6.3. Reversible reactions and equilibrium
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 390 questions
This question is about cobalt and its compounds. A coloured crystal of cobalt(chloride was placed at the bottom of a beaker containing water. After 2 days, the colour had spread throughout the water. at the start after 2 hours after 2 days crystal of cobalt(chloride water Explain these observations using the kinetic particle model. Cobalt(chloride can be used to test for the presence of water. CoCl 2 + 6H2O CoCl 2.6H2O anhydrous hydrated cobalt(chloride cobalt(chloride What is meant by the symbol ? Describe how the colour of anhydrous cobalt(chloride changes when water is added to it. from to  A compound of cobalt can be represented by the structure shown. = cobalt, Co = carbon, C = oxygen, O key Deduce the molecular formula of this compound showing the number of cobalt, carbon and oxygen atoms. The table compares the reactivity of cobalt with that of three other metals. metal reactivity with cold water reactivity with steam barium reacts rapidly cobalt no reaction reacts slowly when heated magnesium reacts very slowly reacts rapidly zinc no reaction reacts easily when heated Use this information to put the metals in order of their reactivity. Put the least reactive metal first. least reactive most reactive  Cobalt is a transition element. Lithium is an element in GroupI of the Periodic Table. Describe three ways in which the properties of cobalt differ from those of lithium.  When cobalt(oxide, CoO, is heated in air, an oxide with the formula Co3O4 is formed. Balance the chemical equation for this reaction. CoO + O2 2Co3O4  When Co3O4 is heated with hydrogen, cobalt metal can be formed. Co3O4 + 4H2 3Co + 4H2O How does this equation show that Co3O4 is reduced? 
0620_s18_qp_33
THEORY
2018
Paper 3, Variant 3
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Hydrogen and iodine react together in a reversible reaction. Hydrogen iodide is formed. H2+ I22HIcolourless purple colourless gas gas gas The forward reaction is exothermic. A gas syringe containing an equilibrium mixture of hydrogen, iodine and hydrogen iodide gases was sealed and heated to 250 °C. The equilibrium mixture was a pale purple colour. end blocked equilibrium mixture of hydrogen, iodine and hydrogen iodide What is meant by the term equilibrium? The plunger of the gas syringe was pressed in while the end of the gas syringe was blocked. This increased the pressure. The position of the equilibrium did not change. The colour of the gaseous mixture turned darker purple. Give a reason why the position of the equilibrium did not change. Suggest why the gaseous mixture turned darker purple, even though the position of the equilibrium did not change. The temperature of the gas syringe was increased to 300 °C. What happened to the position of the equilibrium when the temperature of the gas syringe was increased from 250 °C to 300 °C? What happened to the rate of the forward reaction and the rate of the backward reaction when the temperature of the gas syringe was increased from 250 °C to 300 °C? rate of the forward reaction rate of the backward reaction
0620_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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Cobalt is a transition element. Potassium is in GroupI of the PeriodicTable. State one physical property that is similar for cobalt and potassium. State one physical property that is different for cobalt and potassium. Describe how the physical property given in is different for cobalt compared to potassium. When a small piece of potassium is added to cold water, the potassium floats and disappears as it reacts. Give two other observations that would be made when a small piece of potassium is added to cold water. Cobalt reacts with dilute hydrochloric acid to make the salt cobalt(chloride. Bubbles of hydrogen gas are produced. Describe a test for hydrogen. test result  The rate of reaction of cobalt with dilute hydrochloricacid can be made faster by heating the acid or by increasing its concentration. State one other way to make the rate of reaction faster. Use collision theory to explain how heating the dilute hydrochloricacid makes the rate of reaction faster. When cobalt(chloride is added to water an equilibrium is established. [CoCl 4]2– + 6H2O [Co(H2O)6]2+ + 4Cl – blue pink A student adds water to a blue solution containing [CoCl 4]2– ions. Describe what the student observes. Give a reason for your answer in terms of the position of the equilibrium. Another student cools a blue solution containing [CoCl 4]2–. The blue solution turns pink. What does this information indicate about the forward reaction? Another compound of cobalt is Co(OH)3. Deduce the charge on the cobalt ion in Co(OH)3.
0620_s18_qp_43
THEORY
2018
Paper 4, Variant 3
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