Homework Practice

Printable assignment

Final Assessment: Atoms and Molecules

Section A: Foundations

Question 1mcq

In a closed container,

12\,g

of magnesium reacts completely with

8\,g

of oxygen. What mass of magnesium oxide should be formed?

4\,g

8\,g

20\,g

12\,g

Question 2mcq

Which classroom setup is best for checking the law of conservation of mass during a reaction that may produce a gas?

A.Use an open beaker and weigh only the liquid left behind.

B.Heat the reactants until some gas escapes, then compare masses.

C.Use a closed flask and compare the total mass before and after the reaction.

D.Smell the gas formed and note whether the mass seems to change.

Question 3mcq

Which observation would suggest that a sample is not pure water?

A.Its hydrogen-to-oxygen mass ratio is not

1:8

B.It is colourless.

C.It boils when heated.

D.It is kept in a glass container.

Question 4mcq

Which modern idea shows a limitation of Dalton atomic theory?

A.Elements have symbols.

B.Atoms can contain subatomic particles and isotopes.

C.Compounds contain more than one element.

D.Mass can be measured on a balance.

Question 5mcq

A particle contains two hydrogen atoms and one oxygen atom chemically combined. Which classification is best?

A.Atom of an element

B.Molecule of an element

C.Molecule of a compound

D.Free neutron

Question 6mcq

Why is

O_3

not a molecule of a compound?

A.It has no atoms.

B.It has different elements chemically combined.

C.It is an ionic salt.

D.It contains only oxygen atoms, even though there are three of them.

Section B: Core Processes

Question 7mcq

Which statement best compares ionic and covalent compounds at Grade 9 level?

A.Ionic compounds involve ions, while covalent compounds involve sharing of electrons.

B.Both always contain only positive ions.

C.Covalent compounds are made only of metals.

D.Ionic compounds have no charge balance.

Question 8mcq

An atom gains two electrons. What type of ion does it form?

A.A cation with charge

2+

B.An anion with charge

2-

C.A neutral molecule

D.A proton

Question 9mcq

An atom with configuration

2,6

gains electrons to complete its octet. What charge is expected?

2+

1+

2-

0

always

Question 10mcq

What is the formula of aluminium oxide using

Al^{3+}

and

O^{2-}

AlO

Al_3O_2

Al_2O

Al_2O_3

Question 11mcq

Which notation correctly shows a sodium ion?

Na^+

NA^+

na^-

N_a

Question 12mcq

Which pair correctly uses molecular mass for a covalent molecule and formula unit mass for an ionic compound?

NaCl

— molecular mass only

CO_2

— molecular mass;

CaO

— formula unit mass

O_2

— formula unit mass only

H_2O

— formula unit mass only

Section C: Calculations and Applications

Question 13mcq

Calculate the molecular mass of sulphuric acid,

H_2SO_4

. Given

H=1

S=32

O=16

49\,u

82\,u

98\,u

114\,u

Question 14mcq

Calculate the formula unit mass of magnesium chloride,

MgCl_2

. Given

Mg=24

Cl=35.5

59.5\,u

71\,u

83\,u

95\,u

Question 15mcq

For methane,

CH_4

, what should a simple electron dot diagram show?

A.Carbon sharing one pair of electrons with each of four hydrogen atoms.

B.Carbon gaining four protons from hydrogen.

C.Hydrogen atoms forming four ionic bonds with chlorine.

D.A lattice of positive and negative carbon ions.

Question 16mcq

Which model best represents the law of constant proportions for water?

A.Some models use any number of hydrogen atoms.

B.Every model uses two hydrogen atoms for one oxygen atom.

C.Water models contain only oxygen atoms.

D.Each model changes formula depending on colour.

Question 17mcq

Why is understanding ions useful in daily life?

A.It proves all substances are elements.

B.It shows chemical symbols are unnecessary.

C.It helps explain substances like salts and their behaviour in water.

D.It means compounds have no fixed formula.

Question 18mcq

Why does the total mass remain the same in a closed chemical reaction even though new substances are formed?

A.The colour of products keeps the mass unchanged.

B.The product always becomes lighter than the reactants.

C.Only liquids follow the law of conservation of mass.

D.Atoms are rearranged, but they are not created or destroyed.

Section D: Full Chapter Readiness

Question 19mcq

A student reacts vinegar and baking soda in an open beaker and finds that the final mass is lower. What is the best improvement to test conservation of mass?

A.Use more vinegar so the reaction becomes faster.

B.Ignore the missing mass because gases have no mass.

C.Measure only the mass of the solid reactant before reaction.

D.Repeat the reaction in a sealed container and weigh the whole setup before and after.

Question 20mcq

Pure water always contains hydrogen and oxygen in the mass ratio

1:8

. If a pure water sample contains

4\,g

of hydrogen, how much oxygen will it contain?

8\,g

4\,g

32\,g

36\,g

Question 21mcq

Which statement is consistent with Dalton’s atomic theory?

A.Atoms are destroyed whenever a compound is formed.

B.A compound is formed by mixing elements in any random proportion.

C.Elements are made of molecules only, not atoms.

D.Atoms of the same element are identical in mass and chemical properties.

Question 22mcq

Which option correctly matches an atom, a molecule of an element, and a compound?

O_2

= atom,

O

= compound,

H_2O

= molecule of an element

H_2O

= atom,

O_2

= compound,

O

= mixture

O

= molecule of an element,

O_2

= compound,

H_2O

= atom

O

= atom,

O_2

= molecule of an element,

H_2O

= compound

Question 23mcq

Which pair shows one molecule of an element followed by one molecule of a compound?

NaCl

and

Cl_2

CO_2

and

H_2O

Cl_2

and

HCl

Na

and

Mg

Question 24mcq

Which comparison between sodium chloride and carbon dioxide is most accurate?

A.Sodium chloride is covalent and carbon dioxide is ionic.

B.Both are ionic compounds because both contain non-metals only.

C.Sodium chloride is ionic, while carbon dioxide is covalent.

D.Both are covalent compounds because both have chemical formulae.