Help me in this Question. pls.
-
Zinc reacts with hydochloric acid according to the equation.
Zn + 2HCl --> ZnCl2 + H2
If 0.05 mole of zinc react with 0.075 mole of hydrochloric acid,
(a) identify the limiting reactant
(b) calculate the amount (in mole) of the excess reactant which remain unreacted.
My ans for (a) is HCl. But my teacher says is Zn. Pls enlighten me.
My class and I strongly believe the answer to (a) is HCl. -
You are doing Pure Chemistry?
-
When looking at limiting reactants, you need to convert moles.Originally posted by Darkness_hacker99:Zinc reacts with hydochloric acid according to the equation.
Zn + 2HCl --> ZnCl2 + H2
If 0.05 mole of zinc react with 0.075 mole of hydrochloric acid,
(a) identify the limiting reactant
(b) calculate the amount (in mole) of the excess reactant which remain unreacted.
My ans for (a) is HCl. But my teacher says is Zn. Pls enlighten me.
My class and I strongly believe the answer to (a) is HCl.
When you round off 0.075 moles, you will get 0.08 moles of HCl. Comparing this with 0.05 moles of zinc, HCl has more. That is why zinc is the limiting reactant.
Definition of limiting reactant: Whatever reactant runs out first is called the limiting reactant or limiting reagent. -
My working is:Originally posted by ndmmxiaomayi:When looking at limiting reactants, you need to convert moles.
When you round off 0.075 moles, you will get 0.08 moles of HCl. Comparing this with 0.05 moles of zinc, HCl has more. That is why zinc is the limiting reactant.
Definition of limiting reactant: Whatever reactant runs out first is called the limiting reactant or limiting reagent.
From the equation given:
Mole ratio of HCl and Zn = 2: 1
which is also equals to 2 divide by 1 = 2
From the quantities given:
Mole ratio of HCl and Zn = 0.05 : 0.075
which is also equals to 0.05 divide by 0.075 = 1.5 <2
i.e. The 0.05 moles of HCl are insufficient to react completely with 0.075 moles of Zn. Hence there is an excess of Zn, and HCl is the limiting reagent. -
You look at the red part.Originally posted by Darkness_hacker99:My working is:
From the equation given:
Mole ratio of HCl and Zn = 2: 1
which is also equals to 2 divide by 1 = 2
From the quantities given:
Mole ratio of HCl and Zn = 0.05 : 0.075
which is also equals to 0.05 divide by 0.075 = 1.5 <2
i.e. The 0.05 moles of HCl are insufficient to react completely with 0.075 moles of Zn. Hence there is an excess of Zn, and HCl is the limiting reagent.
In your question, you stated 0.05 moles of Zn reacts with 0.075 moles of HCl. The red part shows the direct opposite. 0.05 moles of HCl reacts with 0.075 moles of Zn.
My question to you: So which is the correct one? 0.05 moles Zn with 0.075 moles HCl OR 0.075 moles Zn with 0.05 HCl? -
Sorry, my mistake.Originally posted by ndmmxiaomayi:You look at the red part.
In your question, you stated 0.05 moles of Zn reacts with 0.075 moles of HCl. The red part shows the direct opposite. 0.05 moles of HCl reacts with 0.075 moles of Zn.
My question to you: So which is the correct one? 0.05 moles Zn with 0.075 moles HCl OR 0.075 moles Zn with 0.05 HCl?
From the quantities given:
Mole ratio of HCl and Zn = 0.075 : 0.05
which is also equals to 0.075 divide by 0.05 = 1.5 <2
Corrected
i.e. The 0.075 moles of HCl are insufficient to react completely with 0.05 moles of Zn. Hence there is an excess of Zn, and HCl is the limiting reagent. -
Now clearer. I check my calculations just now.Originally posted by Darkness_hacker99:Sorry, my mistake.
From the quantities given:
Mole ratio of HCl and Zn = 0.075 : 0.05
which is also equals to 0.075 divide by 0.05 = 1.5 <2
Corrected
i.e. The 0.075 moles of HCl are insufficient to react completely with 0.05 moles of Zn. Hence there is an excess of Zn, and HCl is the limiting reagent.
Careless mistake. So HCl is limiting reactant. Not zinc. -
Must thank you worx. Xie xie
-
No problem. You are welcome.Originally posted by Darkness_hacker99:Must thank you worx. Xie xie -
juz my 2 cents worth.feeling bored anyway..Originally posted by Darkness_hacker99:Zinc reacts with hydochloric acid according to the equation.
Zn + 2HCl --> ZnCl2 + H2
If 0.05 mole of zinc react with 0.075 mole of hydrochloric acid,
(a) identify the limiting reactant
(b) calculate the amount (in mole) of the excess reactant which remain unreacted.
My ans for (a) is HCl. But my teacher says is Zn. Pls enlighten me.
My class and I strongly believe the answer to (a) is HCl.
a) 1 mol Zn reacts stoichiometrically with 2 mol HCl.
0.05 mol of Zn would require 0.05 x 2 = 0.1 mol of HCl to react with.However there is 0.075 mol of HCl,which is < the required 0.1 mol of HCl.Thus less than req. amt. of HCl.
HCl runs out quicker,compared to Zn.HCl is thus the limiting reagent.
OR,
0.075 mol of HCl would require 0.075/2=0.0375 mol of Zn to react with.However there is 0.05 mol of Zn,which is > the required 0.0375 mol of Zn.Thus more than req. amt. of Zn.
HCl runs out quicker,compared to Zn.HCl is thus the limiting reagent.
(a more suitable approach to qn (a) cux it can be used for later part when calculating the correct amt. of Zn required to react with the 0.075 mol of HCl present.)
b) Note:When doing calculations,USE the amt. of limiting reagent,not the excess one!
In the reaction of Zn and HCl,0.075 mol of HCl would require 0.0375 mol of Zn,as calculated in (a).
However,there is 0.05 mol of Zn present.
Therefore,excess amt. of unreacted reagent Zn= 0.05-0.0375 = 0.0125 mol
take note:mole concept is v impt.the basic of all basics,it's the key to solving all ur qns in practical tests and also,equations-related qns.ways to improve?u can try doing more of the tutorial qns and then repeating them with new,substituted values.listen hard during lectures too.
it would be a breeze once u get the hang of it. -
Originally posted by yuko-ogura:
You sounds like a teacher. Thanks for helping me.
juz my 2 cents worth.feeling bored anyway..
a) [b]1 mol Zn reacts stoichiometrically with 2 mol HCl.
0.05 mol of Zn would require 0.05 x 2 = 0.1 mol of HCl to react with.However there is 0.075 mol of HCl,which is < the required 0.1 mol of HCl.Thus less than req. amt. of HCl.
HCl runs out quicker,compared to Zn.HCl is thus the limiting reagent.
OR,
0.075 mol of HCl would require 0.075/2=0.0375 mol of Zn to react with.However there is 0.05 mol of Zn,which is > the required 0.0375 mol of Zn.Thus more than req. amt. of Zn.
HCl runs out quicker,compared to Zn.HCl is thus the limiting reagent.
(a more suitable approach to qn (a) cux it can be used for later part when calculating the correct amt. of Zn required to react with the 0.075 mol of HCl present.)
b) Note:When doing calculations,USE the amt. of limiting reagent,not the excess one!
In the reaction of Zn and HCl,0.075 mol of HCl would require 0.0375 mol of Zn,as calculated in (a).
However,there is 0.05 mol of Zn present.
Therefore,excess amt. of unreacted reagent Zn= 0.05-0.0375 = 0.0125 mol
take note:mole concept is v impt.the basic of all basics,it's the key to solving all ur qns in practical tests and also,equations-related qns.ways to improve?u can try doing more of the tutorial qns and then repeating them with new,substituted values.listen hard during lectures too.
it would be a breeze once u get the hang of it. [/b] -
no prob.come back anytime.Originally posted by Darkness_hacker99:You sounds like a teacher. Thanks for helping me.