AQA GCSE · Question 05.5 · Bonding structure and the properties of matter
Titanium oxide contains Ti⁴⁺ ions and O²⁻ ions. What is the formula of titanium oxide?
Answer options:
A.
TiO₂
B.
TiO₄
C.
Ti₂O
D.
Ti₄O₂
How to approach this question
Ionic compounds must have a neutral overall charge. This means the total positive charge must equal the total negative charge. You have Ti⁴⁺ (a +4 charge) and O²⁻ (a -2 charge). How many oxide ions do you need to balance one titanium ion?
Full Answer
A.TiO₂✓ Correct
TiO₂
To find the formula of an ionic compound, the total positive charge from the cations must balance the total negative charge from the anions.\n- The titanium ion has a charge of 4+ (Ti⁴⁺).\n- The oxide ion has a charge of 2- (O²⁻).\n\nTo make the overall charge zero, we need to find the lowest common multiple of the charges (ignoring the signs), which is 4.\n- We need a total positive charge of +4, which is provided by one Ti⁴⁺ ion.\n- We need a total negative charge of -4. Since each oxide ion is 2-, we need two of them (2 × -2 = -4).\n\nTherefore, the ratio of Ti ions to O ions is 1:2. The formula is TiO₂.
Common mistakes
✗ Not balancing the charges correctly.\n✗ Writing the numbers from the charges directly into the formula (e.g., Ti₄O₂).
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