layers can slide This figure is a simplified model of the arrangement of atoms in graphite. A manufacturer uses graphite powder in lubricants for high-tempe...
Question 1 Report
This figure is a simplified model of the arrangement of atoms in graphite. A manufacturer uses graphite powder in lubricants for high-temperature machinery. A sample is labelled as 96.0 g of pure graphite. Carbon is an element, so its formula is C. Use Ar value C = 12.0.
(a) Name the element shown in Fig. 1. [1]
(b) Give the Mr of graphite. [1]
(c) Use the sample mass to calculate the amount, in mol, of carbon atoms in the graphite. [2]
(d) Use the Avogadro constant, 6.02 × 1023 atoms mol-1, to calculate the number of carbon atoms in this sample. [2]
(e) Suggest why graphite can act as a lubricant. [2]
(f) Give one difference between an element and a compound. [2]
(g) Complete the statement. A 24.0 g graphite sample contains ............ mol of carbon atoms. [1]
Answer Details
(a) The element is carbon. Graphite is an allotrope, or structural form, of carbon. [1]
(b) Graphite contains only carbon atoms, so its relative formula mass is the relative atomic mass of carbon: \(M_r=12.0\). [1]
(c) Amount in moles is found from \(n=\frac{m}{M_r}\):
\[n=\frac{96.0\text{ g}}{12.0\text{ g mol}^{-1}}=8.00\text{ mol}\]
This is the amount of carbon atoms because graphite consists only of carbon. [2]
(d) Use \(\text{number of atoms}=n\times N_A\):
\[8.00\text{ mol}\times6.02\times10^{23}\text{ atoms mol}^{-1}=4.82\times10^{24}\text{ atoms}\]
[2]
(e) Graphite has layers of carbon atoms. The forces between these layers are weak, so the layers can slide over one another easily. This gives low friction, allowing graphite to act as a lubricant. [2]
(f) An element contains only one type of atom. A compound contains atoms of two or more different elements chemically joined together. [2]
(g) \(n=\frac{24.0}{12.0}=2.00\text{ mol}\). [1]
Examination reminder: For a pure element, use its \(A_r\) as the molar mass in \(n=\frac{m}{M_r}\).
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