Chemistry SL Paper 1B, specimen 2025

Deduce the oxidation state of bromine in the reactant and in each of the two products. Reactant $\ce{Br2}$: Product $\ce{HOBr}$: Product $\ce{HBr}$:

When sodium hydroxide solution is added to the water, a larger amount of bromine reacts. Explain this observation.

A student compiles data on the solubility of bromine in water at different temperatures from several websites and textbooks. Source Temperature / °C Solubility of bromine A 5 3.90 g per 100 $\mathrm{cm^3}$ of water B 15 1.15 $\mathrm{cm^3}$ of liquid bromine…

Suggest why hot-tub owners rarely add bromine itself to the water and instead use solid tablets that release HOBr.

In water, HOBr partly ionizes to give the hypobromite ion, $\ce{OBr-}$; the ion is a much weaker sanitizer than the un-ionized acid. The graph shows how the percentages of the dissolved bromine present as HOBr(aq) and as $\ce{OBr-}$(aq) vary with pH at 25 °C.…

Ammonia from sweat and skin-care products reacts with HOBr to form bromamines: $\ce{NH2Br}$, $\ce{NHBr2}$ and $\ce{NBr3}$. (i) Deduce an equation for the reaction of ammonia with HOBr(aq) that produces dibromamine, $\ce{NHBr2}$(aq). (ii) The graph shows how…

Hot tubs are usually kept at 38–40 °C. Suggest two reasons why running a hot tub at a lower temperature would be better for the environment.

Identify two controlled variables in this investigation.

The iron(II) concentration is found by titrating against a standard solution of potassium manganate(VII), $\ce{KMnO4}$. At intervals of a few days, a 20.00 $\mathrm{cm^3}$ sample is withdrawn from each flask and made up to 250.0 $\mathrm{cm^3}$ with water;…

The following readings are recorded during one titration. Final burette reading = $23.20 \pm 0.05\ \mathrm{cm^3}$ Initial burette reading = $3.20 \pm 0.05\ \mathrm{cm^3}$ Calculate the percentage uncertainty in the volume of $\ce{KMnO4}$ solution delivered…

The student's results are shown in the graph. (i) Calculate the average rate at which the iron(II) concentration fell in the 24 h flask during the 21 days. Include units. (ii) Before starting, the student proposed the hypothesis: "The longer a solution is left…

Suggest one way of extending the investigation so that further recommendations about storing the iron(II) solution could be made.