The most common isotope of Cr is chromium-52. Work out the numbers of protons, neutrons and electrons in an atom of chromium-52.
Describe how an atom of chromium-54 is different from an atom of chromium-52. Refer to the numbers of particles in your answer.
The relative isotopic masses of the isotopes of Cr can be found by mass spectrometry. State what extra information is needed to calculate the relative atomic mass, $A_r$, of Cr.
Atoms of $^{52}_{24}\text{Cr}$, $^{53}_{24}\text{Cr}$ and $^{54}_{24}\text{Cr}$ account for more than 95% of naturally occurring chromium atoms. The $A_r$ of naturally occurring Cr is $51.996$. Suggest what these facts show about the relative isotopic mass of the fourth stable isotope of chromium.
The shorthand electronic configuration of chromium is $[\text{Ar}]\,3d^5 4s^1$. Complete the full electronic configuration of chromium.
Deduce the total number of unpaired electrons in an atom of chromium.
Acidified dichromate(VI) ions convert methanal, $\text{CH}_2\text{O}$, into carbon dioxide. Electron transfer to or from the relevant species is shown in the half-equations below: Half-equation 1: $\text{CH}_2\text{O} + \text{H}_2\text{O} \rightarrow \text{CO}_2 + 4\text{H}^+ + 4e^-$. Half-equation 2: $\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$. Identify the species that is reduced in half-equation 2. Explain your answer.
The oxidation state of the carbon atom in methanal is $0$. Calculate the oxidation state of carbon in carbon dioxide.
Construct the ionic equation for the reaction of dichromate(VI) ions with methanal in acidic conditions.
Methanal is a liquid at $-30\,^\circ\text{C}$ but carbon dioxide is a gas at this temperature. Explain why.
In acidic conditions, a dynamic equilibrium is set up between $\text{CrO}_4^{2-}(aq)$ and $\text{Cr}_2\text{O}_7^{2-}(aq)$: $2\text{CrO}_4^{2-}(aq) + 2\text{H}^+(aq) \rightleftharpoons \text{Cr}_2\text{O}_7^{2-}(aq) + \text{H}_2\text{O}(l)$, $\Delta H > 0$. State what is meant by dynamic equilibrium.
Identify the condition needed to establish dynamic equilibrium.
Chromate(VI) ions, $\text{CrO}_4^{2-}(aq)$, are yellow and dichromate(VI) ions, $\text{Cr}_2\text{O}_7^{2-}(aq)$, are orange. State what you observe when the following changes are made to an equilibrium mixture of acidified $\text{CrO}_4^{2-}(aq)$ and $\text{Cr}_2\text{O}_7^{2-}(aq)$ ions. Explain your answers: (1) The equilibrium mixture is warmed gently. (2) Dilute $\text{HCl}(aq)$ is added to the equilibrium mixture.
Chromium(IV) fluoride, $\text{CrF}_4$, is a covalent molecule with chemical behaviour similar to $\text{SiCl}_4$. Suggest the type of reaction that takes place when $\text{CrF}_4$ is placed in water. Write an equation for this reaction.