6.2. Rate of reaction
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 319 questions
The equation for the reaction between sodium thiosulfate and hydrochloric acid is given below. Na2S2O3+ 2HCl → 2NaCl + S+ SO2+ H2OThe speed of this reaction was investigated using the following experiment. A beaker containing 50 cm3 of 0.2 mol / dm3 sodium thiosulfate was placed on a black cross. 5.0 cm3 of 2.0 mol / dm3 hydrochloric acid was added and the clock was started. look down at cross on paper paper solution turns from colourless to cloudy sodium thiosulfate and hydrochloric acid cross on paper view looking down Initially the cross was clearly visible. When the solution became cloudy and the cross could no longer be seen, the clock was stopped and the time recorded. The experiment was repeated with 25 cm3 of 0.2 mol / dm3 sodium thiosulfate and 25 cm3 of water. Typical results for this experiment and a further two experiments are given in the table. experiment volume of thiosulfate / cm3 volume of water / cm3 volume of acid / cm3 total volume / cm3 time / s Explain why it is necessary to keep the total volume the same in all the experiments. Complete the table. How and why does the speed of the reaction vary from experiment 1 to 4? The idea of collisions between reacting particles is used to explain changes in the speed of reactions. Use this idea to explain the following results. volume of sodium thiosulfate / cm3 volume of water / cm3 volume of acid / cm3 temperature / °C time / s
0620_s11_qp_33
THEORY
2011
Paper 3, Variant 3
View
A student investigated the reaction between zinc and hydrochloric acid using the apparatus shown below. The zinc was in excess. zinc + hydrochloric acid → zinc chloride + hydrogen hydrochloric acid small test-tube held by a piece of cotton zinc powder measuring cylinder water What should the student do to start the reaction? The student measured the volume of gas in the measuring cylinder at minute intervals. The results are shown in the table. time / minutes volume of gas / cm3 Plot the results on the grid below and draw the best curve through the points. time / minutes volume of gas / cm3 Explain why the volume of gas stays the same after 5 minutes. Complete the following sentences about this reaction using words or phrases from the list below. concentration decreases increases speed stays the same volume When the of hydrochloric acid is increased, the volume of gas given off in the fi rst two minutes . Decreasing the temperature of the reaction mixture the of the reaction. When the reaction is complete, the fl ask contains a mixture of zinc and aqueous zinc chloride. Describe how you can obtain pure dry crystals of zinc chloride from this reaction mixture.
0620_s12_qp_21
THEORY
2012
Paper 2, Variant 1
View
A length of magnesium ribbon was added to 50 cm3 of sulfuric acid, concentration 1.0 mol / dm3. The time taken for the magnesium to react was measured. The experiment was repeated with the same volume of different acids. In all these experiments, the acid was in excess and the same length of magnesium ribbon was used. experiment acid concentration in mol / dm3 time / s A sulfuric acid 1.0 B propanoic acid 0.5 C hydrochloric acid 1.0 D hydrochloric acid 0.5 Write these experiments in order of reaction speed. Give the experiment with the fastest speed fi rst. Give reasons for the order you have given in . Suggest two changes to experiment C which would increase the speed of the reaction and explain why the speed would increase. The volume of the acid, the concentration of the acid and the mass of magnesium used were kept the same. change 1 explanation change 2 explanation
0620_s12_qp_32
THEORY
2012
Paper 3, Variant 2
View
A length of magnesium ribbon was added to 50 cm3 of sulfuric acid, concentration 1.0 mol / dm3. The time taken for the magnesium to react was measured. The experiment was repeated with the same volume of different acids. In all these experiments, the acid was in excess and the same length of magnesium ribbon was used. experiment acid concentration in mol / dm3 time / s A sulfuric acid 1.0 B propanoic acid 0.5 C hydrochloric acid 1.0 D hydrochloric acid 0.5 Write these experiments in order of reaction speed. Give the experiment with the fastest speed fi rst. Give reasons for the order you have given in . Suggest two changes to experiment C which would increase the speed of the reaction and explain why the speed would increase. The volume of the acid, the concentration of the acid and the mass of magnesium used were kept the same. change 1 explanation change 2 explanation
0620_s12_qp_33
THEORY
2012
Paper 3, Variant 3
View
Questions Discovered
319