2SO4•10H2O(s) Show crystal model of

Na2SO4

Add some H2O models to it.

Solid Hydrate

HydratesCuSO4•5H2O(s)

1 (CuSO4) to 5 ( H2O) ratioIn this solid compound there are 5 water molecules for every one CuSO4.

What is the molar mass of the hydrate?Add the molar mass of CuSO4 and 5 water molecules.

Cu S O4• 5H2O(s)

CuSO4•5H2O(s)

CuSO4•5H2O(s)

What is percent H2O?

Percent H2O Hydrate:

CuSO4•5H2O(s)

What is percent H2O?

What is the molar mass of Na2SO4•10H2O(s)

What is the molar mass of Na2SO4•10H2O(s)

What is the percent water in this hydrate? Na2SO4•10H2O(s)




What is the correct sig fig in the answer: 56%

What is the percent sodium in this hydrate? Na2SO4•10H2O(s)

WOD:

% Chem = Mass Chem x 100% Total Mass

What is the percent sodium in this hydrate? Na2SO4•10H2O(s)

What is the correct sig fig in the answer: 14%

How many grams of water are in a 34g sample of Na2SO4•10H2O(s)?

How many grams of water are in a 34g sample of Na2SO4•10H2O(s)?

56% x 34g = 19g H20

Solubility – g of solute per 100g of solvent at a certain temperature

Below: 2 different liquids, same amount of solute (dye). Note black bars.

Does solubility change with temperature?

Does solubility change with temperature?

saturated solution - will dissolve no more solute (at that temperature). Excess

usually makes a pile of crystals on the bottom.

unsaturated solution – will dissolve more solute (at that temperature)

(left 3 beakers on next slide)

As you add more solute, from left to right Dilute More Concentrated Saturated Saturated

Since 3 on right are saturated, keep adding solute, but they don’t get darker. No more dissolves into them.

Dilute vs concentrated

Supersaturated solution – contains more solute then should be dissolved at a

temperatureex…heating then cooling a

solution

Supersatured videoshttp://www.youtube.com/watch?v=XSGvy2FPfCw

http://www.youtube.com/watch?v=HnSg2cl09PI

3 min Long one if you have extra time: http://www.youtube.com/watch?v=1y3bKIOkcmk

http://www.youtube.com/watch?v=XSGvy2FPfCw

http://www.youtube.com/watch?v=HnSg2cl09PI

http://www.youtube.com/watch?v=1y3bKIOkcmk

New Subject: Gas Solubility: S1 = S2

P1 P2Called Henry’s Law.

Amount of gas dissolved in a liquid.

Solubility of a gas in a liquid is directly related to pressure.

Miscible – liquids dissolve in each other. (liquids that can mix

together)Immiscible – Guess?

Is this lava lamp miscible or immiscible?

16.2 Molarity Pg 526Molarity tells us the number of

moles of solute in exactly 1 liter of a solution.

M = mol ÷ L (of solution)

Do not confuse lower case m (Molality) and Capitol M (Molarity)

Molality: m = moles of Solute Pg 538 kg of solvent

Concentrations(Notice Case of M or m)M = Molarity = Volume basedm = Molality = Mass based

Molarity: M = mol ÷ L (of solution)

molality: m = moles of Solute Pg 538 kg of solvent

Concentrations (Note case of M / m) Molarity: M = Volume based of SOLUTION! (after mix) molality: m = Mass based of SOLVENT! (before mix) Solute + Solvent = Solution

We need two pieces of information to calculate the molarity of a solute

in a solution: The moles of solute present in the

solution. The volume of (final) solution (in

liters) containing the solute.

What is the molarity of a 125mL solution with 12.5g of NaCl

dissolved in it?

What is the molarity of a 125mL solution with 12.5g of NaCl dissolved in it?

Do we have moles and liters?





How many liters of 18.1M HCl are needed to obtain 2.55 mol?

How many liters of 18.1M HCl are needed to obtain 2.55 mol?

Quiz 16.2A 137g sample of BaCl2.5H2O is dried in an oven.

1a) How many grams of water will be driven off?

1b) How many grams of BaCl2 will remain?

2. What would the molarity of a solution be if the above 137g sample of BaCl2.5H2O was instead

dissolved to make a 0.75L solution?

Answers Quiz 16.2A 137g sample of BaCl2.5H2O is dried in an oven. 1a) How many grams of water will be driven off?

1b) How many grams of BaCl2 will remain?

Quiz 16.2A 137g sample of BaCl2.5H2O is dried in an oven. 2. What would the molarity of a solution be if the above 137g sample of BaCl2.5H2O was instead


Quiz 16.2A 137g sample of BaCl2.5H2O is dried in an oven. 2. What would the molarity of a solution be if the above 137g sample of BaCl2.5H2O was instead


• 90/297(100%)=30.3% water• 0.303 (137)= 41.5g water• 137-41.5 or (207/297x137) = 95.5g BaCl2

By adding water you can dilute the molarity

M1V1=M2V2

By adding water you can dilute the molarityM1V1=M2V2

When you ADD WATER, moles of solute stays the same.

A 0.500L bottle of vinegar is 0.88 molar. Water is added until the

Molarity is 0.22. What is the new volume?







A stock solution of 18.1M HCl is available in the store room. How

much stock solution should be obtained to create 2.5L of 0.52M

solution?

A stock solution of 18.1M HCl is available in the store room. How much

stock solution should be obtained to create 2.5L of 0.52M solution?

18.1M (X) = (0.52M) 2.5LX = 0.072L

75.5mL of 1.85M CaCl2 is added to 22.4mL of 3.67M AgNO3

(assume 97.9mL is the final volume and AgCl(s)).

What is the molarity of Ca(NO3)2(aq)?


(assume 97.9mL final and AgCl(s)). What is the molarity of Ca(NO3)2?









A change in a property of a solvent that depends on the concentration of

dissolved solute(s) particles is called a colligative property.

Colligative properties are vapor pressure lowering, boiling point elevation, freezing point lowering

Number of solute particles in a solution determines colligative

properties.

A Comparison of Some of the Properties of Pure Water and an Aqueous NaCl Solution

property pure water NaCl solution

vapor pressure 23.8 torr 23.1 torr

boiling point 100.0oC 100.8oC

freezing point 0.0oC -3.0oC

Why do you add salt to water when cooking pasta?

When a solute is added to a solvent, the vapor pressure of the solvent (above the resulting solution) is less than the vapor

pressure above the pure solvent. The boiling point of a solution, then, will be greater than the boiling point of the pure solvent because

the solution (which has a lower vapor pressure) will need to be heated to a higher temperature in order for the vapor pressure to become equal to the external pressure

(i.e., the boiling point).

Calculate the percent composition and the molarity of the solution.

20g of NaCl is added to 100mL of water. The volume of this solution

is 114mL.

(remember 1.00mL=1.00g for pure water)

Calculate the percent composition and the molarity of the solution.

20g of NaCl is added to 100mL of water. The volume of this solution is 114mL.

(remember 1.00mL=1.00g for pure water)

The mass of the solute in the solution.

The mass of the solution.

Start Bell work 4 here:. Dilution and Stoich problems

Dilution and Stoichiometric ProblemsBW Day 4, Problem 6

What is the M of a 250ml , 12M HCl solution that is diluted to

4.5L.Clue: M1V1 = M2V2

Subscript 1 and 2 refer to the same solution at 2 different

times.

Dilution and Stoichiometric ProblemsBW Day 4, Problem 8

What is the Molarity of the final solution when 66.6mL of 12.57M HCl is added

to 257 mL of 2.77M Clue. M = n/L

Find n = n1 + n2 n1 = moles of 66.6mL 12.57M HCL

n2 = moles of 257mL 2.77M HCLVolume = V1 + V2 (in Liters)

M = n = n1 + n2 V V1 + V2

m = Molality = moles of Solute Pg 526 kg of solvent

Concentrations(Notice Case of M or m)M = Molarity = Volume basedm = Molality = Mass based

Kb is for boiling. Kf is for freezing.ΔT = K x m

Molarity: M = mol ÷ L (of solution)

molality: m = moles of Solute Pg 538 kg of solvent

Concentrations (Note case of M / m) Molarity: M = Volume based of SOLUTION! (after mix) molality: m = Mass based of SOLVENT! (before mix) Solute + Solvent = Solution

WATER ONLY

Remember mass WATER ONLY

1 mL = 1g = .001 kg

1000 mL = 1000g = 1kg

These conversion are for WATER ONLY

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Ch 15/16 Water and its Properties