Calculate concentration in mol dm⁻³ or g dm⁻³ from the amount of solute and the solution volume, rearrange to find moles or volume, handle dilutions, and convert between cm³ and dm³.
Tę umiejętność sprawdzają 42 zadania wzorowane na arkuszach IB z lat 2022–2026.
(b) A variety of ions are dissolved in the water of the Salton Sea. The concentrations of the major ions are shown in the table below, based on two different sources (both scientific journals). (i) Suggest two reasons for the difference in the concentration of…
Potassium also forms compounds with polyatomic ions. 2 KOH(aq) + Cu(NO3)2(aq) → Cu(OH)2(s) + 2 KNO3(aq) (i) 30.0 cm3 of a 0.380 mol dm−3 potassium hydroxide, KOH, solution is mixed with 25.0 cm3 of a 0.310…
(e) The propanoic acid obtained by the distillation was an aqueous solution with a volume of 22.5 cm3. Three 5.00 cm3 samples of this solution were titrated with 0.200 mol dm−3 NaOH to determine the accurate…
Outline why a standard solution of potassium manganate(VII) was needed for this analysis.
State two items of glassware that the dilution required.
Colorimetry is an alternative technique for determining concentration. Iron(II) ions can be converted to a red complex ion by adding 1,10-phenanthroline. (i) Outline why the concentration of iron(II) in a solution can be measured by colorimetry after this…
A sample of chalk is dissolved in acid and titrated with EDTA solution, represented as H2X2−. The titration requires 18.4 cm3 of 0.250 mol dm−3 EDTA. What is the mass of calcium carbonate, CaCO3, in the sample?…
Determine the mass of sodium thiosulfate pentahydrate, Na2S2O3 ⋅ 5 H2O, needed to prepare 250.0 cm3 of a 0.2000 mol dm−3 solution.
Explain how the 0.2000 mol dm−3 solution is prepared in a volumetric flask from the weighed solid.
Suggest how to prepare 100.0 cm3 of a 0.05000 mol dm−3 sodium thiosulfate solution from the 0.2000 mol dm−3 solution.
Before use, the EDTA solution was standardized against a standard solution of Cu2+ ions. An accurately weighed piece of pure copper wire was dissolved in the minimum volume of concentrated nitric acid and the mixture was warmed gently until no more…
Anhydrous copper(II) chloride, CuCl2, takes up water vapour from the air, so it cannot be weighed out accurately to make a standard solution. Suggest a laboratory procedure that would remove all of the absorbed water from a sample of solid CuCl2…
For the AAS method, a series of standards of known concentration was prepared by diluting a stock solution of Cu2+ ions. The instrument was zeroed with deionized water and the absorbance of each standard was recorded. (i) Draw the line of best fit for…
Describe how a standard aqueous solution of potassium manganate(VII) can be prepared from the solid.
Describe the steps by which this standard solution is turned into a calibration curve for the colorimeter.
Explain how the calibration curve is then used to determine the concentration of KMnO4 in a reaction mixture of unknown concentration.
Draw a line of best fit on the graph, extrapolating it beyond the range of the data.
State, in mathematical terms, how the absorbance of these solutions depends on their concentration.
Deduce the equation that relates absorbance to concentration for these solutions, including the numerical value of the constant.
Estimate the absorbance of a 0.400 mol dm−3 solution of nickel(II) sulfate.
Predict the difference, if any, between the absorbance of the 0.400 mol dm−3 solution read from the extrapolated line and the value calculated from the equation in 3d.
Calculate the mass of solid potassium hydroxide that has to be weighed out.
Describe how the student should prepare this standard solution from the weighed solid using a 250.0 cm3 volumetric flask.
The student pipetted 25.00 cm3 of the potassium hydroxide solution into a conical flask and titrated it with nitric acid, HNO3(aq), of concentration 0.1250 mol dm−3. The burette readings before and after the titration are…
Explain why the potassium hydroxide solution has to be standardized before it is used in the titration. Assume that there are no systematic errors in the procedure.
The student then used the potassium hydroxide solution standardized in 1c to titrate ethanoic acid, CH3COOH, whose concentration was not known. (i) Neutralizing 25.00 cm3 of the acid required 40.00 cm3 of the standardized…
4.06 g of hydrated magnesium chloride, MgCl2 ⋅ 6 H2O (Mr = 203), is dissolved in water to make 0.250 dm3 of solution. What is the concentration of chloride ions, in mol dm−3, in this solution? A. 0.0400 B. 0.0800 C.…
A student writing a report on chlorine as a disinfectant collects, from several websites and reference books, values for how much chlorine dissolves in pure water at various temperatures. (i) Identify one difficulty in comparing the solubility values from…
A solution is prepared by dissolving 1.29 g of HA in water and making the volume up to 20.00 cm3. When the whole of this solution is titrated with 0.600 mol dm−3 sodium hydroxide, NaOH(aq), exactly 24.90 cm3 of the…
The iodine number of a fat or oil is the mass, in grams, of iodine that reacts with 100 g of the fat or oil. It is a measure of the degree of unsaturation. A 3.50 g sample of peanut oil reacts completely with 65.5 cm3 of…
Calculate the concentration of oxygen in the water sample, in g dm−3. If you could not answer (b), use 2.00 × 10−4 mol instead; this is not the correct value.
The concentration of copper(II) ions in wastewater from a plating works was determined by colorimetry. Excess ammonia solution was added to each solution so that all the copper(II) ions formed the deep blue complex ion [Cu(NH3)4]2+, and the absorbance…
The end point was reached after 3.0 ± 0.1 cm3 of titrant had been run in. (i) Calculate the percentage uncertainty in this titre. (ii) Suggest one change to the procedure that would lower the percentage uncertainty of a single titration, apart from…
The concentration of dissolved oxygen in a sample of pond water was determined by the Winkler method. The reactions that take place are:…
The concentration of copper(II) ions in a sample of pond water is determined with a colorimeter. The absorbance of standard solutions of known concentration is measured and a calibration curve is plotted. Sketch the typical shape of the calibration curve on…
The concentration of an ethanoic acid solution was found by titration with a 0.150 mol dm−3 standard solution of potassium hydroxide, KOH(aq), using an indicator to detect the end point. (i) Calculate the pH of the potassium hydroxide solution.…
Magnesium hydroxide is the active ingredient of some indigestion remedies, which neutralize excess hydrochloric acid in the stomach. (i) Write an equation for the reaction of magnesium hydroxide with hydrochloric acid. (ii) Calculate the mass, in g, of…
Ethanoic acid acts as a weak monoprotic acid in aqueous solution. At 298 K its acid dissociation constant is Ka = 1.74 × 10−5 mol dm−3. (i) 2.00 dm3 of an ethanoic acid solution was prepared. A 25.0 cm3…
Ethanoic acid is a weak monobasic acid. The acid dissociation constant of ethanoic acid at 298 K is Ka = 1.74 × 10−5. (i) A student dissolved a sample of ethanoic acid in water and made the solution up to 2.00 dm3. Exactly 19.4…
A student mixes 100 cm3 of 0.50 mol dm−3 calcium chloride solution with 150 cm3 of 1.00 mol dm−3 potassium chloride solution. What is the concentration of chloride ions, in mol dm−3, in…
A 0.460 g piece of sodium was placed in 250.0 cm3 of water. (i) Calculate the molar concentration of the sodium hydroxide solution formed. Assume that the volume of the solution is 250.0 cm3. (ii) Calculate the volume of hydrogen gas…
A sample of methylamine gas, volume 120.0 dm3 at 295.0 K and 102.0 kPa, dissolves in water and the solution is made up to 2.50 dm3. Determine the concentration of the solution, in mol dm−3. Use sections 1 and 2 of the…
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