Smart Chemist

Which of these is chemical change?

• Water turns into ice

• Boiled water turns to steam

• Rusting of iron

• Expansion of balloon under hot conditions

Answer explanation

A chemical reaction occurs when chemical bonds are broken and formed to produce chemically different species.

Rusting is an oxidation reaction where iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide.

Which of the following is the property of gas?

• Has definite size

• Has definite volume

• Cannot be compressed

• Shape depends on container

Answer explanation

Gas molecules move around freely. They do not have specific shape and volume. Therefore, gas takes the shape of the container they are in.

Which of the following is a SI Base Unit?

• Pound (lb)

• Feet (ft)

• Fahrenheit (℉)

• Ampere (A)

Answer explanation

There are only 7 SI Base Unit : meter (m), second (s), mole (mol), kelvin (K), candela (cd), kilogram (kg) and ampere (A). While, pound (lb), feet (ft), Fahrenheit (℉) are Imperial units which are mostly used in the United States.

Who discovered electrons?

• Albert Einstein

• J.J. Thomson

• GP Thomson

• Ernest Rutherford

Answer explanation

In 1897, J.J. Thomson discovered the electron by experimenting with a cathode ray tube. He demonstrated that cathode rays were negatively charged particles in motion (electron).

Elements that have same atomic number but different nucleon number are called

• isotopes

• ions

• mixtures

• isoelectronic species

Answer explanation

The atomic number is the number of protons of an atom. Nucleon is the collective term for protons and neutrons. When elements have different nucleon number but the same proton number, it indicates that there are different number of neutrons in their nuclei. In Science, we say that these elements are isotopes.

What is a Redox reaction?

• A reaction that undergoes oxidation and reduction simultaneously

• A reaction that involves change in pH value

• A reaction that forms precipitate

• All of the above

Answer explanation

Redox reaction is a reaction that involves the transfer of electrons from a reducing agent to an oxidising agent, causing the change in oxidation number of elements.

Which of the following are states of matter?

• Liquid

• Solid

• Plasma

• All of the above

Answer explanation

There are four states of matter observable in life, namely solid, liquid, gas and plasma. Plasma is like gas (has no fixed shape or volume, and is less dense than solid or liquid) but it is electrically conductive and responds to magnetic field.

Which of the following is Gas Law?

• Law of conservation of mass

• Avogadro’s Law

• Hess’s Law

• Kepler’s law

Answer explanation

Avogadro’s law is one of the gas laws that relates the volume of a gas to the amount of gas present. It states that, at the same temperature and pressure, equal volumes of all gases contain the same number of molecules.

What is the simplest form of an element?

• Molecule

• Atom

• Compound

• All of the above

Answer explanation

Atoms are the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas and plasma is composed of neutral or ionized atoms.

Who first published the periodic table?

• John Dalton

• Julius Lothar Meyer

• Henry Moseley

• Dmitri Mendeleev

Answer explanation

He formulated the Periodic Law and created a farsighted version of the periodic table of elements.