"IUPAC inorganic nomenclature: binary and ternary compounds"

At home we have very different chemical substances: table salt is $\text{NaCl}$, the gas in fizzy drinks is $\text{CO}_2$, battery acid is $\text{H}_2\text{SO}_4$ and a common fertiliser is $\text{KNO}_3$. The figure represents the particles of the four substances.

1. a) Count how many different chemical elements make up each substance.
2. b) Classify them into binary compounds (two elements) or ternary compounds (three elements).

Name these common substances according to IUPAC nomenclature:

1. a) $\text{NaCl}$, the salt we use for cooking.
2. b) $\text{CO}_2$, the gas we exhale when breathing.
3. c) $\text{CaO}$, quicklime used in construction.

Write the formula of these binary compounds:

1. a) Carbon monoxide, a highly toxic gas released from car exhausts.
2. b) Sulphur dioxide, the gas released by volcanoes.
3. c) Sodium chloride, table salt.

An old bicycle frame gets covered in rust and the red paint of a painting contains a different iron oxide: iron can form $\text{FeO}$ and $\text{Fe}_2\text{O}_3$. The figure shows how the atoms combine in each oxide.

1. a) Name both compounds using Stock nomenclature (iron oxide followed by the oxidation number in brackets).
2. b) Explain why this number is necessary in the case of iron, whereas for calcium oxide, $\text{CaO}$, it is not.

City air contains gases from traffic and industry. Name them using the prefixes mono-, di- and tri-:

1. a) $\text{SO}_2$
2. b) $\text{SO}_3$
3. c) $\text{NO}_2$
4. d) $\text{N}_2\text{O}$

Write the formula of these oxides from their systematic names: nitrogen dioxide, dinitrogen monoxide and diphosphorus pentoxide. Underline in each name the prefix that gave you the clue for each subscript.

Sodium always forms the $\text{Na}^+$ ion, and the hydroxide group is the $\text{OH}^-$ ion. The diagram represents the ions involved, along with their charge.

1. a) Explain what it means for a chemical formula to be electrically neutral.
2. b) Work out the formula of sodium hydroxide.
3. c) Calcium forms the $\text{Ca}^{2+}$ ion. Work out, by reasoning with the charges, the formula of calcium hydroxide.

Milk of magnesia is an antacid containing magnesium hydroxide. Magnesium forms the $\text{Mg}^{2+}$ ion, and the hydroxide ion is $\text{OH}^-$.

1. a) Deduce the formula of magnesium hydroxide by applying the rule of charge balance.
2. b) Verify that in your formula the positive and negative charges add up to zero.

Many drain unblockers contain the substance $\text{NaOH}$ as their active ingredient.

1. a) Write its IUPAC name.
2. b) State which elements make it up and how many atoms of each element are in its formula.

Slaked lime, with formula $\text{Ca(OH)}_2$, is used in vegetable gardens and building work. The figure shows its grouped atoms.

1. a) Write its IUPAC name.
2. b) Taking into account that the subscript $2$ outside the brackets multiplies everything inside, state how many oxygen and hydrogen atoms are in one formula unit.

A car battery contains $\text{H}_2\text{SO}_4$ and in an open fizzy drink $\text{H}_2\text{CO}_3$ forms. Write the names of these two oxoacids and state which element gives its name to each one.

A marble worktop, an eggshell and chalk are essentially the same substance: $\text{CaCO}_3$.

1. a) Write its IUPAC name.
2. b) State the three elements that make it up.

The label of a fertiliser lists nitric acid and potassium nitrate. Write the formula of each and indicate which element their names share.

Sodium sulphate, $\text{Na}_2\text{SO}_4$, is obtained from sulphuric acid, $\text{H}_2\text{SO}_4$.

1. a) Compare the two formulas and explain what has changed.
2. b) The sulphate ion is $\text{SO}_4^{2-}$. Justify why two sodium ions, $\text{Na}^+$, are needed in the formula of the salt.

Another widely used fertiliser is calcium nitrate. Knowing that calcium forms the $\text{Ca}^{2+}$ ion and that the nitrate ion is $\text{NO}_3^-$:

1. a) Work out its formula.
2. b) State how many oxygen atoms one formula unit contains.

Washing soda, used to remove tough stains, is sodium carbonate. The carbonate ion is $\text{CO}_3^{2-}$ and sodium forms the $\text{Na}^+$ ion.

1. a) Work out the formula of sodium carbonate.
2. b) Compare it with that of calcium carbonate, $\text{CaCO}_3$, and explain why one contains two sodium atoms and the other just one calcium atom.

Compare the formulas of the three most common oxoacids: $\text{H}_2\text{SO}_4$, $\text{HNO}_3$ and $\text{H}_2\text{CO}_3$. The figure shows the particle model of each one.

1. a) What features do the three formulas share? Think about which elements appear and in which position.
2. b) Which element changes from one acid to another and gives its name to each one?
3. c) Order them from the smallest to the largest number of oxygen atoms.

A student writes in their notebook that the formula of calcium oxide is $\text{CaO}_2$, "because calcium and oxygen are both two".

1. a) Explain why this is incorrect, using the charges of the $\text{Ca}^{2+}$ and $\text{O}^{2-}$ ions.
2. b) Write the correct formula and name it.

In supermarkets and pharmacies products do not carry IUPAC names: caustic soda, muriatic acid, slaked lime and aqua fortis are, in fact, $\text{Ca(OH)}_2$, $\text{HCl}$, $\text{HNO}_3$ and $\text{NaOH}$, though not in this order.

1. a) Match each commercial name with its formula.
2. b) Write the IUPAC name of all four substances.
3. c) Suggest an advantage of putting systematic names on labels instead of commercial names.

A garden fertiliser lists two components on its label: potassium nitrate and sodium sulphate.

1. a) Write the formula of both.
2. b) Count the oxygen atoms in each formula.
3. c) Which of the two provides more oxygen per formula unit? Give reasons for your answer.

Chromium is a metal that can act with two different oxidation numbers: it forms the $\text{Cr}^{2+}$ and $\text{Cr}^{3+}$ ions.

1. a) Write the formulas of the two possible chromium chlorides, knowing that chlorine forms the $\text{Cl}^-$ ion.
2. b) Name both compounds using Stock nomenclature.
3. c) Explain, using charges, why two chlorine atoms are needed in one and three in the other.

Aircraft fuselages are made of aluminium because this metal becomes coated in a very thin layer of its oxide, which protects it. Aluminium forms the $\text{Al}^{3+}$ ion and oxygen forms the $\text{O}^{2-}$ ion.

1. a) Calculate how many ions of each type are needed for the total charge to be zero (find the lowest common multiple of the charges).
2. b) Write the formula of aluminium oxide.
3. c) Explain why it cannot be $\text{AlO}$.

Counting atoms also serves to check formulas. Answer giving reasons:

1. a) How many hydrogen atoms are in $3$ units of $\text{Ca(OH)}_2$?
2. b) How many oxygen atoms are in $4$ units of $\text{H}_2\text{SO}_4$?
3. c) How many sodium atoms are in $2$ units of $\text{Na}_2\text{SO}_4$?

The plaster cast used in hospitals to immobilise a fracture is calcium sulphate. Calcium forms the $\text{Ca}^{2+}$ ion and the sulphate ion is $\text{SO}_4^{2-}$.

1. a) Work out its formula and explain why in this case one ion of each type is sufficient.
2. b) Write it alongside that of sodium sulphate, $\text{Na}_2\text{SO}_4$, and explain the difference in subscripts by looking at the charges.