Acids, Alkalis and Salts Flashcards
What colour does bromothymol blue go in acids and alkalis?
Acids: Yellow
Alkalis: Light Blue
What colour does methyl orange go in acids and alkalis?
Acids: Red
Alkalis: Yellow
What colour is phenolphthalein in acids and alkalis?
Acids: Colourless
Alkalis: Purple, Pink
What are ions are acids the sources of?
Hydrogen, H+
What ions are alkalis the source of?
Hydroxide, OH-
What colour is litmus in acids, neutral and alkalis?
Acids: Red
Neutral: Purple
Alkalis: Blue
What is an acid?
- Source of H+ ions
- pH less than 7
- Release H+ ions of dissolved in water
- ‘Dissociate in water to produce hydrogen ions’
What is a base?
- Can neutralise an acid
What is the difference between bases and alkalis?
An alkali is a soluble base. It is a source of OH- ions. They have pH above 7.
Acid + Base
Acid + Base -> Salt + Water
Give examples of a strong and weak acids.
Strong: Sulphuric
Weak: Vinegar, Lemon Juice, Bee Sting
Give examples of neutral substances.
Distilled water, salt water
Give examples of weak and strong alkalis.
Weak: Baking powder, Ammonia
Strong: Sodium Hydroxide
What colours does universal indicator turn in different pHs?
Strong acid: Red Weak acid: Yellow Neutral: Green Weak alkali: Blue Strong alkali: Purple
What is the difference between hydrogen chloride and hydrochloric acid?
In water, hydrogen gas dissolves to form hydrochloric acid. The solution is acidic because the hydrogen chloride dissociates into H+ and Cl- ions. pH is a measure of H+ ions, so it is acidic. Hydrogen chloride as a gas is not acidic.
What is the state of hydrogen chloride in room temperature?
Gas
Acid + Carbonate
Acid + Carbonate -> Salt + Water + Carbon Dioxide
Acid + Metal
Acid + Metal -> Salt + Hydrogen
How do H+ ions and OH- ions react?
H+ + OH- -> H2O
What happens to H+ ions in water?
They attach themselves to water molecules:
H+ + H2O -> H3O+
What happens when hydrogen chloride is dissolved in organic solvents, such as methylbenzene?
It cannot ionise to form H+ and Cl-, and it stays as HCl.
Why is HCl acidic in water but not in methylbenzene?
It cannot dissociate into H+ and Cl- ions (the H+ make it acidic) in the methylbenzene like it can in water and so it stays as HCl.
What is a salt?
A substance that is formed when the hydrogen in an acid is replaced by a metal.
What is the formula for hydrochloric acid?
HCl
What is the formula for sulphuric acid?
H2SO4
What is the formula for nitric acid?
HNO3
What is the formula for phosphoric acid?
H3PO4
What is the formula for ethanoic acid?
C2H4O3
What is the test for hydrogen?
Holding a lighted splint near the gas and listening for a squeaky pop.
What are the general rules for soluble salts?
- All nitrates
- All sodium potassium, sodium and ammonium salts
- Most chlorides (except AgCl, PbCl2, Hg2Cl2)
- Group 1 carbonates are soluble (most are insoluble)
- Most sulphates (except PbSO4, CaSO4, BaSO4)
- Group 1 hydroxides + Ca(OH)2, Ba(OH)2 (most are insoluble)
What are the solubility rules about nitrates?
All are soluble
What are the solubility rules about sodium, potassium and ammonium salts?
All are soluble
What are the solubility rules about chlorides?
Most are soluble except:
AgCl, PbCl2, Hg2Cl2
What are the solubility rules about carbonates?
All group 1 are soluble.
Most are insoluble.
What are the solubility rules about sulphates?
Most are soluble except:
PbSO4, CaSO4, BaSO4
What are the solubility rules about hydroxides?
Group 1, Ca(OH)2 and Ba(OH)2 are soluble.
Most are insoluble.
Describe the process of formation of an insoluble salt.
• Mix two solutions - one with the correct positive and one with the negative ion
• Remember each of the first solutions must contain a soluble compound, or it can’t be a solution
• The reaction should form a solution and precipitate
• Filter this to get the precipitate - this is the salt
NO ACID REQUIRED
What is the process of making an insoluble salt called?
A precipitation reaction
Why can’t sodium, potassium or ammonium salts be made using the ‘adding an excess of solid and then filtering it off’ method?
That method requires an insoluble base, and potassium, sodium and ammonium salts and compounds are always soluble.
What method can be used to make a soluble salt which is not a sodium, potassium or ammonium?
• Get the correct metal oxide, carbonate or hydroxide, making sure it is insoluble
• Get the correct acid
• Keep adding the insoluble base to the acid until the reaction stops and there is an excess at the bottom of the acid
• Filter off this excess, heat the remaining solution for some time and evaporate it to get crystals
REQUIRES AN ACID
How can you test for carbon dioxide?
Bubble through limewater, turns cloudy white
How can you test for hydrogen?
Lighted splint would cause a squeaky pop
