4N Sci Chem Paper 3

A series of experiments are carried out to rank the reactivity of four different metals. In each experiment, an equal length of metal strip was added and approximately 30cm³ of hydrochloric acid is poured into a conical flask. The more reactive the metal, the faster the time taken for the metal to fully dissolve.

Which three pieces of apparatus would be needed for the experiment?

• 1, 3 and 5

• 2, 3 and 5

• 3, 4 and 5

• 4, 5 and 6

Answer explanation

Need to measure time, volume of acid and also a container to hold the experiment.

A paper chromatogram was prepared using a mixture of substances. After drying, the chromatogram obtained is shown. Which statement is incorrect?

• The start line should be drawn with a pencil.

• The chromatography paper must be placed with the solvent below level Z.

• Substance X is less soluble compared to substance Y.

• There are two substances present in the mixture.

Answer explanation

The higher the spot, the more soluble it is.

An element, R, has p protons and n neutrons in its nucleus. Which row gives a possible correct number of protons, neutrons in a negative ion of an isotope of R?

• A

• B

• C

• D

Answer explanation

Isotopes have different number of neutrons but same number of protons.

Negative ion means it has more electrons than protons.

What is the number obtained when the proton number is subtracted from the nucleon number?

• Number of neutrons in the nucleus

• Number of protons and electrons in the atom

• Number of protons and neutrons in the atom

• Number of protons in the nucleus

Answer explanation

Nucleon number is the sum of number of protons and the number of neutrons,

Which of the following statements about elements, mixtures and compounds are correct?

• 1 and 3

• 1 and 4

• 2 and 3

• 2 and 4

Answer explanation

Compounds are substances containing two or more atoms of the different type that are combined chemically.

Elements cannot be broken down into simpler substances by chemical processes.

The table below shows the electronic configuration of four elements. Which of the following shows the correct formula for a covalent compound formed from the elements given?

• PR

• SQ₄

• RQ₂

• R₂S

Answer explanation

P is noble gas and does not form bonds. R is a metal. Q and S are non-metals and they will form covalent bonds. One S shares its 4 electrons with 4 Q.

The table below shows the properties of sodium chloride and oxygen. Which set of properties is incorrect?

• A

• B

• C

• D

Answer explanation

Sodium chloride is an ionic compound with high melting point while oxygen is a simple covalent compound with low melting point.

Solution U has a pH of 4. What happens to the pH when a few drops of sodium hydroxide are added into solution U?

• pH becomes 0

• pH decreases

• pH increase

• pH remains the same

Answer explanation

U is acidic and sodium hydroxide (an alkali) neutralizes it so pH increase.

Which two substances react to give salt and water only?

• hydrochloric acid and copper (II) oxide

• magnesium and sulfuric acid

• zinc carbonate and hydrochloric acid

• ammonium chloride and sodium hydroxide

Answer explanation

Acid reacts with base (metal oxide or hydroxide) to give salt and water only.

Which of the following oxides reacts with both acids and bases?

• carbon monoxide

• aluminium oxide

• magnesium oxide

• sulfur dioxide

Answer explanation

An amphoteric oxide reacts with both acids and bases. Amphoteric oxides are lead (II) oxide, aluminium oxide and zinc oxide