Salts Flashcards
Define salt
ionic compounds formed in a reaction with an acid
Name 4 examples of salts
- halides
- nitrates
- sulfates
- phosphates
Guess the correct word to fill in the blank:
Salts are generally acids/neutral/bases.
neutral
What are the 3 properties of salts?
- high mpt (bc of strong electrostatic forces)
- conduct electricity as (l) and (aq)
- soluble in water (with exceptions)
Define ‘dissociating’ in salts
breaking the strong electrostatic forces between particles
Why is CaSO₄ insoluble?
because the solvent cannot break the strong electrostatic forces between particles (the charge of Ca is 2⁺ and the charge of SO₄ is 2⁻ so the electrostatic forces are too strong)
What are the 7 solubility rules?
Most importat (dominant) rules:
1) all compounds of group 1 are soluble
2) all nitrates are soluble
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3) all halides are soluble except if they also contain Ag⁺ or Pb²⁺
4) all sulfates are soluble except if they also contain Ca⁺, Sr⁺, Ba²⁺, Pb²⁺
5) All hydroxides are insoluble
6) all carbonates are insolubles
7) all oxides are insoluble (but gp 1 reacts with water)
Define precipitation
reaction of 2 solutions to form a solid
Give any example of a precipitation reaction
AgNO₃ (aq) + NaBr (aq) → NaNO₃ (aq) + 【AgBr (s) 】➡ precipitate/ppt
What is the difference between a precipitation and a displacement reaction?
displacement: a more reactive element replaces another less reactive element.
precipitation: a more soluble element replaces another less soluble element. a solid is formed.
Write a preparation of PbI₂ (you can use other examples)
PbI₂ → Pb(NO₃)₂ (soluble substance)
→ KI (insoluble substance)
Pb(NO₃)₂ + KI → PbI₂ + 2KNO₃
How are impurities removed from the residue after a precipitation reaction?
Step 1: Wash residue with distilled water to remove soluble impurities
Step 2: evaporate water on hot plate
What are the 5 steps to write an ionic equation?
i) write symbol equation
ii) add state symbols
iii) identify ionic compounds that are aqueous
iv) separate those compounds into ions
v) cancel out left/right
(find examples in notebook)
Acid + base →
salt + water
Acid + metal carbonate →
salt + water + carbon dioxide
Fill in the blanks:
During salt preparation, the salt produced needs to be 1.___________ and therefore the base used needs to be 2.___________.
- isolated / pure
- insoluble
Which of the reactants should be in excess for salt preparation?
the base needs to be in excess
How will the excess base for salt preparation be separated?
- filter
- evaporate
What is the general method for salt preparation?
1) measure 𝑥 cm³ of H₂SO₄ into a conical flask
2) add excess base and heat on a hot-plate (if carbonate, wait until no more effervescing. if oxide, wait until solid disappears)
3) filter to remove excess base (residue = base, filtrate = salt + water)
4) heat filtrate in an evaporating basin until ¾ of water has evaporated or until crystals begin to form
5) leave to crystallise
6) filter to remove excess water
7) collect residue
Why should some of the water be left when evaporating the filtrate during salt preparation?
1) forms large crystals
2) to avoid salt decomposing
3) to form hydrated crystals
What method needs to be used to prepare group 1 salts?
titration
What is the general method for preparing group 1 salts?
1) measure 𝑥cm³ of base into a conical flask (using a pipette)
2) add 2 drops of indicator (methyl orange or phenophalein)
3) fill burette with acid and record initial volume
4) add acid to base (slowly) until it turns red (methyl orange)
What types of particles do ionic compounds consist of?
anions and cations
What are the 4 tests for cations?
1) flame test
2) NaOH test
3) NH₃ test
4) NH₄⁺ test
