What would be the effect on the percent by mass of iron (whether it would be higher, lower or unchanged from what it should be) calculated to be in the unnkown sample and why if the sample contained some Fe3+ as well as some Fe2+
To determine the effect on the percent by mass of iron in the unknown sample, we need to understand the oxidation states of Fe2+ and Fe3+ and how they affect the calculation.
Iron can exist in two common oxidation states: Fe2+ (ferrous) and Fe3+ (ferric). Fe2+ has a +2 charge, while Fe3+ has a +3 charge. When calculating the percent by mass of iron in a sample, we need to consider the mass of both Fe2+ and Fe3+.
If the sample contains some Fe2+ as well as some Fe3+, the percent by mass of iron calculated would be higher compared to if it only contained Fe2+. This is because Fe3+ has a higher molar mass (55.845 g/mol) compared to Fe2+ (55.845 g/mol). When calculating percent by mass, we consider the molar mass of each component and its contribution to the total mass of the compound.
Since Fe3+ has a higher molar mass, its contribution to the total mass of iron in the sample will be greater. Therefore, when calculating the percent by mass of iron, including both Fe2+ and Fe3+, the value will be higher compared to if only Fe2+ was present.
To calculate the percent by mass of iron in the sample, you would need to carry out a chemical analysis or use spectroscopic techniques to determine the concentrations of both Fe2+ and Fe3+. From there, you can calculate the total mass of iron by summing the mass contributions from each oxidation state and divide it by the total mass of the sample, multiplying the result by 100 to get the percentage.