Question

Below are the problems:

1. After balancing the following equation, what would be the coefficient that would be needed for H3PO4? Mg + H3PO4 ? Mg3(PO4)2 + H2

2. According to the following balanced chemical equation, how many moles of iron(III)chloride will be produced from 6.2 moles of iron? 2Fe(s) + 3Cl2(g) ? 2FeCl3(s)

3. How many atoms are there in 35.7 mole sample of silicon?

4. According to the following balanced chemical equation, how many moles of iron(III)chloride will be produced from 6.20 grams of iron? 2Fe(s) + 3Cl2(g) ? 2FeCl3(s) 4. The volume of a 0.419 mol sample of gas increases from 1.9 mL to 43.3 mL after the addition of more gas molecules. How many moles are present in the sample after the volume has increased?

Answer 1

(1) Given reaction is

Mg + H3PO4 ----------> Mg3(PO4)2 + H2

The balanced reaction is

3Mg + 2 H3PO4 --------> Mg3(PO4)2 + 3H2.

The coefficient for H3PO4=2.

(2)

Given reaction is

2 Fe(s) + 3Cl2(g) -----> 2FeCl3(s)

Given moles of Fe=6.2 mol.

From the balanced equation, moles of FeCl3 formed=moles of Fe used

(The mole ratio Fe : FeCl3=2:2=1:1)

Therefore moles of Fe(III)Cl3 formed=6.2 moles.

(3)

Given moles of silicon=35.7 moles.

Since 1 mol=6.023x10^23 atoms

Therefore 35.7 moles=? Atoms.

Number of silicon atoms=(35.7 moles x 6.023x10^23 atoms)/1 mole=2.15x10^25 atoms.

(4) From ideal gas equation,

PV=nRT

Where P=pressure, V=volume, R=gas constant, T=absolute temperature, n=number of moles.

Volume is proportional to number of moles.

V1/n1=V2/n2

Given V1=1.9 mL, n1=0.419 mol, V2=43.3 mL and n2=?

n2=V2 n1/V1

n2=(43.3 mL x 0.419 mol)/1.9 mL

Number of moles=9.548 mol.

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