Topic 3 - Chemical Changes Flashcards
What ions does an acid form in water.
What happens to the ions as the ph decreases ?
-An acid forms H+ ions in water.
- the concentration of H+ ions increases as the ph decreases
What is a base?
A base is a substance that reacts with an acid to produce salt and water.
What is an alkali?
What ions does an alkali form in water?
-An alkali is a base that is soluble in water. Ph of more than 7
- an alkali forms OH- ions in water. The higher the pH the more concentration of OH- ions there is.
What are the 3 types of indicators?
-litmus
-methyl orange
-phenolthalein
What colour does litmus go in acid, neutral and alkaline.
Litmus goes red in acid. Purple in neutral. Blue in alkaline solutions
What colour does methyl orange go in acidic, neutral , alkaline solutions.
Methyl orange goes red in acidic, yellow in neutral and alkaline solutions.
What colour does phenolphthalein go in acidic, neutral and alkaline solutions?
Phenolphthalein is colourless in acidic or neutral solutions. Pink in alkaline solutions
What’s the reaction between an acid and a base called?
What does it produce?
- neutralisation.
-salt and water
Why is something at pH 7 neutral?
Because the concentration of hydrogen ions is equal to the concentration of hydroxide ions
Definition of a strong acid …
Example….
- a strong acid ionises almost completely in water. Acid molecules dissociate to release H+ ions
-hydrochloric acid, sulfuric acid, nitric acid
Definition of a weak acid.
Example…
-weak acids do not fully ionise in solutions. Only a small portion of acid molecules dissociate to release H+ ions.
-ethanoic, citric, carbonic acids
Is the ionisation of a weak acid reversible?
The ionisation of a weak acid is a reversible reaction.
What is the concentration of an acid?
It’s how much there is of it in water. How watered down it is.
What happens to the pH if the concentration of H+ ions increases by a factor of 10?
When the concentration of H+ ions increases by a factor of 10, the pH decreases by 1
Acid + metal —-> …..
Acid + metal ——> salt + hydrogen
How to test for hydrogen?
1) you can test for hydrogen by using a lit splint
2)hydrogen makes a ‘squeaky pop’ with a lit splint
3)the noises comes from hydrogen reacting with oxygen in the air to form water.
Acid + metal carbonate —->……
Acid + metal carbonate—-> salt + water + carbon dioxide
How to test if a gas is carbon dioxide ?
You can test if a gas is carbon dioxide by bubbling it through limewater. If the gas is carbon dioxide the limewater will turn cloudy
How to test if a gas is carbon dioxide ?
You can test if a gas is carbon dioxide by bubbling it through limewater. If the gas is carbon dioxide the limewater will turn cloudy
When do salts form?
Acid + metal hydroxide/oxide ——> salt + water
Acid +metal —> salt + hydrogen
When do salts form?
Acid + metal hydroxide/oxide ——> salt + water
Acid +metal —> salt + hydrogen
How to carry out the practical to investigate the neutralisation reaction between calcium oxide (base) and dilute hydrochloric acid.
1) measure out dilute hydrochloric acid into a conical flask. Then measure out calcium oxide. Add it to the hydrochloric acid.
2)wait for the base to react then measure the ph with universal indicator or a ph probe.
3)repeat this until all the acid has reacted, you’ll know this when you have unreacted base sitting at the bottom of the flask.
What are the insoluble salts?
Carbonates and hydroxides ,except sodium, potassium and ammonium ones
Method of making a soluble salt
1)Heat the acid in a water bath to speed up the reaction.
2)then add the base to the acid , they will react to produce a soluble salt . You will know when the base is in excess because all the excess solid will sink to the bottom.
3)filter of the excess solid
4)heat the solution slowly to evaporate some of the water
5)leave the solution to dry and crystals to form
