Question

The zinc content of a 1.10

g ore sample was determined by dissolving the ore in HCl
, which reacts with the zinc. The excess HCl
is then neutralized with with NaOH
. The reaction of HCl
with Zn
is shown.

Zn(s)+2HCl(aq)⟶ZnCl2(aq)+H2(g)


The ore was dissolved in 150 mL
of 0.600 M HCl
, and the resulting solution was diluted to a total volume of 300 mL
. A 20.0 mL
aliquot of the final solution required 9.12
mL of 0.515
M NaOH
to neutralize the excess HCl
. What is the mass percentage (%w/w) of Zn
in the ore sample?

Answer 1

To calculate the mass percentage (% w/w) of Zn in the ore sample, calculate the moles of Zn in the solution using the volume and concentration of NaOH used to neutralize the excess HCl. The moles of Zn will be equal to twice the moles of HCl neutralized. Then, calculate the mass of Zn in the ore sample using the moles of Zn and the molar mass of Zn. Finally, calculate the mass percentage of Zn by dividing the mass of Zn by the mass of the ore sample and multiplying by 100%.

Step-by-step explanation:

To calculate the mass percentage (% w/w) of Zn in the ore sample, we need to determine the moles of Zn in the solution. We can use the volume of NaOH used to neutralize the excess HCl and the concentration of NaOH to calculate the moles of NaOH used. The moles of NaOH used will be equal to the moles of HCl neutralized, and since the reaction is 1:2 between Zn and HCl, this will be equal to the moles of Zn in the ore sample. From the moles of Zn, we can calculate the mass of Zn in the ore sample and then find the mass percentage.

First, let's calculate the moles of NaOH used:

Moles of NaOH = (volume of NaOH used) × (concentration of NaOH)

Moles of NaOH = (9.12 mL) × (0.515 M) = 4.6992 × 10-3 mol

Since the reaction is 1:2 between Zn and HCl, the moles of Zn will be twice the moles of HCl neutralized:

Moles of Zn = 2 × (moles of NaOH) = 2 × (4.6992 × 10-3) = 9.3984 × 10-3 mol

Now, let's calculate the mass of Zn in the ore sample:

Mass of Zn = (moles of Zn) × (molar mass of Zn)

Mass of Zn = (9.3984 × 10-3) × (65.38 g/mol) = 0.613 g

Finally, let's calculate the mass percentage (% w/w) of Zn in the ore sample:

Mass percentage of Zn = (mass of Zn / mass of ore sample) × 100%

Mass percentage of Zn = (0.613 g / 1.10 g) × 100% = 55.73%