DP Chemistry Questionbank

A student measured the change in mass on heating a sample of calcium carbonate, CaCO₃(s). What is the mass loss?

Mass before heating: 2.347 g ± 0.001
Mass after heating: 2.001 g ± 0.001 

A. 0.346g ± 0.001 

B. 0.346g ± 0.002 

C. 0.35g ± 0.002 

D. 0.35g ± 0.001

What is the density, in g$$cm⁻³, of a 34.79 g sample with a volume of 12.5 cm³?

A.     0.359

B.     0.36

C.     2.783

D.     2.78

Outline why the thermochemical method would not be appropriate for 0.001 mol$$dm⁻³ hydrochloric acid and aqueous sodium hydroxide of a similar concentration.

Heat losses would make this method less accurate than the pH probe method. Outline why the thermometric method would always give a lower, not a higher, concentration.

Suggest how the precision of this measurement could be improved.

Suggest why the final mass of solid obtained by heating 3.760 g of Ag_xO_y may be greater than 3.275 g giving one design improvement for your proposed suggestion. Ignore any possible errors in the weighing procedure.

Calculate the percentage uncertainty for the mass of K₂Cr₂O₇(s) from the given data.

O₂ is consumed in producing CO₂ for electricity generation. The graph shows the relationship between the world’s electricity generation and CO₂ production between 1994 and 2013.

Calculate the mass, in million tonnes, of oxygen gas ultimately found in CO₂ which is consumed in generating 18$$000 terawatts of electricity using the equation given for the best fit line. Give your answer to 2 significant figures.

Assume coal is the only energy source.

The change in APO O₂/N₂ ratio, per meg, is measured relative to an O₂/N₂ reference.

$$\mathrm{\Delta }\text{(}{\text{O}}_{\text{2}}\text{/}{\text{N}}_{\text{2}}\text{)}=\left(\frac{{({\text{O}}_2/{\text{N}}_2)}_{\text{sample}}}{{({\text{O}}_2/{\text{N}}_2)}_{\text{reference}}}-1\right)\times {10}^6$$

Calculate the APO Δ(O₂/N₂) value for an oxygen concentration of 209$$400 ppm assuming that any change in N₂ concentration is negligible. Reference values for O₂ and N₂ are 209 460 and 790 190 ppm respectively.

Suggest one improvement to the investigation.

A student obtained the following data to calculate $q$, using $q=mc\mathrm{\Delta }T$.

$m=20.2 \mathrm{g}\pm 0.2 \mathrm{g}$

$∆T=10°\mathrm{C}\pm 1°\mathrm{C}$

$c=4.18 \mathrm{J} {\mathrm{g}}^{-1} {\mathrm{K}}^{-1}$

What is the percentage uncertainty in the calculated value of $q$?

A.  $0.2$

B.  $1.2$

C.  $11$

D.  $14$

Potassium hydroxide solutions can react with carbon dioxide from the air. The solution was made one day prior to using it in the titration.

Predict, giving a reason, the effect of this error on the calculated concentration of ethanoic acid in 5(e).

Calculate the percentage uncertainty and percentage error in the experimentally determined value of $K_{\mathrm{c}}$ for methanol.

Calculate the percentage of water by mass in the NaCl•2H₂O crystals. Use the data from section 6 of the data booklet and give your answer to two decimal places.

Calculate the uncertainty in the change in pH.

Justify why it is inappropriate to record the uncertainty of the mean as ±0.01 s.

If doubling the concentration doubles the reaction rate, suggest the mean time you would expect for the reaction with 2.00 mol dm⁻³ hydrochloric acid.

Another student, working alone, always dropped the marble chips into the acid and then picked up the stopwatch to start it. State, giving a reason, whether this introduced a random or systematic error.

A student dissolved 0.1240 ± 0.0001 g of Na₂S₂O₃ to make 1000.0 ± 0.4 cm³ of solution to use in the Winkler Method.

Determine the percentage uncertainty in the molar concentration.

A student dissolved 0.1240 ± 0.0001 g of Na₂S₂O₃ to make 1000.0 ± 0.4 cm³ of solution to use in the Winkler Method.

Determine the percentage uncertainty in the molar concentration.

The only significant uncertainty is in the temperature measurement.

Determine the absolute uncertainty in the calculated value of ΔH if the uncertainty in the temperature rise was ±0.2 °C.

Deduce the appropriate number of significant figures for your answer in (d)(i).

Deduce the appropriate number of significant figures for your answer in (e)(i).

The only significant uncertainty is in the temperature measurement.

Determine the absolute uncertainty in the calculated value of ΔH if the uncertainty in the temperature rise was ±0.2 °C.

A student performed an experiment to find the melting point of sulfur, obtaining 118.0 °C. The literature value is 115.2 °C. What was the percentage error?

A.  $\frac{118.0-115.2}{115.2}\times 100\%$

B.  $\frac{115.2}{118.0}\times 100\%$

C.  $\frac{118.0-115.2}{118.0}\times 100\%$

D.  $\frac{118.0}{115.2}\times 100\%$

Determine the percentage uncertainty of the mass of product after heating.

Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).

Determine the percentage uncertainty of the mass of product after heating.

Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).

Carbonates also react with HCl and the rate can be determined by graphing the mass loss. Suggest why this method is less suitable for the reaction of Mg with HCl.

Suggest a reason why the volume of hydrogen gas collected was smaller than predicted.

The experiment gave an error in the rate because the pressure gauge was inaccurate.

Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.

The uncertainty of the 100.0cm³ volumetric flask used to make the solution was ±0.6cm³.

Calculate the maximum percentage uncertainty in the mass of NaHCO₃ so that the concentration of the solution is correct to ±1.0 %.

Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.

Identify one error associated with the use of an accurate stopwatch.

The experiment gave an error in the rate because the pressure gauge was inaccurate. Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.

Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.

Identify one error associated with the use of an accurate stopwatch.

Calculate the percentage uncertainty of the day 5 titre.