How to find the molecular formula out of the molar mass?

In summary, the conversation involves questions about the molar mass and empirical formula of an industrial solvent, as well as the number of moles in a given mass of potassium chloride. The solution involves finding the mass of a hypothetical group and using a periodic table to calculate the mass of KCl.
  • #1
jessicah211
1
0
Here is the problem. I have a series of questions that I don't know how to do. They are all basically the same so I will just give an example of one and if I could get a point the right direction that would be great!

The molar mass of an important industrial solvent is 78.0 g and its empirical formula is CH. What is its molecular formula?

Anther slightly related question that might be answered as part of the first question is

How many moles are in 35 g of potassium chloride?
 
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  • #2
What is molar mass of the hypothetic CH group? How many such groups are needed for the molecule to have molar mass of 78?
 
  • #3
As Borek said,

(CxHy)n = 78.0 (You are given 1 x and 1 y)

1) Find the mass of the hypothetical group
here : x (mass of carbon = 12) + y (mass of hydrogen = 1) = 13

2) Find how many possible hypothetical groups you can have for 78.0 g
here : n = 78.0 / 13.0 = 6,

3) Just multiply replace x,y and n and you will get the actual formula
here : (C1H1)6 = C6H6

... and you found Benzene :)

The second part is as simple. Just use a periodic table to find the mass of K and Cl, thus finding the mass of 1 mole of KCl, then just divide the mass given in the question:

1 mole = (35.5 + 39.1) 74.6 g
35 g = ( 35 / 74.6 ) 0.47 moles
 

1. What is the difference between a molecular formula and a molar mass?

A molecular formula is a representation of a compound's chemical composition, showing the type and number of atoms present in each molecule. Molar mass, on the other hand, is the mass of one mole of a substance, expressed in grams per mole. In other words, while a molecular formula tells us what elements make up a compound, molar mass tells us how much of that compound we have in a specific quantity.

2. How do I calculate the molecular formula from the molar mass?

To calculate the molecular formula from the molar mass, you will need to know the molar mass of the compound and the mass of each element present in the compound. From there, you can divide the molar mass by the mass of each element to determine the ratio of each element in the compound. Finally, use these ratios to write the molecular formula, making sure to simplify if necessary.

3. Can the molecular formula be determined from the molar mass alone?

No, the molecular formula cannot be determined from the molar mass alone. As mentioned earlier, the molar mass only tells us the mass of one mole of a substance, but it does not provide information about the types of atoms present in the compound. To determine the molecular formula, we need to know the specific elements present in the compound and their ratios, which can be obtained through experiments or calculations.

4. What other information is needed to find the molecular formula from the molar mass?

In addition to the molar mass, we also need to know the mass of each element present in the compound. This can be obtained through experiments such as elemental analysis, or it can be calculated using other data such as the empirical formula of the compound. Without this additional information, it is not possible to accurately determine the molecular formula.

5. Are there any shortcuts or tricks for finding the molecular formula from the molar mass?

While there are no shortcuts or tricks for finding the molecular formula from the molar mass, there are certain strategies that can be used to make the process easier. These include using the empirical formula as a starting point, using the Law of Definite Proportions, and double-checking your calculations to ensure accuracy. It is also helpful to have a good understanding of stoichiometry and basic algebra to solve complex problems involving molecular formulas and molar masses.

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