EL 7 Flashcards
What is the pH of an acid?
Less than 7
What is the pH of a base?
Over 7
What is the neutralization reaction?
Acid + base —> salt + water
What is an acid?
A proton donor
What is a monoprotic acid?
An acid that donates one proton eg. HCl, HNO3
What is a diprotic acid?
An acid that donates both Protons eg. H2SO4
How are salts formed?
From positively charge cations and negatively charged anions producing a neutral product
What charge do cations have?
Positive
What charge do anions have?
Negative
Charge of ammonium
NH^4+
Charge of copper (II)
Cu^2+
Charge of zinc (II)
Zn^2+
Charge of lead (II)
Pb^2+
Charge of iron (II)
Fe^2+
Charge of iron (III)
Fe^3+
Charge of nitrate
NO3 ^-
Charge of hydroxide
OH^-
Charge of carbonate
CO3 ^-
Charge of sulphate
SO4 ^2-
How do you form the name of a salt?
Cation Anion
Eg. Zinc sulfate
Are nitrates soluble?
Yes
Which carbonates are soluble?
-ONLY group 1
-(NH4)2CO3
Which sulphates are insoluble? And what precipitates do they form?
BaSO4
PbSO4
SrSO4
White precipitates
Which chlorides are insoluble? And what precipitate do they form?
AgCl
PbCl2
WHITE PRECIPITATES
Which hydroxides are soluble?
- group 1&2
- NH4OH
Which halides are insoluble?
All silver halides
Are all sodium, potassium and ammonium salts soluble?
YES!
How do we make insoluble salts?
-Using a precipitation reaction
- combine a cation and an anion from aqueous solutions to make an ionic salt
- once the salt has been precipitated out and is lying at the bottom of the flask, filter it from the solution, wash it and then dry it on filter paper
How do we make a soluble salt?
- Pick right acid and a suitable metal or an insoluble base
- add the solid metal to the acid - it will dissolve until it has been neutralised
- filter out the excess metal to get the salt solution
- to get pure solid crystals of salt, evaporate some of the water and then leave the rest to evaporate slowly
(CRYSTALLISATION)
What are examples of insoluble bases that can be used to make soluble salts?
Metal oxide or metal hydroxide
How do we test for silver ions?
- Add OH-
- Brown precipitate
How do we test for calcium ions?
- Add OH-
- white precipitate
How do we test for copper (II) ions?
- Add OH-
- blue precipitate
How do we test for lead ions?
- Add OH-
- White precipitate
How do we test for iron(II) ions?
- Add OH-
- Green precipitate
How do we test for iron (III) ions?
- Add OH-
- Reddish-brown precipitate
How do we test for zinc or aluminium ions?
- Add OH-
- White precipitate at first
- redissolves in excess NAOH
- forms colourless solution
How do we test for sulfates?
1) add dilute HCl
2) add barium chloride solution
3) if a white precipitate forms, it means the organic compound contained a sulfate
How do we test for ammonia?
1) ammonia gas (NH3) is an alkaline so a damp red litmus paper will turn blue if present
How do we test for ammonium ions?
1) add dilute hydroxide and gently heat the mixture
2) test for ammonia
3) if ammonia is given odd, there are ammonium ions
How do we test for hydroxides? (Same as testing whether a solution is alkaline)
1) drop pieces of red litmus paper into the solution
2) If present - turns blue
How do we test for halides?
1) add dilute nitric acid
Positive test for chloride
White precipitate
Positive test for bromide
Cream precipitate
Positive test for iodide
Yellow precipitate
Acid + alkali —>
Salt + water
Acid + base —>
Salt + water
Acid + carbonate —>
Salt + water + CO2
Acid + metal —>
Salt + hydrogen
How do we test for nitrates?
1) warm the solution with sodium hydroxide solution and aluminium foil
2) the aluminium reduces nitrate ions to ammonium ions
3)The ammonium ions react with the hydroxide ions to produce ammonia gas and water
4) test for ammonia
Why do we add a dilute acid to test solutions?
- To prevent a false positive
- as the avid will get rid of any working anions that are unwanted
How do we avoid mix-ups when testing a solution?
DO TESTS IN THIS ORDER
1) Test for carbonates
2) Test for sulfates
3) Test for halides
