Given :
A certain compound contains 4.0 g of calcium and 7.1 g of chlorine.
Its relative molecular mass is 111.
To Find :
Its empirical and molecular formulas.
Solution :
Moles of calcium , .
Moles of chlorine , .
The ratio calcium and chlorine is 1 : 2 .
So , the empirical formula is .
Now , molecular mass of is :
So ,
Therefore , the molecular formula is also .
Hence , this is the required solution .
Answer:
The volume of air required is 527,686.25L.
Explanation:
When the question says <em>"burn"</em>, it refers to a combustion reaction, where a substance (in this case octane) reacts with oxygen to produce carbon dioxide and water.
Step 1: Write a balanced equation
Considering it is a combustion reaction, the balanced equation is:
C₈H₁₈ + 12.5 O₂ ⇄ 8 CO₂ + 9 H₂O
In this step, we start balancing elements that are present only in one compound on each side of the equation, namely, carbon and hydrogen.
To finish, it is important to count that there are the same number of atoms on both sides of the equation. In this case there are 8 atoms of Carbon, 18 atoms of Hydrogen and 25 atoms of Oxygen, so it is balanced.
Step 2: Find out the mass of C₈H₁₈
Since the balanced equation gives us information about the mass of C₈H₁₈ involved in the reaction, we need to find out how many grams we have.
The info we have is:
Density relates mass and volume, so we can find out how many grams are represented by 55 L. Since the units used are different, first we need to convert liters into cm³. We use the <em>conversión factor 1 L = 1000 cm³</em>.
Since <em>density = mass/volume</em>, we can solve for mass:
Step 3: Establish the theoretical relationship between the mass of octane and the moles of oxygen.
This relationship comes from the balanced equation.
For octane:
molar mass of C₈H₁₈ = molar mass of C . 8 + molar mass of H . 18 =
12 g/mol . 8 + 1g/mol . 18 = 114 g/mol
According to the balanced equation reacts 1 mol of octane, which means 114 grams of it.
For oxygen:
According to the balanced equation, 12.5 moles of oxygen react.
Then, the relationship is <u>114 g octane : 12.5 moles of oxygen</u>
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Step 4: Use the theorethical relationship to find the moles of oxygen that reacted
We use the mass of octane found in step 2 and apply the proper conversión factor.
Step 5: Find out the volume of oxygen.
We know that 1 mol of any gas at room temperature occupies about 25 L. Then,
Step 6: Look the volume of air that contains such amount of oxygen
Given oxygen represents 20% of air, we can use that relationship to find the volume of air.