MCAS Chemistry Practice Test: Get Ready for Your Exam! (2024 Updated)

The Massachusetts Comprehensive Assessment System (MCAS) test in chemistry is administered by the Massachusetts Department of Elementary & Secondary Education.

This test covers the topics of atomic structure and periodicity, bonding and reactions, properties of matter and thermochemistry, solutions, equilibrium, and acid-base theory.

It contains realistic questions that provide not only review key chemistry concepts, but also familiarize one with the MCAS exam format.

MCAS Chemistry Exam Practice

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Question 1

Please mark the statement which explains why the temperature of ice and water, when mixed together, will remain constant as heat is added:

A	Heat is stored in the solid ice.
B	Heat is stored in the liquid water.
C	Heat is used to turn the solid ice into liquid water.
D	Heat is absorbed equally by the solid ice and the liquid water.

Question 1 Explanation:

Heat is used to turn solid ice into liquid water.

Question 2

Please mark the statement which explains why the alkali metal family contains elements that are highly reactive:

A	Alkali metals are easily ionized.
B	Alkali metals are negatively charged.
C	Alkali metals have an odd number of protons.
D	Alkali metals have an odd number of electrons.

Question 2 Explanation:

Alkali metals are easily ionized.

Question 3

Please mark the statement that describes the role of a buffer:

A	The buffer increases the rate of a reaction.
B	The buffer keeps the pH of a solution within a small range.
C	The buffer changes the oxidation states of elements in a compound.
D	The buffer shifts the reaction equilibrium to favor more product formation.

Question 3 Explanation:

The buffer's role is to keep the pH of a solution within a small range.

Question 4

Please mark the correct quantity of grams of KCI dissolved in 2.00 L of a 0.200 M solution of KCl:

A	0.400 g
B	14.9 g
C	29.8 g
D	400 g

Question 4 Explanation:

29.8 g

Question 5

Why would a leaf that floats on a pond stay on top of the water?

A	The leaf has nonpolar covalent bonds between its atoms.
B	The density of the water is lesser than the density of the leaf.
C	The hydrogen bonding holds the water molecules tightly together.
D	The hydrogen and oxygen atoms in the water are chemically bonded.

Question 5 Explanation:

The hydrogen bonding holds the water molecules tightly together.

Question 6

Each of the atoms of silver (Ag) have 47 protons. Please mark one of the following statements which describe an atom of silver:

A	This atom has no neutrons.
B	This atom has 47 electrons.
C	This atom has 23 neutrons and 24 electrons.
D	This atom has a total of 94 neutrons and electrons.

Question 6 Explanation:

The atom of silver has 47 electrons.

Question 7

A polar covalent bond holds together a hydrogen fluoride (HF) molecule, a hydrogen atom, and a fluorine atom. Why is this bond polar?

A	Due to the large difference in the atomic radii of hydrogen and fluorine atoms.
B	Due to the large difference in the atomic masses of hydrogen and fluorine atoms.
C	Due to the large difference in the electronegativities of hydrogen and fluorine atoms.
D	Due to the large difference in the number of electrons of hydrogen and fluorine atoms.

Question 7 Explanation:

This bond is polar due to the large difference in the electronegativities of hydrogen and fluorine atoms.

Question 8

Please mark the action which occurs in an ionic bond?

A	Two ions share protons.
B	Two ions share electrons.
C	Similarly charged ions attract.
D	Oppositely charged ions attract.

Question 8 Explanation:

Oppositely charged ions attract.

Question 9

Please mark the three states of water in order of increasing entropy:

A	ice, liquid, vapor
B	liquid, ice, vapor
C	ice, vapor, liquid
D	vapor, liquid, ice

Question 9 Explanation:

ice, liquid, vapor

Question 10

Please mark the activity which causes liquid molecules to overcome intermolecular attractive forces and become gas molecules:

A	Adding a solute to the liquid
B	Adding a catalyst to the liquid
C	Increasing the temperature of the liquid
D	Increasing the air pressure above the liquid

Question 10 Explanation:

Increasing the temperature of the liquid.

Question 11

Please mark the observed property which is reliable in classifying a substance as a metal:

A	good conductor of heat
B	low melting temperature
C	unreactive with other elements
D	crumbles when hit by a hammer

Question 11 Explanation:

good conductor of heat.

Question 12

Please mark the observed property which is reliable in classifying a substance as a metal:

A	good conductor of heat
B	low melting temperature
C	unreactive with other elements
D	crumbles when hit by a hammer

Question 12 Explanation:

good conductor of heat.

Question 13

Please mark the one which is most directly involved in chemical bonding:

A	protons
B	neutrons
C	alpha particles
D	valence electrons

Question 13 Explanation:

valence electrons

Question 14

Please mark the statement which describes an exothermic reaction but not an endothermic reaction:

A	During the reaction, energy is destroyed.
B	Energy is used to form chemical bonds.
C	Energy is used to break chemical bonds.
D	Energy is released as heat during the reaction.

Question 14 Explanation:

Energy is released as heat during the reaction.

Question 15

Please mark the statement which explains why oxygen is classified as a pure substance while air is classified as a mixture:

A	Oxygen is more reactive than air.
B	Oxygen has a higher density than air.
C	Oxygen undergoes phase changes, whereas air is always a gas.
D	Oxygen contains only one substance, but air contains several substances.

Question 15 Explanation:

Oxygen contains only one substance, but air contains several substances.

Question 16

Please mark one of the following statements which best describes milk, considering that the pH of milk is 6.4:

A	It is very basic.
B	It is very acidic.
C	It is slightly basic.
D	It is slightly acidic.

Question 16 Explanation:

It is slightly acidic.

Question 17

What is reason for the change of barium to the element lanthanum after a course of several months:

A	exposure to air
B	radioactive decay
C	reactions with the container wall
D	absorption of moisture from the air

Question 17 Explanation:

radioactive decay

Question 18

Please mark the statement that applies to the mixture of water and salt:

A	This mixture is a solution.
B	This mixture is a pure substance.
C	The salt is not evenly distributed throughout this mixture.
D	The salt chemically combines with the water in this mixture.

Question 18 Explanation:

This mixture is a solution.

Question 19

Please mark the statement which explains why elements in the same family of the periodic table have similar bonding properties:

A	The elements have similar atomic sizes.
B	The elements have similar atomic masses.
C	The elements have similar numbers of protons.
D	The elements have similar valence electron configurations.

Question 19 Explanation:

The elements have similar valence electron configurations.

Question 20

Please mark the statement which describes all the exothermic reactions:

A	Exothermic reactions form gases.
B	Exothermic reactions require a catalyst.
C	The energy of the reactants is lower than the energy of the products.
D	The energy of the reactants is higher than the energy of the products.

Question 20 Explanation:

The energy of the reactants is higher than the energy of the products.

Question 21

Why potassium (K) reacts easily with bromine (Br)?

A	Because potassium and bromine both have valence electrons in the fourth energy level.
B	Because potassium and bromine have the same number of electrons in their highest energy levels.
C	Because potassium has one electron in its highest energy level, and bromine needs one electron to complete its highest energy level.
D	Because potassium needs one electron to complete its highest energy level, and bromine has an extra electron in its highest energy level.

Question 21 Explanation:

Because potassium has one electron in its highest energy level, and bromine needs one electron to complete its highest energy level.

Question 22

Why atoms bond?

A	In order to make new substances.
B	In order to become less chemically stable.
C	In order to change from a liquid to a solid.
D	In order to become more chemically stable.

Question 22 Explanation:

Atoms bond in order to become more chemically stable.

Question 23

Please mark the statement that accounts best for the positive charge of the potassium ions, in a case when a sample of potassium chloride dissolves in water, it separates into potassium ions and chloride ions:

A	Potassium ions have extra mass.
B	Potassium ions have a large volume.
C	Potassium ions have fewer electrons than protons.
D	Potassium ions have a high density of neutrons and protons.

Question 23 Explanation:

Potassium ions have fewer electrons than protons.

Question 24

Please mark one of the following characteristics which allow blood to resist changes in pH:

A	acidity
B	basicity
C	buffering capacity
D	clotting factors

Question 24 Explanation:

buffering capacity

Question 25

Please mark the statement which applies to a nuclear fission reaction:

A	The reaction has no commercial applications.
B	The reaction takes place only at very high temperatures.
C	The reaction produces only short-lived radioactive waste.
D	The reaction releases large amounts of energy when nuclei split apart.

Question 25 Explanation:

The reaction releases large amounts of energy when nuclei split apart.

Question 26

Please write how much gold-198 remains in the sample, if a 100 g sample of gold-198 decays for 9 days, considering that gold-198 has a half-life of approximately 3 days:

A	13 g
B	25 g
C	33 g
D	50 g

Question 26 Explanation:

13 g

Question 27

Please mark the event which occurs when the temperature of a sample of formaldehyde rises from -93°C to -91°C, considering that formaldehyde in solution is used as a preservative and has a melting point of -92°C:

A	The molecules move more freely.
B	The molecules lose electrical charge.
C	The molecules break apart into atoms.
D	The molecules become fixed in a crystal structure.

Question 27 Explanation:

The molecules move more freely.

Question 28

Please mark the solution which has the highest concentration of solute:

A	1.0 mol solute in 200 mL solvent
B	2.0 mol solute in 500 mL solvent
C	3.0 mol solute in 1 L solvent
D	4.0 mol solute in 1.5 L solvent

Question 28 Explanation:

1.0 mol solute in 200 mL solvent

Question 29

Why does a wet covering keep the water cool, in a case when a biker carries drinking water in a metal canteen which, during the summer, he covers with a wet cloth to prevent the water from heating?

A	Because a wet covering transfers coolness to the water in the canteen.
B	Because a wet covering insulates the canteen better than a dry covering.
C	Because evaporation of water from the covering transfers heat away from the canteen.
D	Because condensation of water from the covering transfers heat away from the canteen.

Question 29 Explanation:

Because evaporation of water from the covering transfers heat away from the canteen.

Question 30

What happens to a gas inside a balloon as the external pressure on the balloon decreases and the temperature stays constant?

A	The volume increases.
B	The volume decreases.
C	The molecular speed increases.
D	The molecular speed decreases.

Question 30 Explanation:

The volume increases.

Question 31

Why does ice float on water?

A	Because water has a higher specific heat than ice.
B	Because ice has the same molecular mass as water.
C	Because heat is absorbed when water changes from the solid state to the liquid state.
D	Because hydrogen bonding causes water to be less dense in the solid state than in the liquid state.

Question 31 Explanation:

Because hydrogen bonding causes water to be less dense in the solid state than in the liquid state.

Question 32

What did the scientists learn about the atom from Rutherford's gold foil experiment?

A	They learned that atoms combine in simple ratios to form compounds.
B	They learned that electrons travel around the nucleus of an atom in concentric circular paths.
C	They learned that the mass of an atom and its positive charge are concentrated in the nucleus.
D	They learned that the atomic mass of an atom is equal to the number of protons and neutrons in the nucleus.

Question 32 Explanation:

They learned that the mass of an atom and its positive charge are concentrated in the nucleus.

Question 33

Please mark the metalloid:

A	magnesium
B	silicon
C	phosphorus
D	cobalt

Question 33 Explanation:

silicon

Question 34

What holds two elements in a molecule who have the same electronegativity values together and why?

A	They are kept together by an ionic bond, because electrons transfer from one element to the other.
B	They are kept together by a nonpolar covalent bond, because the elements share electrons equally.
C	They are kept together by a polar covalent bond, because the elements do not share electrons equally.
D	They are kept together by an intermolecular force, because the elements do not form a chemical bond.

Question 34 Explanation:

They are kept together by a nonpolar covalent bond, because the elements share electrons equally.

Question 35

Why water vapor condenses as temperature decreases?

A	Because of the collisions between water vapor molecules becomes elastic.
B	Because of the water vapor molecules which chemically react when they collide.
C	Because of the water vapor molecules which are pulled together by the force of gravity.
D	Because of the attractive forces between water vapor molecules which overcome molecular motion.

Question 35 Explanation:

Because of the attractive forces between water vapor molecules which overcome molecular motion.

Question 36

Please mark the element which is located in period 3 and is a member of the halogen family:

A	argon (Ar)
B	bromine (Br)
C	chlorine (Cl)
D	sulfur (S)

Question 36 Explanation:

chlorine (Cl)

Question 37

What is the difference between a mixture and a pure substance?

A	The difference is that a mixture tends to be homogenous, while a pure substance tends to be heterogeneous.
B	The difference is that a mixture has a specific melting point, while the melting point of a pure substance can vary.
C	The difference is that the density of a mixture can change with temperature, but the density of a pure substance cannot change.
D	The difference is that the composition of a mixture can vary from sample to sample, but the composition of a pure substance is always the same.

Question 37 Explanation:

The difference is that the composition of a mixture can vary from sample to sample, but the composition of a pure substance is always the same.

Question 38

Please mark the evidence which supports Bohr’s idea that electrons occupy specific energy levels within an atom:

A	Each element has physical and chemical properties that are unique to that element and different from those of other elements.
B	Beryllium atoms bombarded with alpha particles produce beams that are not influenced by magnetic fields.
C	Each element emits a unique bright-line spectrum when it falls from an excited state to a ground state.
D	Sodium atoms become positive ions when they lose electrons.

Question 38 Explanation:

Each element emits a unique bright-line spectrum when it falls from an excited state to a ground state.

Question 39

Please mark the right result regarding the volume of a ball that contains 0.85 mol of air, considering that the air inside a beach ball is at a temperature of 25°C and a pressure of 1.0 atm:

A	6.1 L
B	21 L
C	27 L
D	1.7 L

Question 39 Explanation:

21 L

Question 40

Please mark the description which correctly pairs a phase of matter:

A	Liquid: Particles are more strongly attached to one another than when in the solid phase.
B	Liquid: Particles expand to fill any container in which they are placed.
C	Gas: Particles have higher amounts of energy than when in the liquid phase.
D	Solid: Particles have no motion.

Question 40 Explanation:

Gas: Particles have higher amounts of energy than when in the liquid phase.

Question 41

Please mark the section of the periodic table which contains only metals:

A	group 2
B	group 18
C	period 2
D	period 6

Question 41 Explanation:

group 2

Question 42

Please mark the bonding which is responsible for the water strider to be able to walk a water surface without sinking:

A	ionic bonding
B	oxygen bonding
C	hydrogen bonding
D	nonpolar covalent bonding

Question 42 Explanation:

hydrogen bonding

Question 43

Mary left a bottle of cola and a bottle of distilled water outside overnight. In the morning, she found only one of the liquids frozen. Please mark the liquid which was frozen and the reason for this reaction:

A	The distilled water froze because pure substances have a higher freezing point than solutions.
B	The sugary drink froze because solutions have a higher freezing point than pure substances.
C	The distilled water froze because pure substances are denser than solutions.
D	The sugary drink froze because solutions are denser than pure substances.

Question 43 Explanation:

The distilled water froze because pure substances have a higher freezing point than solutions.

Question 44

Please mark the characteristic of an element that can be determined by considering the specific position of the element on the periodic table:

A	the density of the solid
B	the radius of each ion
C	the number of protons in each atom
D	the boiling point of the liquid

Question 44 Explanation:

the number of protons in each atom

Question 45

Please mark the order of solutions, from most acidic to most basic:

A	battery acid, blood, laundry detergent, lemon juice
B	laundry detergent, blood, lemon juice, battery acid
C	battery acid, lemon juice, blood, laundry detergent
D	lemon juice, battery acid, blood, laundry detergent

Question 45 Explanation:

battery acid, lemon juice, blood, laundry detergent

Question 46

Please mark the explanation in regard to the reason why the bond in hydrogen chloride (HCI) is polar covalent:

A	The electronegativity of chlorine is greater than that of hydrogen.
B	The diameter of a chlorine atom is greater than that of a hydrogen atom.
C	The atomic mass of chlorine is greater than that of hydrogen.
D	The number of valence electrons in a chlorine atom is greater than that in a hydrogen atom.

Question 46 Explanation:

The electronegativity of chlorine is greater than that of hydrogen.

Question 47

Please mark the sample of sugar which will dissolve fastest in a pitcher of lemonade:

A	5 g of granulated sugar in 5°C lemonade
B	5 g of cubed sugar in 20°C lemonade
C	5 g of granulated sugar in 20°C lemonade
D	5 g of cubed sugar in 5°C lemonade

Question 47 Explanation:

5 g of granulated sugar in 20°C lemonade

Question 48

Please mark the comparison which describes subatomic particles:

A	A proton has a positive charge and a mass smaller than the mass of an electron.
B	An electron has a negative charge and a mass larger than the mass of a proton.
C	A neutron has a negative charge and a mass smaller than the mass of a proton.
D	A neutron has a neutral charge and a mass larger than the mass of an electron.

Question 48 Explanation:

A neutron has a neutral charge and a mass larger than the mass of an electron.

Question 49

Please mark the method which can separate components of some mixtures:

A	a chemical reaction
B	a filtration process
C	a nuclear reaction
D	an electrolysis process

Question 49 Explanation:

a filtration process

Question 50

Please mark the description of separation of the components of a mixture:

A	Salt is isolated from seawater through evaporation.
B	Propane reacts with oxygen to form carbon dioxide and water.
C	Calcium carbonate decomposes to form calcium oxide and carbon dioxide.
D	Water is broken down into hydrogen and oxygen.