Experimental techniques and apparatus

(a) Outline two features of this experiment that ensure that the propanal intermediate is not a major product.

(b) Outline two safety precautions that must be taken during the preparation of propanoic acid, besides wearing a lab coat and safety goggles.

(d) The student used distillation to obtain pure propanoic acid from the reaction mixture. (i) State two impurities, apart from unreacted propan-1-ol, that were present in the propanoic acid before distillation. (ii) The approximate experimental yield of…

Explain how the 0.2000 $\mathrm{mol\,dm^{-3}}$ solution is prepared in a volumetric flask from the weighed solid.

Suggest how to prepare 100.0 $\mathrm{cm^3}$ of a 0.05000 $\mathrm{mol\,dm^{-3}}$ sodium thiosulfate solution from the 0.2000 $\mathrm{mol\,dm^{-3}}$ solution.

State one safety concern arising from a product of this reaction, and a precaution that should be taken because of it.

Before use, the EDTA solution was standardized against a standard solution of $\ce{Cu^2+}$ 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, $\ce{CuCl2}$, 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 $\ce{CuCl2}$…

Portions of the rinse water were then titrated with the standardized EDTA solution in the presence of murexide as indicator. The burette readings are given in the table. Trial 1 Trial 2 Trial 3 Trial 4 Final burette reading / $\mathrm{cm^3}$ (± 0.05…

(i) Suggest, giving a reason for each, two different safety precautions that should be taken when carrying out either of these preparations. (ii) Deduce the coefficients needed to balance the following equation for the reaction of silver with concentrated…

Suggest a sequence of experimental steps that would give a pure sample of each of the three components.

(i) State the independent variable and the dependent variable of the investigation. (ii) Apart from the mass of leaves and the volume of water, suggest two other conditions that should be kept constant for the comparison between boiling times to be valid.…

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.

The colorimeter can record either absorbance or percentage transmittance at a chosen wavelength. Outline why one particular wavelength has to be selected.

(i) Suggest a reason for the slight change in colour observed after the night in the oven. (ii) Suggest how the students could make sure that dehydration in the crucible was complete. (iii) Suggest one way in which the students could reduce the effect of…

Which of the following could be used to follow the progress of the reaction between calcium carbonate and dilute nitric acid? $\ce{CaCO3(s) + 2HNO3(aq) -> Ca(NO3)2(aq) + H2O(l) + CO2(g)}$ I. A balance recording the mass of the open flask and its contents II. A…

Describe how the student should prepare this standard solution from the weighed solid using a 250.0 $\mathrm{cm^3}$ volumetric flask.

The student pipetted 25.00 $\mathrm{cm^3}$ of the potassium hydroxide solution into a conical flask and titrated it with nitric acid, $\ce{HNO3(aq)}$, of concentration 0.1250 $\mathrm{mol\,dm^{-3}}$. 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, $\ce{CH3COOH}$, whose concentration was not known. (i) Neutralizing 25.00 $\mathrm{cm^3}$ of the acid required 40.00 $\mathrm{cm^3}$ of the standardized…

State one other physical property that could be measured to identify the metal while leaving the block intact.

(i) Suggest one hazard to health or safety in Student A's procedure. (ii) Student A plotted the highest temperature of each mixture against the volume of nitric acid. With a ruler, draw two straight lines of best fit: one following the rising set of points and…

Student B pipetted 30.00 $\mathrm{cm^3}$ of the potassium hydroxide solution into a 150 $\mathrm{cm^3}$ glass beaker and added the nitric acid from a burette in portions of 4.00 $\mathrm{cm^3}$, recording the steady temperature after each addition. Volume of…

Explain why the start line must be horizontal and must be above the level of the solvent when the strip is placed in the chamber.

Describe the steps the student would follow to recrystallize the crude benzoic acid.

State the most important property that water must have, with respect to benzoic acid, for it to be a suitable solvent for this recrystallization.

Outline how each of the two by-products is removed from the benzoic acid during the recrystallization. By-product that is almost insoluble in hot water: ... By-product that is much more soluble than benzoic acid: ...

The volume of hot water used to dissolve the crude solid must be chosen carefully. Deduce the effect on the yield or on the purity of the recrystallized benzoic acid of using too much water and of using too little water. Too much water: ... Too little water:…

Describe the setup that would connect the $\ce{Sn^4+}/\ce{Sn^2+}$ half-cell to a second half-cell for comparing the two electrode potentials.

Most pools, including this lido, are dosed with sodium hypochlorite solution, $\ce{NaOCl(aq)}$, instead of chlorine gas. Suggest why pool operators avoid dosing the water with chlorine gas itself.

The student measures the hydrogensulfite concentration by titrating samples against a standard iodine solution, with starch as the indicator. Every three days, 25.00 $\mathrm{cm^3}$ of cordial is withdrawn from each flask, diluted to 250.0 $\mathrm{cm^3}$ with…

Sketch how the combined mass of the flask, the syringe and their contents would change with time during Experiment 1, and give a reason for the shape of your sketch. Label the axes 'Total mass' and 'Time'.