A 300.0 -g sample of a solid is made up of a uniform mixture of Na NO3, MgCl2, and BaCl2 . A 100

step 1 Okay, so we've got a couple steps to this problem. We've got our mixture, and it's got our three

A 300.0 -g sample of a solid is made up of a uniform mixture...

A 300.0 -g sample of a solid is made up of a uniform mixture of $\mathrm{Na} \mathrm{NO}_{3}, \mathrm{MgCl}_{2},$ and $\mathrm{BaCl}_{2} .$ A 100.0 -g sample of the mixture is dissolved in water and treated with an excess of KOH. The precipitate from the reaction has a mass of $13.47 \mathrm{~g} .$ The remaining $200.0-\mathrm{g}$ sample is also dissolved in water and treated with an aqueous solution of $\mathrm{AgNO}_{3} .$ The resulting precipitate has a mass of $195.8 \mathrm{~g}$. What are the masses of $\mathrm{NaNO}_{3}, \mathrm{MgCl}_{2},$ and $\mathrm{BaCl}_{2}$ in the 300.0 -g sample?

Key Concepts

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It enables the calculation of how much of each substance is needed or produced based on balanced chemical equations, ensuring that atoms are conserved throughout the reaction.

Gravimetric Analysis

Gravimetric analysis is a method in analytical chemistry where the amount of an analyte is determined by converting it into a compound of known composition that can be isolated and weighed. The mass of this precipitate is then used to quantify the target substance in the original sample.

Precipitation Reactions

Precipitation reactions involve the formation of an insoluble solid, or precipitate, when two aqueous solutions are mixed. This process is fundamental in qualitative and quantitative analysis, as it allows for the separation and identification of specific ions based on the insolubility rules.

Mass Balance

Mass balance is the principle of conservation of mass, stating that the total mass in a closed system remains constant. In analytical chemistry, mass balance is used to set up equations that relate the masses of different components in a mixture or the mass of precipitates formed to the original mass of the sample.

Transcript

00:01 Okay, so we've got a couple steps to this problem.

00:03 We've got our mixture, and it's got our three solids in it, and we're going to react them with k -o -h.

00:10 So the first thing we're going to recognize is that the sodium nitrate is not going to react with the k -o -h.

00:18 There's no precipitate form, so we're going to have no reaction here.

00:24 But the magnesium chloride will react with the k -o -h in a 2 -1 ratio to make some kcl and some magnesium hydroxide, which is a precipitate.

00:43 But similarly, the barium chloride is going to react with the k -o -h.

00:50 And again, there's no precipitate.

00:53 So we're going to say there's no reaction.

00:57 So what they've done is they've told us how much of this precipitate is going to form.

01:01 We're going to make 13 .47 grams of precipitate.

01:05 So this is our magnesium hydroxide.

01:08 So we're going to go ahead and start with that.

01:10 Okay, so i've got our 13 .47 grams of magnesium hydroxide.

01:20 We'll change grams to moles, change moles to moles, and then back to moles to grams.

01:37 And our goal is to get to our magnesium chloride here.

01:42 So we're changing magnesium hydroxide to magnesium chloride.

01:51 It's important to label things so you don't get things confused.

01:55 So we'll start with the molar mass here.

01:59 58 .33.

02:01 Our molar ratio is 1 to 1 for between the magnesium chloride and the magnesium hydroxide.

02:07 And then the molar mass here is 95 .21.

02:13 So this is going to give us 21 .99 grams of magnesium chloride.

02:20 But we're not quite done, because that was the amount of magnesium chloride that we got starting with just a hundred grams sample.

02:29 So if we look back, we took 100 of our 100 of our 300 gram sample and reacted with it.

02:36 So our original sample really had three times as much of this.

02:41 So we're going to multiply this by three, and we're going to say there was 65 .96 grams of magnesium chloride.

02:51 Chloride in our original 300 gram sample.

03:00 So we've answered the first part of the question.

03:04 All right.

03:06 So now we're going to take the rest of the 200 grams that we had left and instead of reacting it with k -oh, we're gonna react it with silver chloride.

03:15 Okay, so we're gonna take some silver nitrate, sorry, we're reacting with silver nitrate.

03:21 So some silver nitrate reacts with the magnesium chloride to give us some silver, chloride and some magnesium nitrate.

03:36 And we'll go ahead and balance this.

03:40 At the same time, however, the silver nitrate is also going to react with our barium chloride in the same ratio to make more silver chloride.

03:54 These are our solids here and some barium nitrate.

04:03 So they've told us that they've given us the mass of the entire result.

04:08 Resulting precipitate.

04:11 So i'm going to go back and start with what i know about magnesium chloride that i just found out...

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