Chemical Formulas and Equations
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Chemical Formulas and Equations — Free MYP4 Chemistry Practice Questions

1QuestionIdentifying Reactants and ProductsAssessment Practice
3 marks~5 minCriterion C
A 0.50 g piece of magnesium ribbon reacts with excess hydrochloric acid. The graph shows the mass of magnesium remaining plotted against time.
a
Describe the shape of the graph. [1]
b
Explain why the gradient of the graph decreases as the reaction proceeds. [1]
c
A student claims that the graph would reach zero mass if enough time were allowed. Evaluate this claim using your knowledge of limiting and excess reactants. [1]
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Solutions

2QuestionWord Equations and Symbol EquationsAssessment Practice
4 marks~6 minCriterion A
The diagrams below show two models of chemical substances.

Diagram 1: A repeating cubic lattice of alternating spheres labelled Na+Na^+ and Cl−Cl^-.

Diagram 2: Discrete molecules, each with one central sphere labelled O (δ−\delta^-) bonded to two smaller spheres labelled H (δ+\delta^+).
a
Identify the type of compound shown in each diagram. [1]
b
Explain the bonding and structure visible in Diagram 1 and Diagram 2. [2]
c
The partial charges (δ−\delta^- and δ+\delta^+) are shown in Diagram 2 but not in Diagram 1. Explain why partial charges are used to describe the bonding in Diagram 2 and why they would be inappropriate for Diagram 1. [1]
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Solutions

3QuestionIdentifying Reactants and ProductsAssessment Practice
4 marks~6 minCriterion D
A student investigates a gas heater that burns propane (C3H8C_3H_8). The balanced equation for complete combustion is:

C3H8+5O2→3CO2+4H2OC_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O

The student's model assumes all gas heaters undergo only complete combustion. However, if the oxygen supply is limited, incomplete combustion occurs, producing toxic carbon monoxide (COCO) instead of CO2CO_2.
a
Identify one environmental impact of releasing large amounts of CO2CO_2 from millions of household gas heaters. [1]
b
Explain how conditions inside a poorly ventilated room could lead to incomplete combustion and the production of COCO. [1]
c
Evaluate the student's model, discussing why assuming only complete combustion underestimates the health risks associated with gas heaters. [2]
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Solutions

4QuestionState Symbols in Chemical ReactionsAssessment Practice
8 marks~12 minCriterion B
Consider the following balanced equations for the reactions of elements with oxygen:

2Mg(s)+O2(g)→2MgO(s)2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)}

2Ca(s)+O2(g)→2CaO(s)2\text{Ca(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{CaO(s)}

4Na(s)+O2(g)→2Na2O(s)4\text{Na(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{Na}_2\text{O(s)}

C(s)+O2(g)→CO2(g)\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)}
a
Identify the pattern in the state symbols of the products, linking each product's state to the position of the reacting element in the periodic table. [2]
b
Deduce the state symbol of barium oxide (BaO), the product formed when barium reacts with oxygen. Justify your answer using the pattern identified in (a) and barium's position in the periodic table. [2]
c
Discuss how the bonding and structure of BaO and CO2 differ, and explain how these differences account for the contrast in their physical states at room temperature. [4]
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