The mole concept：練習問題

Calculate the number of moles in \( 22\text{ g} \) of carbon dioxide, \( \text{CO}_2 \).

(Relative atomic masses: \( \text{C} = 12; \text{O} = 16 \))

Calculate the total number of ions present in \( 0.25 \) moles of magnesium chloride, \( \text{MgCl}_2 \).

(Avogadro\u2019s constant = \( 6.02 \times 10^{23} \) per mole)

Methane, \( CH_4 \), is a common hydrocarbon fuel. Calculate the number of total atoms present in \( 0.5 \) moles of methane gas.
(Avogadro’s constant = \( 6.02 \times 10^{23} \) per mole)

A sample of hydrated copper(II) sulfate, \( \text{CuSO}_4 \cdot x\text{H}_2\text{O} \), has a relative formula mass (\( M_r \)) of \( 250 \).

Calculate the value of \( x \) in the formula.

(\( A_r: \text{Cu} = 64; \text{S} = 32; \text{O} = 16; \text{H} = 1 \))

Calculate the number of moles in \(20\text{ g}\) of calcium carbonate, \(\text{CaCO}_3\).
(Relative atomic masses: \(\text{Ca} = 40\), \(\text{C} = 12\), \(\text{O} = 16\))

An oxide of nitrogen contains \( 30.43\% \) nitrogen by mass. If the relative formula mass of the compound is \( 92 \), determine its molecular formula.
(\( A_r: \text{N} = 14, \text{O} = 16 \))

Calculate the mass of magnesium oxide produced when \( 0.25 \) moles of magnesium react completely with oxygen.
(\( A_r: \text{Mg} = 24, \text{O} = 16 \))

A sample of methane gas, \( \text{CH}_4 \), occupies a volume of 7.2 dm³ at room temperature and pressure (rtp).

(a) Calculate the number of moles of methane in the sample.
(b) Calculate the mass, in grams, of this sample of methane.
(c) Calculate the number of molecules of methane present in this sample.

(Assume the molar gas volume at rtp is \( 24\text{ dm}^3 \text{/mol} \). Relative atomic masses: \( \text{C} = 12, \text{H} = 1 \). Avogadro’s constant = \( 6.02 \times 10^{23} \text{ per mole} \).)

A sample of a gaseous hydrocarbon is found to contain 85.7% carbon and 14.3% hydrogen by mass.
(a) Calculate the empirical formula of the hydrocarbon.
(b) At room temperature and pressure (RTP), 0.42 g of this gas occupies a volume of 240 cm³. Calculate the relative molecular mass (\( M_r \)) and determine the molecular formula.

(Relative atomic masses: \( C = 12, H = 1 \); Molar gas volume at RTP = \( 24 \text{ dm}^3 \text{/mol} \))