Chapter 14 Acids and Bases in the Environment

Acids and Bases Acids and Bases (video)Acids and Bases H + ions - ? OH - ions - ? Soapy slippery - ? Taste sour - ? Acids give up H + when added to water forming - ? More Hydronium – pH ___________

Safety When diluting a concentrated acid, always add acid to water Weak and strong acids and bases can all be dangerous. Handle with care Rinse with running water immediately if spilled on skin

 Binary Acids A binary compound consists of two elements. Binary acids have the prefix hydro in front of the full name of the nonmetallic element.  They have the ending -ic. Examples include hydrochloric and hydrofluoric acid.  Hydrofluoric Acid - HF Hydrochloric Acid - HCl Hydrobromic Acid - HBr Hydroiodic Acid - HI Hydrosulfuric Acid - H 2 S

 Ternary Acids Ternary acids commonly contain hydrogen, a nonmetal, and oxygen.  The name of the most common form of the acid consists of the nonmetal root name with the -ic ending.  The acid containing one less oxygen atom than the most common form is designated by the -ous ending.  An acid containing one less oxygen atom than the - ous acid has the prefix hypo- and the -ous ending.  The acid containing one more oxygen than the most common acid has the per- prefix and the -ic ending.

 Nitric Acid - HNO 3 Nitrous Acid - HNO 2 Hypochlorous Acid - HClO Chlorous Acid - HClO 2  Chloric Acid - HClO 3 Perchloric Acid - HClO 4 Sulfuric Acid - H 2 SO 4 Sulfurous Acid - H 2 SO 3  Phosphoric Acid - H 3 PO 4 Phosphorous Acid - H 3 PO 3 Carbonic Acid - H 2 CO 3 Acetic Acid - HC 2 H 3 O 2  Oxalic Acid - H 2 C 2 O 4 Boric Acid - H 3 BO 3 Silicic Acid - H 2 SiO 3

 Corrosive ('burns' your skin)  Sour taste (e.g. lemons, vinegar)  Contains hydrogen ions (H + ) when dissolved in water  Has a pH less than 7  Turns blue litmus paper to a red colour  Reacts with bases to form salt and water  Reacts with metals to form hydrogen gas  Reacts with carbonates to form carbon dioxide, water and a salt

General Equations and Review Note the general equations page 319 Complete the revision questions 1, 2 page 319

Common Bases Bases Sodium Hydroxide - NaOH Potassium Hydroxide - KOH Ammonium Hydroxide - NH 4 OH Calcium Hydroxide - Ca(OH) 2 Magnesium Hydroxide - Mg(OH) 2 Barium Hydroxide - Ba(OH) 2 Aluminum Hydroxide - Al(OH) 3 Ferrous Hydroxide or Iron (II) Hydroxide - Fe(OH) 2 Ferric Hydroxide or Iron (III) Hydroxide - Fe(OH) 3 Zinc Hydroxide - Zn(OH) 2 Lithium Hydroxide - LiOH

PROPERTIES OF BASES AND ALKALIS Corrosive ('burns' your skin) Soapy feel Has a pH more than 7 Turns red litmus paper to a blue colour Many alkalis (soluble bases) contain hydroxyl ions (OH - ) – A base that is soluble in water is called an alkali Reacts with acids to form salt and water

Johannes Brønsted Thomas Lowry ( ) ( ) Denmark England

The Lowry-Bronsted theory of acids and bases An acid is a substance that donates a proton (H + ion) to another substance A base is a substance that accepts a proton (H + ion) from another substance Since a hydrogen atom is simply a proton and an electron, removing the electron leaves a proton, H +.

The Lowry-Bronsted theory of acids and bases Acid – proton donor Base – proton acceptor The general reaction for an acid dissolving in water is

A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor acid conjugate base base conjugate acid

The Lowry-Bronsted theory of acids and bases HNO 3 (l) + H 2 O (l)  H 3 O + (aq) + NO 3 - (aq) According to Bronsted-Lowry the water in this equation is acting as a base since it accepts a proton H+H+ Acid loses a protonBase gains a proton

Review Complete question 3 page 321

I ONISATION AND THE PRODUCTION OF THE HYDRONIUM ION Ionisation is a reaction in which a molecule reacts with water to produce two or more ions Water acts as a base accepting a proton from the acid. Forms hydronium ion (H 3 O+)

Hydrolysis When an ionic substance dissolves in water, the resulting solution is often not neutral This is because the ions can act as acids or bases when reacting with water and produce solutions that are either acidic or basic – known as hydrolysis Hydrolysis reaction –An anion reacts with water to produce OH - –A cation reacts with water to produce H 3 O + Not all cations and anions hydrolyse eg NaCl

Hydrolysis Ammonium chloride is dissolved in water. Ammonium and chloride ions are produced. The ammonium ions react as follows NH 4 + (aq) + H 2 O (l)  H 3 O + (aq) + NH 3 (aq) Is the resulting solution acidic or basic?

Hydrolysis Sodium carbonate is dissolved in water, sodium ions and carbonate ions are produced. The carbonate ion reacts as follows CO 3 2- (aq) + H 2 O (l)  HCO 3 - (aq) + OH - (aq) Is the resulting solution acidic or basic?

Dissociation of Bases When ionic bases dissolve in water, they dissociate or separate into their constituent ions. They do not ionise since they do not actually react with the water to produce ions as acids do. NaOH (s) ---> Na + (aq) + OH - (aq) H2OH2O

Dissociation of Bases Molecular bases such as NH3 cannot dissociate as they do not contain ions Ammonia ionises NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq)

Neutralisation Neutralization Reaction - a reaction in which an acid and a base react in an aqueous solution to produce a salt and water: Write the neutralisation equation below as ionic and net ionic equation HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) Note – can the H + ion exist by itself in water? Therefore the ionic equation of neutralisation is H 3 O + (aq) + OH - (aq)  2H 2 O (l)

Neutralisation Neutralisation reactions are one way of producing pure samples of salts. Hydrochloric acid and calcium hydroxide mixed – an aqueous solution of calcium chloride results 2HCl (aq) + Ca(OH) 2 (aq)  CaCl 2 (aq) + 2H 2 O (l) The water can be removed by evaporation How do antacid tablets work in our stomach which contains HCl?

Review Complete the revision question 4 page 323

Acid – Base terms Conjugate acid-base pairs In an acid-base reaction, the substance acting as the acid gives away a proton and forms a conjugate base. The substance acting as a base, after accepting a proton, forms its conjugate acid. An acid-base reaction will therefore form two conjugate pairs, with the formulas of each pair member differing by the H+ ion that was transferred.

Conjugate Pairs

Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O +

Polyprotic Acids A polyprotic acid can donate more than one proton Acids can be classified as monoprotic, diprotic or polyprotic depending on the actual number of protons that can be donated Eg HCl – monoprotic (only one to donate) Eg (Phosphoric acid )H 3 PO 4 – triprotic (3 to donate)

Amphiprotic substances and ampholytes Amphiprotic substances and ampholytes are substances that can act as either acids or bases. The way they react depends on the relative strengths of the acids and bases they are being reacted with. Water is a common example of an amphiprotic substance Ampholytes are electrolytes of ionic substances such as HSO 4 - or HPO 3 -

Review Complete the revision questions 5 – 9 page 324

Strengths of Acids and Bases The strength of an acid or base is related to the ease with which it donates or accepts a proton –A strong acid donates protons readily –A strong base accepts protons readily Weak acids or bases do not donate or accept protons readily

Strengths of Acids and Bases Conductivity is also related to strength. A strong acid will react nearly to completion in water and produce many ions, therefore conducting electricity (a good electrolyte) Write the equation for HCl reacting in water A weak acid will not react to completion and its solution will be a poor conductor of electricity because not many ions are produced. Write the equation for acetic acid CH 3 COOH reacting in water

Strengths of Acids and Bases The strength of a base also affects its conductivity A base is strong if it produces many hydroxide ions in solution because the hydroxide ions readily accept protons Write the equation for NaOH dissociating Ammonia is a weak base and does not readily dissociate, therefore it is a poor conductor of electricity NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq)

HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION.

Strong and Weak Acids/Bases Generally divide acids and bases into STRONG or WEAK ones.Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO 3 (aq) + H 2 O (l) ---> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water.

Weak acids are much less than 100% ionized in water.Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O --> Ca(OH) 2 (slaked lime) Ca(OH) 2 (slaked lime) CaO

Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

Weak Bases

Review Complete the revision questions 10 – 12 page 327

Strength vs Concentration The strength of a solution is determined by the number of ions present Strong acid – many ions in solution Weak acid – few ions in solution Concentration refers to the amount of an acid or base that is dissolved in a given volume of water It is possible to have a weak, concentrated acid or a dilute solution of a strong acid.

The pH Scale The pH scale is usually applied over a range from 1 to 14 7 = _____________ ? 1 – 6 = ___________ ? 8 – 14 = ____________ ?

pH testing There are several ways to test pH There are several ways to test pH – Blue litmus paper (red = acid) – Red litmus paper (blue = basic) – pH paper (multi-colored) – pH meter (7 is neutral, 7 base) – Universal indicator (multi-colored) – Indicators like phenolphthalein – Natural indicators like red cabbage, radishes

Paper testing Paper tests like litmus paper and pH paper Paper tests like litmus paper and pH paper – Put a stirring rod into the solution and stir. – Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper – Read and record the color change. Note what the color indicates. – You should only use a small portion of the paper. You can use one piece of paper for several tests.

pH paper

pH meter Tests the voltage of the electrolyte Tests the voltage of the electrolyte Converts the voltage to pH Converts the voltage to pH Very cheap, accurate Very cheap, accurate Must be calibrated with a buffer solution Must be calibrated with a buffer solution

pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

Review Read the chapter summary and note the terminology and concepts Complete the multiple choice questions 1 – 11 page 331, 332 Complete the review questions 4, 5 (a), (b), (d), 8, 12 (a), (b),(c), 17, 19 (a), 21

Extras Acid Base review on line Review Acids, Bases and pH (video)Review Acids, Bases and pH