Chem prelim question

Maith SG

Just had my exam..everything can do la..except for one question.Think its on the mole concept de.Anyway here's the question:

1)Tungsten metal,W,is manufactured by reducing tungsten(III)oxide,WO3,with carbon.

WO3+3C----->3CO+W

Calculate

i)the mass of carbon needed to reduce 116g of tungsten(III)oxide,

ii)the maximum mass of tungsten that can be formed.

That's all. Hope u guys can help. (:

^tamago^ SG

Mass of C needed
= 116g/[(183.84+16×3)g/mol of WO₃] × 3mol of C/mol of WO₃ × 12g/mol of C
= 18.0g of C

Maximum mass of W
= [183.84g/mol of W]/[(183.84+16×3)g/mol of WO₃] × 116g
= 92.0g of W

secretliker SG

(i)

No. of moles of WO3 = 116 / (184 + 3*16) = 0.5 mol

No of moles of C needed = 3 * 0.5 = 1.5 mol

Mass of C required = 12 * 1.5 = 18g

(ii)

Max no. of moles of W = no. of moles of WO3 = 0.5

Max mass of W = 0.5 * 184 = 92g

UltimaOnline SG

^tamago^ and secretliker are both correct, of course.

Maith SG

ooooh i see i see...so its just making use of the formula no. of mol=mass/molar mass ar...thanks you guys! ^^

Darkness_hacker99 SG

Yup!

Steps:

1) Find the amount of the given sample(X) reacted.
2) Find the mol of X.
3) Using the balance equation, you know the proportion. In this case W03:C = 1:3
4) Find the what you're suppose to find.

Tada!

Darkness_hacker99 SG

For titration, it's also similar. The concept is there.. to find the number of mols reacted to determine the unknown figures.

eagle SG

I like mole concept the most in chem last time because it was the most maths part of chemistry.

seanchua7 SG

Many students find Mole Calculations a tough topic to handle in GCE O Level Chemistry Examinations. But in fact, it is not really that tough like you imagined.

Just remember that you need to convert the information into MOLES and then compared with the stoichiometries in the balanced chemical equations. And that is the reason why this topic is known as "Mole Calculations".

And for reaction that involves all gases, you can compare directly using the information that are given in volumes (i,e. dm3 or cm3) to get the answers.

Hope that helps.

Sean