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