# Atomic Structure Practice Questions

Q1.  Write down the numbers of protons, neutrons and electrons in:

i) a 39K+ ion,

ii) hydrogen (H+) ion,

iii) hydride (H) ion

Q2.   Write the mass number, atomic number and symbol for the atom/ion with:

i) 20 neutrons, 17 protons and 18 electrons

ii) a magnesium ion with 10 electrons and 12 neutrons

Q3.  The table below shows the isotopes of magnesium and their natural abundances. Show that the relative atomic mass of magnesium is 24.3, as indicated in the periodic table.

 Isotope: 24Mg 25Mg 26Mg Relative isotopic mass 24.0 25.0 26.0 % abundance 78.6 10.1 11.3

Q4.   Determine the relative atomic mass of neon to 1 decimal place, given the following mass spectrometry results:  20Ne = 90%; 22Ne = 10%

Q5.   The Ar of lithium is 6.92. The most common isotope is 7Li with an abundance of 92%.  Determine the mass number of the other isotope.

Q6.   Calculate relative molecular/formula masses for:

i) propanol (C37OH)

ii) sulphur dioxide

iii) nitrogen gas

iv) trichloromethane (CHCl3)

v) ammonium nitrate

Q7.   Work out the molar masses (to 1 decimal place) of the following substances:

i) HNO3

ii) Na2CO3.10H2O

iii) (NH4)2SO4.Fe2(SO4)3.24H2O

Q8.   Work out the mass (to 2 sig figs) of:

i) 10 mole of zinc

ii) 1.0 mole of potassium hydrogencarbonate

iii) 0.050 moles of aluminium oxide

Q9.   How many moles are there (to 2 sig figs) in:

i) 7g of bromine molecules

ii) 5g silver nitrate

iii) 2.0kg of sodium hydroxide

Q10.       i) How many molecules are there in 79.9g of Br­2 ?

ii) How many Br atoms are there in 159.8g of Br2 ?

iii)  How many oxygen atoms in 8.5g AgNO3 ?

iv) Polyethene consists of long chains of –CH2– groups. In a polyethene bag the average chain length was found to be 100,000 carbon atoms. Calculate the average mass of a chain, and hence the average number of chains in a plastic bag weighing 2g. Give your answer to an appropriate number of significant figures.

Q11.        i) What is the volume (in dm3) of 300g of hydrogen at r.t.p.?

ii) How many moles of nitrogen at r.t.p. are there in 100cm3 of the gas?

iii) Calculate the density in g cm-3 of carbon dioxide at r.t.p.