5.1 acid, alkalis, salt

8/13/2019 5.1 Acid, Alkalis, Salt

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Acids, Alkalis and Salts


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INDICATORS

Students are able to: To identify the character of acid, base,

and salt by using an indicator

To classify substance in our daily livebased on acid, base, and salt concept

To use an indicator to know the pH of asubstance

Understand the concept of neutralizationreaction


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Acids

Most people think of acids as corrosiveliquids which bubbles when they come intocontact with solids and burn when theytouch the skin.

This description is true for many acids.

Some acids are not corrosive and are

found in our food. They give some foods their sour taste.


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The word acid comes from the Latin wordacidusmeaning sour.

The hazard symbol

for a corrosivesubstance.


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Examples of acids

Acids Animal origin

hydrochloric acid human stomach

lactic acid muscles during vigorous exercise

uric acid urine, excretory product from DNA in food

methanoic acid ant sting


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Acids Plant origin

citric acid orange and lemon juice

tartaric acid grapes

ascorbic acid vitamin C in citrus fruits

methanoic acid nettle sting


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Animals and plants that produce acid.


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Bottles of dilute and concentrated acids.


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Properties of Acids

Acids have a sour taste. Acids turn blue litmus paper red.

Acids react with some metals to give off

hydrogen gas. Acids react with metal carbonates to give

off carbon dioxide gas.


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Acids can be classified into two

types:Organic acids and Inorganic or mineral acids

The acids produced by plants and animals

(with the exception of hydrochloric acid) areknown as organic acids.

Ethanoic acid is an organic acid and was the

first to be used in experiments.


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The first mineral acid to be discovered wasnitric acid.

It was used to separate silver and gold.

These mineral acids are much stronger thanethanoic acid and allow more chemicalreactions to be made.


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Organic acids are weak acids; they are

often found in food.

Organic Acid Source

Citric Acid Oranges, Limes, Lemons

Tartaric Acid Grapes, Health salts, Baking powder

Malic Acid Apples, Goose berries, Grapes

Tannic Acid Tea

Acetic Acid Vinegar


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Organic Acids

Is an organiccompound with acidic properties. produced by plants and animals with the

exception of hydrochloric acid.

A few common examples include:

Formic acid-it is found in the stings and bitesof many insects of the order Hymenoptera,

mainly ants.
http://en.wikipedia.org/wiki/Organic_compoundhttp://rds.yahoo.com/_ylt=A0S020ntRRxIeUoBGG2JzbkF;_ylu=X3oDMTBxMHQ4cTkwBHBvcwM3BHNlYwNzcgR2dGlkA0kwODNfMTA1/SIG=1i8a0bv5a/EXP=1209898861/**http%3A//images.search.yahoo.com/images/view%3Fback=http%253A%252F%252Fimages.search.yahoo.com%252Fsearch%252Fimages%253Fp%253Dant%252Bsting%2526fr%253Dyfp-t-309%2526ei%253Dutf-8%2526js%253D1%2526x%253Dwrt%26w=500%26h=375%26imgurl=static.flickr.com%252F117%252F269134469_f6528d174f.jpg%26rurl=http%253A%252F%252Fwww.flickr.com%252Fphotos%252F42606934%2540N00%252F269134469%252F%26size=83.6kB%26name=Bulldog%20Ant%202%26p=ant%20sting%26type=JPG%26oid=37c12775ad640b02%26fusr=Ravenlike%26tit=Bulldog%20Ant%202%26hurl=http%3A//www.flickr.com/photos/42606934@N00/%26no=7&tt=386http://en.wikipedia.org/wiki/Organic_compound


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Citric acid-is a weak organic acid. A naturalpreservative and is also used to add an acidic,

or sour, taste to foods and soft drinks.

Ethanoic acid or acetic acid- is found invinegar and is produced as wine becomessour.
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Mineral acids

Derived from rocks or mineral sources

Mineral acids are strong acids

is an acid derived by chemical reaction from inorganic minerals, as opposed to

organic acids.

Mineral acids are very important tochemical procedures.


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A few common examplesinclude:

Hydrochloric acid-it is a strong acid, andthe major component of gastric acid. It isalso widely used in industry. It is a highly

corrosive solution.

Nitric acid-also known as aqua fortisandspirit of nitre, is a highly corrosive toxicstrong acid that can cause severe burns.


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Sulphuric acid-(H2SO4)is a strong mineral acid.

It is soluble in water at all concentrations.

Principal uses include ore processing fertilizers

manufacturing, oil refining, wastewater

processing, and chemical synthesis


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Acid rain Sulphur dioxide is produced by the

combustion of sulphur in a fuel when thefuel is burned.

Sulphur dioxide reacts with water vapour

and oxygen in the air to form sulphuricacid.

This may fall to the ground as acid rain oracid snow.

Oxides of nitrogen are converted to nitircacid in the atmospehre and thisfalls to the ground as acid rain or

acid snow.


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The effect of acid rain Acid rain reaches the ground it drains into

the soil, dissolves some of the mineralsthere and carries them away. This processis called leaching.

The acid rain drains into rivers and. lakesand lowers the pH of the water.

If the pH changes, they die and the

animals that feed on them, such as fish,may also die.


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Uses of AcidsAcid Uses

Citric acid Used in making fruit juice

Used as preservatives and flavouring agent in foodTartaric acid Used in making cakes

Used in health salts (efervescent tablets)

Tannic acid Used in tanning leather Used in dyeing fabrics

Used in making inkHydrochloricacid

Present in our stomach which helps in food digestionand kills bacteria

Used as rust remover

Sulphuric acid Used as electrolyte in car batteries Used as soda-acid fire extinguisher

Nitric acid Used to make fertilizers

Carbonic acid Used in making soft drinks

Ethanoic acid The diluted form is used in making vinegar Used as preservatives


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Bases/Alkalis

As bases neutralize acids they aresometimes described as having propertieswhich are opposite to acids. Bases arehydrogencarbonates

A concentrated solution of an alkali iscorrosive and can burn the skin.

Can be found commonly in households Like acids there are strong and weak

alkalis


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Bases/Alkalis

Examples and uses of alkalis
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A concentrated solution of an alkali iscorrosive and can burn the skin. The samehazard symbol as the one used for acids(is used on containers of alkalis whenthey are transported.

Even dilute solutions of alkali such asdilute sodium hydroxide solution react

with fat on the surface of the skin andchange it into substances found in soap.


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Properties of Alkalis

Alkalis are bitter and have a soapy feel.

Some general properties of bases include:

Bitter taste (opposed to sour taste of acids)

Slimy or soapy feel on fingers


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Properties of Alkalis

Concentrated or strong bases are caustic(corrosive) on organic matter and reactviolently with acidic substances

Aqueous solutions or molten basesdissociate in ions and conduct electricity

Reactions with indicators: bases turn red

litmus paper blue and phenolpthalein red


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Detecting acids and alkalis Some substance change colour when an

acid or an alkali is added to them. Litmus isa substance which is extracted from livingorganisms called lichen.

Blue litmus paper turns red when it comesinto contact with an acid.

Red litmus paper turns blue when it comesinto contact with an alkalis.


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Strong and weak acids andalkalis

The strength of an acid or alkali does notdescribe whether the solution is dilute orconcentrated.

It describes the ability of a substance toform particles called ions.

Acids form hydrogen ions and alkalis form

hydroxide ions.


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Strong acid forms a large number ofhydrogen ions and weak acid forms a small

number of hydrogen ions strong alkali forms a large number of

hydroxide ions and weak alkali forms a small

number of hydroxide ions The strength of an acid or alkali is

measured on the pH scale.

On this scale the strongest acid is 0and the strongest alkali is 14.


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A solution with a pH of 7 is neutral. It is

neither an acid nor an alkali.

A strong acid has a pH of 0-2, a weak acidhas a pH of 3-6; a weak alkali has a pH of

8-11 and a strong alkali has a pH of 12-14.

An electrical instrument called a pH meteris used to measure the pH of an acid or

alkali accurately.


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For general laboratory use, the pH of an acidor an alkali is measured with universalindicator. This is made from a mixture of

indicators. Each indicator changes colour overpart of the range of the scale. By combiningthe indicators, a solution is made that givesvarious colours over the whole of the pHrange.


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Mixing Acids and Alkalis

When acids mix with alkalis, a reactioncalled neutralization occurs in which saltand water are formed. This reaction can

be written as a general word equation:

acid + base salt + water


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Examplee.g. hydrochloric acid + magnesium Magnesium chloride + hydrogen gas

reacting acids with carbonates

e.g. Nitric acid + Lead carbonate Lead nitrate + Water + Carbon dioxide gas

2HNO3 + PbCO3 Pb(NO3)2 + H2O +CO2


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Using neutralization reactions

Sometimes the stomach produces toomuch acid, which causes indigestion. Theacid is neutralized by taking a tabletcontaining either magnesium hydroxide,

calcium carbonate, aluminum hydroxide orsodium hydrogencarbonate


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Acidity in the soil affects the growth ofcrops. It makes them produce less food. Lime(calcium hydroxide) is used to neutralizeacidity in soil. When it is applied to fields itmakes them appear temporarily white.


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Shampoos Toothpaste

Antacid tablet Fire extinguisher

Everyday uses of neutralisation
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Uses of AlkalisAlkali Uses

Sodium hydroxide Used to unclog drains and sinks as it eatsup organic matter in them Used to make soap

Potassium hydroxide Used to dye cloth Used in printing Used in making liquid soap

Used in paint varnish removal Used in electroplating

Calcium hydroxide Used in making cement and plaster Used to reduce the acidic condition is soil

Magnesium hydroxide Used in making toothpaste

Ammonia solution Used as a detergent Used as a bleaching agent


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Salts

Salts here do not refer only to table saltwhich we use for preserving food

Some salts are poisonous

eg. Salts of lead and mercury

When acid is added to a base, a salt isformed.


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A salt may be soluble or insoluble in water

Salt Solubility

Carbonates All carbonates are insoluble except forsodium, potassium and ammonium carbonates

Chlorides All chlorides are soluble except for silver and

lead chlorides

Nitrates All nitrates are soluble

Sulphates All sulphates are soluble except for barium,calcium and lead sulphates


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A soluble salt is first prepared as asolution and the crystals are then obtainedby evaporation

An insoluble salt is prepared byprecipitation where the solutes areobtained by filtration


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Salts Uses

Ammonium salts To make fertiliser

Calcium chloride As a drying agent

To increase the cement power inlime for wall plasters

Calcium sulphate To make plaster of Paris forfractures

Magnesium sulphate To make strong, mineral laxative

Potassium nitrate To make fertilisersTo make gun powder andfireworks

Sodium chloride As a food preservativeTo make chlorine gas

Silver chloride As a photographic film emulsion

Zinc sulphate As a wood and skin preservativeTo clarify glue


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E i t


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Experimentthat can be done inside the classroom or inside

the laboratory

Things to bring: House hold items

a. Bebek b. Bayclin c. Wipol

d. Mama lemon e. Fiz f. Others

shampoo, vinegar

Fruits & Veg.

a. Tomato b. Apple c. Grapes

d. Orange/lime e. Manggo f. Others

tea, sprite , coke, salt, mylanta (antacid)


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Things to prepare :

(apparatus/materials needed)1.Litmus paper/phenolpthalein red

2. Universal indicator

3. Dropper & glass rod4. White tile

5. Test tube/ small container

6. Test tube rack7. beaker

5.1 acid, alkalis, salt

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