IB myp 4-5 Chemistry – Practice Questions- All Topics
Topic :Periodic Table-Transition Metals
Topic :Periodic Table- Weightage : 21 %
All Questions for Topic : Metals and Non metals,Transition metals,Noble gases,Periodic trend groups and periods
Question (18 marks)
Cave paintings drawn 100,000 years ago have been found in South Africa. These cave paintings were drawn with iron (III) oxide, manganese dioxide and charcoal (black porous carbon). Manganese dioxide has also been used for body painting.
a (2 marks) State the chemical formulas of iron (III) oxide and manganese dioxide.
▶️Answer/Explanation
Answer:
Iron (III) oxide: Fe2O3
Manganese dioxide: MnO2
Explanation:
Iron (III) oxide indicates iron with a +3 oxidation state (Fe³⁺) combined with oxygen (O²⁻), requiring two Fe³⁺ ions and three O²⁻ ions to balance charges, giving Fe2O3. Manganese dioxide indicates manganese with a +4 oxidation state (Mn⁴⁺) combined with oxygen (O²⁻), requiring one Mn⁴⁺ ion and two O²⁻ ions to balance charges, giving MnO2.
b (3 marks) Use the periodic table to identify another element that could have the same properties as iron or manganese. Justify your answer.
▶️Answer/Explanation
Answer:
Cobalt (Co) or Nickel (Ni) or any other transition metal
Justification: These are transition metals like iron and manganese, have variable oxidation states, form colored compounds, and are good conductors.
Explanation:
Transition metals share similar properties because they have partially filled d orbitals. These properties include variable oxidation states (e.g., Co²⁺ and Co³⁺), ability to form colored compounds (e.g., CoCl2 is pink), and typical metallic properties like conductivity and malleability. They are all found in the d-block of the periodic table.
c (2 marks) The colour of paint comes from pigments that can be either natural or synthetic. Natural pigments are made by crushing minerals into a fine powder and adding them to water, oil or another liquid along with solvents and additives. Identify whether paint is a solution, an emulsion or a pure substance.
▶️Answer/Explanation
Answer:
Emulsion
Explanation:
Paint is an emulsion because it consists of solid pigment particles suspended in a liquid medium (water or oil). The particles are not dissolved (as in a solution) and the mixture is not uniform at the molecular level (as in a pure substance). The suspended particles give paint its heterogeneous nature.
d (3 marks) Outline why it is usually easier to remove watercolour paint than oil paint by washing.
▶️Answer/Explanation
Answer:
1. Watercolour paint is water-soluble
2. Oil paint is not soluble in water
3. Water can dissolve and wash away watercolour paint while oil paint remains
Explanation:
Watercolour paints use water as their solvent, making them polar and easily dissolved by water. Oil paints use non-polar organic solvents that don’t mix with water. When washed with water, the water molecules can surround and dissolve the watercolour pigments, while oil paint forms a separate layer that resists water.
e (4 marks) Use the information from this question to evaluate which type of paint causes less damage to the environment.
▶️Answer/Explanation
Answer:
Watercolour paints are generally more environmentally friendly because:
1. They don’t require harsh solvents for cleaning
2. They don’t release volatile organic compounds (VOCs)
3. They are biodegradable
4. They don’t accumulate in the environment like oil-based paints
Explanation:
Oil paints often contain toxic solvents and heavy metal pigments that can persist in the environment. Their cleanup requires additional solvents that may be harmful. Watercolours, being water-soluble, are easier to clean with just water and typically contain fewer toxic components. However, some watercolour pigments may still contain heavy metals that could enter waterways if not properly disposed.
f (2 marks) Write down the balanced equation for the half-reaction shown above.
▶️Answer/Explanation
Answer:
2 CrO42- (aq) + 10 H+ (aq) + 6e– → Cr2O3 (s) + 5 H2O (l)
Explanation:
The equation is balanced by ensuring:
1. Chromium atoms balance (2 on each side)
2. Oxygen atoms balance (8 + 10 = 18 on left, 3 + 15 = 18 on right)
3. Hydrogen atoms balance (10 on left, 10 on right)
4. Charge balances (-4 + 10 -6 = 0 on left, 0 on right)
g (2 marks) State if the half-reaction in part (f) is an oxidation or a reduction. Justify your answer.
Select:
Justification:
▶️Answer/Explanation
Answer:
Reduction
Justification: The chromium in CrO42- (Cr⁶⁺) gains electrons to form Cr2O3 (Cr³⁺), decreasing its oxidation state.
Explanation:
Reduction is defined as gain of electrons or decrease in oxidation state. Here, each chromium atom changes from +6 to +3 oxidation state by gaining 3 electrons (total 6 electrons for 2 Cr atoms). The presence of electrons on the left side of the equation also confirms this is a reduction half-reaction.