Question

Exactly 3.705 kg of substance Y are needed to neutralise 100 moles of HCl(aq).
What could be substance Y?
A. Ca
B. CaO
C. Ca(OH)2
D. CaCO3

the answer is C BUT i want the method because i need to understand how you ot the answer so please help.

Answer 1

Explanation:

the answer is calcium hydroxide Calcium Hydroxide is a type of base which neutralizes the effect of hydrochloric acid which is a strong acid

Answer 2

The substance Y is $Ca(OH)₂_2$

Explanation:

We are given:

Moles of HCl = 100 moles

We know that:

Calcium is a divalent atom and it reacts with 2 moles of HCl to produce a salt.

The chemical equation for the reaction of calcium ions and HCl follows:

$Ca^{2+}+2HCl\rightarrow CaCl_2+2H^+$

By Stoichiometry of the reaction:

2 moles of HCl reacts with 1 mole of calcium ions

So, 100 moles of HCl will react with = $\frac{1}{2}\times 100=50mol$ of calcium ions containing compound

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Mass of compound = 3.705 kg = 3705 g    (Conversion factor:  1 kg = 1000 g)

Moles of compound containing calcium ions = 50 moles

Putting values in above equation, we get:

$50mol=\frac{3705g}{\text{Molar mass of compound}}\\\\\text{Molar mass of compound}=\frac{3705g}{50mol}=74.1g/mol$

For the given options:

Option A: Ca

The molar mass of calcium is 40 g/mol

Option B: CaO

The molar mass of calcium oxide is 56 g/mol

Option C: $Ca(OH)_2$

The molar mass of calcium hydroxide is 74 g/mol

Option D: $CaCO_3$

The molar mass of calcium carbonate is 100 g/mol

The compound having molar mass equal to 74.1 g/mol is calcium hydroxide

Learn more about acid-base reaction and number of moles:

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