Chem Question - How to determine limiting reactant

• NerdzRulz

  2 Mar 09, 15:43

  0.65g of Zinc is mixed with 50cm^3 of 2.0mol/dm^3 Hydrochloric Acid

  Which is one is in excess and How much Hydrogen Gas is produced?

• eagle

  2 Mar 09, 15:52

  You only gave the concentration of HCl... not the amount of HCl leh...

• UltimaOnline

  2 Mar 09, 16:31

  To determine limiting reactant :

   

  1) Compare Experiment Mole Ratio (of 1st reactant to 2nd reactant) versus Equation Mole Ratio (of 1st reactant to 2nd reactant). Eg. hydrogen:oxygen (experiement) versus hydrogen:oxygen (equation).

   

  2) Having calculated numerical values for the two ratios (eg. 4.5 vs 4.3), write the inequality sign between them (eg. 4.5 > 4.3).

   

  3) Highlight (eg. circle) the name of the numerator reactant (eg. "hydrogen"), for both experiment and equation mole ratios.

   

  4) Interpret your findings, eg. "The hydrogen we have in the experiment is greater than the hydrogen we need in the equation, hence hydrogen is the excess reactant and therefore oxygen is the limiting reactant".

• Mervyn>_<

  2 Mar 09, 19:54

  Something wrong with format,edited
• Mervyn>_<

  2 Mar 09, 19:58

  1 dm3 = 1000 cm3 Number of moles of HCl= (2/1000)X50 = 0.1 moles Number of moles of Zn=0.65/65.4 =0.00994 moles (3 sig figs) HCl is in excess Amount of hydrogen produced= 0.00994 X 24=0.239 dm^3 (3 sig figs) Been eons since I done chemistry Sorry if I am wrong I have no idea why the post is like that >_<
• UltimaOnline

  2 Mar 09, 21:58

  Your calculations are correct.

   

   

  >>> Been eons since I done chemistry <<<

   

  Eons? So you can't be an 'O' or 'A' level student. Then what are you doing Chemistry now for? Giving tuition to an 'O' level student?

• Mervyn>_<

  3 Mar 09, 08:42

  Just graduated from Polytechnic Somehow such calculations got stuck with me Guess my Chemistry teacher was really good,hehe
• eagle

  3 Mar 09, 08:44

  I liked chem at O levels last time.... it was so easy to score, easier than physics and bio at that time :(

  but didn't take chem at A levels....

• Jiemanutz

  4 Mar 09, 17:11

  Firstly,write the equation between zinc and hcl

  Zn + 2HCl  -> ZnCl2 + H2

  Then calculate the no. of mol available

  no.of mol of Zn available= 0.65/65.4=0.00994( 3 sig fig)

  no. of mol of HCl available in 50cm^3= 50/1000 x 2= 0.1

  determine the limiting reagent and excess

  Mol ratio

  1Zn: 2HCl

  no. of mol of hcl required if all Zn is used up= 2 x 0.00994=0.01988

  Hence,

  the no. of mol of hcl required is < no. of mol of hcl available

  thus Hcl is in excess so Zn is the limiting reagent

  Now to find the volume of H2 gas produced, find the no. of mol of H2 first

  Mol ratio

  Zn:H2

  no. of mol of H2=0.00994

  assuming its at r.t.p

  vol. of H2= 0.00994 x 24=0.239dm3  (3 sig fig)

  if its at s.t.p

  vol. of h2= 0.00994 x 22.4= 0.223dm3 ( 3 sig fig)

  * u have to write statements clearly otherwise marks will be deducted

• UltimaOnline

  4 Mar 09, 17:18

  So which JC did you end up in, Jiemanutz?

• Jiemanutz

  4 Mar 09, 17:21

  mjc.

• d3sT1nY

  4 Mar 09, 17:23

  I heard MJC is good.

• eeden.

  4 Mar 09, 17:24

  heard last month or jan got some joker post nonsense abt poly and ite student leh.true nt?