When zinc metal is reacted with hydrochloric acid, zinc chloride and hydrogen gas are produced. If 25ml of 0.2M HCl and 0.3g of zinc metal is used: a. how many M of zinc chloride will be produced? b. how many M of zinc chloride will be produced if 0.5M of HCl was used? c. how many M of zinc chloride will be produced if 1M of HCl was used? d. how many M of zinc chloride will be produced if 2M of HCl was used?
If you are using M for mols, that won't get it. M stands for molarity. I will assume you meant mols. You have four limiting reagent (LR) problems here. I'll do the first two for you; you follow the plan to do the other two.
Zn + 2HCl ==> ZnCl2 + H2
a.
1. mols HCl = M x L = 0.2 x 0.025 = 0.005
2. mols Zn = g/atomic mass = 0.3/65.4 = approx 0.0046. NOte that you need to redo ALL of these calculations since I've estimated here and there.
3. Now you need to convert mols HCl and mols Zn to mols ZnCl2. Use the coefficients in the balanced equation to do this.
HCl: 0.005 mols HCl x (1 mol ZnCl2/2 mols HCl) = 0.0025 mols ZnCl2 formed IF WE HAD all of the Zn needed.
Zn: 0.0046 x (1 mol ZnCl2/1 mol Zn) = 0.0046 IF WE HAD all of the HCl we needed.
Note that you have two answers for ZnCl2 mols. Which do you choose? The correct value in LR problems is ALWAYS the smaller number. So mols ZnCl2 formed will be 0.0025 mols.
For b part.
1. mols HCl = 0.5 x 0.025 = 0.0125
mols Zn still approx 0.046.
2. Convert mols HCl to mols ZnCl2 and convert mols Zn to mols ZnCl2.
0.0125 mols HCl x (1 mol ZnCl2/2 mols HCl) = 0.00625 mols ZnCl2 formed IF WE HAD all of the Zn we needed.
For Zn it is 0.0046 x (1 mol ZnCl2/1 mol Zn) = 0.0046 mols ZnCl2 IF WE HAD all of the HCl we needed.
Here the smaller number is 0.0046 and that is the # mols ZnCl2 formed.
c and d are done the same way.
Post your work if you get stuck.
To determine the molarity of zinc chloride produced, we'll use the stoichiometry of the reaction between zinc and hydrochloric acid.
The balanced chemical equation for the reaction is:
Zn + 2HCl → ZnCl2 + H2
a. To find the moles of zinc chloride produced when 25 mL of 0.2 M HCl and 0.3 g of zinc metal are used, follow these steps:
Step 1: Find the moles of zinc metal.
Molar mass of zinc (Zn) = 65.38 g/mol
Number of moles of zinc = mass of zinc / molar mass
Number of moles of zinc = 0.3 g / 65.38 g/mol
Step 2: Determine the limiting reagent.
To identify the limiting reagent, compare the moles of zinc and moles of HCl. From the balanced equation, it's clear that the reaction requires 1 mole of zinc for every 2 moles of HCl.
For zinc, we calculated the moles to be:
Number of moles of zinc = 0.3 g / 65.38 g/mol
For HCl, we have:
Number of moles of HCl = volume of HCl (L) × concentration of HCl (M)
Number of moles of HCl = 0.025 L × 0.2 mol/L
To determine the limiting reagent, we compare the moles of zinc and moles of HCl (after adjusting to the same units):
Moles of zinc = 0.3 g / 65.38 g/mol
Moles of HCl = 0.025 L × 0.2 mol/L
The ratio of the coefficients in the balanced equation is 1:2 (for zinc:HCl).
So, 1 mole of zinc requires 2 moles of HCl.
Comparing the moles of zinc (0.3 g / 65.38 g/mol) and the adjusted moles of HCl (0.025 L × 0.2 mol/L × 2), we can see that the moles of HCl are in excess.
Step 3: Find the moles of zinc chloride produced.
From the balanced equation, we know that 1 mole of zinc reacts to produce 1 mole of zinc chloride.
Therefore, the number of moles of zinc chloride produced is equal to the number of moles of zinc used.
Since zinc is the limiting reagent, the moles of zinc chloride produced are equal to the moles of zinc used:
Number of moles of zinc chloride = Number of moles of zinc = 0.3 g / 65.38 g/mol
Step 4: Calculate the molarity of zinc chloride.
Molarity (M) = moles / volume (L)
Given that the volume of the solution is 0.025 L (25 mL), the molarity of zinc chloride is:
Molarity of zinc chloride = (0.3 g / 65.38 g/mol) / 0.025 L
b. To find the molarity of zinc chloride produced if 0.5 M of HCl was used, the process is the same. We just need to adjust the calculation to use the new concentration of HCl.
Step 1: Find the moles of zinc chloride produced (same as in part a).
Number of moles of zinc chloride = Number of moles of zinc = 0.3 g / 65.38 g/mol
Step 2: Calculate the molarity of zinc chloride.
Molarity of zinc chloride = (0.3 g / 65.38 g/mol) / 0.025 L
Note that the molarity of HCl does not affect the moles of zinc chloride produced because zinc is the limiting reagent.
c. To find the molarity of zinc chloride produced if 1 M of HCl was used, we'll follow the same steps as in parts a and b, adjusting the concentration of HCl.
Step 1: Find the moles of zinc chloride produced (same as in parts a and b).
Number of moles of zinc chloride = Number of moles of zinc = 0.3 g / 65.38 g/mol
Step 2: Calculate the molarity of zinc chloride.
Molarity of zinc chloride = (0.3 g / 65.38 g/mol) / 0.025 L
As mentioned before, the molarity of HCl does not affect the moles of zinc chloride produced.
d. To find the molarity of zinc chloride produced if 2 M of HCl was used, follow the same steps, adjusting the concentration of HCl.
Step 1: Find the moles of zinc chloride produced (same as in parts a, b, and c).
Number of moles of zinc chloride = Number of moles of zinc = 0.3 g / 65.38 g/mol
Step 2: Calculate the molarity of zinc chloride.
Molarity of zinc chloride = (0.3 g / 65.38 g/mol) / 0.025 L
Again, the molarity of HCl does not impact the moles of zinc chloride produced.
To find the molarity (M) of zinc chloride produced in each case, we need to determine the moles of zinc chloride produced by the reaction.
The balanced chemical equation for the reaction is:
Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)
a. With 25 mL of 0.2 M HCl and 0.3 g of zinc metal:
To start, we need to find the moles of HCl and zinc metal used.
Moles of HCl = volume (in L) × molarity
Moles of HCl = 25 mL × (1 L / 1000 mL) × 0.2 M
Moles of HCl = 0.005 moles
Now, let's find the moles of zinc metal:
Moles of zinc = mass (in g) ÷ molar mass
Moles of zinc = 0.3 g ÷ 65.38 g/mol (molar mass of zinc)
Moles of zinc = 0.0046 moles
According to the balanced equation, two moles of HCl react with one mole of zinc to produce one mole of zinc chloride. Therefore, the number of moles of zinc chloride produced will be equal to the smaller of the two values we found.
Moles of zinc chloride = min(moles of HCl, moles of zinc)
Moles of zinc chloride = min(0.005 moles, 0.0046 moles)
Moles of zinc chloride = 0.0046 moles
Finally, we can calculate the molarity of zinc chloride:
Molarity of zinc chloride = moles of zinc chloride ÷ volume (in L)
Molarity of zinc chloride = 0.0046 moles ÷ (25 mL × (1 L / 1000 mL))
Molarity of zinc chloride = 0.184 M
Therefore, the Molarity of zinc chloride produced in this case is 0.184 M.
b. If 0.5 M HCl was used, the calculation will be the same as in part a, but we'll use 0.5 M as the molarity of HCl:
Moles of HCl = 25 mL × (1 L / 1000 mL) × 0.5 M
Moles of HCl = 0.0125 moles
Again, comparing the moles of HCl and zinc, we find that the limiting reactant is zinc:
Moles of zinc chloride = moles of zinc
Moles of zinc chloride = 0.0046 moles
Molarity of zinc chloride = 0.0046 moles ÷ (25 mL × (1 L / 1000 mL))
Molarity of zinc chloride = 0.184 M
Therefore, in this case, the Molarity of zinc chloride produced is also 0.184 M.
c. If 1 M of HCl was used, the calculation proceeds similarly:
Moles of HCl = 25 mL × (1 L / 1000 mL) × 1 M
Moles of HCl = 0.025 moles
Moles of zinc chloride = moles of zinc
Moles of zinc chloride = 0.0046 moles
Molarity of zinc chloride = 0.0046 moles ÷ (25 mL × (1 L / 1000 mL))
Molarity of zinc chloride = 0.184 M
So, the Molarity of zinc chloride produced in this case is also 0.184 M.
d. If 2 M of HCl was used, the calculation follows the same method as the previous cases:
Moles of HCl = 25 mL × (1 L / 1000 mL) × 2 M
Moles of HCl = 0.05 moles
Moles of zinc chloride = moles of zinc
Moles of zinc chloride = 0.0046 moles
Molarity of zinc chloride = 0.0046 moles ÷ (25 mL × (1 L / 1000 mL))
Molarity of zinc chloride = 0.184 M
Hence, the Molarity of zinc chloride produced in this case is also 0.184 M.
In conclusion, regardless of the HCl concentration used, the resulting Molarity of zinc chloride is always 0.184 M as long as the amount of zinc metal remains constant.