1. What is the theoretical yield of chromium that can be produced by the reactio

Question

1. What is the theoretical yield of chromium that can be produced by the reaction of 40.0 g of Cr203 with 8.00 g of aluminum according to the equation 2Al+Cr2O3--->Al2O3 + 2cr.

2. What is the correct oxidation number for all three elements in Ca(ClO)2 in the order that the elements are shown.

3.How many total electron transferred in the reaction 4p(s)+5O2-->2P2O5

4. If the pressure is tripled and the absolute temperature is quadrupled, by what factor will the volume of the sample change.

5.Calculate the volume occupied by 25.2 g of CO2 at 0.84 atm and 25 degree Celsius.

6. What element is Oxidized in the following chemical reaction? 3Cu+ 8HNO3----> 3Cu(NO3)2+ 2NO+ 4H2O

Explanation / Answer

1. As per the reaction

2Al+Cr2O3--->Al2O3 + 2Cr.

2 moles of aluminium react with 1 mole of Chromium oxide to give 1 mole of aluminium oxide and 2 moles of Chromium.

Now 40 g of Cr2O3 is 40g/152 g/mol (MW of Cr2O3 is 152g/mol)

= 0.263 moles

8 g of aluminium is 8g/27g/mol    (MW of Aluminium is 27g/mol)

= 0.296 moles.

So the limiting reagent is aluminium

Since 2 moles of aluminium will produce 2 moles of Chromium

0.296 moles of aluminium will produce 0.296 moles of chromium so the weight of chromium will be (MW of Cr is 52g/mol)

0.296 moles x 52g/mol = 15.41 g of Chromium is the theoretical yield in this reaction

2) correct oxidation number for all three elements in Ca(ClO)2

Since Chlorine is bonded to oxygen it will get a +ve sign.

Since Calcium will be +2 The anion ClO has to have a -1 charge so that the formula is balanced

+2 + 2(-1) = +2 -2 =0

Now oxygen in the oxide form is -2 charge so Chlorine will have to take a +1 charge

So Calcium is +2, Chlorine is +1 and oxygen is -2

3) How many total electron transferred in the reaction 4P(s)+5O2-->2P2O5

In this reaction phosphorous is in the solid state so its oxidation state is 0

In the final product there are 5 oxygens in oxide form so it is 5 x -2 = -10

so 2 P will have to account for this negative charge so each P will be +5

so Phosphorous is going from 0 to + 5 state and there are 4 atoms of phosphorous taking part in the reaction so total number of electons transferred is 4 x 5e- = 20 elctrons are transferred in the reaction.

4) Let us look at the reaction of an ideal gas

PV = nRT

V1 = nRT/R

Since n and R are constant and the changes are pressure is tripled and the absolute temperature is quadrupled

We have

3 P x V = nR x 4T

V2 = nR x 4 T/3P

V2 = 4/3(nRT/P)

V2 = 4/3V1

V2 = 1.33 V1

So the volume of the sample changes by 1.33 times.

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