Acids, Bases and Salts

Acid

A substance that produces H plus ions in aqueous solutions and are proton donors

Why are acids considered proton donors?

H plus ions are hydrogen nuclei containing only one proton, therefore when H plus ions in acids react, they have a tendency to lose or donate its H plus ions or protons to the other reactant

Properties of acids*

Sour taste, turn blue litmus red, corrosive, conduct electricity (they are electrolytes), have a pH less than 7

Acid anhydride

Compound that reacts with water to form an acid (many are acidic oxides of non-metals)

Basicity of an acid

The number of moles of H plus ions produced per mole of acid

Base

A proton acceptor, a substance which will react with an acid to form a salt and water only

Alkali

A base which dissolves in water to form a solution which contains OH- ions (a base which is soluble in water)

Properties of Alkalis

Bitter taste, corrosive, feel soapy, turn red litmus blue, pH greater than 7, conduct electricity (electrolytes)

Examples of acid anhydrides/acidic oxides

Carbon dioxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide

Strong acid

Fully ionized in aqueous solutions

Weak acid

Partially ionized in aqueous solutions

Antacids

A substance used to neutralize excess acid in the stomach (magnesium hydroxide, magnesium carbonate, calcium carbonate)

Baking powder

Contains a solid mixture of sodium hydrogen carbonate and a salt of a weak acid (tartaric acid) - produces Na ions, water and carbon dioxide gas (raising agent)

Vitamin C/Ascorbic acid (C6H8O6)

Required by human body, deficiency results in scurvy, oxidizes when exposed to heat (heat destroys it)

Citric acid (C6H8O7)

Lime juice can be used to remove rust stains from clothing, acid in juice reacts with iron (lll) oxide (Fe2O3) in rust stains which forms a soluble compound that washes out of clothes, removing the rusty yellow Fe 3 plus ions

Methanoic acid (HCOOH)

Found in ant venom, can cause itching, swelling, redness and pain around stings, can be treated by applying a paste of sodium hydrogen carbonate or calamine lotion (contains zinc) to neutralize the acid

Ethanoic acid (CH3COOH)

In vinegar, used to preserve food items, it’s low pH denatures enzymes that cause decay and prevents the growth of microorganisms

Examples of basic oxides

Copper(ll) oxide, magnesium oxide, sodium oxide, potassium oxide, iron (lll) oxide

Amphoteric oxides

React with both acids and alkalis to form salts

Examples of amphoteric oxides

Lead(ll) oxide, zinc oxide, aluminium oxide

Neutral oxides

They do not react with acids or alkalis

Examples of neutral oxides

Carbon monoxide, nitrogen monoxide, dinitrogen monoxide

Examples of amphoteric hydroxides

Aluminium hydroxide, zinc hydroxide, lead(ll) hydroxide

Universal indicator

A chemical substance which indicates the pH of a solution by colour, can be paper or solution form

pH meter

An electronic instrument consisting of a measuring probe connected to an electronic meter which displays the pH reading

Litmus

Red in acidic solution, blue in alkaline solution

Methyl orange

Red in acidic solution, yellow in alkaline solution

Screened methyl orange

Red in acidic solution, green in alkaline solution

Phenolphthalein

Colourless in acidic solution, pink in alkaline solution

Bromothymol blue

Yellow in acidic solution, blue in alkaline solution

Monobasic acid

Produces one H plus ion per molecule when it dissolves in water (hydrochloric acid, nitric acid)

Dibasic acids

Produces two H plus ions per molecule when it dissolves in water (sulfuric acid)

Tribasic acid

Produces three H plus ions per molecule when it dissolves in water (phosphoric acid)

Dilute acid

Contains a lot of water

Concentrated acids

Contain little water

Salt

A compound formed when some or all of the hydrogen ions in an acid is replaced by a metal or ammonium ion

Acid salt

A salt formed when some of the H plus ions from an acid are replaced, can be produced from a dibasic or tribasic acid

Normal salt

Salt formed when all of the H plus ions from an acid are replaced

Nitrates solubility*

All nitrates are soluble in water

Sodium, potassium, ammonium salts solubility

All sodium, potassium and ammonium salts are soluble in water

Sulfates solubility

All sulfates are soluble in water except lead sulfate and barium sulfate

Chlorides solubility

All chlorides are soluble in water except barium chloride and lead chloride

Carbonates solubility

All carbonates are insoluble except potassium carbonate, sodium carbonate and ammonium carbonate

Metal oxides solubility

Metal oxides are insoluble except potassium oxide, sodium oxide and ammonium oxide

Metal hydroxides solubility

Metal hydroxides are insoluble except potassium hydroxide, sodium hydroxide and ammonium hydroxide

Binary compound

A chemical compound that is made of atoms of two different elements

How are insoluble compound prepared?

Ionic precipitation

Ionic precipitation

Two soluble salts in solution react to form an insoluble salt (a precipitate and a soluble salt)

How are soluble salts prepared?

Direct combination, reactions of acids with insoluble solids (insoluble carbonate/insoluble base), titration

Direct combination

Used to prepare binary salts

Reactions of acids with insoluble solids

Used to prepare soluble salts except sodium, potassium and ammonium salts

Why can’t sodium, potassium and ammonium salts be prepared using reactions of acids and insoluble solids?

Potassium and sodium react violently do the reaction is too dangerous, carbonates and hydroxides of these compounds are all soluble so when the reaction is completed excess solid would dissolve and the salt solution would not be pure

Titration

A technique used to determine the concentration of a solution whose concentration is unknown

Titrant

Solution of known concentration, which is added to another solution whose concentration has to be determined

Titrand/analyte

The solution whose concentration has to be determined

Equivalence point

Point in titration at which the amount of titrant added is just enough to completely neutralize the analyte solution

Endpoint

The point at which the indicator changes colour in an acid-base titration

Indicator

Substance which changes colour in the presence of an acid or base

Standard solution

A solution whose concentration is accurately known

Anhydrous salt

A compound in which all water molecules are removed

How is an acid salt prepared?

Neutralization of a strong acid with a weak base

Inorganic acid

Contains a non-metallic element or polyatomic group as well as hydrogen

Organic acid

Contain the carboxyl group (COOH)

Water of crystallization

Water that is chemically bonded into a crystal structure

What are salts containing water of crystallization referred to as?

Hydrated salts

What are salts without water of crystallization referred to as?

Anhydrous salts

What does water of crystallization do?

Develops the crystalline structure and sometimes the colour of the crystals containing it

CuSO4 . 5H2O

For every mole of Cu 2 plus and SO4 2 minus ions within the crystal lattice, there are five moles of water molecules

Use of Sodium hydrogen carbonate (NaHCO3)

An ingredient in baking powder, baking powder is used to make cakes rise, contains sodium hydrogen carbonate and an acid and when mixed with liquid they react, producing carbon dioxide which forms bubbles in the cake that expand on heating causing the cake to rise

Use of Sodium carbonate (NaCO3, washing soda)

Softens hard water, causes Ca and Mg ions to precipitate out as insoluble calcium and magnesium carbonate

Hard water

Does not lather with soap, caused by dissolved calcium and magnesium salts

Use of Calcium carbonate (CaCO3, limestone)

Manufacture cement for use in the construction industry, calcium carbonate is heated with small quantities of other materials such as silicon dioxide (sand) in a kiln to about 1400 degrees Celsius, the calcium carbonate decomposes forming calcium oxide and carbon dioxide, the calcium oxide is blended with other materials inside the kiln to form clinker which is ground with calcium sulfate (gypsum to form cement

Use of magnesium sulfate (epsom salt, MgSO4.7H2O)

Medicinal uses, added to bath water to ease stress and relax the body, ease muscle strain, reduce inflammation, cure skin issues, heal cuts or used orally as a saline laxative and to help eliminate toxins from body

Use of Sodium chloride

Food preservation via osmosis so that water is unavailable in foods for the reactions which cause decay and withdraws water from microorganisms which cause decay so it prevent them from growing

Use of Sodium nitrate (NaNO3) and sodium nitrite (NaNO2)

Food preservation, used with sodium chloride to preserve meat, destroy certain bacteria that cause sever of food poisoning and retard the development of randicity, sodium nitrite gives a red colour and adds flavor to meat

Use of sodium benzoate (C6H5COONa)

Food preservation, used to preserve food with a low pH, it is converted to benzoyl acid (C6H5COOH) which inhibits the growth of microorganisms

Calcium sulfate (gypsum CaSO4.2H2O)

Manufacture of plaster of Paris, which is used when setting broken bones and as a building material, calcium sulfate is heated to remove water of crystallization, bandages are impregnated with the dry powder and when water is added it forms a paste or water is added to the powder and used to make a paste to coat walls and ceilings

Danger of sodium chloride

Excessive consumption leads to hypertension

Dangers of sodium nitrate and sodium nitrite

May increase a persons risk of developing cancer and can cause brain damage in children

Sodium benzoate

May increase a persons risk of developing cancer, has been implicated in increasing hyperactivity and asthma in children