[pikaboo93]

Ive got like alot of stoichometry questions. hopefully someone can answer them?

Q1) The formula of a complex salt K is [Cu(NH3)X(H20)Y]SO4 (3, X, Y, 2 and Y are at the bottom of the alphabets) and analysis produced the following composition by mass : Cu, 24.1%; H, 6.1%; O, 36.4%. Calculate the values of x and y and hence determine the percentage by mass of S in the salt.

Q2) 1.40g of pure anhydrous sodium carbonate were made up to 250cm^3 of aqueous solution. 25.0cm^3 of this solution required 24.50cm^3 of a hydrochloric acid solution for complete reaction. Calculate the concentration of acid in mol/dm^3 (solved it to be 0.108mol/dm^3) What volume of deionised water has to be added to dilute 800cm^3 of this acid to exactly 0.080mol/dm^3?

Q3)2.50g of a mixture of anhydrous sodium carbonate and sodium chloride were made up to 250cm^3 with deionised water. 25.0cm^3 of this solution required 20.0cm^3 of 0.100mol/dm^3 of hydrochloric acid for neutralisation. Calculate the percentage by mass of sodium chloride in the mixture

Q4) At S.t.p, 2.8dm^3 of hydrogen sulfide were mixed with 1.6dm^3 of sulfur dioxide and the reaction occured as follows:
2H2S(g) + SO2(g) --> 2H20(l) + 3S(s)

What is the volume of gas remaining after the reaciton?

Q5) Ascorbic acid (vitamin C) is an organic compound containing carbon, hydrogen and carbon. When 1.000g of ascorbic acid was completely burnt in oxygen, 1.500g of carbon dioxide and 0.405g of watr were formed. Calculate the empirical formula of ascorbic acid and determine its molecular formula if its relative molecular mass is 176.

Thanks in advance! ^^

[pikaboo93]

sorry. I'll post my workings now

For the first question, i really have no idea on where to start first. But i know that it has got something to do with the mass of the elements in % divided by their mr. However, their percentages only add up to 66.6% and not 100%. So i kind of inferred that the normal way that you use to find the empricial formula requires an additional step before you start calculating their mr normally.

Q2)
i think that you would have to calculate the mols for the acid. So it would be 0.8 X 0.080 = 0.064mol.
Thats the only possible solution i could think of though :/

Q3)
i figured out how to do already xP

Q4)
Amount of H2S = 2.8 / 22.4 = 0.125mol
2H2S = 2H20
Amount of H20 = 0.125 X 22.4 = 2.8dm^3
Amount of S = (0.125 / 2) X 3 = 0.1875dm^3
Vol. gas remaining = 2.9875dm^3

which is wrong...

Q5)
For this question, i have absolutely no clue as to where to start from. Would really appreciate some help

[Schrödinger]

Qn 1 : Can you write the molar mass of the compound in terms of x and y?

[pikaboo93]

Would the molar mass be 159.6 + 1633.7X + 1729.8Y ?

[Schrödinger]

However, their percentages only add up to 66.6% and not 100%.

Of course they add up to only 66.6%. Data given is only for 3 elements. You are required to use these values to find out molar mass, and then finally % of Sulphur in the compound.

Would the molar mass be 159.6 + 1633.7X + 1729.8Y ?

Why do you think that is the molar mass?