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# Unit 5 questions on moles and transition metals Watch

1. I am stuck on these questions and don't know how to approach them
1.
Aqueous C2O ions react with MnO ions in acidic solution according to the equation5 C2O + 2MnO + 16H+ → 2Mn2+ + 10CO2 + 8H2O
Under the same conditions Fe2+ ions also react with MnO ions. How many moles of MnO ionsare required to react exactly with one mole of Fe(C2O4).2H2O?

2.
The percentage of iron in a sample of impure iron(II) sulphate crystals can be determinedby titrating solutions, made from separate weighed samples acidified with dilute sulphuric acid,against a standard solution of potassium manganate(VII).Which one of the following would lead to the greatest error in the calculation of the percentage ofiron(II) in the sample?
- A an error of 0.005 g made when weighing out a sample of mass 0.987 g
- B an end-point error of 0.1 cm3 in 25.0 cm3
- C an error of 5 cm3 when measuring out 25.0 cm3 of dilute sulphuric acid
- D using the average of the titration values 25.4, 25.7 and 25.9 when the correct value is25.5 cm3

3.
The percentage of iron in a sample of impure iron(II) sulphate crystals can be determinedby titrating solutions, made from separate weighed samples acidified with dilute sulphuric acid,against a standard solution of potassium manganate(VII).Which one of the following would lead to an inaccurate result?
- A transferring the weighed sample of iron(II) sulphate into a wet conical flask
- B failing to measure accurately the volume of water used to dissolve each weighed sampleof iron(II) sulphate
- C transferring the standard solution of potassium manganate(VII) from its original containerto the burette using a wet beaker
- D failing to measure accurately the volume of dilute sulphuric acid added to the mixturebefore titration

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Updated: May 1, 2016
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