Unit 5- Solutions, Acids, and Bases - Whitney High...
Transcript of Unit 5- Solutions, Acids, and Bases - Whitney High...
Terms to KnowSolvent= liquid that dissolves
the chemical compound (usually water)
Solute= substance that dissolves into the water
Dissolution= process of dissolving
Aqueous (aq) = water based solutionsex: NaCl(aq) = salt water
Soluble- ability of a solvent to dissolve a solute.
solute + solvent = solution
Ex: Solute & Solvent
• Your blood is a
solution:
• Solvent= plasma
(which is mostly water)
• Solute= white blood
cells, red blood cells,
etc.
Why Water is a Great Solvent
• Water is POLAR!!
– It is unevenly charged
– The highly
electronegative
oxygen hogs the
electrons.
• Polar & ionic solutes
will dissolve in water
because of the
charges.
“Like Dissolves Like”
Rule of Thumb for Solubility:
• Charged things dissolve in
charged things :
– Polar/ Ionic solutes will
dissolve in polar solvents.
• Nonpolar solutes will
dissolve in nonpolar
solvents.
“Like Dissolves Like”Polar/Ionic compounds
dissolve in polar solvents.Non polar compounds dissolve in non polar solvents.
Sugar (polar) mixes with water (polar) for easy cleaning.
Grease, oil and gasoline (non polar) will dissolve one another.
Not all solutes are water soluble
• Nonpolar substances
do NOT dissolve in
water
– Ex: Oil & Water
• Nonpolar substances
will only dissolve in
nonpolar solvents!
Substances that are soluble in H2O: “Like Dissolves Like”
Ionic Compounds (ex: salts) – made up of + cations and -
anions.
– charged ions attracted to the polar ends of water
Polar Substances (ex: Sugar)
– Covalently bonded
– Both sugar and water are polar.
Dissolving of Ionic Substances-ex: NaCl (salt)
•charged (Na+ & Cl-) are more attracted to several polar water molecules and are pulled apart.
•They dissociate (break apart)
Dissolving of Polar Substances-ex: C6H12O6 (Glucose)
• Polar water surrounds the glucose molecules and pulls them away from each other
• Molecules themselves remain intact
Weak hydrogen bond between glucose is broken and glucose is surrounded by
water
FYI-Why does soap dissolve both polar & nonpolar things?
-Alcohol, soap, & acetone will dissolve most substances because contain polar and non-polar regions.
How soap can dissolve a lot of substances
Electrolytes• Electrolyte= a substance containing free ions
(charged particles) that will conduct electricity.
• acids, bases or salts
All these substances disassociate/
break apart in water:
NaCl Na+ + Cl- (in water)
HCl H+ + Cl – (in water)
NaOH Na + + OH – (in water)
Non Electrolytes• Some solutions do not
conduct electricity.
They are called non-electrolytes.
Examples include:
sugar
ethanol (alcohol)
ethylene glycol
FYI:Sports Drinks & Electrolytes
• Electrolytes are important in your body because they are what your cells use to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells.
• As for your body, the major electrolytes are as follows:
– sodium (Na+)
– potassium (K+)
– chloride (Cl-)
– calcium (Ca2+)
– magnesium (Mg2+)
– bicarbonate (HCO3-)
– phosphate (PO42-)
– sulfate (SO42-)
Source: Howstuffworks "What are electrolytes?“. Created 3/19/2008. HowStuffWorks.com.
3/19/2008. http://health.howstuffworks.com/question565.htm
• When you exercise, you lose
electrolytes through your sweat.
• Many sports drinks now contain
electrolytes to replenish what you
have lost.
1) Increase Temperature-makes molecules move faster
2) Increase Surface area-more surfaces to interact with
3) Stirring/ Shaking
4) Increasing Pressure-only works for gases
Factors that Speed up Dissolving Process
-Need to make the solute & solvent come into contact more frequently
Solubility Curves-Show much solvent you can put in H2O @ certain Temp.
• Solubility usually increases as temperature increases
• EX:
• At 20°C, 200 g of sugar will dissolve in 100g (= 100 mL) of H2O.
• If the temp. is increased to 60°C, 300g of the sugar will dissolve in 100g (or 100mL) H2O.
Solubility Practice Problems
1
.
KNO3at
70°C
2
.
NaCl at
100°C
3
.
NH4Cl at
90°C
.
What mass of solute will dissolve in
100mL of water at the following
temperatures. :
Answers:
140g / 100mL
40g / 100mL
72g / 100mL
Saturated
solution
Supersaturated
solution
Unsaturated
solution
Concentration of a Solution
• Amount of solute is dissolved in a given amount of solution.
• Unsaturated Solution (dilute)– more solute can be dissolved
• Saturated Solution (full)–no more solute can be dissolved under @ that temp • Saturation Point
• Supersaturated Solution–the solution has a higher solute concentration than can be reached under normal conditions.
Crystallization
occurring when
solution cools
Concentration=
Can be expressed in:
– %composition
– Parts per million (ppm)
– Grams/ Liter
– Molarity (M)2 Fish
1 L
10 Fish
1 L
Amount of solute (part)
Amount of solvent (whole)
Conversion factors to know:
1 g H2O = 1 mL
1 L = 1000 mL
% Composition
• 1 mL water = 1 gram of water
– These solutions are so dilute, we can assume that 1
mL solution = 1 gram of solution
Example 1: 13.0 grams of NaOH is dissolved in
enough water to make 850 mL of solution.
– Given: 13.0 g NaOH
850 mL solution = 850 g solution
– Find: percent composition
13.0 g NaOHX 100 = 1.53 % NaOH
850 g solution
grams of soluteX 100
grams of solution
Parts per million (ppm)- Used to describe
the concentration of very dilute solutions
Example 1: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution.
• Given: -13.0 g NaOH (solute)
–850 mL solution = 850 g* (solution)
*(1 mL water = 1 gram of water… so dilute we can assume this 1 mL = 1 gram)*
• Find: ppm
13.0 g NaOHX 1,000,000 = 15294 ppm NaOH
850 g solution
grams of soluteX 106
grams of solution
What’s in your drinking water?National Primary Drinking Water Standards as of 10/03
Contaminant Parts per
Million (ppm)
Potential Health Effects from
Ingestion of Water
Arsenic 0.010 Skin damage or problems with circulatory
systems, and may have increased
risk of getting cancer
Asbestos (fibers >10
micrometers)
7 (million
fibers per
Liter)
Increased risk of developing benign
intestinal polyps
Carbon
tetrachloride
0.005 Liver problems; increased risk of cancer
Lead 0.015 Infants and children: Delays in physical
or mental development; children could
show slight deficits in attention span
and learning abilities; Adults: Kidney
problems; high blood pressure
Mercury (inorganic) 0.002 Kidney damage
Source: US EPA. Water On Tap: What You Need To Know. Modified 12/14/2004. EPA. 3/13/2008.
http://www.epa.gov/safewater/wot/pdfs/book_waterontap_full.pdf
Grams per liter
• Used to discuss the solubility of a solid in solution.
• Example: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution.
– Given: 13.0 g NaOH
850 mL solution = 0.850 L solution
– Find: g/L
– Solve:
grams of solute
Liters of solution
13.0 g NaOH= 15.3 g/L
0.850 L
Step 1: Molarity = moles
Liters
Step 2: Convert grams to Moles
24.5 g NaCN x 1 mole NaCN = 0.500 mol
49.01 g
Step 3: Convert mL to L
250.0 mL x 1 L = .2500 L
1000mL
Step 4: Plug into equation
M = 0.500 mol = 2.00 M NaCN
0 .2500
PROBLEM: What is the molarity of a solution prepared by dissolving 24.5 g of NaCN in water to a final volume of 250.O mL?
Ex #1 (no calculator needed)
How many moles of HNO3 are needed to prepare 5.0L of 2.0 M solution of HNO3?
Solution: Molarity= moles
Liter
2.0 M = moles = 10 moles5.0 L
Kool- Aid Lab- a little history
Over 900 people died in a
“mass suicide” by drinking
punch laced with poisons
Common Acids
HC2H3O2 Acetic Acid Vinegar
HCl Hydrochloric Acid Stomach acid
H3C6H5O7 Citric Acid Citrus Fruit
HNO3 Nitric Acid
H2SO4 Sulfuric Acid Battery Acid
Some Common Bases
NaOH sodium hydroxide lye/ Drano
KOH potassium hydroxide liquid soap
Ba(OH)2 barium hydroxide stabilizer for plastics
Mg(OH)2 magnesium hydroxide Milk of magnesia
Al(OH)3 aluminum hydroxide Maalox (antacid)
NH3 Ammonia Windex & cleaners
What Are Acids & Bases?(Arrhenius theory)
• Acids - Increase the concentration of hydrogen ions (H+) in aqueous solution.– Examples: HCl, H2SO4,
HNO3
• Bases - Increase the concentration of hydroxide ions (OH-) in aqueous solution.– Examples: NaOH,
Mg(OH)2, KOH,
Characteristic Ions of AcidsHydrogen Ion (H+)• Many acids contain H+
• Acids dissociate in H2O, # of H+ ions increases in the solution
Hydronium Ion (H3O+)• As H+ interact with water
molecules, they combine to form H3O+
HCl + H2O H3O+ + Cl-
Acid donates to
H2O
H3O+ = hydronium
ion
gives solution the
acidic properties
Hydronium Ion (detailed FYI)H2O with extra proton (H+)
H & Cl form a polar covalent bond, but H is very attracted to water.
Some Properties of Acids• Produce H+ ions (+ H2O) H3O+, hydronium ion
• 0-7 on pH scale
• Taste sour
• Acids are Electrolytes
• Acids are neutralized with a base (forms salt + water)
• Turns blue litmus paper to “Red”
• Reacts with metals to form H2 gas
Capsaicin- Acid found in chilis
• All sorts of interesting applications:
– Pain relief for topical application on arthritic limbs
– Animal deterrent
– Drug abuse deterrent
– Diet functionPepper spray
Characteristic Ion of Bases
• Hydroxide Ion (OH-)
• Many bases contain OH-
• As bases dissociate in water, the concentration of OH- ions increases in the solution
2 ways to explain Bases:
1) Donators of OH- ions
2) Acceptor of H+ ions
water
NaOH Na+ (aq) + OH- (aq)
Some Properties of Bases Produce OH- ions in water (hydroxide) / Accept H+
ions
pH greater than 7-14
Taste bitter, chalky
Are electrolytes
Feel soapy, slippery
Are neutralized by acids (form salt + water)
Turns red litmus paper to blue “Basic Blue”
Strong vs. Weak Acids & Bases
• Strength of an acid or base is determined by the amount of ionization (how often it dissociates in water)
• Examples:
– Strong acid: hydrochloric acid (HCl)
– Weak acid: Acetic acid (vinegar)
– Strong Base: sodium
hydroxide (NaOH)
– Weak Base: Ammonia (NH3)
Strong- break apart easily
Weak – Do NOT ionize as much
Ex: Strong vs. Weak Acids/Bases
HCl= strong acid that completely
breaks apart in water.
Acetic Acid= weak acid that does
not completely break apart in water
Strong acids/ bases = strong
electrolytes• Strong acids (dissociate 100% in water)=
HNO3, HCl, H2SO4 and HClO4
• Weak acid = acetic acid (aka vinegar) -CH3CO2H
• Strong base (dissociate 100% in water) =
NaOH (aq) ---> Na+ (aq) + OH- (aq)
• Weak base = Ammonia (NH3)
NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)
pH testing- Lots of ways!
pH meter
Phenolphthalein (PPT)
responds to bases only
pH- paper
Some chemicals respond
to acids &/or bases by
changing colors
pH indicator: Cabbage JuiceBy boiling purple
cabbage, the
natural pigments
can serve as an
indicator.
Neutralization- a special type
of double replacement reaction
Tums neutralizes the acid in
your stomach.
Neutralization Reactions Cont.
• Acids React with Carbonates
You may have made a volcano :
2HC2H3O2 + Na2CO3 2 NaC2H3O2 + H2O + CO2
Vinegar + Baking Soda Sodium acetate (salt)
Titration- way of determining the
molarity of an unknown solution.
acid of unknown strengthW/ indicator in it
drop base of known Molarity into acid until it’s neutralized
By knowing how much base it took to neutralize
acid (& a little math) you can find the strength.
Formula: MV = MV (see problem on next slide)
Use formula:
(Molarity acid) (*Volume acid) = (Molarity base) (*Volume base)
*Volume must be in Liters (1 L = 1000 mL)*
Titration Problem:35 mL of NaOH is neutralized
with 25 mL of 0.1 M HCl by titration to an
equivalence point. What is the concentration of the
NaOH?
Solution: Plug & Chug …(0.1 M ) (0.025 L) = (?M) (0.035 L)
M= 0.07 M NaOH