4.1 – Concentration & Dilution
Concentration is determined by the ratio
between the mass of solute and the volume
of solvent in a particular solution
Increasing the solute or decreasing the solvent will
concentrate a solution
Decreasing the solute or increasing the solvent will
dilute a solution
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4.1 – Concentration and Dilution
Concentrated products have a lot of solute per
volume of solvent.
More and more products are being sold in
concentrated form.
e.g. Frozen orange juice concentrate
Manufacturers sell concentrated solutions as a
way of reducing their costs.
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4.1 – Concentration and Dilution
Dilute solutions have low solute per
solvent ratios and typically have a high
water content.
Large containers of ready-serve orange juice
are examples of dilute solutions.
e.g. Bottled Gatorade
Ms. Baier's Science 14 5
4.2 - Acids and Bases
Solutions can be divided into three main
categories:
Acid – is a corrosive, sour tasting substance
that turns blue litmus paper red.
Base – is a slippery, bitter tasting substance
that turns red litmus paper blue.
Neutral – these solutions are neither acid nor
base.
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4.2 - Acids and Bases Name Uses
acid Hydrochloric acid Breaks down food in stomach
Toliet bowl cleaner
Etch concrete
acid Sulfuric acid Make plastics, fertilizers & dyes
Conducts electricity in car batteries
acid Vinegar (acetic
acid)
Cooking
As a preservative
base Ammonia Household cleaning
In fertilizers and explosives
base Baking soda
(sodium
bicarbonate)
Makes cakes rise in the oven
In antacids
base Sodium hydroxide In drain and oven cleaners
To make soap and detergents Ms. Baier's Science 14 8
4.2 - Acids and Bases
b) Properties of Acids and Bases
The physical properties of acids and bases
(acids are sour and bases are bitter) are not a
safe or reliable way to identify and classify
solutions.
Scientists use the chemical properties of acids
and bases to identify and classify them. Ms. Baier's Science 14 9
4.2 - Acids and Bases
Scientists can readily identify acids and bases using indicators. An indicator is a natural substance that changes colour
in the presence of an acid or a base.
The most reliable indicator is litmus, a dye made from lichen. Litmus paper is a convenient indicator strip that has been treated with a litmus solution.
Ms. Baier's Science 14 10
4.2 - Acids and Bases
c) The pH Scale
Chemists have developed a scale that classifies how acidic or basic substances are. This scale classifies substances form 0 to 14.
Greater than 7 = base
Less than 7 = acid
Equal to 7 = neutral
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4.3 – Acids and Bases in Action Uses of Acids and Bases
Baking – Many recipes call for sour milk. Cooks often sour milk with lemon juice. When sour milk (acid) and baking soda mix they form a frothy mass. This reaction makes pancakes, cookie and dough rise.
Cooking – the pH of cooking liquid effects the colour of the cooked vegetables. Vegetables cooked in acid mixtures do not soften and take longer to cook. Those cooked in basic mixtures soften more easily.
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4.3 – Acids and Bases in Action
Health Care – heartburn occurs when too much acid is produced by your stomach. Antacids (basic) neutralize your stomach acid.
Deodorizing – Baking soda (a base) cancels out acid food odours.
Combining acids and bases can be useful; it can also be dangerous!
Remember the reaction caused by mixing bleach and ammonia?
Ms. Baier's Science 14 13
4.3 – Acids and Bases in Action
Corrosion
Substances found at either end of the pH scale
are highly corrosive.
They can cause severe skin burns and eat through
substances such as rock and metal.
Corrosion is the wearing away of materials by
chemical action.
Oxygen is the primary cause of his reaction.
Substances such as acid rain, salt and water speed up
the process.
• E.g. A car exposed to salt from road slush will rust quickly.
However a battleship at the bottom of the ocean will rust
very slowly. Ms. Baier's Science 14 14
4.3 – Acids and Bases in Action
Corrosion and Metals
Silver – turns black
Copper – turns green
Iron – rusts (orange-brown)
Aluminum – forms a transparent layer on the
surface
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Web Graphic Citations
http://shopuncleharrys.dukestores.duke.edu/images/cooler%20014.jpg
http://www.yummy.com/images/products/minute%20maid%20box%20orange.gif
http://rms.hamp.k12.wv.us/alkire/NeutralNot%20Acid%20or%20BaseCommon%20Examples.jpg
http://www.anr.state.vt.us/dec/waterq/bass/images/bs_acidrain-phscale.gif
http://www.bbc.co.uk/schools/gcsebitesize/img/gcsechem_59.jpg
http://www.funsci.com/fun3_en/acids/acids_03.jpg
http://www.neoanathema.com/gallery/albums/upload/do_not_lick.jpg
http://www.haruko.ca/pictures/Lissar/tank.jpg/tank.jpg
http://images.allrecipes.com/site/allrecipes/area/community/userphoto/small/16276.jpg
http://static.flickr.com/50/143267874_82c6bb3acb.jpg
http://www.bookofjoe.com/images/p111915b.jpg
http://drberniedental.com/images/concerns/cracked.jpg
Ms. Baier's Science 14 16