acids and bases Flashcards
what are acids?
- substances that produces hydrogen ions (H+) when dissolved in water
- acids can conduct electricity in water due to mobile ions
- will turn damp blue litmus paper red
what is a base?
- a metal oxide or metal hydroxide which react with acid to give salt and water only
- most bases are insoluble in water
- turns damp red litmus paper blue
what are alkalis?
alkalis are soluble bases that dissolve in water to produce hydroxide (OH-) ions
what does the pH of a solution relate to?
it relates to the concentration of hydrogen ions (H+) in the solution
H+ > OH- (acidic solution)
H+ = OH- (neutral solution)
H+< OH- (alkaline solution)
why does the chemical formula NH4OH for aqueous ammonia not exist?
it gets broken down immediately into NH4+ and OH-
what are the 3 reactions of acids?
acid + metal –> salt + hydrogen gas (MASH)
acid + base (metal oxide/ metal hydroxide) –>salt + water (neutralisation) (ABSW)
acid + carbonate –> salt + water + carbon dioxide (CASWC)
between amphoteric, basic, neutral and acidic, which ones are metal oxides and which ones are non-metal oxides?
amphoteric and basic are metal oxides while neutral and acidic are non-metal oxides
how to identify amphoteric metal oxides?
- react with both acids and alkalis
- ZnO, Al2O3, PbO only (ZAP)
how to identify basic metal oxides?
- react with acids only
- other metal oxides other than zinc oxide, aluminium oxide, lead (II) oxide
- most basic oxides are insoluble in water
- basic oxides such as sodium oxide and potassium oxide dissolve in water to form alkaline solutions
how to identify neutral non-metal oxides?
- do not react with acids or alkalis
- NO, CO, H2O only (monoxides)
how to identify acidic non-metal oxides?
- react with alkalis only
- other non-metal oxides that are not NO CO H2O
- most acidic oxides dissolve in water to form a acid
What are the 2 reactions of alkalis?
alkali + acid = salt + water (neutralisation)
alkali + ammonium salt = salt + water + ammonia (displacement of ammonia)
What is the ionic equation for:
sodium hydroxide;
potassium hydroxide;
aqueous ammonia
NaOH (aq) –> Na+ (aq) + OH- (aq)
KOH (aq) –> K+ (aq) + OH- (aq)
NH3 (g) + H2O (l) <–> NH4+ (aq) + OH- (aq)
What are salts?
Salts are ionic compounds. The metal will displace the hydrogen ions in the acid.
What is the ionic equation for:
hydrochloric acid;
nitric acid;
sulfuric acid
HCL (aq) –> H+ (aq) + CL- (aq)
HNO3 (aq) –> H+ (aq) + NO3- (aq)
H2SO4 (aq) –> 2 H+ (aq) + SO4^2- (aq)
What are weak acids and alkalis?
Weak acids and weak alkalis (ammonia) ionise partially in water to produce a low concentration of H+ ions and OH- ions respectively.
What are strong acids and alkali?
Strong acids (HCL, HNO3, H2SO4) and strong alkali (NaOH, KOH) ionise completely in water to produce a high concentration of H+ ions and OH- ions respectively.
What chemical substances have different colours in acidic and alkaline solutions?
methyl orange and phenolphthalein indicators
If a few drops of methyl orange indicator are added into a solution and it turns yellow, what does it suggests?
It suggests that the pH of the solution is greater than 5
What do farmers often add to their soil to allow their plants to grow better and how?
They often add calcium hydroxide Ca(OH)2 to neutralise the excess acid in the soil. This increases the pH of the soil and allows the plants to grow better.
If a few drops of phenolphthalein indicator are added into a solution and it turns colourless, what does it suggest?
It suggests that the pH of the solution is lesser than 8
If the pH of the solution is greater than 10 and a few drops of phenolphthalein indicator was added, what colour would the solution be?
The solution would turn pink
If the pH of the solution is less than 3 and a few drops of methyl orange indicator was added, what colour would the solution be?
The solution would turn red
