Relative Masses of Atoms & Molecules (CIE AS Chemistry)

The element chromium has several naturally occurring isotopes whose abundances are shown in Table 1.1

Table 1.1

Calculate the relative atomic mass of chromium to two decimal places.

Chromium can form a variety of compounds. Chromium(III) chloride hydrate is the dark green complex [CrCl₂(H₂O)₄]Cl.

Write the full electronic configuration for the chromium ion in this compound.

Calculate the relative molecular mass of [CrCl₂(H₂O)₄]Cl.

Nitrous oxide is used as a sedative in dentistry and has the formula N₂O.
Different sources of N₂O contain different ratios of ¹⁴N and ¹⁵N.           

State the name of the instrument used to distinguish between ¹⁴N and ¹⁵N and outline two characteristic differences seen in the analysis of ¹⁴N and ¹⁵N.

A sample of nitrous oxide was enriched so that it contained 4% by mass of ¹⁵N. Calculate the relative molecular mass of the resulting nitrous oxide.

An atom has twice as many protons, and twice as many neutrons, as an atom of ¹⁵N.

Determine the chemical symbol for this atom, including the mass number, and deduce the number of electrons.

Ethanoic acid has a relative molecular mass of 60.0.

Explain what is meant by the term relative molecular mass.

State the empirical formula of ethanoic acid.

Ethanoic acid reacts with aqueous sodium carbonate to form a neutral salt solution and a gas.

Name the salt produced in this reaction and calculate its relative formula mass.

Copper is an easily moulded base metal that is often added to precious metals to improve their elasticity, flexibility, hardness, colour, and resistance to corrosion.

Table 3.1 shows the number of protons, neutrons and electrons of different isotopes and ions of copper.

Calculate the percentage abundance of ⁶³Cu with a mass of 62.9296 and ⁶⁵Cu with a mass of 64.9278, when the average mass of the Cu isotope is 63.546.

Express your answer to an appropriate number of significant figures.

Explain why the isotopes of copper exhibit the same chemical reactions but their densities differ.

Copper can form a salt with chlorine to form copper(II) chloride. This reacts with sodium phosphate to form two different salts only.

Write a balanced equation for this reaction.