The most common isotope of Cr is chromium-52. Determine the numbers of protons, neutrons and electrons in an atom of chromium-52.
Describe how an atom of chromium-54 differs from an atom of chromium-52. Refer to numbers of particles in your answer.
The relative isotopic masses of the isotopes of Cr can be found by mass spectrometry. State what other information is required to calculate the relative atomic mass, $A_r$, of Cr.
Atoms of $^{52}\mathrm{Cr}$, $^{53}\mathrm{Cr}$ and $^{54}\mathrm{Cr}$ make up more than 95% of naturally occurring chromium atoms. The $A_r$ of naturally occurring Cr is 51.996. Suggest what these statements imply about the relative isotopic mass of the fourth stable isotope of chromium.
The shorthand electronic configuration of chromium is $[\mathrm{Ar}]\,3d^5 4s^1$. Complete the full electronic configuration of chromium.
Deduce the total number of unpaired electrons in an atom of chromium.
Acidified dichromate(VI) ions oxidise methanal, $\mathrm{CH_2O}$, to carbon dioxide. Electron transfer for the relevant species is shown in the following half-equations: half-equation 1: $\mathrm{CH_2O + H_2O \rightarrow CO_2 + 4H^+ + 4e^-}$; half-equation 2: $\mathrm{Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O}$. 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 $-30\,^{\circ}\mathrm{C}$ but carbon dioxide is a gas at this temperature. Explain why.
In acidic conditions, a dynamic equilibrium is established between $\mathrm{CrO_4^{2-}(aq)}$ and $\mathrm{Cr_2O_7^{2-}(aq)}$: $\mathrm{2CrO_4^{2-}(aq) + 2H^+(aq) \rightleftharpoons Cr_2O_7^{2-}(aq) + H_2O(l)}$ $\Delta H > 0$. State what is meant by dynamic equilibrium.
Identify the condition necessary to establish dynamic equilibrium.
In the equilibrium $\mathrm{2CrO_4^{2-}(aq) + 2H^+(aq) \rightleftharpoons Cr_2O_7^{2-}(aq) + H_2O(l)}$ $\Delta H > 0$, $\mathrm{CrO_4^{2-}(aq)}$ ions are yellow and $\mathrm{Cr_2O_7^{2-}(aq)}$ ions are orange. State what is observed when the following changes are made to an equilibrium mixture of acidified $\mathrm{CrO_4^{2-}(aq)}$ and $\mathrm{Cr_2O_7^{2-}(aq)}$ ions. Explain your answers: (1) The equilibrium mixture is warmed gently. (2) Dilute $\mathrm{HCl(aq)}$ is added to the equilibrium mixture.
Chromium(IV) fluoride, $\mathrm{CrF_4}$, is a covalent molecule that shows similar chemical properties to $\mathrm{SiCl_4}$. Suggest the type of reaction that occurs when $\mathrm{CrF_4}$ is placed in water. Construct a relevant equation for this reaction.