Chemical Reactions | Class Exercises | Chemistry | Form 2 | CBC

KASEMPA DAY SECONDARY

NATURAL SCIENCE

CLASS EXERCISE

FORM: 2

SUBJECT: CHEMISTRY

TEACHER: MASUMBA

INSTRUCTION: Answer ALL questions.

1. In the laboratory you add a small strip of zinc metal to dilute hydrochloric acid and see bubbles form. a) Describe this chemical change in one sentence using the phrase "chemical reaction". b) Write the word equation for the change. c) Construct a balanced chemical equation with correct state symbols. 2. A pupil mixes aqueous solutions of sodium chloride and silver nitrate and a white solid forms. The teacher gives you the chemicals. a) State the observation that shows a chemical reaction has occurred. b) Write the balanced molecular equation with state symbols. c) Construct the net ionic equation. 3. While heating copper(II) carbonate powder a pupil observes a green solid change to a black powder and a gas is given off. a) Describe this chemical reaction as one of the types listed in class (synthesis, decomposition, single displacement, double displacement, chain reaction). b) Write the balanced chemical equation for the decomposition, with state symbols. 4. At home you mix iron nails with a copper(II) sulphate solution to see if a reaction happens. a) Predict what you will observe if a single displacement reaction occurs. b) Write the balanced chemical equation showing the displacement, with state symbols. 5. A cook heats maize flour and water to make nshima. The teacher compares this to an endothermic change. a) Explain in two short sentences why making nshima is like an endothermic chemical process or not. b) Give one classroom chemical example of an endothermic reaction and write its balanced equation with state symbols. 6. In a practical, you add pieces of marble (calcium carbonate) to dilute hydrochloric acid. You measure the time taken for bubbling to stop. a) Explain which factor from class (temperature, concentration, surface area, pressure, catalyst, light) you change to speed up the reaction. b) Describe one safety point for this experiment. 7. A teacher gives two beakers. Beaker A has 0.5 mol of powdered calcium carbonate in 100 cm³ of 1.0 mol dm^-3 HCl. Beaker B has one large lump of the same mass of calcium carbonate in the same acid volume. a) Predict which beaker reacts faster. b) Explain your answer using particle/collision ideas in two short sentences. 8. In a kitchen you see leftover potato added to a beaker of hydrogen peroxide producing rapid bubbling. a) Name the factor from class that the potato provides to speed the reaction. b) Write the balanced chemical equation for hydrogen peroxide decomposition, with state symbols. 9. A class measures time for magnesium ribbon to dissolve in HCl at 20°C and at 40°C. a) Predict which temperature gives the faster rate. b) Give one short reason referring to collision frequency or energy. 10. During a school practical you dilute acid in two trials. Trial 1 uses 1.0 mol dm^-3 HCl, trial 2 uses 0.5 mol dm^-3 HCl. Equal masses of zinc powder are added. a) State which trial shows a faster rate. b) Explain why in one sentence referring to concentration. 11. A learner mixes aqueous lead(II) nitrate and aqueous potassium iodide and notices a yellow solid forms quickly. a) Identify the type of chemical reaction. b) Write the balanced molecular equation with state symbols. 12. Your teacher asks you to write net ionic equations in class. You are given the balanced molecular equation: BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2 NaCl(aq). a) List the strong aqueous ions present before cancellation. b) Write the net ionic equation showing only the species that change state. 13. A community clinic uses quicklime (calcium oxide) to heat a pile of damp maize husks. The pile warms up noticeably. a) Suggest whether the chemical change of CaO with water is exothermic or endothermic. b) Give the balanced chemical equation for the reaction, with state symbols. 14. In a classroom test you mix two clear solutions and the mixture becomes cloudy slowly over 5 minutes. The teacher asks you to explain the meaning of "rate of reaction" using this observation. a) Define "rate of a chemical reaction" in one sentence. b) Say whether the observed reaction is slow or fast. 15. A pupil times how long it takes for a cross under a flask to disappear when sodium thiosulphate reacts with dilute HCl. The times are shorter when the temperature is higher. a) Describe one safe step to take during this experiment. b) Explain why increasing temperature shortens the time in two short sentences. 16. A farmer adds powdered aluminium to a bucket of water and notices no reaction. He then adds a small amount of iron filings and sees heating. a) Suggest what the iron filings did in class terms (from the factor list). b) Name the factor and explain briefly how it changed the rate. 17. In an experiment you mix aqueous solutions of potassium permanganate and hydrogen peroxide in the presence of dilute sulphuric acid. The purple colour fades quickly. a) Identify this as a redox reaction or not, using one short sentence. b) State one classroom method to show that the reaction rate increases when concentration increases. 18. A data table shows gas volumes collected at equal time intervals from reaction of marble chips with acid. The first column is time (s); the second is total gas volume (cm³). The gas volume increases rapidly then levels off. a) Explain what the graph of volume against time tells you about the reaction rate. b) Name two factors that could make the initial slope steeper. 19. In a practical you are asked to produce a net ionic equation from a balanced reaction that forms an insoluble salt. The teacher gives the word change: "aqueous silver nitrate reacts with aqueous sodium chloride to form solid silver chloride and aqueous sodium nitrate". a) Write the balanced molecular equation with state symbols. b) Show the ionic equation and then the net ionic equation. 20. During exam revision you must design a short class experiment using household materials to investigate one factor affecting reaction rate. a) State the factor you will investigate. b) List three simple materials or apparatus you will use. c) Give three numbered steps you will follow in the experiment.

assignment — Chemistry (Chemical Reactions)

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