How Good are you in Chemistry? Test 2?

Question

The percentage composition of a compound is 92.3% C and 7.7% H. If the molecular mass is 78 u, what is the molecular formula?


Find the formulas for the hydrates with the following analysis.

a.) 5.262 g Tl(NO3)3 and 0.728 g H2O
b.) 2.94 g Sn(NO3)2 and 4.37 g H2O
c.) 8.351 g UO2(HCOO)2 and 0.421 g H2O
d.) 17.02 g UO2HPO4 and 3.42 g H2O

Name each of the following hydrates.
a.) MgSO4.H2O
b.) Mn(NO3)2.4H2O
c.) CaCrO4.2H2O
d.) Na2SO4.10H2O

Answer 1

you bug me! lol. i don't know.

Answer 2

1.- 92.3% C and 7.7% of H

M(X) = 78 umas

Moles of C = 92.3 g / 12 g/mol = 7.7 moles
Moles of H = 7.7 g / 1 g/mol = 7.7 moles

Ratio of moles C/H = 7.7 / 7.7 = 1

Hence, the empirical formula of compound is:

CH

knowing that M(CH) = 13 umas the molecular formula can be determined as:

M(X) / M(CH) = 78 / 13 = 6 then, the molecular formula is:

C6H6

2.- Formulas of each hydrate can be determined as follows:

i) Compute the number of moles of each compound [example, number of moles of 5.262 g of Tl(NO3)3]. Name it "n1"
ii) Compute the number of moles of water present in that compound (0.728 g H2O in the same example). Name it "n2"
iii) Check the ratio n2/n1.
iv) Round the result and this will be the coefficient of molecules of water present in each compound.

3.- Names of each hydrate:

a) Magnesium Sulphate hydrated
b) Manganesum Nitrite tetrahydrated
c) Calcium Chromate dihydrated
d) Sodium Sulfate decahydrated

Hope it helps!

Answer 3

C6H6

a)Magnesium Sulphate monohydrate
b)Manganese(II)Nitrate tetrahydrate
c) Calcium Chromate dihydrate
d) Sodium Sulphate decahydrate