science 20fh chemistry in action acids and...
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Science 20FH Chemistry in Action
Acids and Bases
Acid comes from the Latin word “acidus” meaning “sour”
Acid - substance that produces hydrogen ions, H+ when dissolved in water.
Example: HCl ➡ H+ + Cl-
Common acids:
Name Formula Uses
Hydrochloric acid HCl Stomach acid, in the lab
Sulphuric acid H2SO4 Car batteries, acid
rain
Citric Acid C6H8O7 Citrus fruits
Base - substance that produces hydroxide ions, OH- when dissolved in
water.
Example: NaOH ➡ Na+ + OH-
Common bases:
Name Formula Uses
Sodium bicarbonate NaHCO3 Baking powder
Magnesium hydroxide Mg(OH)2 Indigestion tablets
Potassium Hydroxide KOH Soap
Properties of Acids - Acids have a sour taste
- Produces hydrogen gas upon reaction with
metals
- Conductors of electricity
- React with carbonates to produce carbon dioxide
- [H+] concentration greater than [OH-] concentration
- Identified by colour change with indicators
- Acid corrodes metals
Properties of Bases - Bases have a bitter taste
- Feels slimy or slippery
- Conductors of electricity
- Produce ammonia (NH3) when reacted with
ammonium chloride
- Identified by colour change with indicators
- [OH-] concentration greater than [H+] concentration
pH Scale
pH means Power of Hydrogen
● The pH scale measures the concentration of H+ ions, the acidity of a
solution.
● pH ranges from 0-14
● A solution with a pH of 7 is neutral
● Acidic solutions have a pH less than 7
● Basic solutions have a pH greater than 7
● The pH scale is a base ten logarithmic scale
o pH = - log [H+]
o Each whole pH value below 7 is ten times more acidic than the
next higher value
o Using the concept of money, let’s say pH 7 is 1 cent, pH 6 (or 8) is
ten times stronger so worth 10 cents. A pH of 5 (or 9) is ten times
stronger than that so it’s worth 100 cents ($1). A pH of 4 (or 10) is
10 times stronger than that, so worth $10.
Determine pH from concentration of H+ ions:
Solution of 0.00001M = 1 x 10-5 pH = - log[1 x 10-5] = 5
Example 1: Determine the concentration of H+ ions from pH:
pH = 3
1 x 10-3 = 0.001 Moles per liter -Acid
pH = 7
1 x 10-7 = 0.0000001 Moles per liter - Neutral
pH= 10
1 x 10-10 = 0.0000000001 Moles per liter -Base
Example 2: Classify each of the following solutions as acid, basic, or neutral.
Then arrange the solutions in order of increasing acidity.
a) Human blood – 7.4 (base)
b) Tomatoes – 4.5 (Acid)
c) Liquid drain cleaner – 14.0 (Base)
d) Battery acid – 1.0 (Acid)
e) Pure water – 7.0 (Neutral)
f) Sea water – 8.0 (base)
Liquid drain cleaner < seawater < Human blood < Pure water < Tomatoes <
Batter acid
Indicators A chemical indicator is a substance that changes color in the presence of H+
and OH-. Indicators are used as a safe way to determine if the substance is an
acid or a base.
Litmus Paper
Litmus paper is filter paper stained with litmus (dye from lichens) used to
indicate is a substance is an acid or a base.
Litmus paper can be red or blue and changes colour accordingly:
Red Litmus Blue Litmus
Acid Stays Red Turns red
Neutral Stays red Stays blue
Base Turns blue Stays blue
Phenolphthalein
Phenolphthalein is an organic compound that changes
colour in a basic solution (C20H14O4)
Colourless in solution that is below 8 (acid)
Pink in a solution that is above 10 (base)
Bromothymol Blue
Bromothymol Blue is a chemical indicator for weak acids
and bases, substances that are close to neutral.
● Below pH 6 it turns the solution yellow
● pH of 7 the solution is green
● Above pH 8 the solution is blue
Universal Indicator
Universal indicator is a solution that changes a variety of colours over a range
of pH’s. Universal indicators are usually mixtures of several indicators. An
example of a universal indicator is red cabbage juice that contains the pigment
anthocyanin that changes colour in various pH.
pH Indicator Activity
1) In groups of two (one person needs to have a device)
you are assigned an “unknown substance” that you will
test using the cabbage indicator.
2) Go to Padlet to post:
a. What you think your substance is
b. A picture of video of the colour change
c. Why might it be important for us to be able to
identify acids and bases?
d. Sign both names
https://padlet.com/katlyn_paslawski/AcidBase