Transcript concentrated solution - Village Christian School
What Is a Solution?
• Solutions can be made from any combinations of solids, liquids, and gases.
Particles in a Solution • When a solution forms, particles of the solute leave each other and become surrounded by particles of the solvent.
Colloids and Suspensions • Colloids and suspensions are mixtures that have properties different from those of solutions.
Effects of Solutes on Solvents • At 0ºC, pure water freezes, but water mixed with a solute does not. Solutes lower the freezing point of a solvent.
Solid (frozen) water Liquid water solution
Assessment
1. What is a solution?
2. Suppose you mix food coloring in water to make it blue. Have you made a solution or a suspension? Explain.
3. How are solutions different from colloids and suspensions?
Assessment
1. What happens to the solute particles when a solution forms?
2.
What affects do solutes have on a solvent’s freezing and boiling points?
3. Why is the temperature needed to freeze ocean water lower than the temperature needed to freeze the surface of a freshwater lake?
4. Why does salt sprinkled on icy roads cause the ice to melt?
CONCENTRATION Definition:
The amount of a substance per defined space. Concentration usually is expressed in terms of mass per unit volume .
Calculating a Concentration • To calculate the concentration of a solution, compare the amount of solute to the amount of solution and multiply by 100 percent.
• For example, if a solution contains 10 grams of solute dissolved in 100 grams of solution, then its concentration can be reported as 10 percent.
Try This • A solution contains 12 grams of solute dissolved in 36 grams of solution. What is the concentration of the solution?
Solubility • Solubility is a measure of how much solute can dissolve in a solvent at a given temperature.
Key Terms
: unsaturated solution supersaturated solution
Examples:
An
unsaturated solution
more solute.
can continue to dissolve A
supersaturated solution
has more dissolved solute than is predicted by its solubility at the given temperature.
dilute solution concentrated solution solubility saturated solution A
dilute solution
is a mixture that has only a little solute dissolved in a certain amount of solvent.
A
concentrated solution
is one that has a lot of solute dissolved in the same amount of solvent.
Solubility
is a measure of how much solute can dissolve in a solvent at a given temperature.
A
saturated solution
more dissolves.
contains so much solute that no
Assessment
1. What is concentration?
2. What quantities are compared when the concentration of a solution is measured?
3. Solution A contains 50 g of sugar. Solution B contains 100g of sugar. Can you tell which solution has a higher sugar concentration? Explain.
Assessment
1. What is solubility?
2. How can solubility help identify a substance?
3. What are the three factors that affect solubility?
Acid:
A substance that releases H+ ions in an aqueous solution
“aqueous” means: water
Characteristics of Acids:
Acids have a sour taste Acids react with metals
Acids contain Hydrogen Many are poisonous and corrosive to skin H
Strong Acids (break down completely to give off many H+ ions)
Weak Acids (only partially breaks down, gives less H+)
Common Acids: Strong Acids The Formula
Sulphuric acid Hydrochloric acid Hybrobromic acid Hydroiodic acid Nitric acid Perchloric acid H 2 SO 4 HCl HBr HI HNO 3 HClO 4
All others considered Weak (examples) Weak Acid The Formula Acetic acid (vinegar) Carbonic acid HC 2 H 3 O 2 HCO 3
Base: A substance that releases OH- ions in an aqueous solution
Characteristics of Bases:
Bases usually taste bitter
Bases feel slippery Bases contain hydroxide ions STRONG bases are also poisonous and corrosive to skin
OH
-
Common Bases: Strong Bases The Formulae
Lithium hydroxide Sodium hydroxide Potassium hydroxide Rubidium hydroxide Caesium hydroxide Barium hydroxide Calcium hydroxide Strontium hydroxide LiOH NaOH KOH RbOH CsOH Ba(OH) 2 Ca(OH) 2 Sr(OH) 2
(Hydroxides of Group 1 and Group 2 Metals are STRONG) All others are WEAK
Some bases (VERY FEW) don’t have OH Most commonly: ammonia NH3
Section 3 Assessment
1. What are four properties of acids? Of bases?
2. How can you use litmus paper to distinguish and acid from a base?
3. How might you tell if a food contains an acid as one of its ingredients?
Section 3 Assessment
1. What are three practical uses of an acid? Of a base?
2. Where are you most likely to find acids and bases in your own home? Explain.
3. Why is it wise to wear gloves when spreading fertilizer in a garden?
Salts
Reactions between acids and bases
When and acid and a base react with each other, the characteristic properties of both are destroyed. This is called neutralization .
Reactions between acids and bases
General formula for acid base reaction:
Acid + Base → H
2
O + Salt
“Salt” means any ionic compound formed from an acid/base reaction NOT JUST NaCl !!
Neutralization
HCl + NaOH → H
2
O + NaCl
acid base water salt
Neutralization
Another Example
HNO
3
+ KOH → H
2
O + KNO
3
H NO
3
K OH
acid base water salt
pH pH stands for “potential hydrogen” and is a measure of how many H+ ions there are in solution.
The MORE H+ there are, the LOWER the pH will be.
Indicators
An indicator is a compound that will change color in the presence of an acid or base
Red Litmus-Turns blue in base
Blue Litmus-Turns red in acid
Universal indicator (pH paper) Used for the full pH range
Phenolphthalein-Turns pink in base
pH Scale
Shows the range of H+ concentrations High H+ concentration Low H+ concentration
Section 4 Assessment
1.
What does a substance’s pH tell you?
2. If a solution has a pH of 6, would the solution contain more or fewer hydrogen ions (H + ) than an equal volume of solution with a pH of 3?
Digestion and pH