Acids vs. Bases

Acids: form hydrogen ions in a solution.

Bases: form hydroxide ions in a solution.

Alkalis: bases which are soluble in water

 

Bases and acids have high conductivity because they split up into ions which can flow as charges

 

Examples of acids, bases and Neutral

• Acids : hydrochloric acid, vinegar, battery acid, acid rain , lemon juice
• Bases: sodium hydroxide, bleach, ammonia
• Neutral : water, salty solution, sugary solution

 

Acid formulas to remember

• Hydrochloric acid: HCl
• Nitric acid: HNO3
• Sulfuric acid: H2SO4
• Carbonic Acid: H2CO3

 

Strength of acid/bases vs. Concentration

 

Strength

When acids and bases dissolve in water they split apart into ions

 

Strong acids/bases: These ionize completely meaning there is nothing of the original acid/base left.

weak acids/bases: These react reversibly so they don’t ionize completely. This means they have a mix of the original acid/base and the ions.

 

E.g strong acid : HCL → H+ and Cl-  

 

E.g weak acid: CH3COOH ⇌ CH3COO– + H+

 

Concentration

 

Concentration of acids/bases, is simply the proportion of acids/bases in the solution.

 

One way of changing the concentration is with Serial Dilutions

Here are the steps for carrying out a Serial dilution

 

• Take a small amount of full strength, stock solution and add 9 times its mass of water. The concentration has now decreased by a factor of ten to become  0.1 mol/dm3  

 

• Repeating this process will again lower the concentration by a factor of ten. Aka after two dilutions the solution has a 1% concentration or 0.01 mol/dm3 .

PH Scale

Definition: the pH of a solution depends upon the concentration of Hydrogen ions

 

pH vs Strength vs Concentration

People often get confused about whether pH, is to do with an acids strength or it’s concentration and the answer is it’s both. This is because they the hydrogen ion concentration depends on both the overall concentration and the strength of the acid/base.

 

However strong acids ionize more than weak acids and so they will have more hydrogen ions. So at the same concentration the following is true:

 

Strong acid: 0-3

Weak acid : 4-6

Neutral: 7

Weak base: 8-10

Strong base: 11-14

 

Note: Ph is a log scale and so a change of one pH unit represents a 10 fold change in concentration of hydrogen ions. pH = -log[H+]

Reactions of acids

 

Acid + Base → Salt + Water

Acid + Metal → Salt + Hydrogen

Acid + Metal carbonate → Salt + Water + Carbon dioxide

 

Tests for gases

Hydrogen: squeaky pop with flame

Carbon dioxide: lime water turn cloudy.

 

Reaction given the salt produced

HB + AOH → AB + H2O

HB + A      → AB + H

HB + ACO → AB + H2O +CO2

E.g salt produced is sodium nitrate, NaNO3

1. Look at salt name E.g NaNO3
2. Find an acid which has the second part of the name. E.g HNO3
3. Find either a metal, metal carbonate or a base, which has the first part E.g NaOH
4. All reaction types make a salt, you can choose any. E.g HNO3 + NaOH → NaNO3 + H2O +CO2
5. Balance sides of equation E.g 2HNO3 + NaOH → NaNO3 + 2H2O +CO2

Acid rain

 

How is acid rain formed?

• Nitrogen oxide (NOx) is produced under extreme temperatures and pressures inside cars engines. When this then dissolves in rainwater it reacts to form Nitric acid.

NOx+H2OHNO3

• Fossil fuels are made of plants, which contain sulphur. When the fossil fuels are burnt, the sulphur reacts to form sulphur trioxide. This dissolves in rain water and reacts to form sulphuric acid

SO3+H2OH2SO4

What are the causes of effect?

1. It causes damage to buildings and statues, particularly those made of limestone.
2. It can also reduce the growth of, or even kill, trees and crops.
3. It lowers the pH of water in lakes, killing fish.
4. It causes toxic metals like aluminum to come out of solution. This makes it difficult for plant roots to absorb water and clogs the gills of fishes.

How can the effects of acid rain be minimized?

Solution	How it works
Washing fuel	The coal is broken up  and then dumped in a tank of water. Sulphur is heavier than water and so sinks while coal is lighter so it floats. This separates the sulphur from the coal.
Renewable energy	Does not produce any sulphur dioxide or nitrogen oxide, as the energy is not generated by burning fossil fuels.
Scrubbing air with limestone	A mist of limestone powder and water is sprayed over the power plant emissions, reacting with the sulphur dioxide to form calcium sulphate.
Using catalytic converters	Catalyses the natural breakdown of nitrogen oxide into oxygen and nitrogen which is harmless.
Use low nox burners.	Increases the fuel to air ratio, forcing air to bond with the fuel instead of nitrogen

 

Ionic formulas

The formula of an ionic compound can be worked out by taking the two elements in the compound and matching there charges. E.g Calcium Chloride = CaCl2

 

Note: With a polyatomic ion the charge will be given. Treat it as an element with that charge. E.g Calcium Nitrate = Ca(NO3)2

 

Ionic equations

Ionic equation: the reaction with all the (aq) compounds split into their ions

Spectator ions: the elements which remain unchanged after being split into its ions.

Net ionic:  the ionic equation but without the spectator ions. This reveals the underlying reaction which takes place.

 

State symbols

Aq - dissolves in water

S -solid

L -liquid

G -gas

 

Solubility rules

To figure out if a salt is soluble or not you can use the solubility rules, it is not needed to memorize them as they will be given. E.g salts containing group 1 elements are soluble therefore Sodium chloride is soluble.

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