A sample of aluminium oxide, $Al_2O_3$, has a mass of $5.10\ \text{g}$. Use $M(Al_2O_3) = 101.96\ \text{g mol}^{-1}$ and $N_A = 6.022 \times 10^{23}\ \text{mol}^{-1}$.

A student prepares $250.0\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ sodium carbonate solution, $Na_2CO_3(aq)$. Use $M(Na_2CO_3) = 105.99\ \text{g mol}^{-1}$.

Carbon monoxide reacts with oxygen according to the equation:

$2CO(g) + O_2(g) \to 2CO_2(g)$

$50.0\ \text{cm}^3$ of $CO(g)$ is mixed with $40.0\ \text{cm}^3$ of $O_2(g)$ at the same temperature and pressure.

Equal volumes of $N_2(g)$ and $NH_3(g)$ are compared at the same temperature and pressure. Under these conditions, $1.00\ \text{dm}^3$ of any gas contains $2.46 \times 10^{22}$ molecules.

A solution of magnesium chloride, $MgCl_2(aq)$, has a mass concentration of $12.0\ \text{g dm}^{-3}$. Use $M(MgCl_2) = 95.21\ \text{g mol}^{-1}$.

A student compared samples containing different specified elementary entities. The table shows the amount or number of entities in each sample. Use $N_A = 6.022 \times 10^{23}\ \text{mol}^{-1}$.

The mass spectrum of an element contains two main isotopic peaks. The table gives the relative isotopic masses and percentage abundances.

A calibration curve was prepared for aqueous copper(II) sulfate solutions using a colorimeter. An unknown solution gave an absorbance within the range of the standards.

A student heated magnesium in a crucible until the mass was constant.

Mass of empty crucible: $25.64\ \text{g}$

Mass of crucible and magnesium before heating: $25.88\ \text{g}$

Mass of crucible and product after heating: $26.04\ \text{g}$

A coloured solution, X, was too concentrated to measure directly. A student pipetted $10.0\ \text{cm}^3$ of X into a $100.0\ \text{cm}^3$ volumetric flask and made the solution up to the mark. The absorbance of the diluted solution was then measured and compared with a calibration curve.

Ethene burns completely in oxygen according to the equation:

$C_2H_4(g) + 3O_2(g) \to 2CO_2(g) + 2H_2O(g)$

$30.0\ \text{cm}^3$ of $C_2H_4(g)$ is mixed with $80.0\ \text{cm}^3$ of $O_2(g)$ at the same temperature and pressure.

A compound contains $40.00\%$ carbon, $6.71\%$ hydrogen and $53.29\%$ oxygen by mass. Its molar mass is $180.18\ \text{g mol}^{-1}$.

A sample of anhydrous magnesium chloride was analysed. The table gives the mass of the sample and selected relative atomic masses.

Iron powder was heated strongly in a crucible until it formed an oxide. The mass data are shown.

Nitrogen and hydrogen react to form ammonia according to the equation:

$N_2(g) + 3H_2(g) \to 2NH_3(g)$

All gas volumes are measured at the same temperature and pressure. The graph shows trials in which $60\ \text{cm}^3$ of hydrogen was reacted with different volumes of nitrogen.

A medicine label states that each tablet contains calcium carbonate, $CaCO_3$, as its active ingredient. The table shows the mass of calcium carbonate in one tablet and selected relative atomic masses.

A $0.2904\ \text{g}$ sample of an organic compound containing carbon, hydrogen and oxygen is completely combusted. The products are $0.660\ \text{g}$ of $CO_2$ and $0.270\ \text{g}$ of $H_2O$. The molar mass of the compound is $116.16\ \text{g mol}^{-1}$.

A pure organic compound containing carbon, hydrogen and oxygen was completely combusted. The table shows the mass of the sample, the masses of combustion products and the molar mass of the compound.

A student used serial dilution to prepare dilute potassium manganate(VII) solutions from a stock solution. A separate unknown sample was diluted before its absorbance was measured on the same calibration curve.

A hydrated salt, $MgSO_4 \cdot xH_2O$, was heated to constant mass. The mass data and relative atomic masses are shown.

A standard solution of aluminium sulfate, $Al_2(SO_4)_3$, was prepared by dissolving a measured mass of the solid and making the solution up to the mark in a volumetric flask.

A sealed vial contains $0.0185\ \text{mol}$ of pure ethanol, $C_2H_5OH$. The Avogadro constant is $6.022\times 10^{23}\ \text{mol}^{-1}$.

A student heats a sample of magnesium ribbon in a crucible to determine the empirical formula of magnesium oxide. The lid is lifted occasionally during heating and the crucible is heated, cooled and weighed until constant mass is obtained. The initial mass of magnesium is $0.486\ \text{g}$ and the final mass of magnesium oxide is $0.806\ \text{g}$.

A technician prepares a standard solution of sodium carbonate, $Na_2CO_3$, to use in an acid-base titration. A mass of $1.325\ \text{g}$ of anhydrous $Na_2CO_3$ is dissolved and made up to $250.0\ \text{cm}^3$ in a volumetric flask.

A stock solution of copper(II) sulfate, $CuSO_4(aq)$, has concentration $0.200\ \text{mol dm}^{-3}$. A student prepares a diluted solution by transferring $25.00\ \text{cm}^3$ of the stock solution into a $250.0\ \text{cm}^3$ volumetric flask and making up to the mark with deionized water.

A gaseous hydrocarbon, $C_xH_y$, was completely combusted in oxygen. The water formed was condensed before the final gas volume was measured. All gas volumes in the table were measured at the same temperature and pressure before condensation or after cooling as stated.

Nitrogen monoxide reacts with oxygen to form nitrogen dioxide. A mixture of $45.0\ \text{cm}^3$ of $NO(g)$ and $30.0\ \text{cm}^3$ of $O_2(g)$ is reacted.

$2NO(g)+O_2(g)\to 2NO_2(g)$

All gas volumes in this question are measured at the same temperature and pressure.

A compound containing only carbon, hydrogen and oxygen is analysed by complete combustion. A $0.450\ \text{g}$ sample produces $0.660\ \text{g}$ of $CO_2$ and $0.270\ \text{g}$ of $H_2O$. The molar mass of the compound is $180.18\ \text{g mol}^{-1}$.

A colorimeter is used to determine the concentration of an unknown nickel(II) sulfate solution. Standard solutions are prepared by diluting a $0.100\ \text{mol dm}^{-3}$ stock solution. The absorbance of the unknown solution is measured after it is diluted by transferring $10.00\ \text{cm}^3$ of the unknown to a $100.0\ \text{cm}^3$ volumetric flask and making up to the mark.

A hydrated salt has formula $MCl_2\cdot xH_2O$, where $M$ is a metal ion. A $2.000\ \text{g}$ sample of the hydrate is heated to constant mass. The mass of anhydrous $MCl_2$ remaining is $1.287\ \text{g}$. A separate analysis shows that the molar mass of the anhydrous salt is $129.84\ \text{g mol}^{-1}$.

Aluminium reacts with chlorine to form aluminium chloride.

$2Al(s)+3Cl_2(g)\to 2AlCl_3(s)$

A sample of aluminium with mass $1.35\ \text{g}$ is reacted with excess chlorine.

Ammonia reacts with oxygen over a catalyst to form nitrogen monoxide and steam.

$4NH_3(g)+5O_2(g)\to 4NO(g)+6H_2O(g)$

$80.0\ \text{cm}^3$ of $NH_3(g)$ is mixed with $120.0\ \text{cm}^3$ of $O_2(g)$ at the same temperature and pressure.

A gaseous hydrocarbon contains only carbon and hydrogen. Complete combustion of $0.210\ \text{g}$ of the hydrocarbon produces $0.660\ \text{g}$ of $CO_2$ and $0.270\ \text{g}$ of $H_2O$. The molar mass of the hydrocarbon is found to be approximately $84.16\ \text{g mol}^{-1}$.

A compound used as a fertilizer contains ammonium ions and sulfate ions and has formula $(NH_4)_2SO_4$. A manufacturer claims that a $50.0\ \text{kg}$ bag contains $10.6\ \text{kg}$ of nitrogen.