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
——————————————————————————-
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
What are the 5 tests for anions?
1) halide test
2) SO₄²⁻ test
3) SO₃²⁻ test
4) CO₃²⁻ test
5) NO₃⁻ test
When a cation is heated, the particle moves from ground state to…?
exited state
Explain what happens when an electron is promoted
the electron absorbs energy and moves further from the nucleus
What happens when the heat previously put on a cation is removed?
as the electron returns back to ground state, energy is released as light
What does the color of light produced when an electron moves from exited state to ground state depend on?
the color of light depends on the wave length of the light emitted
Which color in the electromagnetic spectrum has the most energy and which has the least energy?
most energy - purple
least energy - red
Why do some ions release more energy when going from ground state to exited state?
because depending on the charge, the attraction force is stronger. in ²⁺ ions, the attraction force is stronger than those in a ⁺ ion.
What is the method for the flame test?
1) clean wire / needle with concentrated HCl
2) dip wire in acid (HCl) (to wet needle) and place in compound
3)place compound in blue bunsen flame
Complete the table to determine the light each cation emits:
+———–+———————|
| Li ⁺ | |
+———–+———————|
| Cu⁺ | |
+———–+———————|
| Na⁺ | |
+———–+———————|
| Ba⁺ | |
+————+——————–|
| K⁺ | |
+————+——————–|
| Mg²⁺ | |
+————+——————–|
| Ca²⁺ | |
+————+——————–|
Cation | Color |
+———–+———————|
| Li ⁺ | bright red |
+———–+———————|
| Cu⁺ | blue/green |
+———–+———————|
| Na⁺ |orange/yellow|
+———–+———————|
| Ba⁺ | apple-green |
+————+——————–|
| K⁺ | lilac |
+————+——————–|
| Mg²⁺ | colorless |
+————+——————–|
| Ca²⁺ | brick-red |
+————+——————–|
Cation | Color |
What state is a precipitate?
solid
What 2 ions can be used for a cation test? Which one is preferable?
OH⁻ or CO₃²⁻
OH⁻ is preferable
GO MEMORISE THE PRECIPITATION CATIONS TESTS IN NOTEBOOK
ok…
What cations could be used for the sulfate anion test? Which one would be preferable and why?
Ca²⁺/Sr²⁺/Ba²⁺/Pb²⁺
Ba²⁺ is preferable because it is most insoluble
What is the method for the sulfate test?
1) dissolve sample in water
2) add any acid except H₂SO₄ (to neutralise or remove OH⁻/CO₃²⁻)
3) add Ba(NO₃)₂
4) if sulfate is present, ppt. is formed
What is the method for the sulfite test?
1) add any acid (HCl)
2) collect gas produced
3) expose gas to KMnO₄ or K₂Cr₂O₇
What is the equation for the sulfate test?
Ba(NO₃)₂ + NaSO₄ → BaSO₄ + 2NaNO₃
What is the equation for the sulfite test?
XSO₃ + HCl → XCl₂ + H₂O + SO₂
What is the method for the carbonate test?
1) add any acid (except carbonic acid)
2) collect gas produced
3) add gas to limewater
What is the equation for the carbonate test?
XCO₃ + 2HCl → XCl₂ + H₂O + CO₂
What is the method for the ammonium test?
1) react compound with NaOH
2) heat
3) collect gas and expose to damp red litmus paper → blue
What is the equation for the ammonium test?
NH₄X + NaOH → NaX + H₂O + NH₃
What is the method for the nitrate test?
1) add compound to NaOH
2) react with aluminium powder
3) heat
4) collect gas and expose to damp red litmus paper → blue
What is the method for the halide test?
1) dissolve sample in water
2) add any acid (HNO₃) except for HCl (to remove OH⁻/CO₃²⁻)
3) add AgNO₃ and observe color of ppt.
Which test should you do before halide?
SULFATE TEST FIRST!!!
What are the results for the halide test?
