A small piece of zinc is dissolved in 22.29 mL of 0.968 M HCl.
Zn (s) + 2 HCl (aq) ----> ZnCl2 (aq) + H2 (g)
At the end of the reaction, the concentration of the 22.29-mL sample is redetermined and found to be 0.691 M HCl.
What must have been the mass of the piece of zinc that dissolved?
1. Calculate mols HCl initially.
mols = M x L.
2. Calculate mols HCl at the end of the reaction.
3. Subtract and that is mols HCl used.
4. Using the coefficients in the balanced equation, convert mols HCl to mols Zn.
5. Convert mols Zn to grams Zn.
mols x molar mass = grams.
Post your work if you get stuck.
To find the mass of the piece of zinc that dissolved, we can use the concept of stoichiometry and use the balanced chemical equation given:
Zn (s) + 2 HCl (aq) ----> ZnCl2 (aq) + H2 (g)
First, let's calculate the number of moles of HCl initially present in the 22.29 mL of 0.968 M HCl solution.
Molarity (M) = moles solute / liters of solution
0.968 M = moles HCl / 0.02229 L
moles HCl = 0.968 M × 0.02229 L
moles HCl = 0.0216 moles (rounded to four decimal places)
According to the balanced equation, the stoichiometric ratio between zinc (Zn) and hydrochloric acid (HCl) is 1:2. This means that 1 mole of Zn reacts with 2 moles of HCl.
Since the moles of HCl that reacted is twice the moles of Zn, the number of moles of Zn is half of the moles of HCl.
moles Zn = 0.0216 moles / 2
moles Zn = 0.0108 moles (rounded to four decimal places)
Now, we need to calculate the mass of Zn using its molar mass.
The molar mass of Zn is 65.38 g/mol.
mass Zn = moles Zn × molar mass Zn
mass Zn = 0.0108 moles × 65.38 g/mol
mass Zn = 0.702 g (rounded to three decimal places)
Therefore, the mass of the piece of zinc that dissolved is approximately 0.702 grams.