Download Chemistry Chapter 9.1 Making Predictions About Solubility

Chemistry Chapter 9.1 Making Predictions About Solubility
FACTORS THAT AFFECT THE SOLUBILITY OF IONIC SUBSTANCES
- Nearly all alkali metal compounds are soluble in water
- Sulphide and phosphate compounds are usually insoluble
EFFECT OF ION CHARGE ON SOLUBILITY
- Compounds of ions with small charges tend to be soluble
- Compounds of ions with large charges tend to be insoluble
- Due to: increasing the charge increases the force that holds the ions together, thus
harder to break down when creating a solution
- Alkali metal cations have a single positive charge so the force that holds the ions
together is less
EFFECT OF ION SIZE ON SOLUBILITY
- When an atom gains/loses an electron, the size of ion that results is different from the
original atom’s size
- Ions of metals tend to be smaller than their corresponding neutral atoms, since it tends
to lose the electron
- Ions of non-metals tend to be later than their corresponding neutral atoms, since it tends
to gain the electron
- Small ions bond more closely together than large ions; bond between small ions are
stronger than the bonds between large ions with the same charge
- Compounds with small ions tend to be less soluble than compounds with large ions, as
bonds are weaker between large ions
MAKING PREDICTIONS ABOUT SOLUBILITY
- Sulphide (compounds of S2-) and oxides (compounds of O2-) are influenced by both ion
size and ion charge
- These compounds tend to be insoluble because their ions have a double charge and are
relatively small
- Few sulphides and oxides are soluble
SOLUBLE OR INSOLUBLE: GENERAL SOLUBILITY GUIDELINES
- Nearly all salts that contain ammonium ions or alkali metal are soluble
- Doesn’t tell you how soluble these salts are
GENERAL SOLUBILITY GUIDELINES – useful summary of ionic compound interactions with
water
- Higher guideline number always takes precedence over a lower guideline number
Ex. Barium Chloride, BaCl
Barium: Guideline 4, Chlorine: Guideline 3, Therefore soluble
Chapter 9.2 Reactions in Aqueous Solutions
-
In a double displacement, the cations exchange anions
Double displacement occurs if:
 The formation of a precipitate happens (ions are removed from solution as an
insoluble solid)
 The formation of a gas (ions are removed from solution as a gaseous product)
 The formation of water (H+ and OH- are removed from the solution as water)
DOUBLE DISPLACEMENT REACTIONS THAT PRODUCE A PRECIPITATE
PRECIPITATE REACTION – a double displacement reaction that results in the formation of an
insoluble substance
- Use the general solubility guidelines to predict if a compound is soluble or insoluble
- The element with the higher class will determine if the compound is soluble or insoluble
DOUBLE DISPLACEMENT REACTIONS THAT PRODUCE A GAS
- Double displacement reactions are responsible for producing a number of gases:
 Hydrogen
 Hydrogen sulphide (poisonous gas that smells like rotten eggs)
 Sulfur dioxide (reactant in forming acid rain)
 Carbon dioxide
 Ammonia
Reaction to produce Hydrogen Gas
- Alkali metals form bonds with hydrogen to produce compounds called hydrides
- Hydrides react readily with water to produce Hydrogen gas
Ex. LiH(s) + H2O(l)  LiOH(aq) + H2(g)
Reaction to produce Hydrogen Sulphide Gas
- Sulphides react with certain acids such as HCl to produce hydrogen sulphide gas
- Acids have hydrogen in it
Ex. K2S(aq) + 2HCL(aq)  2KCL(aq) + H2S(g)
Reaction to produce Sulphur Dioxide Gas
- Some reactions produce a compound that decomposes into a gas and water
- NaSO3 used in photography as a preservative
- Reacts with HCl to form H2SO3
Ex. Na2SO3(aq) + 2HCl(aq)  2NaCl(aq) + H2SO3(aq)
Reaction to produce Carbon Dioxide Gas
- Carbonate reacts with an acid to produce carbonic acid
- Carbonic acid decomposes into carbon dioxide and water
- Ex. Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2CO3(aq)
Reaction to produce Ammonia Gas
- Ammonia gas is soluble in water
- Sharp, pungent smell
DOUCLE DISPLACEMENT REACTIONS THAT PRODUCE WATER
- Neutralization reaction between acid and base creates water
- H+ ion bonds with OH- ion to create H2O
Ex. H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
- Most metal oxides are bases, thus metal oxides will react with an acid in a neutralization
reaction to form a salt and water
Ex. 2HNO3(aq) + MgO(s)  Mg(NO3)2(aq) + H2O(l)
- Non metal oxides are acidic, thus it will react with a base
Ex. 2LiOH(s) + CO2(g)  LiCO3(aq) + H2O(l)
REPRESENTING AQUEOUS IONIC REACTIONS WITH NET IONIC EQUATIONS
SPECTATOR IONS – ions that are not important to the net result
TOTAL IONIC EQUATION – shows the dissociated ions of the soluable ionic compounds,
written with charges
NET IOIC EQUATION – an ionic equation written without the spectator ions
- Do not dissociate the solid
Ex. AgNO3(aq) + NaCl(aq)  NaNO3(aq) + AgCl(s)
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  Na+(aq) + NO3-(aq) + AgCl(s)
Ag+ (aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  Na+(aq) + NO3-(aq) + AgCl(s)
Ag+ (aq) + Cl-(aq)  AgCl(s)
IDENTIFYING IONS IN AQUEOUS SOLUTION
WET CHEMICAL TECHNIQUES – experimental tests, submitting a sample to a series of double
displacement reactions
QUALITATIVE ANALYSIS – ion identification process, chemists use wet chemical techniques to
determine the identity through different double displacement reactions
Ex. Colour of an aqueous solution, flame test (dissolved ionic compound placed in a flame, flame
colour determines ion; only useful for metallic ions in aqueous solution)
Chapter 9.3 Stoichiometry in Solution Chemistry
-
Stoichiometry involves calculating the amounts of reactants and products in a chemical
reaction
If you know the atoms or ions in a formula/reaction, you can use stoichiometry to
determine the amounts of these atoms/ions that react
Sample Problem: The concentration of Ions
Problem: Calculate the concentration (in mol/L) of chloride ions in each solution.
a) 19.8g of potassium chloride dissolved in 100mL of solution
b) 26.5g of calcium chloride dissolved in 150mL of solution
c) a mixture of the 2 solutions in a) and b), assuming the volumes are addictive
Required:
a) and b) requires the concentration (mol/L) of chloride ions in 2 solutions
c) find the concentration of chloride ions when the 2 solutions are mixed
Given: 19.8g of potassium chloride dissolved in 100mL
26.5g of Calcium chloride dissolved in 150 mL
Strategy:
a) and b): determine the molar mass and find the amount in mol, then write equations
for dissociation of the substances (total ionic equation), use coefficients in the
dissociation equation to determine amount in mol of chloride ions present, calculate
concentration (mol/L) of chloride ions from the amount/volume of solution
c) Add the amounts of chloride ions in the 2 solutions (this is the total), add the volume
of solutions to find the total volume, calculate concentration of chloride ions (mol/L)
Solve:
a) and b)
c)
Sample Problem: Mass Percent of Ions
Problem: Leaves of a rhubarb plant has a high concentration of oxalate ions, C 2O42-. A
student tested 238.6g of leaves. The dried mass of calcium oxalate was 0.556g. What was
the mass percent of oxalate ions in the leaves.
Required: Mass percent of oxalate ions in leaves
Given: Mass of leaves is 238.6g, mass of dried calcium oxalate is 0.556g
Strategy: Find the molar mass of calcium oxalate. Find the amount in mol of calcium
oxalate. Write the net ionic equation for the formation of calcium oxalate. Using coefficients
from the net ionic equation, find the amount in mol of oxalate ions. Calculate the mass of
oxalate ions then calculate the mass percent from mass of leaves and mass of oxalate ions
present
Solve:
Sample Problem: Finding the minimum volume to precipitate
Problem: Aqueous solutions that contain silver ions are usually treated with
chloride ions to recover silver chloride. What is the minimum volume of
0.25mol/L magnesium chloride needed to precipitate all silver ions in 60mL of
0.30 mol/L silver nitrate?
Required: Minimum volume of magnesium chloride that will precipitate all
silver ions
Givern:60mL of 0.30mol/L silver nitrate, 0.25mol/L magnesium chloride
Strategy: Find the amount in mol of silver nitrate from the volume and
concentration of solution. Write a balanced chemical equation for the
reaction; use mole ratios from the coefficients in the equation to determine
the amount in mol of magnesium chloride needed. Find volume needed using
mol of magnesium chloride and concentration of solution
Solve:
LIMITING REACTANT PROBLEMS IN AQUEOUS SOLUTIONS
- Determine which one of the two reactants is limiting
- In aqueous solutions, this usually means finding the amount of a reactant,
given the volume and concentration of the solution
Sample Problem: Finding the Mass of a Precipitated Compound
Problem: Mercury ions must be removed from waste water. Suppose that
25.00mL of 0.085mol/L aqueous sodium sulphide is added to 56.6mL of
0.10mol/L mercury (II) nitrate. What mass of mercury (II) sulphide
precipitates?
Required: Mass of mercury (II) suphide that precipitates
Given: 25.00mL of 0.085mol/L sodium sulphide, 56.6mL of 0.10mol/L
mercury (II) nitrate
Strategy: Write a balanced chemical equation for the reaction. Find the
amount in mol of each reactant. Determine the amount in mol of mercury (II)
sulphide that forms. Calculate the mass of mercury (II) sulphide that
precipitates
Solve:
Sample Problem: Finding the Mass of Another Precipitate Compound
Problem: Calculate the mass of solver chromate that forms when 50.0mL of
0.100mol/L Silver nitrate reacts with 25.0mL of 0.150mol/L sodium chromate.
Required: Mass of Silver chromate that precipitates
Given: 50.0mL of 0.100mol/L silver nitrate, 25.0mL of 0.150mol/L sodium
chromate
Strategy: Write a balanced chemical equation for the reaction. Find the
amount in mol of each reactant. Identify the limiting reactant. Determine the
amount in mol of silver chromate that forms. Calculate the mass of silver
chromate that precipitates
Solve:
Chapter 9.4 Aqueous Solutions and Water Quality
-
Water is a powerful solvent, this easily polluted
Canada with less than 1% of the world’ population has 22% of its fresh water
Quality of water is of great concern than the quantity available
ACCEPTABLE CONCENTRATIONS OF SUBSTANCES IN DRINKING WATER
SOURCES THAT COMPROMISE WATER QUALITY
- Pure water doesn’t exist in nature
- All water naturally contains dissolved substances or ions (Rainwater is naturally acidic;
water droplets dissolve atmospheric gases such as carbon dioxide to form carbonic acid
- Water filters through soil and rock thus leaches/dissolves ions and compounds such as
Calcium, magnesium, Iron (II and III) and sulphates; poses little-no threat to plants,
animals, humans
-
-
-
Point sources: manufacturing/processing plant that discharges untreated or insufficiently
treated waste water into a lake or river is a point source of pollution. Includes: wrecked
tankers that leak oil, factories that discharge metallic ions, organic compounds, acids and
bases. Point source water can be of thermal pollution when thermal power plants
discharge warm water into a lake.
Diffuse Sources: pollution that comes from a wide range of sources, rather from a single
source. Heavy downpour can cause run-off from farm fields to enter rivers and lakes.
This run-off carries fecal matter, pesticides, fertilizer compounds such as nitrates and
phosphates
Indirect sources: air, water, soil can be polluted from a variety of indirect sources. Motor
vehicles and factory smokestacks release gases that can indirectly cause many different
types of pollution. Acidic gases (Sulphur dioxide and nitrogen oxides) that are produced
dissolve and form acidic rain. Concentration of ions in ground water affected by how
acidic the water is
TREATING WATER FOR YOUR HOME
- Farm/remote areas obtain water through a well
- Urban community obtain water from a municipal or regional water authority
- Before available to you, water is processed at a water treatment plant to remove
pollutants
- Lake, river, reservoir water enters treatment plant where physical/chemical processes
take place
HARD WATER AND SOFT WATER
- Water that flows through your faucet has been treated to remove, limit many pollutants
- Far from pure, still contains dissolved ions
- These ions such as calcium and magnesium make it difficult to form lather with soap
- Water with high concentrations of these ions is called hard water, it is hard to lather
- Water with lower concentrations of these ions is called soft water, it is easy to lather
- Ground water is usually harder than surface water in the same region
- Extent of hardness depends on types of rocks through which water flows
- Depends on the length of time that the water is in contact with the rocks
-
Most common type of rock to cause hard water is limestone (calcium carbonate);
Limestone considered insoluble; Small amount that does dissolve forms low
concentrations of important ions:
-
When water contains dissolved acids (usually carbonic acid), the H+ ion increases the
concentrations of calcium and hydrogen carbonate ions
-
Hydrogen carbonate ions can be economically costly. Solutions that contain these ions
decompose when heated to form carbonates
-
Carbonate ions recombine with calcium ions to form calcium carbonate deposits
These deposits form a coating on heating elements in kettles and boilers and build up
inside hot water pipes; commonly called boiler scale; reduces flow of water in pipes;
increases cost of heating water
Simple way of removing boiler scale from inside a kettle or coffee maker is to add
vinegar; acetic acid reacts with calcium (and magnesium) carbonates to form soluble
salts (All acetates are soluble)
-
TREATING WATER AT HOME
- Ions that cause hard water are not health hazards but can be nuisances
- Not always removed at municipal treatment plants
- You can remove some of these ions yourself; for small volumes of water, add sodium
carbonate decahydrate
-
, washing soda
Carbonate ion precipitates the unwanted ions
Sodium ions in washing soda behave as spectator ions, leaving the water soft
For large volumes of water, people install an ion exchange water softener that
exchanged one kind of ion for another
Hard water passes through a column packed with beads, bead are made of an insoluble
plastic material and are coated with sodium salts (NaCl), salt coated beads called ion
exchange resin
Ions in the water displace the sodium ions on the resin, after most of the sodium ions
have been exchanged for calcium ions, resin regenerated by passing a very concentrated
solution of sodium chloride (brine ) through the column; calcium ions flushed out of
system with excess sodium chloride solution
WASTE-WATER TREATMENT
- Treatment of waste water (sewage) often divided into 3 types: primary, secondary and
tertiary treatment
 Primary: removing solids from waste water, physically using filters and settling tanks
 Secondary: using bacteria to chemically decompose dissolved and suspended organic
compounds
 Tertiary: chemical treatments to remove the majority of remaining ions and disease
causing micro-organisms