Ch 11 - Chemical Changes Flashcards
A physical change occurs when…
no new subtsances are formed.
What are some examples of physical changes?
- boiling
- melting
- condensation
Physical changes are (reversible/irreversible).
reversible
How do you reobtain salt from a salt solution?
Evaporate the water out.
A chemical change occurs when…
new substances are formed.
What is an example of chemical change?
Reaction of potassium metal with water –> potassium hydroxide & hydrogen
Chemical changes are…
reverse
not easily reversed.
The reversal of chemical changes requires…
large amounts of energy.
What is a process used to reverse chemical changes?
Electrolysiss
What is electrolysis?
It is the breakdown/decomposition of the product using electricity.
During both physical and chemical changes, heat energy…
can be taken in or given out!
What are the types of chemical change?
- Oxidation
- Combustion
- Thermal decomposition
- Neutralisation
What is oxidation?
It is the chemical change whenn a substance reacts wih oxygen.
What are examples of oxidation?
- Rusting of iron
- ‘Browning’ of apples
- Cellular respiration
What is combustion?
It is when a substance is heated in the presence of oxygen to form one or more new substances.
It’s another example of oxidation!
( ) & ( ) are usually given out during combustion.
Heat and light
What are examples of combustion?
- Burning of sparklers
- Charcoal (carbon) in a barbecue pit burns in oxygen
What is thermal decomposition?
It is when a substance breaks down into two or more simpler substances upon heating.
What are examples of thermal decomposition?
- copper(II) carbonate –>copper (II) oxide + carbon dioxide
- lead(II) nitratae –> lead oxide + nitrogen oxide + oxygen
What is neutralisation?
It is when an acid is mixed with an alkali.
What is produced during neutralisation?
- salt
- water
What is an acid?
A substance that dissolves in water and dissociates to give hydrogen ions, H+
How can you classify acids?
- mineral acids
- organic acids
What are examples of mineral acids?
- nitric acid (HNO3)
- sulfuric acid (H2SO4)
- hydrochloric acid (HCl)
What are examples of organic acids?
- folic acids (in avocadoes)
- ascorbic acid (vitamin c)
- ethanoic acid (vinegar)
What are the physical properties of acids?
- taste sour (citric acid)
- change the colour of indicators
- corrosive (ph < 7)
- can conduct electricity
What is an alkali?
A substance that dissolves in water and dissociates to give hydroxide ions, OH-
What are some example of common alkalis?
Group 1 metal hydroxides:
sodium _ NaOH, potassium _ KOH
Group 2 metal hydroxides:
calcium _ Ca(OH)2, barium _ Ba(OH)2
What are the physicla properties of alkalis?
- taste bitter, slippery soapy feel
- change the colour of indicators
- corrosive (pH > 7)
- can conduct electricity
What is the range of a pH scale/universal indicator?
0 to 14
What does a pH value less than 7 mean?
the solution is acidic
What does a pH value of 7 mean?
the solution is neutral
What does a pH value greater than 7 mean?
the solution is alkaline
What are examples of indicators?
- litmus paper
- universal indicator
- pH meter
What do the color changes of litmus paper mean?
1. turns/remains red
2. turns/remains blue
- acid
- alkali
What are the three reactions of acids?
- with alkali
- with metal
- with metal carbonate
What does the reaction of acids with alkalis (neutralisation) produce?
salt and water
Whats does the reaction of acids with metals produce?
salt and hydrogen gas
How do you test for hydrogen?
- place a lighted splint at the mouth of the test tube
- if hydrogen is present, the lighted splint will be extinguished + ‘pop’ sound
POP test
What does the reaction of acids with carbonates produce?
salt, water and carbon dioxide gas
How do you test for carbon dioxide?
- bubble the gas through limewater
- if carbon dioxide is present, a white precipitate will form
limewater test!
What are the effects of rusting?
causes damage to iron and steel objects
How do you prevent rusting?
- painting
- galvanising (zinc coat)
- oiling
- drying
