Formulae, Equations and Amounts of Substance - exam practice

Sodium hydroxide neutralises acid.

H⁺ + OH^- ➔ H₂O

In a 11.0 dm³ sample of an aqueous solution, the concentration of acid, [H⁺], is 1.26 × 10^-3 mol dm^-3.

Which mass of solid sodium hydroxide neutralises the acid?

The gas laws can be summarised in the ideal gas equation.

pV = nRT

0.960 g of oxygen gas is contained in a vessel of volume 7.00 × 10^-3 m³ at a temperature of 30°C.

Assume that the gas behaves as an ideal gas.

What is the pressure in the vessel?

Which gas sample contains the fewest molecules?

The relative atomic mass is defined as

Which reaction produces the smallest atom economy of BaCl₂?

A student mixes 100 cm³ of 0.200 mol dm^-3 NaCl_(aq) with 100 cm³ of 0.200 mol dm^-3 Na₂CO_3(aq).

What is the total concentration of Na⁺ ions in the mixture formed?

Sodium reacts with water as shown below.

2Na_(s) + 2H₂O_(l) ➔ 2NaOH_(aq) + H_2(g)

Which mass of sodium reacts with water to produce 960 cm³ of hydrogen gas at RTP?

What is the number of oxygen atoms in 88.0 g of CO₂?

What is the empirical formula of an oxide of nitrogen that contains 26% nitrogen by mass?

30 cm³ of xenon are mixed with 20 cm³ of fluorine. The gases react according to the following equation. Assume that the temperature and pressure remain constant.

Xe_(g) + F_2(g) ➔ XeF_2(g)

What is the final volume of gas after the reaction is complete?

In a car airbag, sodium azide (NaN₃) decomposes to form sodium metal and nitrogen gas.

2NaN_3(s) ➔ 2Na_(s) + 3N_2(g)

The sodium metal then reacts with potassium nitrate to produce more nitrogen gas.

10Na_(s) + 2KNO_3(s) ➔ N_2(g) + 5Na₂O_(s) + K₂O_(s)

If 2.00 mol of sodium azide react in this way, how many molecules of N₂ will be formed?

The Avogadro constant, L = 6.022 x 10²³ mol⁻¹.

A 20.0 cm³ sample of a 0.400 mol dm^-3 aqueous solution of a metal bromide (MBr_n) reacts exactly with 160 cm³ of 0.100 mol dm^-3 aqueous silver nitrate.

What is the formula of the metal bromide?

What is the mass, in mg, of carbon formed when 3.0 × 10^-3 mol of propene undergoes incomplete combustion?

2C₃H₆ + 3O₂ ➔ 6C + 6H₂O

The equation for the reaction between zinc and hydrochloric acid is

Zn + 2HCl ➔ ZnCl₂ + H₂

What is the minimum mass, in mg, of zinc (A_r = 65.4) needed to react with 50.0 cm³ of 1.68 mol dm^-3 hydrochloric acid?

A student is provided with 5.00 cm³ of 1.00 mol dm^-3 ammonia solution. The student was asked to prepare an ammonia solution with a concentration of 0.050 mol dm^-3

What volume of water should the student add?

Nitration of 1.70 g of methyl benzoate (M_r = 136.0) produces methyl 3-nitrobenzoate (M_r = 181.0). The percentage yield is 65.0%

What mass, in g, of methyl 3-nitrobenzoate is produced?

In an experiment to identify a group 2 metal (X), 0.102 g of X reacts with an excess of aqueous hydrochloric acid according to the following equation.

X + 2HCl ➔ XCl₂ + H₂

The volume of hydrogen gas given off is 65 cm³ at 99 kPa pressure and 303 K.

The gas constant is R = 8.31 J K^–1 mol^–1.

Which is X?

When heated, a sample of potassium chlorate(V) (KClO₃) produced 67.2 cm³ of oxygen, measured at 298 K and 110 kPa

2KClO_3(s) ➔ 2KCl_(s) + 3O_2(g)

What is the amount, in moles, of potassium chlorate(V) that has decomposed?

The gas constant, R = 8.31 J K^–1 mol^–1.

Which sample, measured at room temperature and pressure, contains the greatest number of the stated particles?

5.0 g of an oxide of molybdenum contain 4.0 g of molybdenum.

What is the empirical formula of this oxide?

What is the percentage yield when 20 g of aluminium are produced from 50 g of aluminium oxide?

2Al₂O₃ ➔ 4Al + 3O₂

In which mixture is NaOH the limiting reagent?

What is the percentage yield when 7 g of ethene produces 6 g of ethanol?

M_r (ethene) = 28 and M_r (ethanol) = 46

How many moles of FeS₂ are required to produce 32 g of SO₂? (A_r : S = 32, O = 16).

4FeS_2(s) + 11O_2(g) ➔ 2Fe₂O_3(s) + 8SO_2(g)

What volume, in cm³, of 0.200 mol dm^-3 NaOH_(aq) is needed to neutralise 0.050 mol of H₂S_(g)?

H₂S_(g) + 2NaOH_(aq) ➔ Na₂S_(aq) + 2H₂O_(l)

The general gas equation can be used to calculate the M_r value of a gas.

For a sample of a gas of mass mg, which expression will give the value of M_r?

Which of the following equations has the correct state symbols for the reaction of dilute hydrochloric acid with magnesium oxide?

Which piece of equipment has the smallest measurement uncertainty for the measurement of 50.0 cm³ of sodium hydroxide solution?