formulas_&_yields_011108

Test ID = 68

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1. (109253722) Copper (II) sulphate pentahydrate, CuSO4.5H2O, was prepared by adding excess copper (II) oxide to 50cm3 of hot 0.2 mol dm-3 sulphuric acid. The equation for the reaction is: CuO(s) + H2SO4(aq) + 4H2O CuSO4.5H2O(aq) The solution was filtered to remove any unreacted solid and allowed to evaporate until crustals of product formed.The crystals were collected and dried with filter paper.The dry crystals has a mass of 1.964g. (a) How many moles of sulphuric acid were used?
REF: 29



2. (109253723) (b) What was the percentage yield for the reaction?
REF: 29



3. (10925374) Which one of the following statements about empirical and molecular formulas is correct?
    (A) The empirical formula of a compound is the smallest whole, or part-number ratio of atoms in a compound
    (B) The molecular formula is made up of a whole number of empirical units
    (C) The molecular formula gives the smallest whole number ratio of atoms in a compound



4. (109253728) Why is this more wasteful than an addition reaction? Give the % atom economy for the reaction.
REF: 34



5. (109253718) Write down the formula for calculating percentage yield.
REF: 29



6. (109253735) Why do reaction with high atom economy save chemical companies moeny and cause less environmental impact?
REF: 35



7. (109253736) Reactions 1 and 2 below show two possible ways of preparing the compound chloroethane (C2H5Cl): 1 C2H5 OH + PCl5 C2H5Cl + POCl3 + HCl 2 C2H4 + HCl C2H5Cl (a) Which of these is an addition reaction?
REF: 35



8. (109253737) Calculate the atom economy for reaction 1. (At massess: C = 12, H = 1, O = 16, P = 31, Cl = 35.5)
REF: 35



9. (109253738) (c) Reaction 2 has an atom economy of 100%. Explain why this is, in terms of the products of the reaction.
REF: 35



10. (109253729) 0.475g of CH3Br reacts with excess NaOH in this reaction: CH3Br + NaOH CH3OH + NaBr 0.153g of CH3OH is produced. What is the percentage yield?
REF: 35



11. (109253724) State whether the following is true or false: The Efficiency of a reaction tells you how wasteful the process is and is measured by percentage yield. The Atom Economy of a reaction tells you how how wasteful the the reaction is in terms of how many many atoms wind up as by-products rather than the desired product.
REF: 34



12. (10925371) How do you calculate the number of moles of a gas? (what is the equation)
REF: 19



13. (109253717) Why is it never possible to prepare a salt with a 100% yield?
REF: 29



14. (10925376) A compound is found to have percentage composition 56.5% potassium, 8.7% carbon and 34.8% oxygen by mass. Calculate its empirical formula.
REF: 20



15. (109253725) Give the equation to calculate the % atom economy.
REF: 34



16. (109253711) When 19.8g of an organic acid, A, is burnt in excess oxygen, 33g of carbon dioxide and 10.8g of water are produced. Calculate the empirical formula for A and hence its molecular formula, if Mr(A) = 132
REF: 21



17. (109253716) In this example, work out the actual yield of the ammonium iron(III) sulphate if the crystals are weighed and found to be 5.2g.
REF: 29



18. (10925379) Hydrocarbon X has a relative molecular mass of 78. It is found to have 92.3% carbon and 7.7% hydrogen by mass. Calculate the empirical and molecular formulae of X.
REF: 21



19. (109253733) How many products are there in an addition reaction?
REF: 35



20. (109253731) State 3 negative impacts of low atom economy in terms of economic effects on a company?
REF: 35



21. (10925373) What is the molecular formula of a compound?
REF: 20



22. (109253732) State 2 negative impacts of low atom economy in terms of environmental effects on a company?
REF: 35



23. (109253713) In one sentence, what 2 things do you need to calculate the theoretical yield for a reaction.
REF: 29



24. (109253712) What is meant by 'the theoretical yield of product'?
REF: 29



25. (109253739) Phosphorous trichloride (PCl3) reacts with chlorine to give phosphorous pentachloride (PCl5): PCl3 + Cl2 PCl5 (Atomic massess: P = 31, Cl = 35.5) (a) If 0.275g of PCl3 reacts with 0.142g of chlorine, what is the theoretical yield of PCl5?
REF: 35



26. (109253740) (b) When this reaction is performed 0.198g of PCl5 is collected. Calculate the percentage yield.
REF: 35



27. (109253741) (c) Changing conditions such as temperature and pressure will alter the percentage yield of this reaction. Will changing these conditions affect the atom economy? Explain your answer.
REF: 35



28. (109253714) You react 1.4g iron filings with ammonia and sulphuric acid in water to produce hydrated ammonium iron(III) sulphate. Calculate the theoretical yield of the product. (Note mol formula for product is (NH4)2Fe(SO4)2.6H2O (s)
REF: 29



29. (109253715) Will the actual yield always be less than the theoretical yield? Give 2 reasons for your answer.
REF: 29



30. (109253734) Does the percentage yield for a reaction always have the same value as the percentage atom economy?
REF: 35



31. (10925372) What is the empirical formula of a compound?
REF: 20



32. (109253726) Is the atom economy of addition reactions always 100%? Give an example using ethene plus hydrogen (write equation)
    (A) True
    (B) False
REF: 34



33. (109253727) Is the atom economy of substitution reactions always 100%? Give an example using bromomethene plus NaOH (write equation)
    (A) True
    (B) False
REF: 34



34. (10925377) When 4.6g of an alcohol, with relative molecular mass 46, is burnt in excess oxygen, it produces 8.8g of carbon dioxide and 5.4g of water. Calculate the empirical formula for the alcohol and then its molecular formula.
REF: 21



35. (10925375) When a hydrocarbon is burnt in excess oxygen, 4.4g of carbon dioxide and 1.8g of water are made. What is the emprical formula of the hydrocarbon?
REF: 20



36. (109253730) State 2 benefits of companies selecting reactions with high atom economies over ones with low atom economies.
REF: 35



37. (109253710) When 1.2g of magnesium ribbon is heated in air, it burns to form a white powder, which has a mass of 2g. What is the empirical formula of the powder?
REF: 21



38. (109253719) A sample of hydrated calcium sulphate, CaSO4.XH2O, was prepared by reacting calcium hydroxide with sulphuric acid. 1.883g of hydrated salt was produced.This was then heated until all the water of crystallisation was driven off and the product was then reweighed. Its mass was 1.133g. (a) How many moles of anhydrous calcium sulphate were produced?
REF: 29



39. (109253720) (b) What mass of water was present in the hydrated salt?
REF: 29



40. (109253721) (c) Calculate the value of X in the formula CaSO4.XH2O. (X is an integer)
REF: 29



41. (10925378) What is the difference between a molecular formala and an empircal formula?
REF: 21






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