Empirical and Molecular formula, Hydrates

Question 1

Define empirical formula.

Answer 1

The empirical formula of a compound is the simplest whole number ratio of all the elements.

Question 2

How do you determine empirical formula from the percentages by mass?

Answer 2

First, assume the weight in mass as 100g and multiply each percentage by it. Next, divide each number by it’s molar mass to get the number of mols for each element. Take the lowest number and divide all numbers by it. The closest whole numbers to the results will be the subscript for each element (you can also multiply if necessary).

Question 3

Given both the molar mass of the compound and the empirical formula for the compound, how do you find the molecular formula?

Answer 3

First, find the molar mass of the empirical formula. Next, divide the molar mass of the substance by the molar mass of the empirical formula. Then, multiply each subscript by the result, that’s the molecular formula.

Question 4

How do you determine the empirical formula in a compound if you’re given the grams of each element?

Answer 4

First, convert each N. of grams to N. of moles by dividing them by their molar mass. Then, divide each number by the smallest. The closest whole numbers (or multiplied to get the smallest whole numbers) is the empirical formula.

Question 5

What is a hydrate?

Answer 5

A hydrate is anything that contains a specific amount of water as one of it’s primary substances.

Question 6

How do you write the chemical equation from a hydrated compound to an anhydrous compound?

Answer 6

(Anhydrous compound)X(H2O) –> Anhydrous compound + H2O

Question 7

What is the molar mass of water?

Answer 7

18.016 g/mol

Question 8

How do you calculate the empirical formula of a hydrated compound given the mass of the hydrated compound in grams and the mass of the anhydrous result in grams(the hydrated compound is boiled)?

Answer 8

First, subtract the mass of the anhydrous result from the mass of the hydrated compound. This is the mass of water in grams. Now, take the mass of the water and anhydrous result, convert them both to moles by dividing them by their molar mass. Finally, take both numbers, find the lowest and divide both numbers by the lowest. These are the subsets for the empirical formula.

Question 9

How do you find the empirical formula of the hydrocarbon if given grams of CO2 and H2O in a combustion reaction without oxygen in the compound?

Answer 9

First, convert grams of CO2 to moles of CO2 by dividing the number of grams by 44.01. Divide the grams of H2O by 18.016. Now, since there is 1 mol of C per mol of CO2, we multiply the number of moles of CO2 by 1 to get moles of carbon. As for H2O, there are 2 H for every H2O, so we multiply the number of moles of H2O by 2 to get moles of hydrogen. Divide both results by the lowest result to get the subscripts for both in the empirical formula.

Question 10

How do you find the empirical formula of the hydrocarbon if given grams of the compound, CO2 product, H2O product in a combustion reaction WITH oxygen in the compound?

Answer 10

First, find the grams of elements carbon and hydrogen:
(G. of CO2) / (44.01) x (12.01) = G. of carbon
(G. of H2O) / (18.016) x (2) x (1.008) = G. of hydrogen
Now, oxygen in the compound but not air:
(G. of compound) - ((G. of carbon) + (G. of hydrogen)) = G. of oxygen
Now, back to moles:
(New G. of carbon) / 12.01 = Mols of carbon
(New G. of hydrogen) / 1.008 = Mols of hydrogen
(New G. of oxygen) / 16 = Mols of oxygen
Divide all number of moles by the lowest number of moles to get the subscript of each element.