Core Definitions And The Mole Concept

Which statement correctly defines an ion?

Octane has the molecular formula C₈H₁₈. What is its empirical formula?

Calculate the number of CO₂ molecules in 22.0 g of carbon dioxide. ($M_{\mathrm{r}}$(CO₂) = 44.0; L = 6.02 × 10²³ mol⁻¹)

How many moles of NaOH are present in 20.0 g of solid sodium hydroxide? ($M_{\mathrm{r}}$(NaOH) = 40.0)

Aqueous barium nitrate is added to aqueous sodium sulfate, producing a white precipitate. Which equation is the correct ionic equation for this reaction?

Which equation correctly represents the reaction of solid calcium carbonate with dilute hydrochloric acid, including state symbols?

Calculate the relative formula mass of calcium hydroxide, Ca(OH)₂. ($A_{\mathrm{r}}$ values: Ca = 40.1, O = 16.0, H = 1.0)

The relative atomic mass of chlorine is 35.5 rather than a whole number. Which statement gives the correct reason?

Which statement correctly describes the relationship between the molar mass (M) and relative molecular mass ($M_{\mathrm{r}}$) of a substance?

A river water sample contains 0.015 g of dissolved lead in 5000 g of water. Calculate the concentration of lead in ppm.

5.85 g of sodium chloride is dissolved in distilled water and made up to 500 cm³ of solution. Calculate the concentration in mol dm⁻³. ($M_{\mathrm{r}}$(NaCl) = 58.5)

A 0.250 mol dm⁻³ solution of potassium hydroxide is prepared. Calculate the concentration in g dm⁻³. ($M_{\mathrm{r}}$(KOH) = 56.1)

An aquarium hobbyist measures the ammonia level in their fish tank as 5 ppm. The tank contains 200 000 g of water. What mass of ammonia is dissolved in the tank?

A medical syringe contains 2.50 cm³ of glucose solution with concentration 0.200 mol dm⁻³. The molar mass of glucose (C₆H₁₂O₆) is 180.0 g mol⁻¹. What mass of glucose is in the syringe?

A student writes the following ionic equation for the reaction of magnesium with hydrochloric acid: Mg(s) + H⁺(aq) → Mg²⁺(aq) + H₂(g). Why is this equation incorrect?