Chemistry sac- acids and bases

Formulae of hydrochloric, sulphuric, nitric, ethanoic (acetic), carbonic, phosphoric, caustic soda, ammonia, calcium hydroxide, magnesium hydroxide, sodium carbonate

*HCl, H2SO4, HNO3,* CH3COOH, H2CO3, H3PO4, NaOH, NH3, Ca(OH)2, Mg(OH)2, Na2CO3

Basic safety rules for working with acids and bases

- The corrosive nature of acids and bases make them very dangerous and all contact should be avoided with skin and eyes -All acid and base spills should be reported to the teacher immediately - wear your safety glasses -wear your lab coat -label all bottles and containers - Always when diluting add acid to water NOT water to acid

Concentrated acids and bases

A large amount of solute has been dissolved in a given volume of solvent

Dilute acids and bases

A small amount of solute has been dissolved in a given volume of solvent

Base

A substance capable of accepting a hydrogen ion (proton)

Explain the relationship between increasing acid strength and decreasing pH numbers

Strong acid is at 1, neutral is at 7 and a strong basic is at 14.

Carbon dioxide in the oceans

- CO2 is slightly soluble in water -enters the ocans mainly by disslution of CO2 gas -Mostly CO2 (g), but some can form carbonic acid -More CO2, causes an increase in the concentration of carbonic acid, which in turn increase the concentration of H3O+ (aq) ions and causes increase in ocean acidity -The pH of earth's oceans are decreasing -Scientist conclude that between 1/3 and 1/2 of the CO2 emissions from human activities are absorbed by the oceans. Although this reduces the greenhouse affect, the pH of oceans has decreased by 0.11 since the industrial revolution

General properties of all acids

- Change colour in the presence of indicators (limus blue-> Red) -Tend to be corrosive -Taste sour -React with bases -Low pH <7 (at 25 C) -Solutions can conduct electricity (free moving charged particles)

General properties of all bases

- Change colour in the presence of indicators (red->blue) -Caustic/ slippery -Bitter tasting -React with acids -High pH >7 at 25 C -Solutions conduct electricity

Environmental impact of ocean acidity

- Global issue affecting all oceans -Has a detrimental effect on cold ocean organisms such as plankton and krill -A collapse of the krill population will have a disastrous effect on the oceans

Calcification

- Many aquatic organism eg some corals and snails, have a protective covering made of calcium carbonate (CaCO3) -These organisms absorb calcium and carbonate ions from seawater to build and maintain the calcium carbonate structure essential for their survival Health and growth of these animals depends critically on the concentration of carbonate ions and therefore carbon dioxide in the oceans.

Impact of ocean acidity on humans

- Social and economic impacts particularly for people in coastal communities -Food supply: may affect stocks of fish, molluscs and crustacean that are consumed by humans Coastal protection: Coral reefs provide protection from storm and erosion. The destruction of coral reefs could threaten coastal communities Tourism: The colour and diversity of coral reefs make them a popular tourist attraction. Their destruction will affect economies of communitiesF that rely on tourism.

Carbon dioxide in the atmosphere

- Varied over thousands of years -Scientists have used ratios of carbon isotopes to distinguish between natural and human caused contributions -Believed that changes of CO2 levels are influencing surface land temp and causing global warming which affects the chemical processes in the oceans.

Carbon dioxide in nature

-Essential to life on Earth -Carbon is exchanged within the biosphere (the global sum of all ecosystems) -Taken from the atmosphere via photosynthesis and caused to make chemicals such as glucose (C6H12O6) 6CO2(g)+6H2O(l)=C6H12O6(aq)+6O2(g)

How have the definitions of acids and bases have changed over the years, especially Arrhenius Lowry Bronsted

-Mineral acids hydrochloric, nitric and sulphuric were discovered after the 12th century -Initially acids were thought to be sharp pointed molecules, and bases were thought to be spherical due to their slippery touch -In the 17th century, BOYLE defined acids and bases in terms of taste, action as a solvent and colour change in indications. Bases are the opposite of acids -In the 18th century, LAVOISER defined acids in terms of acidic properties are due to the presence of oxygen - In the early 1800's Humphrey DAVY suggested acids properties are due to the presence of H -ARRHENIUS- a swedish chemist defined acids as chemicals with produced a H+ ion in water and bases as those which produced an OH- ion. When they reacted together, they produced water as was observed in neutralization reactions: H+ (AQ) + OH- (AQ) -> H20 (l) -This only applies to acids and bases that dissolved in water (alkalis) -LOWRY BRONSTED (Danish chemist Johannes Bronsted and English chemist Thomas Lowry) independently came up with the current definition of acids and bases in 1923.

Decalcification

-The increasing acidity of the oceans causes some of the additional hydronium ions to react with carbonate ions in the following reaction: -This reactions has the effect of reducing the concentration of free CO3^2- iona in seawater, making it more difficult for marine creatures to build or maintain their protective structures.

Dilution of acids and bases

-the concentration of acids and bases is usually measured in M -The most convenient way of preparing a solution of dilute acid is by mixing concentrated acid with water -Done using a pipette and a volumetric flask

Acidic, basic and neutral solutions

Acidic if :[H30+] >10^-7 M and [OH-] < 10^-7 M Basic if: :[H30+] < 10^-7 M and [OH-] > 10^-7 M Neutral if: [H30+]=[OH-]=10^-7 M

Acidic, basic and neutral solutions in terms of pH

Acidic, basic and neutral solutions in terms of pH at 25 C. Neutral solutions have a pH equal to 7 Acidic have a pH less than 7 Basic solution have a pH greater than 7

Lowry- Bronsted acids and bases definition

Acids as substances that could donate a proton or hydrogen ion, and a base as a substance that could accept a proton or a hydrogen ion.

Alkali

An aqueous solution of a base. *All alkalis are bases but not all bases are alkalis*

Strong acids and bases

Completely dissociate or ionize in water, so that the proton donation or acceptance is complete. Only the products are present in the solution- none of the solute is present in its original form. For example, HCl is a strong acid. This means that only water, hydronium and chloride ions are present in the final solution.

Conjugate acid base pairs

Conjugate acid base pairs are two species that differ form each other by the addition of a proton. HCl is the acid, Cl- is the base. OH- is the base, H2O is the acid. H2SO4 is the acid, HSO4- is the base. NH3 is the base, NH4+ is the acid. If given the acid, you remove a proton to find the conjugate base. If given the base, you add a proton to find the conjugate acid.

Weak Acids and bases

Do not completely ionise or dissociate in water and so the donation or acceptance of protons is not complete. It means that in the final solution there will be the products, but also some unreacted reactants. This is shown with the double arrow.

Monoprotic

Have only one proton to donate and so require only one equation. For example, hydrochloric acid is a monoprotic acid.

Triprotic

Have three protons to donate, and so require three equations. For example, phosphoric acid is a triprotic acid.

Diprotic

Have two protons to donate and so require two equations. For example, sulphuric acid is a diprotic acid

The ionic product of water at 25 degrees

In pure water at 25 C, it has been measured that [H3O+]=10^-7 M[OH-]=10^-7 M [H30+]=[OH-]. At 25 C, the ionic product of water is Kw=[OH-]X[H30+]=10^-7 X 10^-7 = 10^-14 M2 If either [H30+] or[OH-] in an aqueous is increased, then the concentration of the other must decrease proportionally, so that the product can remain at 10^-14M^2. This relationship is only strictly true at 25 C - the ionic product of water will vary slightly at different temperatures.

Explain the origin of the scale of pH from 1-14

Ionization of water Kw= [OH-]x [H3O+]=10^-7x10^-7=10^-14M^2 It was first proposed by Danish chemist Soren Sorensen as a convenient way to remove the cumbersome calculations involving powers of 10.

Weak and strong

Refer to the acids ability to completely or partially donate or accepts its protons

Concentrated and dilute

Refer to the amount of the solute, in this case acids and bases, that have been added to a set amount of solvent, in this case water

pH

The pH scale is a useful way of indicating the acidity of a solution. pH= -log[H30+] or [H30+]= 10^-pH

Ocean acidity definition

The reduction in the pH of the ocean caused by absorption of atmospheric carbon dioxide/

Amphiprotic substances

They can behave as an acid or a base, depending on what they are reacting with. All amphiprotic substances must have at least one proton. For example HSO4-:

Self ionisation of water

Water is an amphiprotic substance, it can act as an acid or a base. To a very small extent it can SELF IONIZE or react with itself.

Indicator

plant extracts eg red cabbage that change colour in the presence of acid or base. Phenolpthalein acid- colourless base- pink Litmus acid- red base- blue Methyl orange acid- red base- yellow