The Mole & the Avogadro Constant — Structured Questions (Cambridge International A-Level Chemistry): Exam Questions

State the number of particles in one mole of a chemical.

Extract:

State the number of particles in one mole of a chemical.

The number of particles in one mole of a chemical: 6.02 x 10^23 OR 6.022 x 10^23

i) State the number and type of atoms present in a molecule of water.

ii) Calculate the total number of particles and atoms present in one mole of water.

Extract:

The number of particles in one mole of a chemical: 6.022 × 10^23

i) State the number and type of ions present in one mole of sodium carbonate, Na₂CO₃.

ii) Calculate the number of metal ions present in two moles of sodium carbonate.

Extract:

State the number of particles in one mole of a chemical.

The number of particles in one mole of a chemical: 6.02 x 10²³ OR 6.022 x 10²³

This value is Avogadro's constant, symbol L. L = 6.022 × 10²³ mol⁻¹.

i) State the conditions when one mole of a gas occupies a volume of 24.0 dm³.

ii) Complete Table 2.1.

Table 2.1

5.0 g of an unknown Group 2 nitrate was decomposed to produce 0.0843 mol of gas.

2X(NO₃)₂ (s) → 2XO (s) + 4NO₂ (g) + O₂ (g)

i) Calculate the amount, in mol, of the unknown Group 2 nitrate.

ii) Calculate the number of ions in 0.03372 mol of the unknown Group 2 nitrate.

Extract:

5.0 g of an unknown Group 2 nitrate was decomposed to produce 0.0843 mol of gas.

2X(NO3)2 (s) → 2XO (s) + 4NO2 (g) + O2 (g)

moles of X(NO3)2 = 0.03372 mol

Identify the unknown element X.

Extract:

2X(NO3)2 (s) → 2XO (s) + 4NO2 (g) + O2 (g)

X = magnesium / Mg

Using your answer to part (b), calculate the mass, in grams, of the metal oxide produced in the complete decomposition of 0.03372 mol of X(NO₃)₂.

Give your answer to 3 significant figures.

Extract:

5.0 g of an unknown Group 2 nitrate was decomposed to produce 0.0843 mol of gas.

2X(NO3)2 (s) → 2XO (s) + 4NO2 (g) + O2 (g)

X = magnesium / Mg

State whether strontium nitrate would need to be heated more or less strongly than X(NO₃)₂ to decompose. Explain your answer.

Barium sulfate is a white insoluble solid and is used in stomach X-rays and as a pigment for paint.

Calculate the number of particles in 74 mg of barium sulfate.

State the ionic equation for the formation of barium sulfate.

A different barium compound, barium carbonate, was reacted with hydrochloric acid.

i) Write the balanced symbol equation for this reaction.

ii) 0.03 moles of carbon dioxide were formed in this reaction. Calculate the number of hydrogen ions that reacted.

When magnesium reacts with hydrochloric acid, the following reaction occurs:

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

During the reaction, the hydrogen produced occupies 103 cm³ at 25.0 °C and 100 kPa.

Calculate the amount, in moles, of hydrogen gas produced during the reaction.

Extract:

When magnesium reacts with hydrochloric acid, the following reaction occurs:

Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)

A student completed the same reaction as in part (a), using 3.75 g of magnesium.

Calculate the mass, in grams, of magnesium chloride produced by the student during this reaction. Give your answer to 3 significant figures.

Extract:

When magnesium reacts with hydrochloric acid, the following reaction occurs:

Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

A student completed the same reaction as in part (a), using 3.75 g of magnesium.

Calculate the number of hydrogen atoms produced during the student's reaction in part (b).