QUESTIONSHEETS ACID-BASE TITRATIONS PREPARATION OF A STANDARD SOLUTION SIMPLE VOLUMETRIC CALCULATIONS

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1 CHEMISTRY QUESTIONSHEETS AS Level AS TOPIC 3 ACID-BASE TITRATIONS Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 Questionsheet 12 Questionsheet 13 MOLAR SOLUTIONS PREPARATION OF A STANDARD SOLUTION SIMPLE VOLUMETRIC CALCULATIONS CALCULATIONS REQUIRING MOLAR CONCENTRATION OF A PRIMARY STANDARD DILUTION QUESTIONS WATER OF CRYSTALLISATION PERCENTAGE PURITY TEST QUESTION I TEST QUESTION II TEST QUESTION III EXPERIMENT TO FIND THE EQUATION FOR A REACTION ESTIMATING THE CONCENTRATION OF SALTS IN SEA WATER EXPERIMENT TO FIND THE EQUATION FOR A REACTION DECOMPOSITION OF POTASSIUM HYDROGEN CARBONATE 15 marks 14 marks 12 marks 16 marks 15 marks 14 marks 14 marks 15 marks 16 marks 16 marks 12 marks 9 marks 16 marks Authors Trevor Birt Donald E Caddy Andrew Jones Adrian Bond Editors John Brockington Stuart Barker John Brockington Kevin Frobisher Andy Shepherd Stuart Barker Curriculum Press Licence Agreement: Paper copies of the A-Level Chemistry Questionsheets may be copied free of charge by teaching staff or students for use within their school, provided the Photocopy Masters have been purchased by their school. No part of these Questionsheets may be reproduced or transmitted, in any other form or by any other means, without the prior permission of the publisher. All rights are reserved. This license agreement is covered by the laws of England and Wales Curriculum Press March Curriculum P ress Curriculum Press Bank House 105 King Street Wellington Shropshire TF1 1NU

2 AS Level TOPIC 3 Questionsheet 1 MOLAR SOLUTIONS a) Define the terms molar concentration (or molarity ) and molar solution. Molar concentration... Molar solution... b) What is the molar concentration of each of the following? Hydrochloric acid containing 146 g dm -3 of HCl. Potassium iodide solution containing 300 g dm -3 of KI. c) A solution of ethanedioic acid-2-water, H 2 O 4.2H 2 O, was made by dissolving 1.48 g of the pure solid in water and making up to the graduation mark in a 250 cm 3 graduated flask. Calculate the concentration of the solution: in g dm -3 in mol dm -3 d) How much anhydrous sodium carbonate must be weighed out in order to prepare 250 cm 3 of solution of concentration 0.05 mol dm -3? e) What mass of sodium hydroxide is present in 500 cm 3 of a solution of concentration mol dm -3? TOTAL / 15

3 AS Level TOPIC 3 Questionsheet 2 PREPARATION OF A STANDARD SOLUTION a) What is meant by a primary standard in volumetric analysis? State three requirements of a primary standard. b) Anhydrous sodium carbonate can be used as a primary standard in acid-base titrations. In an experiment, a student weighed an empty weighing bottle on an analytical balance. She took the bottle off the balance pan, added some anhydrous sodium carbonate and reweighed the bottle, after which she tipped the sodium carbonate into a 100 cm 3 beaker and weighed the bottle again. Using a stirring rod, she dissolved the sodium carbonate in deionised water, and then poured the solution into a 250 cm 3 graduated volumetric flask. She washed the beaker and stirring rod with deionised water and transferred the washings also to the graduated flask. With more deionised water she made the solution up to the graduation mark, adding water dropwise at the end. Finally, she inserted the stopper and slowly inverted the flask about six times. Why did the student use an analytical balance? Why did she take the bottle off the balance pan before adding the sodium carbonate? (iii) Why did she reweigh the bottle after tipping the sodium carbonate into a beaker? (iv) Why did she use deionised water rather than tap water? (v) Why did she wash out the beaker and transfer the washings? (vi) When filling the flask to the graduation mark, why did she add deionised water dropwise at the end? (vii) How did the student know when she had added the correct amount of water? (viii)why did she invert the flask about six times? (ix) Why did she invert the flask slowly? (x) What would the student have done if she had overfilled the graduated flask with deionised water? TOTAL / 14

4 AS Level TOPIC 3 Questionsheet 3 SIMPLE VOLUMETRIC CALCULATIONS NOTE Throughout this Questionsheet marks are awarded for correctly balanced chemical equations. a) What volume of sulfuric acid containing 0.20 mol dm -3 is required to neutralise completely 20.0 cm 3 of a solution of potassium hydroxide containing 0.50 mol dm -3? b) 25.0 cm 3 of a solution of sodium hydroxide is neutralised by 19.8 cm 3 of a solution of hydrochloric acid containing 0.15 mol dm -3. Calculate the concentration of the sodium hydroxide solution. c) Calculate the volume of sodium hydroxide solution, containing mol dm -3, required to neutralise a solution containing g of ethanoic acid, CH 3 COOH. d) A sample of sodium carbonate solution was neutralised by 19.6 cm 3 of hydrochloric acid of concentration mol dm -3. Calculate the mass of sodium carbonate in the sample solution. TOTAL / 12

5 AS Level TOPIC 3 Questionsheet 4 CALCULATIONS REQUIRING MOLAR CONCENTRATION OF A PRIMARY STANDARD NOTE Throughout this Questionsheet marks are awarded for correctly balanced chemical equations. a) g of anhydrous sodium carbonate were dissolved in deionised water and the solution was made up to 250 cm 3 in a graduated flask cm 3 of this solution neutralised 24.6 cm 3 of dilute sulfuric acid. Calculate, first, the concentration of sodium carbonate, then that of the sulfuric acid, both in moles per dm [5] b) Why is sodium hydroxide unsuitable as a primary standard? In order to standardise a solution of sodium hydroxide, a chemist first prepared a solution of ethanedioic acid-2-water, H 2 O 4.2H 2 O, by dissolving 14.6 g of crystals in water and making the solution up to 250 cm 3 in a graduated flask. He then pipetted 25.0 cm 3 of this solution into a conical flask, added phenolphthalein solution as indicator, and titrated it against the sodium hydroxide solution: 24.1 cm 3 of the latter were required. Calculate, first, the molar concentration of the ethanedioic acid solution, and then that of the sodium hydroxide.... [5] (iii) The chemist then used the standardised sodium hydroxide to estimate the concentration of sulfuric acid from a car battery. He found that 2.00 cm 3 of battery acid were neutralised by 20.7 cm 3 of the sodium hydroxide solution. Calculate the concentration of sulfuric acid in the battery acid in grams per dm [4] TOTAL / 16

6 AS Level TOPIC 3 Questionsheet 5 DILUTION QUESTIONS NOTE Throughout this Questionsheet, marks are awarded for correctly balanced chemical equations. a) Why must concentrated solutions be diluted before being titrated by normal laboratory standard solutions? b) 10.0 cm 3 of concentrated hydrochloric acid were pipetted into a 1dm 3 graduated flask and diluted to the graduation mark with deionised water cm 3 of this diluted solution were titrated by 23.6 cm 3 of aqueous sodium hydroxide containing mol dm -3. Calculate, first, the molar concentration of the diluted hydrochloric acid, and then that of the concentrated hydrochloric acid.... [4] c) In an experiment to determine the ethanoic acid content of vinegar, 25.0 cm 3 of vinegar were diluted to 200 cm 3 with deionised water cm 3 of the diluted solution were titrated by 25.5 cm 3 of sodium hydroxide solution of concentration mol dm -3. Calculate the following. The mass of ethanoic acid in a 350 cm 3 bottle of vinegar.... [6] The mass of ethanoic acid in a 1.14 dm 3 bottle of vinegar. (iii) The volume of M NaOH(aq) which would have been needed to titrate 25.0 cm 3 of the original vinegar. TOTAL / 15

7 AS Level TOPIC 3 Questionsheet 6 WATER OF CRYSTALLISATION NOTE Throughout this Questionsheet, marks are awarded for correctly balanced chemical equations. a) 1.33g of hydrated ethanedioic acid, H 2 O 4.nH 2 O, were dissolved in deionised water and the solution made up to 250 cm 3 in a graduated flask cm 3 of this solution were titrated by 21.1 cm 3 of aqueous sodium hydroxide of concentration mol dm -3. Calculate the number of molecules of water of crystallisation in the hydrated ethanedioic acid by answering the following questions. How many moles of anhydrous H 2 O 4 are there in 1 dm 3 of solution? Convert this to a mass of anhydrous H 2 O 4 in 1 dm 3. (iii) What is the mass of water of crystallisation in 1 dm 3? (iv) Convert this to the number of moles of water of crystallisation in 1 dm 3. (v) How many moles of water are associated with 1 mole of anhydrous H 2 O 4? b) g of hydrated potassium carbonate, K 2 CO 3.xH 2 O, were dissolved in deionised water to make 1 dm 3 of solution cm 3 of this solution required 30.0 cm 3 of a solution of sulfuric acid, containing mol dm -3, for neutralisation. Calculate the value of x.... [6] TOTAL / 14

8 AS Level TOPIC 3 Questionsheet 7 PERCENTAGE PURITY NOTE Throughout this Questionsheet, marks are awarded for correctly balanced chemical equations. a) On storage, calcium hydroxide (agricultural slaked lime ) is slowly converted into calcium carbonate. What is the cause of this deterioration? Write a chemical equation for the change. b) In an experiment to determine the purity of a batch of slaked lime, g was weighed out, transferred to a beaker, and sufficient water added to dissolve the calcium hydroxide. The insoluble calcium carbonate was filtered off and discarded. The solution was then titrated by 20.8 cm 3 of hydrochloric acid of concentration mol dm -3. Why was the calcium carbonate filtered off before the solution was titrated? Calculate the percentage purity of the slaked lime.... [4] c) A bottle of sodium chloride had become contaminated by sodium carbonate g of the mixture were dissolved in deionised water and made up to 250 cm cm 3 of this soution were titrated with 18.6 cm 3 of hydrochloric acid of concentration mol dm -3. Calculate the percentage purity of the sodium chloride.... [6] TOTAL / 14

9 AS Level TOPIC 3 Questionsheet 8 TEST QUESTION I NOTE Throughout this Questionsheet marks are awarded for correctly balanced chemical equations. a) 1.15 g of a monobasic (monoprotic) organic acid were dissolved in water to make 250 cm 3 of solution cm 3 of this solution required 25.0 cm 3 of sodium hydroxide solution containing mol dm -3 for complete neutralisation. Calculate the molar mass of the organic acid.... [4] b) Find the volume of a solution of nitric acid, containing 0.40 mol dm -3, which will react exactly with 1.00 g of magnesium carbonate.... [4] c) A road tanker has crashed on a motorway, spilling 1000 dm 3 of 10 M hydrochloric acid (i.e. of concentration 10 mol dm -3 ). Calculate the minimum mass of calcium carbonate that the fire brigade would need to neutralise this acid. Suggest two reasons why the fire brigade neutralised the acid with calcium carbonate rather than sodium hydroxide ( caustic soda ). Reason [2] Reason [2] TOTAL / 15

10 AS Level TOPIC 3 Questionsheet 9 TEST QUESTION II Two brands of washing soda, Deluxwash and Econosoda, are available in a supermarket. Both brands contain sodium carbonate but in different percentages. The percentage of sodium carbonate in each brand was determined by titration against hydrochloric acid. a) The concentration of the hydrochloric acid to be used was first determined by titration against a sodium hydroxide solution of known concentration. Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide. It required 19.2 cm 3 of 0.5 M sodium hydroxide to neutralise 25.0 cm 3 of hydrochloric acid. Calculate the molarity of the hydrochloric acid. b) 20.0 g of Econosoda was fully dissolved in 1 dm 3 of water cm 3 of this solution was pipetted into a conical flask. It required 19.1 cm 3 of the hydrochloric acid to neutralise the solution of Econosoda in the conical flask. Write a balanced equation for the reaction between sodium carbonate and hydrochloric acid. Calculate the molarity of the sodium carbonate solution in the conical flask. (iii) Calculate the percentage by mass of sodium carbonate contained in Econosoda. c) In a similar experiment it was found that Deluxwash contained 98% sodium carbonate by mass. 500 g of Econosoda cost 1.75 and 500 g of Deluxwash cost Determine by calculation which brand of washing soda is better value for money.... [4] TOTAL / 16

11 AS Level TOPIC 3 Questionsheet 10 TEST QUESTION III The human stomach contains a weak solution of hydrochloric acid. If excess hydrochloric acid is produced, it may lead to painful indigestion. This can be treated by solid indigestion tablets which contain sodium hydrogencarbonate to neutralise the excess hydrochloric acid. a) Write a balanced equation for the reaction between hydrochloric acid and an aqueous solution of sodium hydrogencarbonate. b) A 5.00 g indigestion tablet, containing 85% sodium hydrogencarbonate, was crushed and dissolved in 250 cm 3 of water. Calculate the concentration of the sodium hydrogencarbonate solution formed. Calculate the volume of 0.15 M hydrochloric acid that 25 cm 3 of the sodium hydrogencarbonate solution would neutralise. c) Whilst doing some car repairs, a mechanic spilt 10 cm 3 of car battery acid on his hand. The battery acid was 2 mol dm -3 sulfuric acid. He decided to neutralise the acid using the indigestion tablets referred to in b). Calculate the number of indigestion tablets required to neutralise the acid fully.... [5] d) Another popular indigestion cure is Milk of Magnesia, which contains a suspension of magnesium hydroxide. Give two reasons why Milk of Magnesia is better as an indigestion cure than solid sodium hydrogencarbonate tablets. Advantage 1... Advantage 2... TOTAL / 16

12 AS Level TOPIC 3 Questionsheet 11 EXPERIMENT TO FIND THE EQUATION FOR A REACTION Weigh a clean dry test tube, add about 0.5 g of iron filings, and reweigh. Weigh another clean dry test tube, add about 2.5 g of copper(ii) sulfate, and reweigh. Add distilled water to the tube containing copper(ii) sulfate until it is about a third full, then heat until almost boiling to dissolve the crystals. Add this solution of copper(ii) sulfate to the iron filings in two stages, mixing together thoroughly. Leave for one minute for the reaction to complete. Allow the solid to settle and remove the solution with a teat pipette. Wash the copper with distilled water and the propanone. Dry by putting in an oven for a few minutes. Finally reweigh the tube. Results Mass of tube and iron Mass of tube empty Mass of iron Mass of tube and copper Mass of tube empty Mass of copper g g g g g g a) Calculate the: moles of iron used;... [1] moles of copper formed;... [1] (iii) ratio of moles of copper formed: moles of iron reacted (iv) Hence write the equation for the reaction.... [1] b) What are the most significant errors in the experiment? How reliable is the result? (iii) How could the experiment be improved? Quality of language [1] TOTAL / 12

13 AS Level TOPIC 3 Questionsheet 12 ESTIMATING THE CONCENTRATION OF SALTS IN SEA WATER A litre of sea water was given to a student, who carried out the following experiment to determine the concentration of salts in it: 1. A large evaporating basin was weighed. 2. A 25 cm 3 sample of sea water was delivered into the evaporating basin from a measuring cylinder. 3. The evaporating basin was placed on a tripod and gauze. The solution was evaporated to dryness by heating using a Bunsen burner. 4. The evaporating basin was reweighed when it had cooled. 5. The procedure was repeated with another 25 cm 3 sample. Results Sample 1 Sample 2 Mass of evaporating basin + residue = g g Mass of evaporating basin empty = g g Mass of salt residue = g g a) Calculate the concentration of salt in g per dm 3 in each of the samples to three significant figures. b) Comment on the values obtained. c) What do you think are the significant errors in the experiment? d) How could the experiment be modified to produce more accurate results? Quality of language [1] TOTAL / 9

14 AS Level TOPIC 3 Questionsheet 13 EXPERIMENT TO FIND THE EQUATION FOR A REACTION DECOMPOSITION OF POTASSIUM HYDROGEN CARBONATE A crucible containing a sample of potassium hydrogen carbonate, that had been kept dry in a desiccator, was heated gently at first, then more strongly, for 4 minutes. The crucible was allowed to cool in a desiccator and then reweighed. The mixture was heated to constant mass. Results Mass of tube + potassium hydrogen carbonate = g Mass of tube empty = g Mass of potassium hydrogen carbonate = g Mass of tube + solid after first heating = g Mass of tube + solid after second heating = g Mass of tube + solid after third heating = g a) Calculate the % loss in mass which occurred when potassium hydrogen carbonate was heated. b) Using the formula mass of the compounds in the equations below, calculate the theoretical % loss in mass for all the equations: i. A. 2KHCO 3 (s) K 2 CO 3 (s) + H 2 O(l) + CO 2 (g) [2] ii. B. 2KHCO 3 (s) K 2 O 5 (s) + H 2 O(l) [1] iii. C. 2KHCO 3 (s) K 2 CO 4 (s) + H 2 O(l) + CO(g) [1] iv. D. 2KHCO 3 (s) K 2 O(s) + H 2 O(l) + 2CO 2 (g) [1] v. E. 2KHCO 3 (s) K 2 O 3 (s) + H 2 O(l) + O 2 (g) [1] [1] TOTAL (Continued...) /

15 AS Level TOPIC TOPIC 3 3 Questionsheet 13 Continued 14 EXPERIMENT TO FIND THE EQUATION FOR A REACTION DECOMPOSITION OF POTASSIUM HYDROGEN CARBONATE c) Compare the values in parts a and b to deduce the correct equation for the reaction d) What are the most significant errors in the experiment? e) How reliable is the result, give reasons for your answer? f) How could the experiment be improved? Quality of language [1] TOTAL / 16

QUESTIONSHEETS GROUPS 1 AND 2 REACTIONS OF THE ELEMENTS WITH WATER REACTIONS OF THE ELEMENTS WITH DILUTE ACIDS

QUESTIONSHEETS GROUPS 1 AND 2 REACTIONS OF THE ELEMENTS WITH WATER REACTIONS OF THE ELEMENTS WITH DILUTE ACIDS CHEMISTRY QUESTIONSHEETS AS Level AS TOPIC 10 GROUPS 1 AND 2 Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet