Chem Chapter 6 Chemical Composition

Calculate water molecules in 1.5 mol of water.

1.5 mol x (6.022 x 10^23 molecules /1 mol) = 9.03 x 10^23

A sample of propane, C3H8, contains 15.8 moles of carbon atoms. How many total moles of atoms does the sample contain?

(C moles) 15.8 /3 = 5.26 5.26 x 8 = 42.13 (H moles) 42.13 + 15.8 = 57.9 moles

Water has a molar mass of 18 grams per mole. If there are 36 grams of water, how many water molecules are there?

1.2 × 10^24

If a sample of carbon dioxide contains 3.8 moles of oxygen atoms, how many moles of carbon dioxide are in the sample?

1.9

How many formula units make up 28.6 g of magnesium chloride (MgCl2)?

28.6g * (1 mol/ 95.21g) = .3 mol .3 mol of MgCl2 * ( 6.022 x 10^23 fu/ 1 mol) = 1.81 x 10^23 fu/ formula molecules pf MgCl2

Ascorbic acid (vitamin C) contains 40.92% carbon, 4.58% hydrogen, and 54.50% oxygen by mass. Assume a 100-g sample of ascorbic acid. How many moles of carbon, hydrogen, and oxygen are present in a 100-g sample of ascorbic acid? Use the periodic table as needed.

3.407 C , 4.53 H , 3.406 O 40.92/12.01 4.58/1.01 54.5/16

The most common source of copper (Cu) is the mineral chalcopyrite (CuFeS2). How many kilograms of chalcopyrite must be mined to obtain 300. g of pure Cu?

300g (1mol/63.65g) =4.72 mol 4.72 mol (183.54g/ 1 mol) = 866.4358 g 866.4 g ---> 0.866 kg

How many moles of chlorine, Cl, are there in 8 moles of carbon tetrachloride, CCl4?

32

One mole of oxygen gas has a mass of ________ g.

32.0 (O2, molecular oxygen)

What is the mass of 0.560 moles of chlorine gas?

39.7 (Cl 2) 2(.56 x 35.45)

What is the pseudoformula of ascorbic acid, given that ascorbic acid contains 3.407 mol of carbon, 4.53 mol of hydrogen, and 3.406 mol of oxygen?

C3.407H4.53O3.406

What is the empirical formula of ascorbic acid, given that the pseudoformula is C3.407H4.53O3.406? Express your answer as a chemical formula.

C3H4O3

The chemical formula clearly indicates the relationship between the mass of each element in the formula

False

The empirical formula mass must be 25.0 if the molecular formula mass is 250 and n = 5.

False

How can you efficiently determine the number of atoms in a sample of an element?

First determine the mass of the sample and then convert it to the number of atoms using Avogadro's number and the molar mass of the element.

What is the mass of 1 mol of atoms for an element?

It is equal to the molar mass of the element.

Why is chemical composition important?

It provides an analysis of the amount of an element found within a sample consisting of a certain compound or a mixture of compounds.

How to calculate mass of a single water molecule.

One water molecule = 1 molecule (1 mol/ 6.022 x 10^23 molecules) = 1.660 x 10^-24 mol of H2O 1.660 x 10^-24 mol (18.0 g/ 1 mol) = 2.99 x 10^-23 (Note that is to a negative power, not positive. It will be a very very small decimal.)

Which of the following statements correctly describes a relationship between empirical formula and molecular formula?

The empirical formula molar mass is less than or equal to the actual molar mass for all compounds

Why is counting them not an option?

They are so incredibly small it makes traditional counting impossible.

Why is it important to be able to calculate an empirical formula from experimental data?

This allows to determine the amounts (relative masses or moles) of the element in an unknown compound.

Mass is used as a method of counting atoms.

True

The empirical formula mass is 18.0 and the molecular formula mass is 90, therefore n = 5.

True