Calculate the percent by mass of the element mentioned first in the formulas for each of the fol

Calculate the percent by mass of the element mentioned first...

Key Concepts

Percent by Mass

Percent by mass, also known as mass percent, is a way of expressing the composition of a compound in terms of the mass of a specific element compared to the total mass of the compound. It is calculated by taking the mass contribution of the element in one mole of the compound, dividing it by the formula mass (or molar mass) of the compound, and then multiplying by 100 to convert it to a percentage.

Molar Mass Calculation

Molar mass is determined by summing the atomic masses of all the atoms present in the molecular formula of a compound. This calculation takes into consideration the number of atoms of each element as indicated by their subscripts in the formula, providing a total mass per mole that is essential for various stoichiometric calculations, including percent by mass.

Atomic Mass

Atomic mass is the mass of an individual atom of an element, typically expressed in atomic mass units (amu) or grams per mole (g/mol). This fundamental value is used in calculating the molar mass of compounds and is obtained from the periodic table, which provides a standard for each element's atomic weight.

Chemical Formula Interpretation

Interpreting a chemical formula involves understanding the representation of a compound in terms of its constituent elements and their respective quantities. The formula indicates which element is present first and how many atoms of each element are in the compound, which is crucial when identifying the element of interest and performing stoichiometric calculations like percent by mass.

Transcript

00:01 All right, so here we have eight chemical compounds, and we're going to find the mass percent of the first element present.

00:13 Let's recall the mass percent formula.

00:20 The way that we calculated is we take the mass of the element, whatever element in question, mass of the element, and divided by the total mass.

00:35 But the total mass of one mole of substance, like one more of the chemical.

00:47 Alright, so first we have sodium azide.

00:56 And we're gonna start off by listing each element in this chemical compound.

01:11 Now we're going to calculate the mass of each compound.

01:17 So let's remember the formula for mass.

01:21 We can calculate mass by taking moles and multiplying it by molar mass.

01:28 All right.

01:29 So we know we have one mole of substance, one mole of sodium azide.

01:36 So if we have one mole of sodium azide, that means we also have one mole of sodium.

01:42 And that means we then have three moles of nitrogen, right? and then we'll multiply by the molar mass of each substance.

01:54 So sodium's molar mass is around 22 .9897, so i'll just write 23.

02:04 And nitrogen's molar mass is 14 grams per mole.

02:10 Okay.

02:11 And once we totaled this up, we get 65, which is now our mass total.

02:19 So now the mass percent of sodium, the first element, simply going to be this 23, that's the mass of sodium, over the mass total.

02:40 65.

02:46 These are both in grams.

02:51 If you take your calculator and probably include more of the digits, we get a mass percent of 35.

03:02 0 .36.

03:11 All right.

03:14 Okay, let's move on.

03:17 Next we have copper sulfate.

03:18 So we're going to do the exact same methods.

03:26 List out the elements and now calculate the mass of each element so we can find a total mass.

03:35 All right, so remember always one mole of the chemical, one more, the copper to sulfate.

03:42 So one mole of copper to sulfate is one mole of copper, one mole of sulfur, and four moles of oxygen.

03:56 And we'll multiply these moles by the molar mass of the element.

04:06 And here we've now calculated mass.

04:13 Okay.

04:16 Now, once we sum all of these masses up, we get 159 .6, which is the total mass.

04:35 So then we'll take the mass of copper.

04:41 So we're looking for the mass percent of the first element.

04:52 So mass percent of copper is the mass of copper over the total mass.

05:07 0 .6.

05:20 Okay, and that equals 39 .81.

05:38 39 .81%.

05:42 Okay.

05:44 Now let's move a bit faster.

05:46 Here we have gold 3 chloride.

05:50 So yep, we're going to list out each compound and then calculate their mass, one mole of gold, and one mole of gold 3.

06:07 Chloride gold mol mass is 196 .9 and you have three moles of chloride.

06:29 Okay, let's find the total mass, which is 303.

06:42 And then the mass percent of gold is just this mass over the total mass, which gives us a mass percent 64 .94.

07:11 Okay.

07:14 Next, we have silver nitrate.

07:17 I'm gonna do the exact same thing.

07:30 One mole of silver nitrate means one mole of silver.

07:35 Silver's molar mass is 107 .8...

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