Balancing Equations and Conservation of Mass
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Balancing Equations and Conservation of Mass — Free MYP5 Chemistry Practice Questions

1QuestionBalancing Complex Reactions with Polyatomic IonsConcept Practice
2 marks~3 minCriterion A
Ammonium sulfate, (NH4)2SO4(NH_4)_2SO_4, is used as a nitrogen-rich fertiliser. It dissociates in water to release two types of polyatomic ion.
a
State the name and chemical formula of each polyatomic ion present in (NH4)2SO4(NH_4)_2SO_4. [1]
b
Deduce the charge on each ion and explain how the charges confirm that ammonium sulfate is electrically neutral. [1]
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Solutions

2QuestionBalancing Simple Chemical EquationsAssessment Practice
3 marks~5 minCriterion C

Data

Time (s): 0, 10, 20, 30, 60, 90

Mass of O2O_2 produced (g): 0, 0.2, 0.4, 0.6, 0.8, 1.0

Line A reaches a plateau of 1.0 g at 30 s. Line B reaches a plateau of 1.0 g at 90 s.
During the decomposition of hydrogen peroxide, oxygen gas is collected over time under two conditions: with manganese dioxide catalyst (Line A) and without catalyst (Line B).

2 H2O2 (aq)→2 H2O (l)+O2 (g)2\,H_2O_2\,(aq) \rightarrow 2\,H_2O\,(l) + O_2\,(g)

Graph
a
Identify which line represents the catalysed reaction. [1]
b
Explain how the graph supports your identification in part (a). [1]
c
Both lines reach the same final mass of 1.0 g. Analyse what this tells you about the role of a catalyst in this reaction. [1]
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Solutions

3QuestionBalancing Simple Chemical EquationsAssessment Practice
4 marks~6 minCriterion D
A factory near a residential area burns methane (CH4CH_4) for electricity generation. Complete combustion produces carbon dioxide and water, but incomplete combustion also occurs, releasing carbon monoxide (COCO) and soot (carbon particles).

CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O
a
Construct the balanced equation for the incomplete combustion of methane that produces only carbon monoxide and water. [1]
b
Discuss the environmental and health implications of incomplete combustion for the nearby residential community, referring to both products of incomplete combustion and their effects on air quality and human health. [3]
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Solutions

4QuestionBalancing Simple Chemical EquationsAssessment Practice
6 marks~9 minCriterion B
When a hydrocarbon burns completely in excess oxygen, the only products are carbon dioxide (CO2CO_2) and water (H2OH_2O). The table below shows combustion data for four alkanes.

HydrocarbonCH4CH_4C2H6C_2H_6C3H8C_3H_8C4H10C_4H_{10}
CO2CO_2 molecules produced1234
H2OH_2O molecules produced2345
a
Deduce the relationship between the molecular formula of a hydrocarbon and the number of CO2CO_2 and H2OH_2O molecules produced during complete combustion. [2]
b
Predict the number of CO2CO_2 and H2OH_2O molecules produced when one molecule of pentane (C5H12C_5H_{12}) burns completely in excess oxygen, and explain your reasoning. [2]
c
A student claims: "The pattern in the table is just a coincidence — it does not have to follow the law of conservation of mass." Justify whether this claim is correct or incorrect, using the balanced equation for the complete combustion of pentane as evidence. [2]

Solutions

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