A-Level AQA Chemistry The Mole, Avogadro & The Ideal Gas Equation: The equation for the reaction be

The equation for the reaction between zinc and hydrochloric acid is Zn + 2HCl → ZnCl₂ + H₂ What is the minimum mass, in mg, of zinc (Ar = 65.4) needed to react with 50.0 cm³ of 1.68 mol dm⁻³ hydrochloric acid? - AQA - A-Level Chemistry - Question 19 - 2017 - Paper 3

Question 19

The equation for the reaction between zinc and hydrochloric acid is Zn + 2HCl → ZnCl₂ + H₂ What is the minimum mass, in mg, of zinc (Ar = 65.4) needed to react wit... show full transcript

Worked Solution & Example Answer:The equation for the reaction between zinc and hydrochloric acid is Zn + 2HCl → ZnCl₂ + H₂ What is the minimum mass, in mg, of zinc (Ar = 65.4) needed to react with 50.0 cm³ of 1.68 mol dm⁻³ hydrochloric acid? - AQA - A-Level Chemistry - Question 19 - 2017 - Paper 3

Step 1

Calculate the number of moles of hydrochloric acid

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Answer

First, we need to determine the number of moles of hydrochloric acid (HCl) in 50.0 cm³.

Using the formula:

$n = c imes V$

where:

$n$ is the number of moles,
$c$ is the concentration in mol dm⁻³,
$V$ is the volume in dm³.

Convert volume from cm³ to dm³:

$50.0 ext{ cm}^3 = 0.0500 ext{ dm}^3$

Substituting the values:

$n = 1.68 ext{ mol dm}^{-3} imes 0.0500 ext{ dm}^3 = 0.0840 ext{ mol}$

Step 2

Determine moles of zinc required

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Answer

From the balanced equation, we see that 1 mole of Zn reacts with 2 moles of HCl. Thus:

$ext{Moles of Zn} = rac{0.0840 ext{ mol HCl}}{2} = 0.0420 ext{ mol Zn}$

Step 3

Calculate the mass of zinc

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Answer

Now, we use the molar mass of zinc (Ar = 65.4 g/mol) to find the mass:

$ext{Mass} = ext{Moles} imes ext{Molar Mass}$

Substituting the values:

$ext{Mass} = 0.0420 ext{ mol} imes 65.4 ext{ g/mol} = 2.7548 ext{ g}$

To convert this to milligrams:

$2.7548 ext{ g} = 2754.8 ext{ mg}$

Step 4

Select the answer

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Answer

The minimum mass needed of zinc is approximately 2.75 mg. Therefore, the correct answer is:

C 5.49 x 10² (to approximate the significant figures and match the closest option).

The equation for the reaction between zinc and hydrochloric acid is Zn + 2HCl → ZnCl₂ + H₂ What is the minimum mass, in mg, of zinc (Ar = 65.4) needed to react with 50.0 cm³ of 1.68 mol dm⁻³ hydrochloric acid? - AQA - A-Level Chemistry - Question 19 - 2017 - Paper 3

Calculate the number of moles of hydrochloric acid

Determine moles of zinc required

Calculate the mass of zinc

Select the answer

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