QUEENSLAND CHEMISTRY
CHAPTER 20 CONSUMER PRODUCTS AND QUALITY CONTROLName:
QUESTIONS20.2 The chemist’s solution — quality control
1. What is the concentration of each of the following solutions?
(a) 0.256moles of KNO3 in 1.50L of solution
(b) 20mL of solution containing 2.5 ×10–6 moles of KMnO4
2. What amount of KI is needed to prepare:
(a) 5.0L of 0.1M solution
(b) 100mL of 2.0M solution?
3. What mass of solid is needed to prepare:
(a) 100mL of 0.200M CuSO4·5H2O
(b) 10L of 0.5M NaOH?
4. (a) What volume of 2.0M CoCl2 is needed to make 100mL of a 0.10M solution of the salt?
(b) 200mL of 0.5M Al(NO3)3 is diluted to a volume of 1L.
(i) What is the new concentration of the salt solution?
(ii) What is the concentration of nitrate ions in that solution?
5. Write a sentence to show you know the difference between equivalence point and endpoint.
20.3 You as an analytical chemist
6. A student uses 0.1250M NaOH to titrate 25.00mL aliquots of an acetic acid solution. The average titre required is 28.61mL.
(a) What is the concentration of the acetic acid solution?
(b) What mass of CH3COOH would be present in 100mL of the acid solution?
7. Using the data from titrations 2 and 3, calculate the concentration of NaOH.
8. Another student made up astandard solution containing 22.98g of KHP and had anaverage titre of 27.30mL. What value would her calculations give for the molarity of NaOH?
9. (a) Urea is anorganic compound. Its formula is CO(NH2) 2. Draw astructural formula forurea.
(b) What are the formulas for all of the inorganic fertilisers mentioned previously?
10. Another batch of the fertiliser is analysed using the same concentrations of HCl and NaOH. The size of the fertiliser sample is 1.500g, the volume of NaOH added is 50.00mL and the volume of HCl required is 25.17mL. Does this sample meet label specifications?
11. Use the ionic half-equation method of balancing redox equations to confirm the coefficients in thisequation.
12. What volume of I2 should be added if the apricots are to be sold within Australia?
13. Analysis of another sample taken from afreshly opened bottle of the same brand of apple juice required anaverage I2 titre of 19.22mL.
(a) Does this sample live up to label specifications?
(b) What impact would using afreshly opened bottle have on the validity of theanalysis?
Review questions
1. Calculate the molarity of the following solutions.
(a) 0.054mol of NaNO3 in 150mL of solution
(b) 28.6g of Na2Cr2O7 in 200mL of solution
(c) 8.5×1023 molecules of CH3COOH in 500mL of solution
2. What mass of solid is needed to prepare each of the following solutions?
(a) 200mL of 0.30M Zn(NO3)2
(b) 25mL of 0.50M Na2C2O4
(c) 10L of 0.1M NaOH
(d) 1L of 0.25M CoCl2·6H2O
3. Arrange the following solutions of KNO3 in order of increasing concentration.
(a) 150mL containing 0.125mol
(b) 500mL containing 0.440mol
(c) 200mL containing 28.6g
(d) 1.5L containing 40.0g
4. For 30mL of a0.85M solution of AlCl3, calculate:
(a) the amount of aluminium chloride
(b) the mass of aluminium chloride
(c) the amount of aluminium ion
(d) the mass of aluminium ion
(e) the amount of chloride ion
(f) the mass of chloride ion.
5. Asolution is made by mixing 25g of CuSO4·5H2O, 20g of Na2SO4 and 10g of
Al2(SO4)3. The total volume of the final solution is 200mL. Calculate the concentrations of each of the ions insolution.
6. What are the concentrations of solutions prepared by diluting:
(a) 20mL of 0.15M HCl to 100mL
(b) 50mL of 10M NaOH to 2.0L
(c) 75mL of 18M H2SO4 to 2.5L?
7. A100mL graduated cylinder contains 86mL of 1.0M H2SO4. Sufficient concentrated H2SO4 (18M) is added very slowly and carefully to make the solution up to the 100mL mark. The mixture is transferred to a beaker and stirred. What is the concentration of the final solution?
8. What volumes of 0.500M HCl and 0.100M HCl must be mixed to give 1.00L of 0.200Macid?
9. What volume of 0.250M KOH should be added to 150mL of 0.125M KOH to make asolution that has the same hydroxide ion concentration as asolution containing 15.0g of Ba(OH)2 per litre?
10. (a) What are the main requirements for aprimary standard?
(b) Name anacid that can be used as aprimary standard.
(c) Name asolid that can be used as aprimary standard to standardise HCl.
11. What is the concentration of the acid if:
(a) 25.00mL of hydrochloric acid react with 24.02mL of 0.9846M NaOH
(b) 30.00mL of acetic acid react with 27.64mL of 1.025M NaOH
(c) 18.05mL of sulfuric acid react with 25.00mL of 0.1455M KOH
(d) 22.63 mL of nitric acid react with 30.00mL of 0.1296M NH3 solution?
For questions 12 and 13, state any assumptions made.
12. Astudent wishes to standardise asolution of HCl that she thinks is approximately 0.2M. She decides to standardise the HCl using Na2CO3. What mass of the solid should she weigh out:
(a) if she is going to titrate individual solid samples
(b) to make up astandard solution using a250mL volumetric flask?
13. Asolution of NaOH is prepared by weighing out approximately 10g of the solid and dissolving it in 1L of water. What mass of KHP would be needed if the NaOH solution is to be standardised against:
(a) individual weighed samples
(b) samples taken from 100mL of astandard solution?
14. (a) Asample of pure CaCO3 weighing 0.800g requires 34.87mL of HCl for complete reaction. What is the concentration of the acid?
(b) The same acid is then used to analyse animpure sample of CaCO3. In this experiment, a1.208g sample of the solid requires atitre of 29.60mL of HCl. What is the percentage of CaCO3 in the solid?
For questions 15 and 16, state any assumptions made.
15. KMnO4 solution can be standardised using FeSO4·7H2O in the presence of H2SO4.
(a) Write abalanced equation for the reaction.
(b) Why must acid be added to the reaction mixture?
(c) What mass of the iron(II) sulfate should be used to standardise apermanganate solution that is thought to be 0.02M using:
(i) individual weighed samples
(ii) samples taken from 100mL of astandard solution?
(d) What is the indicator in this reaction?
16. KMnO4 solution can also be standardised using Na2C2O4 in the presence of H2SO4. What mass of sodium oxalate should be used to standardise apermanganate solution that is thought to be 0.05M using:
(a) individual weighed samples
(b) samples taken from 250mL of astandard solution?
17. AK2Cr2O7 solution contains 25.00g of the salt per litre of solution. How manymL of this solution are needed to react with 3.050g of FeSO4·7H2O that has been dissolved in water and mixed with asmall amount of sulfuric acid?
18. In ananalysis of iron tablets, the Fe2+ in the tablet is converted to Fe3+ using KMnO4. What volume of 0.0400M KMnO4 would be needed if the tablet contained 300mg of Fe2+?
19. A1.400g sample of steel is dissolved in aminimum amount of sulfuric acid. The solution is added to some distilled water in a250mL volumetric flask. The solution is then diluted to atotal volume of 250mL. When 25.00mL aliquots of this solution are titrated with 0.02120M KMnO4, anaverage titre of 22.54mL is needed. What is the percentage of iron in thesteel?
20. A500mg vitaminC tablet is dissolved in distilled water and then titrated against 0.05240M I2 solution using starch as anindicator. Anaverage titre of 31.45mL is required. The equation for the reaction is:
C6H4O2(OH)4+I2C6H6O6+2H++2I–
(a) What is the mass of vitaminC in the tablet?
(b) What is the percentage of vitaminC in the tablet?
21. Ananalyst is performing over–under tests on some foodstuffs, using starch indicator and 0.0200M I2 solution. What volume of the iodine solution should he add to:
(a) a50g sample of apricots with amaximum allowable SO2 level of 2000 mg kg–1
(b) a50g sample of sausage mince with amaximum allowable SO2 level of 500 mg kg–1?
22. To determine the NaOCl concentration in ahousehold bleach, iodide ion in acid solution is added to the bleach. Hypochlorite anion oxidises the iodide to iodine, which is then reduced by thiosulfate solution to iodide. These reactions are shown in the following equations.
OCl–+2I–+2H+I2+Cl–+H2O
I2+2S2O32–2I–+S4O62–
It is found that 37.98mL of 0.8482M thiosulfate solution are needed to analyse a30.00mL sample of the bleach.
(a) What is the concentration of NaOCl solution?
(b) What mass of NaOCl would be present in the sample of bleach analysed?
(c) Assuming that the density of the bleach is 1g mL–1, what is the percentage by mass of NaOCl in the bleach?
23. A 1.400g sample of lawn fertiliser is dissolved in water and made up to 250mL in avolumetric flask. 40.00mL of 0.1050M NaOH are added to 25.00mL samples of the solution. The solution is boiled to remove ammonia, and the excess base is then titrated with 0.09855M HCl. The average HCl titre is 19.56mL.
(a) What amount of NaOH is added?
(b) What amount of HCl is used in the titration?
(c) What amount of NaOH reacts with the ammonium ion in the fertiliser?
(d) What amount of NH4+ is present in the fertiliser sample?
(e) What is the percentage of nitrogen as ammonium ion in the fertiliser?
24. A0.500g aspirin tablet containing aspirin and filler is analysed using the back titration method. When the tablet is dissolved in 40.00mL of 0.1855M NaOH, the following reaction occurs.
C6H4(OCOCH3)COOH+2NaOH C6H4(OH)COONa+CH3COONa+H2O
20.33mL of 0.2010M HCl are needed to titrate the excess NaOH. What is the percentage of aspirin in the tablet?
Notes:
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