Mr Study's 3/4 Questions

[Mr. Study]

Hey,

Just this question for today. (Abbreviated a little bit)

A technician takes 5g of vegemite and dissolves it in water. Enough silver nitrate is added to precipitate all chlorine ions present. After filtering and drying, 1.05g of silver chloride is obtained. Calculate the percentage of sodium chloride in the sample.

Thanks!

[Phy124]

NaCl + AgNo₃ -> AgCl + NaNo₃

n(AgCl) = m/M = 1.05/143.32 = 7.33 x 10^-3 mol

n(NaCl) = n(AgCl) = 7.33 x 10^-3 mol

m(NaCl) = n x M = 7.33 x 10^-3 x 58.44 = 0.428g

%m(NaCl) = (0.428/5)x100 = 8.56%

I hope that's right anyway 

[Mr. Study]

Thanks for that.

Here's another question that's bugging me: The calcium content of a sample can be determined gravimetrically by first precipitating the calcium ions present as calcium oxalate. When this precipitate is heated, it decomposes completely to produce calcium oxide. In testing the purity of a calcium chloride sample, a chemist used gravimetric analysis and obtained 8.81 g of calcium oxide from an original 18.0 g
sample of calcium chloride. Calculate the percentage purity of the calcium chloride.

This is my reasoning so far. The guy has 18g of CaCl₂ and after using a gravimetric technique, he obtained 8.81g of CaO.

Would the chemical equation be: Ca(COO)₂ + {Heat, I dont really know what the reactants are. :S} --> CaO(aq) + {Another product}

Could someone tell me if what I'm thinking is so far correct? And if it is, Could someone explain what the other reactant/product is/are and explain why.

Thank you.

UPDATE: Just this other question about empirical formula.

I have the ratio 0.0616:0.185, I figured the ratio is 3:1. (Doesn't it take 0.06 x 3 = 0.18??).
But the answer has it as 1:3. Could someone help me out with this?

[Panicmode]

Thanks for that.

Here's another question that's bugging me: The calcium content of a sample can be determined gravimetrically by first precipitating the calcium ions present as calcium oxalate. When this precipitate is heated, it decomposes completely to produce calcium oxide. In testing the purity of a calcium chloride sample, a chemist used gravimetric analysis and obtained 8.81 g of calcium oxide from an original 18.0 g
sample of calcium chloride. Calculate the percentage purity of the calcium chloride.

This is my reasoning so far. The guy has 18g of CaCl₂ and after using a gravimetric technique, he obtained 8.81g of CaO.

Would the chemical equation be: Ca(COO)₂ + {Heat, I dont really know what the reactants are. :S} --> CaO(aq) + {Another product}

Could someone tell me if what I'm thinking is so far correct? And if it is, Could someone explain what the other reactant/product is/are and explain why.

Thank you.

See my attached scan for working =D.

I really wouldn't worry about the equations in this case since they're not necessary/required. All you have to know is that the number of moles of calcium is the same in all substances. From here we can work out the mass/number of mole of all the other substances.


EDIT: To answer your second question, you divide each of the speices by the lowest number.

0.0616 is the lowest

therefore 0.0616/0.0616 = 1

0.185/0.616 ~ 3

The ratio is 1 : 3

[Mr. Study]

You didnt have to go that far to help!! But thank you so much for it!!

Ah!, A lot easier to understand!

Thanks again.

[Mr. Study]

Okay, Here are my questions for today. (Hopefully).

This is related to the mass spectrum of chlorine, no pictures but a description. Chlorine shows two peaks, one with m/z=35 and relative abundance of 3 and another at m/z=37 abd relative abundance of 1.

a) How many isotopes of Chlorine?
I think it will be two but I am not sure why. My reasoning that since two peaks are produced, there are two charged atoms. Is this reasoning correct?

b) Calculate relative atomic mass of chlorine
I am guessing 35.5, as the chlorine is now positive and no element has been added. Correct reasoning?

c) Which isotope will be most deflected?
I know deflection occurs to the lightest ion but I have no idea on identifying which chlorine (isotope?) is the lighter one.

Thank you very much!

EDIT: Just a quick question about the fragments that are produced.


With that butance picture, Can fragments on be produced from either end but joining?

Example: CH₃⁺ can be produced as a peak but NOT CH₂⁺, as it is in the middle? BUT a CH₃CH₂⁺ can be produced, as it's joint to one of the ends? Is my reasoning correct?

Thanks again.

[Phy124]

Okay, Here are my questions for today. (Hopefully).

This is related to the mass spectrum of chlorine, no pictures but a description. Chlorine shows two peaks, one with m/z=35 and relative abundance of 3 and another at m/z=37 abd relative abundance of 1.

a) How many isotopes of Chlorine?
I think it will be two but I am not sure why. My reasoning that two peaks are produced, as there are two peaks. Could someone explain how I could correctly tell how many isotopes are present?

b) Calculate relative atomic mass of chlorine
I am guessing 35.5, as the chlorine is now positive. Correct reasoning?

c) Which isotope will be most deflected?
I know deflection occurs to the lightest ion but I have no idea on identifying which chlorine (isotope?) is the lighter one.

Thank you very much!

EDIT: Just a quick question about the fragments that are produced.
(Image removed from quote.)

With that butance picture, Can fragments on be produced from either end but joining?

Example: CH₃⁺ can be produced as a peak but NOT CH₂⁺, as it is in the middle? BUT a CH₃CH₂⁺ can be produced, as it's joint to one of the ends? Is my reasoning correct?

Thanks again.

a) Yes there are 2, because there are 2 peaks

b) Yes, 35.5: 3/4 x 35 + 1/4 x 37 = 35.5 g/mol

c) Yes, the lightest ion is deflected most. This is the one which has m/z 35 as it has 35g/mol rather than 37g/mol

edit: damn missed the edit;

I believe that is correct, but I'm not entirely sure. I might have to try and find my old textbook .pdf and read up on this for you.

[Mr. Study]

Thanks for that, hopefully those questions weren't 'newbie'. xD

[Mr. Study]

Just some questions regarding carbon compounds.

1. If a carbon compound contained the functional groups, chloro, ethanol and a double bond, Who do I give the LOWEST number too?

2. Why are carboxylic acids more souble in water than alcohols?

Thanks.

[Phy124]

Just some questions regarding carbon compounds.

1. If a carbon compound contained the functional groups, chloro, ethanol and a double bond, Who do I give the LOWEST number too?

2. Why are carboxylic acids more souble in water than alcohols?

Thanks.

1. Here is a naming table from the mid year exam tsfx lectures I went to. From what you have listed it appears the hydroxyl (I assume that's what you meant by ethanol) group will take preference.

2. Carboxylic acids are more polar than alcohols, because polar dissolves polar the more polar it is the more it will dissolve, I believe... I'll also check this when I get home.

[Mr. Study]

Thanks Phy124, Don't worry about the rest.

Just a quick stoichiometry question.

2.203g of organic compounds C_xH_yO_z, was burned in oxygen. Hydrogen was converted to H₂O and Carbon was converted to CO₂. Find the empirical formula.

Thanks.

[Phy124]

Thanks Phy124, Don't worry about the rest.

Just a quick stoichiometry question.

2.203g of organic compounds C_xH_yO_z, was burned in oxygen. Hydrogen was converted to H₂O and Carbon was converted to CO₂. Find the empirical formula.

Thanks.

Does it gives mass or volumes of the H₂O and CO₂ being produced?

Also, please note my edit in the post above yours, I found the preferences table for naming compounds and it appears hydroxyl comes before double bonds.

[Mr. Study]

Thanks Phy124, Don't worry about the rest.

Just a quick stoichiometry question.

2.203g of organic compounds C_xH_yO_z, was burned in oxygen. Hydrogen was converted to H₂O and Carbon was converted to CO₂. Find the empirical formula.

Thanks.

Does it gives mass or volumes of the H₂O and CO₂ being produced?

Also, please note my edit in the post above yours, I found the preferences table for naming compounds and it appears hydroxyl comes before double bonds.

Hey, thanks for that! I've never heard of ammonio before. :S

Damn it! I always forget to add something. The mass of Water produced was 1.32g and the mass of Carbon dioxide produced was 3.23g.

[Shenz0r]

First find out the mass of Carbon and Hydrogen, then use conservation of mass to find the mass of oxygen in CxHyOz.

m(C) = 12/44 x 3.23 = 0.88091 g
m(H2) = 2/18 x 1.32 = 0.1467g
m(O in CxHyOz) = 2.203 - 0.88901 - 0.1467 = 1.167g

C                H2             O
0.88901     0.1467      1.167
0.074 mol  0.074 mol  0.074 mol

Therefore the empirical formula is CH2O.

[Mr. Study]

Just a quick question.

For the compound Fe(NO₃)₃.9H₂O, What exactly does the dote, inbetween (NO₃)₃ and 9H₂ actually do?

If, hyptothetically, I needed to find the mole of Fe(NO₃)₃, and I were given the mass of it, Do I factor in the 9H₂O?

Thanks.