Question

Elementary analysis showed that an organic compound contained C,H,N and O as its elementary constituents. A 1.279g sample was burned completely as a result of which 1.60g of carbon dioxide and .77g of water were obtained. A separately weighed 1.625g sample contained .216g nitrogen. What is the empirical formula of the compound?


When solid ammonium dichromate is heated, it decomposes to Cr2O3(s) and N2 (g) and H2O (g). In a given experiment, the following data were obtained.
Crucible + ammonium dichromate. 33.622g
crucible + Cr2O3(s). 29.608g
What is the weight of the crucible?


Water is added to 4.267 g of UF6. The only products are 3.730 g of a solid containing only uranium, oxygen and fluorine and .970 g of a gas. The gas is 95% fluorine, and remainder is hydrogen.

A) from this data, determine empirical formula of the gas.
B) what fraction of fluorine of the original comp is in solid and what fraction in the gas after the reaction?
C) what is the formula of the solid product
D) write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of the gas is the true formula.

Answer 1

@triciaal these are the questions

Answer 2

Elementary analysis showed that an organic compound contained C,H,N and O as its elementary constituents. A 1.279g sample was burned completely as a result of which 1.60g of carbon dioxide and .77g of water were obtained. A separately weighed 1.625g sample contained .216g nitrogen. What is the empirical formula of the compound?


Find moles of CO2 and H2O, consequently find moles of C and H.
Convert to mass and find the mass percent of C and H in the first compound.

Use the mass percents to find the weights of C and H in the second.
Subtract these and the weight of N from the total mass to find the mass of O.

Convert the masses of N and O to their moles.

Divide all the by one with least amount of moles (normalizing).
Get them to whole numbers by multiplying all by a factor. (if they're close to a whole number like 5.9, round accordingly.

Answer 3

When solid ammonium dichromate is heated, it decomposes to Cr2O3(s) and N2 (g) and H2O (g). In a given experiment, the following data were obtained.
Crucible + ammonium dichromate. 33.622g
crucible + Cr2O3(s). 29.608g
What is the weight of the crucible?


\((NH_4)_2Cr_2O_7 -> Cr_2O_{3~(s)}+ N_{2~(g)} + 2~H_2O_{(g)}\)

The mass lost is \(N_{2~(g)} ~and~ H_2O_{(g)}\)

33.622g-29.608g=4.014 g = \(m_{N_2}+m_{H_2O}=n_{N_2}*M_{N_2}+n_{H_2O}*M_{H_2O}\)

(recall M is molar mass, n is moles.)

from the balanced equation: \(n_{N_2}=2~n_{H_2O}\)

\(4.014 ~g=2~n_{H_2O}*M_{N_2}+n_{H_2O}*M_{H_2O}\)


Solve for moles of water, \(n_{H_2O}\).

Correlate these to moles of \((NH_4)_2Cr_2O_7 \), find mass of this and of \(Cr_2O_{3~(s)}\) find weight of crucible.

Answer 4

Water is added to 4.267 g of UF6. The only products are 3.730 g of a solid containing only uranium, oxygen and fluorine and .970 g of a gas. The gas is 95% fluorine, and remainder is hydrogen.

To start, find moles of UF6, and use these to decompose 3.730 g of solid to the individual masses. Find mass of oxygen.

A) from this data, determine empirical formula of the gas.

0.970 g of a gas. The gas is 95% fluorine, and remainder is hydrogen.

Assuming it's 95% by mass, find masses of each (by multiplying it's percentage by the total mass), convert to moles. Divide all by the one with least amount of moles to normalize, etc.

B) what fraction of fluorine of the original comp is in solid and what fraction in the gas after the reaction?

Find the mass of F in UF6 (with mass percent composition).

\(mass ~\%~F~composition~in~UF_6=\dfrac{6*M_F}{M_{UF_6}}*100\%\) (M is molar mass)

You know the mass of F in the solid.
You the know the mass in the gas from A)

C) what is the formula of the solid product

you can get this from the first step.

D) write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of the gas is the true formula.

you have all the formulas, put them together and balance.