Counting Particles by Mass: The Mole · Paper 1 — Free Chemistry HL Practice Questions

A student dissolves $12.485 \text{ g}$ of hydrated copper(II) sulfate, $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ (molar mass $= 249.7 \text{ g mol}^{-1}$), in water. Excess sodium hydroxide solution is added, precipitating all copper(II) ions according to: $$\text{Cu}^{2+}(\text{aq}) + 2\text{OH}^-(\text{aq}) \rightarrow \text{Cu(OH)}_2(\text{s})$$ What is the maximum number of moles of $\text{Cu(OH)}_2$ produced?

A technician obtains $3.024 \text{ g}$ of pure paracetamol ($\text{C}_8\text{H}_9\text{NO}_2$, molar mass $= 151.2 \text{ g mol}^{-1}$) after recrystallisation. How many molecules of paracetamol are present in this sample? ($N_A = 6.02 \times 10^{23} \text{ mol}^{-1}$)

A sample of dry air contains $3.01 \times 10^{20}$ molecules of carbon dioxide. What is the mass of $\text{CO}_2$ in this sample? (Molar mass of $\text{CO}_2 = 44.01 \text{ g mol}^{-1}$; $N_A = 6.02 \times 10^{23} \text{ mol}^{-1}$)

A student heats a 2.50 g sample of hydrated copper(II) sulfate, $\text{CuSO}_4 \cdot x\text{H}_2\text{O}$, to constant mass and obtains 1.60 g of anhydrous $\text{CuSO}_4$. Using $M(\text{CuSO}_4) = 159.6 \text{ g mol}^{-1}$ and $M(\text{H}_2\text{O}) = 18.0 \text{ g mol}^{-1}$, what is the value of $x$?