AP Style Net Ionic Equations...You perform an acid-base titration to standardize an HCl solution by placing 50.00mL of HCl in a flask with a few drops of indicator solution. You put

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AP Style

Net Ionic Equations

Part I:

Precipitation and Acid-Base Reactions

Warm-Up Determining Moles of Ions in Aqueous Ionic Solutions

How many moles of each ion are in the

following solutions?

10.7 g of aluminum bromide dissolved in water

(1) ___ moles aluminum ions

(2) ___ moles bromide ions

35mL of 0.84M zinc chloride

(3) ___ moles zinc ions

(4) ___ moles chloride ions

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Demo: Conductivity

Lab Quest Conductivity of Solutions

0.100 M KCl

0.100 M CuCl2

0.100 M AlCl3

the molarity of a solution determines conductivity

AND the number of ions per mole determines conductivity

Warm-Up

• Write the net ionic equation for each of the

following:

2 K+(aq) + SO42−(aq) + 2 Ag+(aq) + 2 NO3

−(aq)

→ 2 K+(aq) + 2 NO3−(aq) + Ag2SO4(s)

2 Ag+(aq) + SO42−(aq) → Ag2SO4(s)

2 Na+(aq) + CO32−(aq) + 2 H+(aq) + 2 Cl−(aq)

→ 2 Na+(aq) + 2 Cl−(aq) + CO2(g) + H2O(l)

CO32−(aq) + 2 H+(aq) → CO2(g) + H2O(l)

1. K2SO4(aq) + 2 AgNO3(aq) → 2 KNO3(aq) + Ag2SO4(s)

2. Na2CO3(aq) + 2 HCl(aq) → 2 NaCl(aq) + CO2(g) + H2O(l)

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WARM-UPWrite the molecular, complete ionic & net ionic

equations for the reaction between solutions of barium nitrate with ammonium sulfate.

Ba(NO3)2 (aq) + (NH4)2SO4 (aq) � BaSO4 (s) + 2 NH4NO3 (aq)

Ba2+ (aq) + 2 NO3- (aq) + 2NH4

+ (aq) + SO42- (aq) �� BaSO4 (s) + 2NH4

+ (aq) + 2NO3- (aq)

Ba2+ (aq) + SO42- (aq) � BaSO4 (s)

Spectator ions: NH4+ and NO3

-

AP Style

Net Ionic Equations

Part I:

Precipitation and Acid-Base Reactions

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Writing equations on the AP Exam

• Prompts that ask for written equations have historically been

found in the free response section of the AP test.

• Often, you will have 3 equations, each followed by a question

about the reaction. The equations are of mixed types.

• You will often be asked to write equations in net ionic form: all

spectator ions must be left out and all ions must be written in

ionic form.

• Scoring for equations is often: 1 pt for reactants, 2 points for

products, and 1 pt for each question.

Our Goals

• What types of reaction will I be asked to write equations for?

• How do I write net ionic equations for

those reactions?

• What kind of questions might I be asked

about these reactions?

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Reaction TypesThere are many ways of classifying reactions. One approach commonly used in introductory chemistry recognizes these 5 reaction types:

• Addition (aka Synthesis)

• Decomposition

• Single Displacement

• Double Displacement

• Combustion

Reaction TypesAnother approach recognizes these 3 reaction types which can occur in solutions:

• Precipitation Reactions

–Includes double displacement reactions

• Acid-Base Neutralization Reactions

–Includes gas formation reactions

• Oxidation-Reduction Reactions

–Includes single displacement, combustion, & some addition and decomposition reactions.

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We will focus on these types of

reactions in aqueous solutions:

1) Precipitation Reactions

2) Acid—Base Reactions

3) Oxidation—Reduction Reactions

Our Goals

• What types of reaction will I be asked to

write equations for?

• How do I write net ionic equations for those reactions?

• What kind of questions might I be asked

about these reactions?

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Dissociation Decisions(Which substances exist as dissociated ions?)

In order to write NIE’s, we need to identify

which substances exist as dissociated ions,

and which exist as molecules.


• All molecular substances and non-soluble

compounds must be written ‘together’ (not

ionized/dissociated).

Example:

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• Strong electrolytes (strong acids, strong

bases, and soluble ionic compounds) will

be dissociated unless the state is solid.

Example:

Sidenote: you will sometimes see concentrated sulfuric acid written as a

molecular (undissociated) substance, only because when it is 18M, it really is

97% H2SO4 and 3% water in the jug.


• All weak electrolytes should be written as

un-dissociated, molecular formulas.

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Know your solubility rules*:

– Ba(OH)2 is soluble

– Ca(OH)2 and Sr(OH) 2 are moderately soluble and

can be written together or as ions.

– Mg(OH)2 is insoluble.

See a pattern there?

– CaSO4 and SrSO4 are moderately soluble and can be

written together or as ions.

Let’s Practice writing NIE’s for these reaction types, and answering questions about each.




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Two compounds react to form two new compounds.

No changes in oxidation numbers occur.

• Solutions of potassium phosphate and

zinc nitrate are mixed

Practice: NIE for DD rxns

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• Manganese(II) nitrate solution is mixed

with a sodium hydroxide solution

Questions about precipitation reactions …will include solution stoichiometry and and understanding of ion concentration

CuSO4 (aq) + 2 NaOH (aq)�Cu(OH)2 (s) + Na2SO4 (aq)

Calculate the mass of solid formed when 1.25 L

of 0.0500 M CuSO4 and 2.00 L of 0.0250 M NaOH are mixed.

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When 1.25 L of 0.0500 M CuSO4 and 2.00 L of 0.0250 M

NaOH are mixed, calculate the molarity of all ions that remain

in the resulting solution after the reaction.

[Na+] = ????


[(SO4)2- ] = ????

The NIE can help us here; the number of moles of spectator ions will be

in the same after the reaction as before; just consider the new volumes.


When 1.25 L of 0.0500 M CuSO4 and 2.00 L of 0.0250 M

NaOH are mixed, calculate the molarity of all ions that remain

in the resulting solution after the reaction.

[Cu2+ (aq) ] =


[(OH)-(aq) ] = 0 M

NaOH was the limiting reagent; so no (OH)- ions remain.

CuSO4 was in excess; so we need to account for the number of

moles of Cu2+ that did NOT react, which are still in solution.

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• Hydrogen sulfide gas is bubbled through a

solution of lead(II) nitrate


• Excess hydrochloric acid is added to an

aqueous solution of potassium sulfite

Practice: NIE for DD rxns*

* What type of reaction is this one?

Let’s come back to this one later,

at the end of this presentation!

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We will also include gas formation reactions in this

category. These problems are similar to the precipitation

reactions in some ways; instead of forming a solid

precipitate, we form a molecular substance such as

water or a gas.

Acid–Base Reactions

• Acid–base Reaction:

– An acid–base reaction is also called a neutralization reaction.

– An acid reacts with a base and the two neutralize each other, producing water (or in some cases a weak electrolyte).

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Some Common Acids and Bases

Many of these weaker acids

are “organic” acids that contain a

“carboxyl” group.

The carboxyl group does not easily give up its

hydrogen.

Weak acids such as lactic

acid usually ionize less than

5% of the time.

Strong vs. Weak Acids

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Other organic acids and their sources include:

o Citric acid – citrus fruit

o Malic acid – apples

o Butyric acid – rancid butter

o Amino acids – protein

o Nucleic acids – DNA and RNA

o Ascorbic acid – Vitamin C

This is an enormous group of compounds;

these are only a few examples.

Because of the carboxyl group, organic acids are

sometimes called “carboxylic acids”.

Strong vs. Weak Acids

Practice: Net Ionic Equations for Acid-Base Reactions

Writing Ionic Equations for Acid-Base Reactions

Write net ionic equations for each reaction and identify the

spectator ions.

(a) strontium hydroxide(aq) + perchloric acid(aq)

(b) barium hydroxide(aq) + sulfuric acid(aq)

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• The net ionic equation for any strong acid–

strong base reaction is

H+(aq) + OH−(aq) → H2O(l)

– as long as the salt that forms is soluble in water.

1. HCl(aq) + Ba(OH)2(aq) →

2. H2SO3(aq) + LiOH(aq) →

2 HCl(aq) + Ba(OH)2(aq) → 2 H2O(l) + BaCl2(aq)

H2SO3(aq) + 2 LiOH(aq) → 2 H2O(l) + Li2SO3(aq)

2 H+(aq) + 2(OH)-

(aq) → 2 H2O (l)

H2SO3 (aq) + 2(OH)-(aq) → 2 H2O (l) + (SO3)

-(aq)


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• The net ionic equation for any

weak acid – strong base reaction is

HA (aq) + OH−

(aq) → A-(aq) + H2O

Weak acid + hydroxide � conjugate base + water



spectator ions.

(a) nitrous acid and sodium hydroxide

(b) hydrobromic acid and ammonia (NH3)

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strong acid – weak base reaction is

H+(aq) + B (aq) → HB+

(aq)

hydrogen ion + weak base � conjugate acid

H3O+

(aq) + B (aq) → HB+(aq) + H2O

hydrogen ion + weak base � conjugate acid + water



spectator ions.

(a) ammonia and nitric acid

(a) ammonia and nitrous acid

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weak acid – weak base reaction is

HA (aq) + B (aq) → HB+(aq) + A-

(aq)

Weak acid + Weak base � conjugate base + conjugate acid



spectator ions.

(a) hypochlorous acid and pyrindine (C5H5N), a weak base.

(a) Nitric acid is added to crystals of pure calcium oxide

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Our Goals

• What types of reaction will I be asked to

write equations for?

• How do I write net ionic equations for

those reactions?

• What kind of questions might I be asked about these reactions?

Our Goals

• What kind of questions might I be asked about these reactions?

• You might be asked to identify the conjugate acid or the

conjugate base of a reactant or product

• You might be asked about some solution stoichiometry

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Practice

Finding the Concentration of Acid

from an Acid-Base TitrationPROBLEM:

You perform an acid-base titration to standardize an HCl solution

by placing 50.00mL of HCl in a flask with a few drops of indicator

solution. You put 0.1524M NaOH into the buret, and the initial

reading is 0.55mL. At the end point, the buret reading is

23.85mL. What is the concentration of the HCl solution?

If you were standardizing a solution of H2SO4,

would the calculation be done the same?

Practice

Finding the Concentration of Acid from an Acid-Base Titration

PROBLEM:

When a 5.00 mL sample of phosphoric acid is titrated with

standardized 0.750 M NaOH solution, 28.5 mL of NaOH are

needed to reach the endpoint. What is the concentration of the

phosphoric acid solution?

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Gas-Evolution Reactions

• Gas-evolution reactions

– In a gas-evolution reaction, a gas forms, resulting in bubbling.

• In both acid–base and gas-evolution

reactions, as in precipitation reactions,

the reactions occur when the anion from

one reactant combines with the cation of

the other.

– Many gas-evolution reactions are also acid–base reactions.

Gas-Evolving Reactions

• Some reactions form a gas directly from the

ion exchange.

K2S(aq) + H2SO4(aq) → K2SO4(aq) + H2S(g)

• Other reactions form a gas by the

decomposition of one of the ion exchange

products into a gas and water.

NaHCO3(aq) + HCl(aq) → NaCl(aq) + H2CO3(aq)

H2CO3(aq) → H2O(l) + CO2(g)

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Gas-Evolution Reactions

• Excess hydrochloric acid is added to an

aqueous solution of potassium sulfite

Practice: Gas Evolution Reactions*

Remember this one?

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• Baking Soda and Vinegar!


Remember this one?

• A solution of ammonium sulfate is added

to a potassium hydroxide solution


If it looks like there is no NIE (all spectator

ions, consider the possibility that a gas might

form when one of the products decomposes.

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• aqueous solutions of ammonium thiocyanate and barium hydroxide are combined. (assume all thiocyanates are soluble.)


Remember this one?



These may include the following reaction types:

• Single Displacement

• Addition (Synthesis)

• Decomposition

• Combustion

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Continued in next Presentation

AP Style Net Ionic Equations...You perform an acid-base titration to standardize an HCl solution by placing 50.00mL of HCl in a flask with a few drops of indicator solution. You put

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