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Warmup 1/7/16
What does the term "precipitation" mean? What might this mean in chemistry?
Objective Tonight’s Homework
To define a precipitate and see a few examples
Finish the worksheet from today
Notes on Precipitates
We’re going to skip a couple chapters (as they contain mostly side stuff), but there’s one concept that we want to make sure we cover.
Notes on Precipitates
We’re going to skip a couple chapters (as they contain mostly side stuff), but there’s one concept that we want to make sure we cover.
Take a look at the following image:What appears to be happeninghere?
Notes on Precipitates
We’re going to skip a couple chapters (as they contain mostly side stuff), but there’s one concept that we want to make sure we cover.
Take a look at the following image:What appears to be happeninghere?
Two liquids are being combinedand something yellow isappearing.
This yellow substance is a solid.
Notes on Precipitates
When we mix two liquid chemicals and get a solid, we call that solid a precipitate.
Given enough time, thesolid will settle downto the bottom as seenhere.
If two substancesstay liquid when combined, we say that the substances are soluble. They dissolve in water.
Something that is insoluble is a precipitate or solid.
Notes on Precipitates
So how do we show something like this as part of a chemical equation? Let’s look at an example:
AgNO3 (aq) + KCl (aq) → AgCl (s) + KNO3 (aq)
Notes on Precipitates
So how do we show something like this as part of a chemical equation? Let’s look at an example:
AgNO3 (aq) + KCl (aq) → AgCl (s) + KNO3 (aq)
Right away you’ll see something new. The letters in parenthesis after each chemical. These letters tell us what state the chemical is in. i.e. solid, dissolved, gas, etc. Chemicals can have the following codes:
(s) - solid (l) – liquid (g) - gas(aq) – “aqueous”. This means dissolved in water,
but can be solid if dried out
Notes on Precipitates
How do we know if combining chemicals will yield a precipitate? There are a series of terrible rules to help you remember. (They have a lot of exceptions, sorry.)
Notes on PrecipitatesSolubility Rules:1) Salts containing Li, Na, K, Cs, Rb are soluble. Salts containing the ammonium ion (NH4) are also soluble.
2) Salts containing nitrate(NO3) are generally soluble.
3) Salts containing Cl, Br, and I are generally soluble. Important exceptions to this rule are halide salts of Ag, Pb, and (Hg2)
4) Most silver salts are insoluble. AgNO3 and Ag(CH3COO) are exceptions5) Most sulfate (SO4) salts are soluble. Exceptions to this rule include BaSO4, PbSO4, Ag2SO4 and SrSO4
6) Except for rule 1, carbonates (CO3), hydroxides (OH), oxides, silicates, and phosphates (PO4) are insoluble
7) Sulfides (S#) are insoluble except for calcium, barium, strontium, magnesium, sodium, potassium, and ammonium8) Chromates (CrO4), phosphates (PO4), and fluorides (F) are frequently insoluble.
Precipitate Practice
Those rules are somewhat of a handful. Let’s practice.CHEMICAL FORMULA
NAME SOLUBLE?
NH4CH3COOBa(OH)2
Iron (II) Carbonate
NaOH
RbNO3
Cesium Sulfate
MgSO4
ZnCl2
Zinc Hydroxide
Zn3(PO4)2
AgBr
KNO3
CHEMICAL FORMULA
NAME SOLUBLE?
Al2S3
Silver AcetateSr2CrO4
Aluminum PhosphateBaSO4
Ca(OH)2
BaCO3
MgCrO4
Iron (III) SulfideNH4CN
Silver IodideHg2SO4
Lithium Chloride
Precipitate Practice
Those rules are somewhat of a handful. Let’s practice.CHEMICAL FORMULA
NAME SOLUBLE?
NH4CH3COO Ammonium Acetate YBa(OH)2 Barium Hydroxide NFeCO3 Iron (II) Carbonate N
NaOH Sodium Hydroxide Y
RbNO3 Rubidium Nitrate Y
Cs2SO4 Cesium Sulfate Y
MgSO4Magnesium Sulfate Y
ZnCl2 Zinc Chloride Y
Zn(OH)2 Zinc Hydroxide N
Zn3(PO4)2 Zinc Phosphate N
AgBr Silver Bromide N
KNO3 Potassium Nitrate Y
CHEMICAL FORMULA
NAME SOLUBLE?
Al2S3 Aluminum Sulfide NAgCH3COO Silver Acetate YSr2CrO4
Strontium Chromate NAlPO4
Aluminum Phosphate NBaSO4 Barium Sulfate NCa(OH)2 Calcium Hydroxide NBaCO3 Barium Carbonate NMgCrO4
Magnesium Chromate NFe2S3 Iron (III) Sulfide NNH4CN Ammonium Cyanide YAgI Silver Iodide NHg2SO4 Mercury Sulfate YLiCl Lithium Chloride Y
Exit Question
What is the precipitate in the following reaction?
LiBr (aq) + AgNO3 (aq) LiNO3 (?) + AgBr (?)
a) LiNO3
b) AgBrc) Both are precipitatesd) Neither are precipitates