Formula and equations Flashcards
Write a balanced equation, with state symbols for this statement:
When chlorine gas is bubbled into an aqueous solution of potassium iodide, iodine (I2) appears as a black solid suspended in potassium chloride solution.
2Cl(g) + 2KI (aq) –> I2 (s) + 2KCl (aq)
Take note that it is not 2KI2 for (aq) and also not I for the (s) because:
Chemical Formula of Potassium Iodide (KI):
Charge Balance:
Potassium (K) is a Group 1 metal with a +1 charge (K⁺).
Iodine (I) is a Group 17 halogen with a -1 charge (I⁻).
To form a neutral compound, one K⁺ ion pairs with one I⁻ ion:
Formula: KI (1:1 ratio)
.
Formula: KI (1:1 ratio).
Why Not KI₂?
KI₂ would imply two I⁻ ions (-2 total charge) paired with one K⁺ ion (+1 charge), resulting in a net charge of -1.
This violates the rule of charge neutrality in ionic compounds.
Chemical Formula for Iodine (I₂):
Elemental Iodine:
Exists as diatomic molecules (I₂) in its pure form (like other halogens: Cl₂, Br₂).
Iodide Ion:
When iodine gains an electron (e.g., in ionic compounds like KI), it becomes I⁻.
Key Takeaways:
Ionic Compounds (e.g., KI):
Formed by transfer of electrons.
Formula reflects charge balance (K⁺ + I⁻ → KI).
Molecular Elements (e.g., I₂):
Exist as diatomic molecules in their pure state.
Common Mistake to Avoid:
Confusing elemental iodine (I₂) with the iodide ion (I⁻) in compounds.
KI contains iodide ions (I⁻), not elemental iodine (I₂).
Final Answer:
Potassium iodide: KI (not KI₂).
Elemental iodine: I₂.
Write a balanced equation, with state symbols for this statement:
Copper powder reacts with hot nitric acid to form copper (II) nitrate and water, and also releases the brown gas, nitrogen dioxide.
Chemical equations are balanced by writing a ______ in front of each formula in the equation.
Number. (If necessary—> if it is 1, don’t need to write)
To be considered balanced, the number of each type of atoms must be the ______ in both the left hand side and the right hand side of the equation.
Same
Substance on the left side of the equation are called ______ and substances on the right hand side are called ________.
Substances on the left hand side are called reactants and substances on the right hand side are called products.
A state symbol is used to ________. Where is it written at?
A state symbol is used to describe whether the reactant or product is in the solid, liquid, gaseous, or aqueous form during the condition of the reaction.
The state symbol is written i brackets after each formula; (s) for solid, (l) for liquid, (g) for gas, and (at) for aqueous. (All in small letters)
A solid that is insoluble in water gets the state symbol ______. A solid that is soluble in water usually gets the state symbol _____ since _____________.
A solid that is insoluble in water gets the state symbol (s). A solid that is soluble in water usually gets the state symbol (aq) since reactions are normally carried out in a watery medium.
Are all nitrate salts soluble? What is the state symbol?
Yes. The state symbol is (aq)
Are all chloride salts soluble? What is the state symbol?
Most chloride salts are soluble except for lead (II) chloride and silver chloride.
Most chloride salts except lead (II) chloride and silver chloride has the state symbol of (aq)
While lead (II) chloride and silver chloride has the state symbol (s)
Are all surface salts soluble? What is the state symbol?
Most sulphate salts are soluble except for lead (II) sulfate, barium sulfate and calcium sulfate.
Most sulfate salts except lead (II) sulfate, barium sulfate and calcium sulfate have the state symbol of (aq) while lead (II) sulfate, barium sulfate and calcium sulfate has the state symbol of (s)
Are all carbonates soluble? What is the state symbol?
Only carbonates of sodium, potassium and ammonium are soluble, therefore the state symbol is (aq).
Most other carbonates have the state symbol (s)
Are all hydroxides and oxides soluble? What is the state symbol?
hydroxides and oxides of sodium, potassium and ammonium are soluble and have the state symbol (aq) while most other metal hydroxides and oxides are insoluble and have the state symbol (s)
What is one way to write the formula of an ionic compound?
one way to write the formula of an ionic compound is to consider its ions and make the sum of the positive charges equal to the sum of the negative charges.
Example 1 the ions of sodium chloride are Na + and Cl- and since the charges of 1+ and 1- are balanced, the formula of sodium chloride is NaCl.
Example 2: the ions of ammonium oxide are Al 3+ and O2- and since it takes two Al 3+ to balance the charges of three O2- the formula of aluminium oxide is Al2O3.
Most of the common acids and alkalis are used in the __________ form.
Aqueous
These common acids and alkalis include:
Acids:
- hydrochloric acid, HCl
- Nitric acid, HNO3
- sulfuric acid, H2SO4
Alkalis:
- sodium hydroxide NaOH
- potassium hydroxide KOH
-aqueous ammonia NH3
Sometimes, a _________ is required to clarify the number of ions in combination and to avoid confusion of two individual numbers. Give an example.
Bracket
E.g. the formula of magnesium nitrate is Mg(NO3)2, where one Mg2+ balances two NO3-.
What is the formula of sodium ion?
Na+
What is the formula of potassium ion?
K+
What is the formula of lithium ion?
Li +
What is the formula of ammonium ion?
NH4 +
What is the formula of silver ion?
Ag +
What is the formula of hydrogen ion?
H+
What is the formula of barium ion?
Ba 2+
What is the formula of calcium ion?
Ca 2+
What is the formula of copper (II) ion?
Cu 2+
What is the formula of iron (II) ion?
Fe 2+
What is the formula of lead (II) ion?
Pb 2+
What is the formula of magnesium ion?
Mg 2+
What is the formula of manganese (II) ion?
Mn 2+
What is the formula of zinc ion?
Zn 2+
What is the formula of aluminium ion?
Al 3+
What is the formula of iron (III) ion?
Fe 3+
What is the formula of the chloride ion?
Cl -
What is the formula of the hydroxide ion?
OH -
What is the formula of the iodide ion?
I -
What is the formula of the nitrate ion?
NO3 -
What is the formula of nitrite ion?
NO2-
What is the formula of the manganate (VII) ion?
MnO4 -
What is the formula of the hydrogen carbonate ion?
HCO3 -
What is the formula of the carbonate ion?
CO3 2-
What is the formula of the dichromate (VI) ion?
Cr2O72-
What is the formula of the oxide ion?
O2-
What is the formula of the sulfate ion?
SO4 2-
What is the formula of the sulfite ion?
SO3 2-
What is the formula of the sulfide ion?
S 2-
What is the formula of silicate ion?
SiO3 2-
What is the formula of the nitride ion?
N 3-
What is the formula of the phosphate (V) ion?
PO4 3-
Metals are _______ charged.
Metals are NOT charged.
Students must not confuse metal ions with metals.
Metals are represented using their symbols as found in the Periodic Table. Thus, calcium metal is Ca, iron metal is Fe, sodium metal is Na, gold metal is Au, etc.
Which ions do you need to write (II) and (III) etc?
copper (II)
Iron (II)
Iron (III)
Lead (II)
Lead (IV)
Manganate (VII)
Dichromate (VI)
manganese (II)
Phosphate (V)
What is the formula of aqueous ammonia?
NH3 (aq) and NOT NH4OH
What is the difference between SO₃ and SO₃²⁻?
Answer:
SO₃ (Sulfur Trioxide):
A neutral, covalent gas.
Reacts with water to form sulfuric acid (H₂SO₄).
Example: Industrial chemical.
SO₃²⁻ (Sulfite Ion):
A 2- charged anion.
Cannot exist alone; part of ionic compounds (e.g., Na₂SO₃).
Reacts with acids to release SO₂ gas.
Key Difference:
SO₃ is a molecule; SO₃²⁻ is an ion in salts.
Common Mistake:
Writing “SO₃²⁻” alone—it must be paired with cations (e.g., Na⁺, Ca²⁺).
Example:
SO₃: Gas used in H₂SO₄ production.
Na₂SO₃: Solid preservative containing SO₃²⁻.
Study Tip:
Remember: “-ite” = ion (SO₃²⁻), no suffix = molecule (SO₃).
Visual Cue:
Draw SO₃ (linear molecule) vs. SO₃²⁻ (trigonal pyramidal ion).
Use This Flashcard To:
Avoid confusing formulas.
Correctly name/write compounds (e.g., “sodium sulfite” = Na₂SO₃, not SO₃).
Predict reactions (SO₃ → acid; SO₃²⁻ → SO₂ gas with acids).
