CAIE
Chemistry
(9701)
Questions & Answers
You should assume that gas X behaves like an ideal gas and so use PV = nRT. R = 8.31 J K^-1 mol^-1. Calculate the moles of gas X.
The sample of gas X is found to have a mass of 0.251 g. Explain how the student should use this information and their results to determine the Mr of X.
Not all of gas X is absorbed by the soda lime. State what effect, if any, this has on the student's calculated value of the Mr of gas X.
In Experiment 2, the same mass of gas X is used, but the student did not record the temperature and pressure. The calculated Mr of X for Experiment 2 is higher than the value calculated by the student for Experiment 1. State and explain how the value of P/T changes from Experiment 1 to Experiment 2.
State how the reliability of the results in Experiment 1 could be improved.
A different gas, methylamine, is alkaline. State a change that would have to be made to the apparatus so that the Mr of methylamine could be determined.
Each student carries out the following steps in the order shown in the list. Some of the measurement steps are missing from the list. State the two additional measurement steps that each student must perform in order to find the formula of the chloride of iron.
The flow of dry chlorine gas must start before the iron wire is heated. Explain why.
State an assumption that has to be made for the measurements made in this experiment to be valid.
The class results are shown in the table. Calculate the mass of chlorine that reacts with the iron wire in each experiment. Record each mass to two decimal places. Calculate the amount of iron, in mol, and amount of chlorine atoms, in mol, that reacts in each experiment. Record the number of moles to three significant figures. [Ar: Fe, 55.8; Cl, 35.5]
Plot a graph on the grid of the amount of chlorine atoms against the amount of iron. Use a cross (×) to plot each data point. Draw a line of best fit through the plotted points. You should consider whether (0,0) should be on the line of best fit.
Circle the point on the graph you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure.
Use the graph to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be on your line of best fit. Give your answer to three significant figures.
The formula of the chloride of iron produced in this experiment is FeCl3. State how the results student 4 obtains could be used to determine this formula.
Student 3 weighs the conical flask using a balance accurate to two decimal places and records its mass. After the chloride of iron is produced the mass increases by 4.03 g. Calculate the percentage error in measuring the mass of this chloride of iron.
Student 8 follows the same procedure as student 3. State whether the results from student 8 will have more or less percentage error than those from student 3. Explain your answer.
A sample of a chloride of iron prepared by reaction between iron wire and hydrochloric acid contains 44% iron by mass. Show that the formula of this chloride of iron is FeCl2. [Ar: Fe, 55.8; Cl, 35.5]
Explain, using the electrode potential values in the table, why the methods in (a) and (f) do not produce the same chlorides of iron. [Fe2+(aq) + 2e- -> Fe(s), Eo = -0.44 V; 2H+(aq) + 2e- -> H2(g), Eo = 0.00 V; Fe3+(aq) + e- -> Fe2+(aq), Eo = +0.77 V]