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Chemical cells produce a voltage. A chemical cell can be made by placing the metals copper and iron in a beaker of sodium chloride solution as shown in Figure 1 (copper electrode in sodium chloride solution with another iron electrode). Describe what will happen to the reading on the voltmeter over a long period of time.
The reading on the voltmeter will decrease and over a long period of time the reactants will be used up and the READING ON THE VOLTMETER WILL BE 0
Complete Figure 3 by drawing and labelling apparatus that could be used to collect and measure the volume of the carbon dioxide gas
Marble chip experiment: The student repeats the experiment using the same mass of smaller marble chips. All other conditions remain the same. Explain the effect on the rate of reaction of using smaller marble chips
The rate of reaction will increase due to the higher surface area and the higher frequency of collisions
Explain why solid sodium carbonate cannot conduct electricity but a solution of sodium carbonate can conduct electricity
This is because the ions in solid sodium carbonate are regularly arranged and vibrate about fixed points, so they are immobile. However in a solution of sodium carbonate the ions are mobile and are able to carry an electrical current, because the strong electrostatic bonds have been weakened.
Explain how the atom economy of the fermentation reaction can be improved with the equation C12H22O11 + H2) —> 4C2H5OH + 4CO2
Find a use for the CO2, so the carbon dioxide becomes a useful product
This question is about the extraction of metals. Give two advantages of obtaining metals by recycling rather than by extracting them from their metal ores
Ores are finite, uses less energy, prevents waste of the metal
Small amounts of some metals are extracted using displacement reactions. In one process, zinc dust is used to precipitate cadmium metal from a solution containing cadmium ions. Cadmium ions + Zinc —> Cadmium + Zinc ions. Explain why this displacement reaction can be described as a redox reaction.
Reduction and oxidation is occurring. Reduction is the gain of electrons but the loss of oxygen. Oxidation is the loss of electrons but the gain of oxygen. Zinc dust has been oxidised because it has lost 2 electrons to form a positive ion (cation). Cadmium ions have been reduced because it has gained 2 electrons to form a cadmium atom.
One of the alternative biological methods of extracting metals from very low grade ores is bioleaching using bacteria. Give one disadvantage of this method of extracting metals from low-grade ores.
Very slow, low yield
Bioleaching and phytoextraction definitions to remember
Bioleaching:
Uses biological processes
Avoid significant environmental damage
Very slow
Require electrolysis or displacement to purify the extracted metal
Used to extract metals from mining wastes which may contain small quantities of metals or toxic metals that need to be removed from that environment
Doesn’t require high temps
Phytoming:
Biological processes
Avoids significant environmental damage
Very slow
This process takes advantage of how some plants absorb metals through their roots
The plants are grown in areas known to contain metals of interest in the soil
Concentrated in specific parts such as their shoots and leaves
Parts of the plant here are harvested, dried and burned
The ash left contains the useful metal compounds which can be extracted by displacement reactions or electrolysis
Lead is low in the reactivity series. Describe how to obtain a sample of lead from some lead oxide in the laboratory
You need to react the lead oxide with a more reactive element to displace the lead by itself: carbon, hydrogen, methane - add heat.
Complete and balance the half equation for the formation of oxygen at the positive electrode in electrolysis
4OH- —> O2 + 2H2O + 4e-
When hydrocarbon fuels are burned, the products are water and carbon dioxide. Describe what needs to be done to the apparatus in Figure 8 to collect the water and show that carbon dioxide has been produced.
Place ice cold water in the beaker around tube A to condense the water vapour into water
Bubble tube B through lime water and if carbon dioxide is present it will go from clear to cloudy white
Describe what should be done to the copper cathode, after it has been removed from the copper sulfate solution, before its final mass is determined
Explain, in terms of ions, the change in mass of the cathode shown in Figure 6 (before electrolysis mass was 5.32g but after electrolysis mass was 5.87g)
Positive copper ions were all reacted and moved towards the cathode where they gained electrons to form copper atoms (cathode is the negative electrode), increasing the mass of the cathode as it gained copper atoms.
Explain why the appearance of the copper sulfate solution did not change during the electrolysis
Explain the meaning of the terms dilute and strong acid
Dilute: Low concentration of OH- ions and H+ ions and most of the substance has been dissolved so the pH of the solution is lower and therefore weaker
Strong acid: There are more H+ ions as they have fully disassociated in the water, so there is a stronger, higher concentration of them in the acid, as the maximum number of H+ ions were produced.
Equilibrium and rate of attainment
An increase in temperature reaches equilibrium faster because molecules move faster
Therefore there are more frequent collisions because molecules have more energy
More energy is used up in collisions so the yield will decrease
Catalyst causes the reaction to reach equilibrium faster
Increases both forward and backward reactions
Lowers the activation energy but does not lower the yield
A decrease of pressure will cause the equilibrium to shift to the side of the reaction with more gas molecules
An increase in pressure will cause the rate of attainment of equilibrium to increase because the particles have more kinetic energy so there would be more successful collisions occurring
A decrease in pressure will slow the rate of attainment of equilibrium because there are less frequency of collisions occurring as the particles are further away from each other
