Chemistry_Grade_10-12 (1).pdf

B the reactions c o 2 co 2 and 2kclo 3 2kcl 3o 2 are

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(b) The reactions C + O 2 CO 2 and 2KClO 3 2KCl + 3O 2 are examples of redox reactions. 3. For each of the following questions, choose the one correct statement from the list provided. A The following chemical equation represents the formation of the hydronium ion: H + (aq) + H 2 O(l) H 3 O + (aq) In this reaction, water acts as a Lewis base because it... i. accepts protons ii. donates protons iii. accepts electrons iv. donates electrons B What is the concentration (in mol.dm 3 ) of H 3 O + ions in a NaOH solution which has a pH of 12 at 25 0 C? i. 1 × 10 12 ii. 1 × 10 2 iii. 1 × 10 2 iv. 1 × 10 12 (IEB Paper 2, 2005) C When chlorine water is added to a solution of potassium bromide, bromine is produced. Which one of the following statements concerning this reac- tion is correct? i. Br is oxidised ii. Cl 2 is oxidised iii. Br is the oxidising agent iv. Cl is the oxidising agent (IEB Paper 2, 2005) 4. The stomach secretes gastric juice, which contains hydrochloric acid. The gastric juice helps with digestion. Sometimes there is an overproduction of acid, leading to heartburn or indigestion. Antacids, such as milk of magnesia, can be taken to neutralise the excess acid. Milk of magnesia is only slightly soluble in water and has the chemical formula Mg(OH) 2 . 284
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CHAPTER 15. TYPES OF REACTIONS - GRADE 11 15.4 a Write a balanced chemical equation to show how the antacid reacts with the acid. b The directions on the bottle recommend that children under the age of 12 years take one teaspoon of milk of magnesia, whereas adults can take two teaspoons of the antacid. Briefly explain why the dosages are different. c Why is it not advisable to take an overdose of the antacid in the stomach? Refer to the hydrochloric acid concentration in the stomach in your answer. In an experiment, 25.0 cm 3 of a standard solution of sodium carbonate of concentration 0.1 mol.dm 3 was used to neutralise 35.0 cm 3 of a solution of hydrochloric acid. d Write a balanced chemical equation for the reaction. e Calculate the concentration of the acid. (DoE Grade 11 Exemplar, 2007) 285
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15.4 CHAPTER 15. TYPES OF REACTIONS - GRADE 11 286
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Chapter 16 Reaction Rates - Grade 12 16.1 Introduction Before we begin this section, it might be useful to think about some different types of reactions and how quickly or slowly they occur. Exercise: Thinking about reaction rates Think about each of the following reactions: rusting of metals photosynthesis weathering of rocks (e.g. limestone rocks being weathered by water) combustion 1. For each of the reactions above, write a chemical equation for the reaction that takes place. 2. How fast is each of these reactions? Rank them in order from the fastest to the slowest. 3. How did you decide which reaction was the fastest and which was the slowest?
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