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Percent Mass and Stoichiometry

1) You are the science officer on the Starship Enterprise. The ship is circling a new planet. The away team comes back with some rocks and minerals. Some of the minerals contain iron and you want to determine the amount of iron in the sample.

You take 9.000 g of this mineral and treat it with excess bromine (bromine reacts with iron metal to produce iron(III) bromide, which is soluble in water). The solution containing the iron(III) bromide and bromine is then treated with excess silver nitrate. The mass of the silver bromide obtained is found to be 46.34 g. What is the percent of iron in the mineral sample?

2) A common laboratory experiment for introductory chemistry courses involves the analysis of a mixture of BaCl2 and BaCl2.2H2O. You are given a white powder that is a mixture of these compounds and are asked to determine the weight percent of each.
You find that 1.392 g of the mixture has a mass of 1.157 g after heating it to drive off
all of the water present.
(A) What is the weight percent of water in the mixture?
(B) What is the weight percent of BaCl2 in the mixture?
(C) What is the weight percent of Ba in the mixture?

3) If a bottle of wine is not kept under appropriate conditions, the ethanol (C2 H5 OH) is oxidized to a limited extent (it turns to acetic acid) and the wine becomes very sour and is no longer drinkable. This can be expressed by the following reaction.
C2 H5 OH + O2--> C2 H4 O2 (Unbalanced)
If the wine contains 15% by mass ethanol (assume the only other ingredient in the wine is water), how many moles of acetic acid are produced in a liter of this wine.
The density of the wine is 1.010 g/mL. Assume that all the ethanol is converted to acetic acid. The molar masses of C, H, and O are 12.011, 1.00794, and 15.9994 g/mole,respectively.

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Please help me with the following stoichiometric problems
1) You are the science officer on the Starship Enterprise. The ship is circling a new planet. The away team comes back with some rocks and minerals. Some of the minerals contain iron and you want to determine the amount of iron in the sample.
You take 9.000 g of this mineral and treat it with excess bromine (bromine reacts with iron metal to produce iron(III) bromide, which is soluble in water). The solution containing the iron(III) bromide and bromine is then treated with excess silver nitrate. The mass of the silver bromide obtained is found to be 46.34 g. What is the percent of iron in the mineral sample?

The first thing you need to do is write equations for the reactions:
2 Fe + 3 Br2 → 2 FeBr3
FeBr3 + 3 AgNO3 → Fe(NO3)3 + 3 AgBr
You can work backwards if you know the mass of AgBr. First convert the 46.34 g to moles:

According ...

Solution Summary

This solution explains how to determine the percent iron in a mineral sample based on a series of quantitative tests and how to determine the mass of salt and water in a hydrate. It also considers how to calculate the moles of vinegar formed from a bottle of wine.

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