Topic 3- Chemical Changes Flashcards
What colours does litmus paper turn?
Red In acidic solutions
Purple in neutral solutions
Blue in alkaline solutions
What colours does methyl orange turn?
Red in acidic solutions
Yellow in neutral and alkaline
What colours does phenolphthalein turn?
Colourless in acidic and neutral
Pink in alkaline solutions
What is an acid?
- An acid is a substance with a pH of less than 7
- Acids form H+ ions in water
- The higher the concentration of hydrogen ions in the solution the more acidic
What is an alkali?
- An alkali is a base that is soluble in water
- Alkalis have a pH of more than 7
- They form OH- ions (hydroxide ions) in water
What is a base?
A base is a substance that reacts with an acid to produce a salt and water
What is a neutral substance?
A neutral substance has a pH of 7
What is a strong acid?
•strong acids ionise completely in a solution
•they usually have low pHs (pH 0-2)
Eg. Sulphuric, hydrochloric, nitric
(Not to be confused with high concentration)
What is a weak acid?
- weak acids don’t fully ionise in a solution
* There pHs are usually 2-6
What happens when acids react with bases?
•A salt is formed
Salts are formed during a neutralisation reaction
What happens when acids react with a metal?
•Salts form
How do you test for hydrogen?
•using a lit splint, if a hydrogen is present you’ll hear a squeaky pop
How do you test for carbon dioxide?
To see if a gas is carbon dioxide you can test it by bubbling it through limewater
If it’s carbon dioxide the limewater will turn cloudy
What is electrolysis?
- Electrolysis is the breaking down of a substance using electricity
- In electrolysis oxidation and reduction occur
- oxidation is the loss of electrons
- reduction is the gain of electrons
