Exercises: Simple substances, ions and inorganic compounds

On the label of an isotonic drink, the ions $\text{Na}^+$, $\text{K}^+$, $\text{Cl}^-$ and $\text{Mg}^{2+}$ are listed, which replenish the salts lost through sweat during exercise.

1. a) Write down the name of each of the four ions.
2. b) Classify them into cations and anions and explain, based on the sign of their charge, how they differ from each other.
3. c) Reason why the sodium ion is named the same as the atom it comes from, whereas the chloride ion changes the ending of the name of chlorine.

Air is a mixture of substances: $\text{N}_2$, $\text{O}_2$, $\text{O}_3$ (in the ozone layer), $\text{Ar}$, $\text{CO}_2$ and water vapour, $\text{H}_2\text{O}$. The figure represents the particles of oxygen and ozone.

1. a) Name the first three substances.
2. b) Classify all six into simple or compound substances and justify the criterion you have applied.
3. c) Oxygen and ozone are composed solely of oxygen atoms and yet are different substances: explain what sets them apart and state what simple substances of the same element displaying this relationship are called.

A car tailpipe emits carbon monoxide and carbon dioxide, and quicklime used in construction is calcium oxide.

1. a) Write down the formulae of carbon monoxide and carbon dioxide from the prefixes of their systematic names.
2. b) Deduce the formula of calcium oxide knowing that calcium forms the $\text{Ca}^{2+}$ ion and oxygen the $\text{O}^{2-}$ ion, and that every formula must be electrically neutral.
3. c) Over time, a balcony railing becomes coated with an oxide of formula $\text{FeO}$, in which iron has an oxidation number of $+2$: name it using Stock nomenclature.

Oven cleaner contains $\text{NaOH}$ and slaked lime used to whitewash walls is $\text{Ca(OH)}_2$. Both are hydroxides, compounds formed by a metal and the hydroxide ion, $\text{OH}^-$. The diagram shows how the ion charges balance each other in each compound.

1. a) Name the two compounds.
2. b) Explain what the brackets in the second formula indicate and count how many hydroxide ions are in each formula unit of the two compounds.
3. c) Reason, using the charges of the $\text{Na}^+$ and $\text{Ca}^{2+}$ ions, which of the two metals requires two hydroxide ions for the formula to be neutral.

A car battery contains $\text{H}_2\text{SO}_4$, $\text{HNO}_3$ is used in laboratories, and $\text{H}_2\text{CO}_3$ forms in an open soft drink. All three are oxoacids.

1. a) Name the three acids using traditional nomenclature.
2. b) State which non-metallic element gives its name to each of them.
3. c) Indicate which two elements always appear in the formula of any oxoacid, in addition to the one that gives it its name.

The marble of a worktop is $\text{CaCO}_3$, a garden fertilizer lists $\text{KNO}_3$ and Chile saltpetre, a natural fertilizer, is $\text{NaNO}_3$. All three are oxysalts: a metal bound to a negative ion containing oxygen.

1. a) Name the three salts.
2. b) State which negative ion two of them share and write its formula with its charge.
3. c) Explain from which oxoacids the carbonate and nitrate ions derive, and what change the ending of the acid's name (-ic) undergoes when converting into an ion (-ate).

Bicarbonate taken for heartburn is $\text{NaHCO}_3$; its IUPAC name is sodium hydrogencarbonate. The diagram compares the hydrogencarbonate ion with the carbonate ion.

1. a) Write down the name of the negative ion $\text{HCO}_3^-$ and explain what the prefix "hydrogen" before "carbonate" indicates.
2. b) Write down the formula and name of the oxoacid from which this salt derives.
3. c) Reason why it is called an acid salt: what does its negative ion retain that a normal salt, such as sodium carbonate, $\text{Na}_2\text{CO}_3$, no longer has?

In a village agricultural cooperative there are sacks of potassium chloride, potassium nitrate, calcium sulphate and sodium sulphate. Given: the ions $\text{K}^+$, $\text{Na}^+$, $\text{Ca}^{2+}$, $\text{Cl}^-$, $\text{NO}_3^-$ and $\text{SO}_4^{2-}$.

1. a) Write down the formula of each of the four salts, applying the principle that every formula must be electrically neutral.
2. b) In which of them did you need two positive ions for every negative ion? Justify your answer using the charges.

Chlorine disinfects swimming pool water and drinking water because it forms oxoacids. Depending on whether it has an oxidation number of $+1$, $+3$, $+5$ or $+7$, it forms the acids $\text{HClO}$, $\text{HClO}_2$, $\text{HClO}_3$ and $\text{HClO}_4$.

1. a) Name the four acids using traditional nomenclature, which uses the prefixes hypo- and per- and the suffixes -ous and -ic.
2. b) Assign each acid its corresponding chlorine oxidation number.
3. c) Write down the systematic name of $\text{HClO}$ and $\text{HClO}_4$ (guideline: prefix + "oxo" + stem of element + "ate" + "of hydrogen").

In the laboratory there are two bottles of iron chloride: one containing $\text{FeCl}_2$ and another containing $\text{FeCl}_3$. Iron can have oxidation numbers of $+2$ and $+3$, and chlorine forms the $\text{Cl}^-$ ion.

1. a) Name the two compounds using Stock nomenclature.
2. b) Name them using traditional nomenclature (suffixes -ous and -ic).
3. c) Justify, based on the charges of the ions, why one of the two contains two chloride ions and the other three.

Potassium permanganate, $\text{KMnO}_4$, is used in dilute solutions as a skin disinfectant and to purify drinking water.

1. a) Deduce the oxidation number of manganese knowing that potassium has $+1$ and oxygen has $-2$, and that the compound is neutral.
2. b) Name the compound using traditional nomenclature.
3. c) Following the guideline for oxysalts, name it using Stock nomenclature (prefix + "oxo" + stem + "ate" + oxidation number in Roman numerals + "of" + metal).

In caves, water rich in calcium ions, $\text{Ca}^{2+}$, and hydrogencarbonate ions, $\text{HCO}_3^-$, eventually forms stalactites.

1. a) Deduce the formula of calcium hydrogencarbonate and write its systematic name.
2. b) Check that in your formula the positive and negative charges add up to zero.
3. c) To lower the pH of a swimming pool, sodium hydrogensulphate is used, formed by the ions $\text{Na}^+$ and $\text{HSO}_4^-$: write its formula and explain why it is also considered an acid salt.

The sulphate sprayed on vineyards against fungi is $\text{CuSO}_4 \cdot 5\ \text{H}_2\text{O}$ and plaster used in construction is $\text{CaSO}_4 \cdot 2\ \text{H}_2\text{O}$. Both are hydrates: salts containing molecules of water of crystallisation. The figure represents a formula unit of hydrated copper sulphate.

1. a) Name the two salts without counting the water (copper has an oxidation number of $+2$ here).
2. b) Explain what the dot followed by the water molecules in each formula means.
3. c) Name both complete compounds indicating their corresponding hydrate prefix (penta-, di-) and state how many water molecules there are per formula unit.

Many nitrogen fertilisers contain the ammonium ion, $\text{NH}_4^+$, combined with the nitrate ion, $\text{NO}_3^-$, or with the sulphate ion, $\text{SO}_4^{2-}$.

1. a) Write down the name of the $\text{NH}_4^+$ ion and deduce the formula of ammonium nitrate.
2. b) Deduce the formula of ammonium sulphate, taking care with subscripts and the use of brackets.
3. c) Name the two salts and explain, using the charges, why in one case a single ammonium ion is sufficient while in the other two are required.

Hydrogen peroxide in first-aid kits is a solution of $\text{H}_2\text{O}_2$, hydrogen peroxide. In peroxides, oxygen forms the $\text{O}_2^{2-}$ ion, which is different from the oxide ion, $\text{O}^{2-}$. The diagram compares the two ions.

1. a) Name $\text{H}_2\text{O}_2$ and explain what makes peroxides distinct from oxides.
2. b) Deduce the formula of sodium peroxide, knowing that sodium forms the $\text{Na}^+$ ion.
3. c) Over time, hydrogen peroxide decomposes according to the equation $2\ \text{H}_2\text{O}_2 \rightarrow 2\ \text{H}_2\text{O} + \text{O}_2$: name the three participating substances and classify them into simple or compound substances.

Rockets and future fuel-cell cars use hydrogen, and storing it is a challenge: a solution being studied is metal hydrides, such as $\text{NaH}$ and $\text{CaH}_2$. In these, hydrogen has an oxidation number of $-1$, meaning it forms the $\text{H}^-$ ion.

1. a) Name the two hydrides.
2. b) Justify, using the charges of the $\text{Na}^+$ and $\text{Ca}^{2+}$ ions, why one contains a single hydrogen atom and the other two.
3. c) Explain what is striking about hydrogen having a negative oxidation number here, comparing it to water, $\text{H}_2\text{O}$, in which it has $+1$.

A sachet of effervescent health salts contains $\text{NaHCO}_3$ mixed with a solid acid; when added to water, it fizzles because $\text{CO}_2$ is released.

1. a) Write the IUPAC name of $\text{NaHCO}_3$ and the name of the gas released.
2. b) Explain why $\text{NaHCO}_3$ is an acid salt: which oxoacid it derives from and which hydrogen its negative ion still retains.
3. c) Write the formula and name of the salt that would be obtained if the second hydrogen of the acid were also replaced by sodium, and reason whether that salt would be an acid salt or a normal salt.
4. d) Count the oxygen atoms in the acid, the acid salt, and the normal salt, and explain what actually changes when hydrogen is replaced by sodium.

Bleach is a solution of $\text{NaClO}$, sodium hypochlorite, a salt derived from $\text{HClO}$ acid.

1. a) Name $\text{HClO}$ using traditional nomenclature and deduce the oxidation number of chlorine in it (hydrogen acts with $+1$ and oxygen with $-2$).
2. b) Name $\text{NaClO}$ using traditional and systematic nomenclature, taking into account the oxidation number you deduced.
3. c) The label forbids mixing bleach with ammonia, $\text{NH}_3$, or with limescale removers, which contain $\text{HCl}$: name these two substances (the name "ammonia" is accepted by IUPAC and $\text{HCl}$ is a binary acid) and explain why you think the manufacturer includes this warning.

On the label of a cured meat product, preservatives E-250 and E-251 appear, which are the salts $\text{NaNO}_2$ and $\text{NaNO}_3$.

1. a) Name the two salts using traditional nomenclature.
2. b) Deduce the oxidation number of nitrogen in each (sodium acts with $+1$ and oxygen with $-2$).
3. c) Name them using Stock notation.
4. d) Write the formula and traditional name of the two oxoacids from which they derive, and relate their endings (-ous and -ic) to the oxidation numbers you calculated.

When marking an exam, a teacher finds these formulas written: $\text{CaCl}$, $\text{NaCO}_3$, $\text{AlOH}_3$, and $\text{Fe}_2\text{SO}_4$. Data: the ions $\text{Ca}^{2+}$, $\text{Cl}^-$, $\text{Na}^+$, $\text{CO}_3^{2-}$, $\text{Al}^{3+}$, $\text{OH}^-$, and $\text{SO}_4^{2-}$; iron in the last compound acts with an oxidation number of $+3$.

1. a) Identify the error in each formula applying electrical neutrality and write the four corrected formulas.
2. b) Name the four correct compounds (the last one using Stock notation).
3. c) State in your own words the general rule to be applied when placing subscripts in the formula of an ionic compound.

Iron is everywhere: the ochre pigment in cave paintings is an iron oxide, anti-anaemia supplements contain an iron sulphate, and ferruginous waters contain its hydroxides. Iron acts with oxidation numbers $+2$ and $+3$; you have the ions $\text{O}^{2-}$, $\text{OH}^-$, and $\text{SO}_4^{2-}$ available.

1. a) Write the formulas of iron(II) oxide and iron(III) oxide.
2. b) Write the formulas of the two corresponding iron hydroxides.
3. c) Write the formulas of iron(II) sulphate and iron(III) sulphate.
4. d) Name the six compounds using traditional nomenclature (ferrous/ferric) and explain what criterion this nomenclature follows regarding oxidation numbers.

Potassium alum stone sold as a mineral deodorant is a hydrated double salt with the formula $\text{KAl(SO}_4)_2 \cdot 12\ \text{H}_2\text{O}$.

1. a) Check that the formula is electrically neutral by adding the charges of the ions $\text{K}^+$, $\text{Al}^{3+}$, and $\text{SO}_4^{2-}$ it contains.
2. b) Name it knowing that in double salts the two metals are listed in alphabetical order after the negative ion, and that the water of crystallisation is indicated at the end with the corresponding hydrate.
3. c) State how many ions of each type and how many water molecules there are in one formula unit.
4. d) Reason why it makes sense to call it a double salt and not simply a mixture of two salts.

Many toothpastes contain $\text{NaF}$ and others contain $\text{Na}_2\text{PO}_3\text{F}$; both compounds provide fluorine to prevent tooth decay.

1. a) Name $\text{NaF}$.
2. b) Deduce, from electrical neutrality, the charge of the ion $\text{PO}_3\text{F}$ that accompanies the two ions $\text{Na}^+$ in the second formula.
3. c) Compare this ion with the phosphate ion, $\text{PO}_4^{3-}$, and explain how they differ and why the charge changes.
4. d) Knowing that this ion is called monofluorophosphate, write the full name of the salt $\text{Na}_2\text{PO}_3\text{F}$ and explain what the prefix "mono-" refers to.

Emissions from power stations and traffic contain sulphur and nitrogen oxides which, with rainwater, form oxoacids: this is known as acid rain. The diagram summarises the process.

1. a) Name the oxides $\text{SO}_2$ and $\text{SO}_3$ using systematic nomenclature.
2. b) With water they form $\text{H}_2\text{SO}_3$ and $\text{H}_2\text{SO}_4$: name these two oxoacids using traditional nomenclature and write, using formulas, the equation for the formation of the second from $\text{SO}_3$ and water.
3. c) The acid falls on marble facades, $\text{CaCO}_3$, and gradually transforms them into $\text{CaSO}_4$, a crust that crumbles: name the two salts and explain in your own words the deterioration suffered by a monument exposed to acid rain.
4. d) Nitrogen oxides from traffic also give rise to nitric acid: write its formula and deduce the oxidation number of nitrogen in it (hydrogen acts with $+1$ and oxygen with $-2$).

Unit challenge. What chemical substances live in your kitchen? Become a household chemical auditor by analyzing everyday consumer products.

1. Search and nomenclature: Check the label of a bottle of mineral water and two everyday products (table salt and baking soda). Identify and name using IUPAC nomenclature (systematic and Stock/additive) an ambient element/elementary substance ($O_2$ or $N_2$), four ions from the label ($Ca^{2+}$, $Mg^{2+}$, $Na^+$, $HCO_3^-$, or $Cl^-$), and three neutral inorganic compounds ($H_2O$, $NaCl$, $NaHCO_3$).

2. Taking measurements: Using a measuring cup ($\pm 10\text{ mL}$) and a kitchen scale ($\pm 1\text{ g}$), measure the mass of four increasing volumes of tap water: $100$, $150$, $200$, and $250\text{ mL}$.

3. Data processing: Prepare a table with your measurements and uncertainties ($V \pm 10\text{ mL}$; $m \pm 1\text{ g}$) and plot $m$ versus $V$. From the slope, determine the density of dihydrogen monoxide / oxidane ($H_2O$) expressed in $\text{g/cm}^3$, approximating with a decimal comma (e.g., $0,98\text{ g/cm}^3$).

4. Final report: Submit a reasoned proposal (1-2 pages) containing the classification of substances, the table, the graph, and an assessment of possible ionic impurities in the water.

Evaluation criteria:

• Correctness and rigor in IUPAC formulation and nomenclature of elementary substances, ions, and compounds.

• Metrological rigor in data recording, stating uncertainties in both table and graph.

• Consistency in the physical interpretation of the slope and quality of the report.