Chapter 4 Flashcards by Ishir Sharma

What happens when acids are dissolved in water (aqueous)?

They release H+ ions into the solution

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HCl dissolve in water equation

HCl (g) + aq (excess of water to form solution with gas) -> H+ (aq) + Cl- (aq)

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Carboxylic acids functional group

(Methyl, ethyl etc) COOH

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What is a strong acid?

HCl - releases all its hydrogen atoms into solution as H+ ions and completely DISSOCIATES in aqueous solution

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Complete dissociation of HCl?

HCl (aq) -> H+ (aq) + Cl- (aq)

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Weak acid?

CH3COOH - only releases a small proportion of its available hydrogen atoms into solution as H+ ions - PARTIALLY DISSOCIATES

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Partial dissociation of Ethanoic acid

CH3COOH (aq) -> <- H+ (aq) + CH3COO- (aq)

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Most organic acids are…

Weak acids

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What are bases?

Metal oxides, hydroxides, carbonates and Ammonia (NH3)

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What do bases do?

Neutralise acids to form a salt

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What is an alkali?

A base that dissolves in water by releasing OH- ions

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Sodium Hydroxide Alkali Dissolving

NaOH (s) + aq -> Na + (aq) + OH- (aq)

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Neutralisation reaction?

H+ ions react with a base to form a salt and water

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Ammonium ion

NH4+

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Ammonium ethanoate

NH4+ , CH3COO- therefore CH3COONH4 (ACID GOES FIRST IN THIS INSTANCE)

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Acid + metal oxide/hydroxide

Salt + water

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Acid + metal carbonate

Salt + water + carbon dioxide

Ionic equation of sodium hydroxide and hydrochloric acid?

OH- + H+ -> H2O (ONLY WORKS WITH ALKALIS AS THEY ARE AQUEOUS)

What is special about dissociation of H2SO4

It is a strong acid but this is only true for 1 of the 2 hydrogen atoms - when mixed with water H2SO4 dissociates but releases JUST ONE of its two hydrogen atoms as an H+ ion

What would dissociation of H2SO4 look like?

At first it is a strong acid
H2SO4 (aq) -> H+ (aq) + HSO4- (aq)
Now it partially dissociates
HSO4- (aq) ->

What is a titration?

Technique used to accurately measure the volume of one known solution that reacts with another solution

What are they used for?

Finding the concentration of a solution
Identification of unknown chemicals
Finding purity of a substance

Why is checking purity important?

Quality control for compounds manufactured for human use - pharmaceuticals should have high level of ourity

How to prepare standard solution?

Solution of known concentration - volumetric flask is used to make it very accurately
100 cm cubed - 0.20 cm cubed +/-
250 cm cubed - 0.30 cm cubed +/-

Stages in preparing standard solution?

Solid weighed accurately Dissolved in a beaker using less distilled water than will be needed to fill volumetric flask to mark Transferred to volumetric flask and washings rinsed with distilled water Drip by drip distilled water until graduation line (bottom of meniscus) - eye level for accuracy (if too much then becomes dilute) Volumetric flask slowly inverted several times to mix thoroughly - makes sure titration results are consistent

Burette apparatus used

50 cm cubed - +/- 0.1 cm cubed | Nearest half division therefore always ends in 5 or 0

Acid base titration procedure

Add measured volume of alkali or acid to conical flask using pipettes Add other solution to burette (0.05 cm cubed) Add indicator to solution in flask Swirl conical flask as you run burette solution to mix evenly - eventually indicator changes colour to end point ; record final reading Titre = final - initial ; approximate tire first and the repeated until they are concordant (within 0.1)

Mean titre

Repeat titres until they are within 0.1 and reject any inaccurate titres If you include all tires then lost accuracy of titration technique

Original values you have from results of titration

Both concentration and reacting volume of one solution | Only reacting volume of other solution

What is oxidation number?

Number fo electrons involved in bonding to a different element

What is oxidation number for elements?

For pure elements - always 0 as it is bonding to atoms of same element

How to write oxidation number?

Sign placed before the number and each atom in compound has oxidation number

H in metal hydrides

Usually +1 but now -1

O in peroxides (H2O2)

-1 (usually -2)

O bonded to F

Oxidation numbers on ions?

Sum of oxidation numbers = charge

What do Roman numbers show?

Oxidation number of an element without the charge

NO2-

Oxidation number of nitrogen is +3 therefore nitrate (III)

NO3-

Nitrate - oxidation number of nitrogen is +5 so nitrate (V)

Oxidation

Addition of oxygen Loss of electrons Gain in oxidation number

Reduction

Removal of oxygen Gain of electrons Loss in oxidation number

Does oxidation number apply to each atom or whole compound?

EACH ATOM - do not look at balancing numbers