ACIDS AND ph MODULE 2 WORKSHEET10. Syllabus reference 9.3.3

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1 MODULE 2 WORKSHEET10 ACIDS AND ph Syllaus reference For questions 110 circle the letter which corresponds to the correct answer. 1 Which of the following is incorrect with respect to acids? Acids: A are proton donors B react with many metals to give a salt plus hydrogen C turn litmus red D react with non-metals to give a salt plus oxygen 2 A strong acid compared to a weak acid: A has a stronger taste B contains only H C ionises completely D has a ph of 7 3 The acid most commonly found in soft drinks is: A caronic acid B hydrochloric acid C carolic acid D sulfuric acid 4 The ph of pure water is: A 0 B 1 C 7 D 14 5 The ph most likely to e measured for a strong ase is: A 0 B 5 C 8 D 13 6 The acid present in largest amounts in oranges and lemons is: A ascoric acid B citric acid C acetic acid D caronic acid 7 In going from a ph of 4 to a ph of 5 the concentration of hydrogen ions: A increases y a factor of 10 B decreases y a factor of 10 C doules D increases y 1

2 8 Which one of the following statements aout the relative concentrations of molecules and CH 3 COO ions in an aqueous solution of acetic acid is correct? A only CH 3 COOH molecules are present in the solution B the concentration of CH 3 COOH molecules is greater than the concentration of CH 3 COO ions C the concentration of CH 3 COOH molecules is less than the concentration of CH 3 COO ions D all acetic acid has dissociated to H and CH 3 COO ions 9 In a neutral solution: A [H 3 O ] [OH ] B [H 3 O ] [OH ] C [H 3 O ] [OH ] D ph 0 10 The ph of a rand of cola is 3.0. The concentration of hydrogen ions in solution is: A 10 3 mol/l B mol/l C log 3.0 mol/l D 3.0 mol/l 11 In the space provided, explain how the meanings of the two terms in each pair differ. For some terms there may e no difference. a ph and hydrogen ion concentration ph log [H ] strong acid and weak acid Strong acid ionises completely, no neutral acid molecules present. In weak acid only some molecules have ionised to produce H. c hydronium ion and hydrogen ion hydronium ion H 3 O hydrogen ion H d ph 5 and ph 9 ph 5 [H ] 10 5 mol/l ph 9 [H ] 10 9 mol/l e litmus and acidase indicator Litmus is an example of an acid ase indicator.

3 f ph 7 and neutral solution Neutral solution has a ph 7. g ph meter and indicator solution Both give an indication of ph of solution. h concentration and strength Concentration is a measure of numer of ions or molecules present. Strength is the degree to which an acid ionises. i K w and ph K w ionic product constant for water ph measure of concentration of H 12 Lael each of the four diagrams elow as one of the following: concentrated strong acid, concentrated weak acid, dilute strong acid, dilute weak acid. In order: concentrated strong acid, dilute strong acid, concentrated weak acid, dilute weak acid. positive ion negative ion un-ionised neutral molecule 13 Write an ionic equation to show: a self-ionisation of water 2H 2 O H 3 O OH ionisation of HBr (a strong acid) in water HBr(aq) H 2 O(l) H 3 O (aq) Br (aq)

4 c ionisation of CH 3 COOH (a weak acid) in water CH 3 COOH(aq) H 2 O(l) H 3 O (aq) CH 3 COO (aq) 14 Calculate the ph of a solution that contains: a mole of H per L g of H per L 2.7 c mol of H per L 2.52 d mol of OH per L e g OH per 100 ml Calculate the hydrogen ion concentration of solutions having a ph of: a mol/l mol/l

5 c mol/l 16 Complete the following tale. ACID SYSTEMATIC NAME FORMULA ACETIC ethanoic CH 3 COOH acid NATURAL OR SYNTHETIC natural SOURCE made from wine y oxidation of ethanol CITRIC 2-hydroxypropane- 1,2,3-tricaroxylic acid C 6 H 8 O 7 natural citrus fruit HYDROCHLORIC hydrochloric acid HCl natural stomach SULFURIC sulfuric acid H 2 SO 4 synthetic manufactured 17 Indicators can e used to determine if solutions are acidic or asic. A group of students was testing a household sustance to decide on its acidity or asicity. Four indicators and their colour change points are given elow. INDICATOR Methyl red Bromothymol lue Phenol red Phenolphthalein COLOUR CHANGE Pinkyellow Yellowlue Yellowred Colourlessred ph RANGE A mixture of all four indicators turned a solution yellow. One student said this indicated the solution was neutral, while another determined it must e acidic. a Assess the validity of the two students claims. Solution most likely acidic ecause in an acidic solution methyl red is yellow, romothymol lue is yellow, phenol red is yellow and phenolphthalein is colourless, resulting in a yellow solution.

6 Suggest one way in which the ph of the solution could e determined more accurately. Use a ph meter mol/l solutions of hydrochloric, acetic and citric acids were prepared. The concentration of H in the HCl solution was found to e 0.10 mol/l, in the acetic acid solution mol/l and in citric acid mol/l. a Calculate the ph for each acid. HCl ph 1.00 Acetic acid ph 3 Citric acid ph 2.1 c Arrange them in order of acid strength from strongest to weakest acid. HCl, citric acid, acetic acid Explain the difference in strengths of each of the three acids in terms of the numer of intact molecules compared to the ions. HCl ionises completely so no intact molecules, citric acid some intact molecules, acetic acid many intact molecules. 19 Give two reasons why acids are frequently added to food, naming acids commonly used. To improve taste and preserve the food. Acids commonly used are acetic acid, citric acid, and occasionally phosphoric acid. 20 Complete the following tale. BASE Ammonia Amine Metallic oxide Caronate Sodium hydroxide Calcium oxide FORMULA NH 3 R NH 2 MO x M CO 3 NaOH CaO NATURAL OR SYNTHETIC SOURCE USE Synthetic Synthetic Urine Anaeroic decomposition Ores Mineral, limestone Made from common salt Heating limestone Fertiliser, cleaning agent Proteins, making nylon Source of metals Manufacturing glass, paper, soap, detergent Making soap, detergent, synthetic fires Making cement