Give the formula for calcium phosphate and then answer the following questions: a. Calculate the

Give the formula for calcium phosphate and then answer the...

Key Concepts

Percent Composition

Percent composition is the calculation of the mass percentage of each element in a compound. It is used to determine the relative amount of each element by mass, which is essential for analyses in chemistry, including purity assessments and formulation of compounds.

Conversion Between Mass, Moles, and Formula Units

This concept deals with converting a given mass of a substance to moles using the molar mass, and then to individual particles such as molecules or formula units using Avogadro’s number. This step-by-step conversion process is crucial for linking the macroscopic measurements in the laboratory with the number of discrete particles present at the molecular level.

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction, or between the different elements in a compound. It provides the framework for calculating quantities such as mass, moles, and the number of formula units, based on balanced ratios defined by the chemical formula.

Chemical Formulas

Chemical formulas represent the composition of compounds using the symbols of the constituent elements and the ratios in which they combine. This concept is fundamental for understanding compound identity, determining the proportions of each element, and for further calculations such as molar mass and stoichiometry.

Molar Mass and Atomic Weights

Molar mass, derived from the atomic weights of the elements present, is the mass of one mole of a compound. It is pivotal in converting between the mass of a substance and the number of moles, bridging the gap between the microscopic scale of atoms and the macroscopic scale of laboratory measurements.

Transcript

00:01 In this video, we're going to be learning how to find a chemical formula based on a given chemical name.

00:06 We're going to be learning how to calculate percent composition and how to use percent composition to determine the mass and moles and formula units of the given molecule.

00:17 So the molecule that we're given is calcium phosphate.

00:21 So we need to find the chemical formula of this.

00:24 So what we're going to do is we're going to first look at calcium.

00:27 This is just, you know, an element.

00:29 And it's right here number 20 on the periodic table.

00:36 We'll notice that it's in group 2, which means it's an alkaline earth metal, and therefore is going to have a plus 2 charge.

00:44 So that's going to be ca with a plus 2 charge.

00:50 Phosphate is something different entirely.

00:53 It's a polyatomic ion.

00:55 The formula is p .o .4, and it has a negative 3 charge.

01:02 So what we need to do is we need to make this into a molecule that's going to have a neutral charge.

01:10 And the way i like to do that is we can see that this one has a plus two charge, this one has a negative three charge.

01:15 So we're going to just take these charges and move them down into the subscripts.

01:20 And if you were to multiply those out, we'd find that then this one would have a plus six charge and this one would have a negative six charge and therefore it would be neutral.

01:30 So we're going to write that as ca3, p -o -4, and that is our chemical formula.

01:42 The next thing we're going to do is we're going to calculate the percent composition.

01:46 And the first step in doing that is we're going to have to find the total molar mass of our calcium phosphate.

01:53 So the first thing i'm going to do is i'm going to write out each of the individual elements that we have in our molecule.

02:00 So c -a -p and o.

02:06 I'm going to note that we have three calcium atoms.

02:13 Then i'm going to note that we have two phosphorus atoms.

02:17 We need to remember that we have to multiply by our subscript out here.

02:21 We have two of these.

02:23 And same thing with our oxygen, we have eight of them.

02:30 We're going to multiply what we have here by their atomic mass, which we're going to find on our periodic table right down here.

02:37 So for calcium, it's 40 .078.

02:43 For phosphorus, it's 30 .974, and for oxygen, it's 15 .999.

02:58 We're going to multiply all those out and get 120 .234, and that's grams, 61 .948 for our phosphorus, and 127 .992 for our oxygen.

03:25 And then we're going to sum all of those together to get our total molar mass, which is 310, 0 .174 grams per mole.

03:38 To find the percent composition, we're going to take our individual element masses here and divide them by our total, and then multiply those by 100%.

03:48 So our ca is going to equal our individual mass, 120 .234, divided by our total 310 .174.

04:06 And then multiply that by 100%.

04:10 And that is going to give us 38 .76%.

04:18 For our phosphorus, we're going to do the same thing.

04:23 61 .948 over 310 .174 times 100 % to give us 19 .97%.

04:36 And then finally, for oxygen, 127 .992 over 310 .17.

04:49 4 times 100%, which is going to give us 41 .26.

04:58 Now before we move on, we need to check our values here...