Chapter 11. Chemical Changes Flashcards
Matter
Anything that has mass or volume
Composition
Types and amounts of simpler substances that make up a sample of a matter
Properties
The characteristics that give each substance a unique identity
Physical properties
Properties a substance shows itself without interaction with another substance:
- Colour
- Boiling point
- Melting point
- Density
Chemical properties
Properties a substance shows as it interacts with, or transforms into, other substances:
- Flammability
- Corrosiveness
Physical vs chemical change
In physical changes, the appearance or form of the matter changes but the kind of matter in the substance does not
- Changes in the physical state are reversible (by temperature)
In chemical changes, at least one new substance is created with different properties
- Cannot be reversed using physical methods
Law conservation of mass
Matter cannot be created nor destroyed by chemical reactions or physical changes
- Mass stays the same before and after the reaction
- Number and type of atoms do not change
Particle arrangement of solids
Particles are close together and organised
Particle arrangement of liquids
particles are close together but disorganised
particle arrangement of gases
particles are far apart and disorganised
Types of chemical changes
- Combustion
- Thermal decomposition
- Oxidation
- Neutralisation
Combustion
Chemical reaction is which a substance is heated in the presence of oxygen
Thermal decomposition
A process in which a substance breaks into two or more simpler substances upon heating
Oxidation
Gain of oxygen
Neutralisation
A neutralisation reaction is where an acid and a base react to each other to form water and salt
acid + metal =
salt + hydrogen
acid + carbonate =
salt + carbon dioxide + water
acid + alkali =
salt + water
Effervescence
bubbles
Test for carbon dioxide (acid + carbonate)
Lime water (calcium hydroxide)
- Bubble the gas into limewater
> White precipitate will form in the presence of carbon dioxide
Test for hydrogen (acid + metal)
Lighted splint
- Introduce a lighted splint into the gas
> Will be extinguished with a “pop” sound in the presence of hydrogen
Water
H20
Hydrogen gas
H2
Carbon dioxide
CO2
Oxygen gas
O2
Sulfate ion
SO4 2-
Hydroxide ion
OH -
Nitrate ion
NO3 -
Carbonate ion
CO3 2-
Chloride ion
Cl -
Sodium ion
Na +
Potassium ion
K +
Magnesium ion
Mg 2+
Calcium ion
Ca 2+
Copper (II) ion
Cu 2+
Iron (II) ion
Fe 2+
Iron (III) ion
Fe 3+
Silver ion
Ag +
Zinc ion
Zn 2+
Aluminium ion
Al 3+
PH scale
- Set number 1-14
- Indicates if a solution is acidic, neutral or alkaline
- the pH of a solution is related to the concentration of H+ and OH- present in solution.
pH 0-6
Acid (Strong acid -> weak acid)
pH 7
Neutral
pH 8-14
alkali (weak alkali -> strong alkali)
Indicators
Subtances that show different colours in acidic and alkalic solution
Litmus
Alkali: Blue
Acid: Red
Methyl orange
Acid: Red
Alkali: Yellow
Screened methyl orange
Acid: violet
Alkali: green
Phenolphthalein
acid: colourless
alkali: pink
Application of pH scale
pH of soil
> Important to control pH of soil because it will affect the growth and development of plants (e.g. potatoes grow well at pH 5.5 - 6.5 , while cabbages grow well at pH 7.5 - 8.5)
* Most plants grow well in neutral or slightly acidic soils
pH of soil may become unsuitable for plant growth due to
- Too much fertiliser
- Environmental pollution (acid rain)
To treat acidity in soil, add
- Calcium oxide (quicklime)
- Calcium hydroxide (slaked lime)
*This process is known as liming. These bases neutralise the acid in the soil
