Acids and Bases
The words acid and alkaline (i.e. bases) are derived from direct sensory experience.
The word acid comes from the Latin word acere, which means "sour." All acids taste sour.
Can you name some acids
Some acids were well known from ancient times,vinegar, sour milk and lemon juice.
Early in the 1200s, the strong mineral acids were first isolated.
Sulphuric acid was made by heating green vitriol [iron(II) sulphate] and condensing the vapour into water. Other vitriol gave the same product. Mixing a vitriol with nitre (potassium nitrate) and heating produced vapours which gave nitric acid.
Adding sal ammoniac (ammonium chloride) to nitric acid gave aqua regia, so named for its ability to dissolve gold.
Hydrochloric acid ("spirit(s) of salt" - a name still used in commerce/pharmacy as late as the early 1970s) also was known to the Middle Ages; certainly it was known to Paracelsus (early 1500s).
The word alkaline comes from the Arabic al-qily, which means "to roast in a pan" or "the calcinated ashes of plants". By leaching (dissolving) the ashes with water, one can obtain a solution of sodium or potassium carbonate (to use the modern terms). This is then mixed with slaked lime (calcium hydroxide) and you get a solution of NaOH or KOH. This technique was described in writing in the 900s, but may have existed for many years prior.
What are acids and bases?
Both these types of substance react vigorously with materials, often leading us to say that they 'eat' or 'burn' away materials.
The reason they do this is to create a more stable molecule. Even though the Acids and Bases are stable compounds they will readily (and often violently) react with materials they can form more stable compounds with.
Acids are ionic compounds that have a (number of) Hydrogen atom(s) attached to a nonmetal element.
Bases are more complex compounds that have the -OH ion (oxygen and a single hydrogen atom) attached to a metal atom.
Acids V Bases
Acids V Metals
OC18 use litmus or a universal indicator to test a variety of solutions, and classify these as
acidic, basic or neutral
Classifying substances as acidic, basic or neutral
So how can we tell if something is
Acidic Basic or neither.
Ants can spray a solution in defense of their nest, this can change the colour of .... from blue to red
If you tackle this section early October / early november you might find dead wasps to test in your house.
So how can we tell if something is
Acidic Basic or neither.
we use Indicators
OC19 investigate the pH of a variety of materials using the pH scale
OC20 give examples of everyday acids and bases.
So from your study of Acidity and Basicity, the pH scale.
you should be able to complete a table of 7 acids and bases, try to include the following ...
.... Batterys, toothpaste, bleach, indigestion remedies, soap, Citrus fruits, over cleaner,
but which are acid and which are bases? make 2 lists
In your copy give enough room to add in more substances as you try them out ....
OC35 state the names and formulae of common strong acids and bases:
OC36 show the neutralisation of an acid with a base using an indicator (actually use an acid on a base to observe the neutralisation)
Have you ever had Indigestion ?? Heartburn ???
Why do you get indigestion / heartburn ??
because you have a strong acid in your stomach,
then you eat too much too quickly
the acid overflows into the oesophagus
So how could you fix this indigestion ??
Take a Base to Neutralise the acid !!!
Indigestion Remedies / Ant-acids
Materials: hydrochloric acid(0.1M); conical flask (100ml); measuring cylinder (50ml); methyl orange indicator; various antacid powders, petri dish; electronic balance.
1) Put a spatula of antacid powder into a petri dish.
2) Weigh the petri dish and powder. Record in results table.
3) Measure 50 ml of hydrochloric acid into a conical flask (250ml).
4) Add 3-4 drops of methyl orange indicator to the flask.
5) Use the spatula to add the antacid, bit by bit to the acid with swirling.
6) Stop adding when the solution turns yellow.
7) Reweigh the petri dish to determine the amount of antacid used. Record mass below.
8) Repeat steps 1) – 7) for a different antacid
Acid + Base → Salt + Water
OC37 understand that, when an acid reacts with a base, a
salt and water are formed
Acid + Carbonate → Salt + Water + CO2
OC51 investigate the reaction between zinc and HCl, and test for hydrogen (word equation and chemical equation)
Metals Vs Acid, try a few metals in acids, note the gas being produced test each
Test tube, lab acid (1M), strips/ lumps of metal, wooden splints,
Tie up hair
Wear gloves when handling the Acid,
In case of any spillages remove gloves & Wash affected areas
Add some acid (20ml) to a test tube.
Carefully drop some metal in the bottom of the test tube
Place your thumb over the mouth of the test tube.
Observe / watch the metal,
Observe any sensations
After 60 seconds get a wooden splint and light it on fire
Quickly remove your thumb & hold the burning splint in the test tube.
Make note of what happens
Results / Observations
What did you see or notice
1 for a fair test to take place the masses should be proportional to the relative atomic masses of each element to be tested
Magnesium + HCl → MgCl + H2.
When we add a metal to an acid, we get a Metal Salt & Hydrogen Gas
What do we know about it ??
- Hydrogen is the least dense material. So as a gas it floats.
- Hydrogen is a Flammable gas.
- When it burns it makes a 'POP'
OC52 investigate the relative reactivities of Ca, Mg, Zn, and Cu based on their reactions with water and acid (equations not required)
this is covered in the metals section, but make sure to come back here
Cats Make Zebras Cry
OC55 describe the role of the combustion of fuels and of SO2 in the production of acid rain, and describe the effects of acid rain
A demonstration of the effects of acid in the air can be done in the lab
Get a fresh rose, sulphur, tongs, goggles, fume cupboard.
- Set up video camera
- Turn on extractor fan
- In a jar burn some suphur
- Hold the fresh red rose in the jar with the fumes
Sulphur Dioxide has a bleaching effect on the plant, destroying the chlorophyll and thus preventing photosythesis.
Acid rain is caused by water dissolving the gases of combustion. These materials form acids.
Common gases that dissolve in Water in the atmosphere are
Carbon Dioxide, Sulphur dioxide, Nitrous Oxides.
Making Carbonic acid, Sulphuric Acid and Nitric Acid.
These acids are weak
Two containers to collect rain water. pH meter. Buffer tablets.
Standardise pH meter.
Collect rain water over a period of time, one urban one rural.
OC56 describe the effect of acid rain on limestone and on plants
Statue in 1908 and 100 years later
Acid rain eats away at limestone statues, and buildings, but we can notice this on statues much more readily than we can on buildings.
To Investigate the effect of acid rain on rocks.
Weathering of rock.
Samples of different rock. Electronic balance. Range of acids. Dropper pipette. Trough. Timer. Filter paper.
Place rocks in trough.
Weigh before and after.
Leave acids on rocks for the same time.
Mop dry with filter Paper.
Wear rubber gloves. Re weigh.
Calculate % weight loss.
EFFECT OF ACID RAIN ON PLANTS experiment
Test yourself here
Physics and chemistry
Applications of pH measurement are endless. Just about everything made in or from or of water will have its pH measured at some stage. This could range from the Pacific Ocean to a can of Coke. Living organisms are "designed" to operate between various limits (of temperature for example) and attempts to interact with any liquid outside these limits (say between pH 6 and 9) could give rise to severe problems. Not wonder oven cleaners have strong warnings about skin contact!
The Arrhenius Theory:
An acid is a neutral molecule that dissociates in water to form a hydrogen ion and an anion.
The acidic properties of the solution are due to the presence of H+ ions.
A base dissociates in water to form a hydroxide ion and an cation
The basic properties of the solution are due to the presence of OH- ions
In solution strong acids and bases are fully dissociated
In solution weak acids and bases are only slightly dissociated
Note: all reactions took place in water
CH3COOH + H2O CH3COO- + H30+
NH3 + CH3COOH NH4+ + CH3COO
HNO3 + H2O H30+ + NO3-