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Questions tagged [stoichiometry]

Stoichiometry refers to the relationship between the amounts of substances of the reactants and the amount of substances of the formed products. This tag should be used for specific questions about chemical reaction equations.

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24
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1answer
4k views

How can there be decimal subscripts in a molecular formula?

While learning about how batteries work I have encountered the following notation for a Li-ion cathode: $\ce{Li_{0.5}FePO4}$.[1] According to Wikipedia, the subscript number in a reaction equation ...
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Can a chemical reaction have two balanced equations?

I was recently studying Xenon compounds and read this reaction: $$\ce{6XeF4 + 12H2O -> 4Xe + 2XeO3 + 24HF + 3O2}$$ However this reaction can also be written as the following: $$\ce{4XeF4 + 8H2O ...
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5answers
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Why can't I balance this reaction algebraically?

$$\ce{aCu + bHNO3 -> cCu(NO3)2 + dNO + eH2O}$$ (Source) I calculated: \begin{align} a &= c &(\ce{Cu})\\ b &= 2e &(\ce{H})\\ b &= 2c + d &(\ce{N})\\ 3b &= 6c + d + ...
16
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1answer
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Are matrices a good way to do stoichiometry?

I was never taught in school to use matrices to balance my equation in stoichiometry. But I recently started to review my chemistry and, as I have taken linear algebra, I was suddenly struck by the ...
15
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1answer
913 views

What is the analogue of “molecule” for ionic compounds?

In a system, if we have $\pu{18 g}$ of $\ce{H2O}$ ($M_\mathrm r = 18$), we can say we have a mole of water molecules or $6 \times 10^{23}$ molecules. But in another system, if we have $\pu{342 g}$ of $...
11
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2answers
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Do coefficients matter in rate law?

For reaction $\ce{2A→B}$ (elementary step), according to the rate law, rate $= k [A]^2$. In some calculations, we use $k[A]^2$ as the production rate of B. Why isn't it ${1 \over 2} k[A]^2$? In this ...
10
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1answer
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Can 1 mole of H2 react partially with one mole of O2?

I am currently studying stoichiometry (high school level) and we came across the following equation in school: $\ce{2H2 + 1O2 -> 2H2O}$ which is clear to me. We learned in school that reactions ...
10
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3answers
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Law of mass action & Collision Theory

I don't understand why the stoichiometric coefficients of reactants and products are expotentialized in law of mass action. So I checked on Wikipedia. And this popped out: In the 1879 paper[9] the ...
10
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2answers
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How to determine the equivalent weight of carbon dioxide correctly?

I just started learning about equivalent weight and encountered this solved example. Problem Statement: $4.215~\mathrm{g}$ of a metallic carbonate was heated in a hard glass tube and the $\ce{...
9
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3answers
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Unknown notation relating to stoichiometry

I have never seen the highlighted symbol before. What is the name of the symbol itself, and what does it mean in this context?
9
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CH4 + O2 => CO2 + 2H2, what's wrong with it?

It says in my textbook that: $$\ce{CH4 + 2 O2 -> CO2 + 2 H2O}$$ which seems like a displacement reaction to me. Shouldn't the reaction be: $$\ce{CH4 + O2 -> CO2 + 2 H2}$$ since $\ce{4H}$ ...
9
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2answers
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How to determine the empirical formula for an unknown iron oxide?

I have to determine the empirical formula of an oxide of iron which has $69.9\%$ iron and $30.1\%$ dioxygen by mass in it. I have started as follows: For our convenience we take $\pu{100 g}$ of that ...
9
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1answer
30k views

How to find the molecular formula for a hydrocarbon compound from known combustion products?

What is the molecular formula of a compound containing only carbon and hydrogen if combustion of $1.05~\mathrm{g}$ of the compound produces $3.30~\mathrm{g}~\ce{CO2}$ and $1.35~\mathrm{g}~\ce{H2O}$ ...
8
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2answers
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Simplest way to balance any chemical equation

In your opinion, what would be the simplest way to balance any size of the chemical equation? For example here is an equation: $$\ce{C12H26 + O2 -> CO2 + H2O}$$ I saw some ways by putting ...
8
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3answers
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Law of Multiple Proportions: What is the significance of small whole numbers?

I'm new to Chemistry and in my textbook, it describes the Law of Definite Proportions (aka Proust's Law) and then goes on to describe the Law of Multiple Proportions. The example they give is carbon ...
8
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2answers
1k views

What's the difference between reactant, excess reactant and limited reactant in a balanced equation?

In some reactions, the reactant is mentioned as being "excess". For example, "phosphorus pentoxide forms in excess oxygen" or "pentahalides form with excess halogen". But since the balanced equation ...
8
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2answers
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How to calculate the pH of an acetic acid/ calcium acetate buffer?

Problem: A buffer was made by mixing $\pu{500 mL}$ of $\pu{1 M}$ acetic acid and $\pu{500 mL}$ of $\pu{0.5 M}$ calcium acetate. What are the resulting concentrations of acetic acid (henceforth ...
8
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1answer
440 views

How do I determine whether it is the *ferrous* or *ferric* ion that is implied in this displacement reaction?

I'm supposed to write a balanced equation for: $$\ce{Iron(s) + copper(II) sulfate(aq) -> ?}$$ If I use Iron(II)/ferrous I get $$\ce{Fe + CuSO4 -> FeSO4 + Cu}$$ and if I use Iron(III)/ferric, ...
8
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1answer
160 views

How come the same reaction can be balanced in two distinct ways?

I faced this reaction which can be balanced in $2$ distinct ways which are not multiples of each other. $$\begin{align}\ce{6XeF4 + 12H2O &-> 2XeO3 + 24HF + 4Xe + 3O2}\tag{1}\\[0.4em] \ce{4XeF4 ...
8
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1answer
234 views

Why do these two calculations give me different answers for the same acid-base titration?

In class, I performed an weak acid-strong base titration using commercial white vinegar and sodium hydroxide with the aim of finding the concentration of of ethanoic acid in the vinegar, and I used ...
7
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6answers
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After completing an experiment, a student finds that the percentage yield exceeded 100%. What could have occurred to the sample to lead to this? [closed]

I am looking for a general answer; nothing too detailed. And no. This is not a homework question. It happened to me in lab and I am wondering what error I could have committed.
7
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1answer
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Determine what the unknown element is

A piece of electronic equipment originally contained $\pu{1.250 g}$ of a valuable metal. Corrosion over time has given a compound of formula $\ce{M(OH)3}$, which is isolated but not weighed. This ...
7
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2answers
490 views

Relation between moles, molar mass and mass

You are asked to prepare a 0.8500 M solution of aluminum nitrate. You find that you have only 50.00 g of the solid. What is the maximum volume of solution that you can prepare? I'm confusing my ...
7
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Equivalence ratio explained

To let you know where I'm coming from: I haven't studied chemistry since high school. I am now studying something else, but I have a dataset coming from your field and I would like some help in ...
7
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2answers
1k views

How to find the mass of the solute given a concentration as a mass fraction?

Formalin is a $37\%~\mathrm{W/W}$ solution of methanal in water. What mass of water must be added to $250~\mathrm{g}$ of methanal to make formalin. Here's what I've done so far. It's wrong though. ...
7
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1answer
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What happens when potassium iodide is added to a copper (II) salt?

$$\ce{Cu^2+ + KI -> ??}$$ I thought of this reaction: $$\ce{Cu^2+ + 2KI -> CuI2 + 2K+}$$ But since $\ce{CuI2}$ doesn't exist, the $\ce{I-}$ ions must reduce $\ce{Cu^2+}$ to $\ce{CuI}$ and ...
7
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1answer
266 views

Bicycle tube inflation with 16g CO2 cartridge

How much pressure will a 16 gram cartridge of $\ce{CO2}$ (carbon dioxide) provide in a bicycle tire? Remembering my high school chemistry (forty years ago) and googling, I came up with this answer: ...
6
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2answers
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How much sulphuric acid can be obtained from 5 kg of sulfur

How much sulfuric acid $(\ce{H2SO4})$ can be obtained from 5 kg of sulfur $\ce{S8}$? answer: 15.312 kg To make 1 molecules of $\ce{H2SO4}$ we need 1 atoms of S. Now coming to $\ce{S8}$. ...
6
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2answers
354 views

Error in formula for the solution to a chemical problem

The problem in my textbook goes like this: Burning $0.68\ \mathrm{g}$ of an unknown substance, we obtained $1.28\ \mathrm{g}$ of sulfur oxide (IV) and $0.36\ \mathrm{g}$ of water. Find the chemical ...
6
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1answer
2k views

More than one way of balancing a chemical equation

My textbook had this question on balancing chemical reactions Ozone reacts with nitric oxide to give nitrogen dioxide and oxygen gas Here's how I balanced it: $$\ce{O3 + NO -> NO2 + O2}$$ ...
6
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1answer
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How is the the law of chemical equivalence defined and what are its limitations?

I've heard that the law of chemical equivalence states that the gram equivalence of each of the reactants equals the gram equivalence of each of the products. But I'm facing difficulties in ...
6
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1answer
102 views

How much additional hydrochloric acid should be added to arrive at ‘excess acid’?

I am an IB student. And I am trying to find the mass percentage of $\ce{NaHCO3}$ in antacid. I am dissolving the antacid in $\pu{0.1 M}$ $\ce{HCl}$ solution. So, first of all I conducted some ...
6
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1answer
475 views

Calculating stoichiometry of a reaction between xenon and fluorine

Xenon and fluorine were mixed in a 1:1 ratio by volume and sealed in a vessel attached to a barometer. After some time, crystals were found to have formed on the walls of the vessel and the barometer ...
6
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1answer
178 views

Why does one of Dalton's compound elements with oxygen and phosphor consists of four atoms instead of two?

I stumbled across a peculiar detail while reading the chapter about the Chemical Revolution in Bowler and Morus' book Making Modern Science. According to this book, Dalton argued that compound ...
6
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1answer
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Proof that Equilibrium Constant is a Ratio of Rate Constants

I have a question about this proof that shows the relationship between the rate constant and the equilibrium constant. In this proof, the assumption is that the reaction is $(a+b)$th order in the ...
6
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1answer
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Rate and order confusion

I just learned about rate and order... I just want to confirm if these three ideas are correct: If the first elementary step is the slow step, will the stoichiometric coefficients of the reactants in ...
6
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1answer
669 views

How to calculate the equilibrium pressure when ammonia and hydrogen gasses react in a closed system?

There is a container that has a volume of $5~\mathrm{L}$ on one side and $3~\mathrm{L}$ on the other and is separated in the middle. There are $2~\mathrm{mol}$ of $\ce{N2}$ on one side at $0~^\circ\...
6
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1answer
224 views

Dimensional Analysis in Chemistry

I was once told on this site that it was incorrect form to use units that specify the chemical being referred to in dimensional analysis. For example: $$150.~\mathrm{g}~~\ce{KNO3} \cdot \frac{1~\...
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3answers
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Is there a better way balancing reaction equations than systematic trial and error? [duplicate]

I was introduced to the concept of balancing chemical equations in school and I did some practice examples, which were easy and took me about 2 minutes per question. I used the systematic trial and ...
5
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4answers
23k views

Number of atoms in NaCl unit cell

Consider this picture of an $\ce{NaCl}$ unit cell: It appears to show 14 $\ce{Cl-}$ ions and only 13 $\ce{Na+}$ ions. Given that discrepancy, how is table salt balanced for charge? Why isn't there ...
5
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3answers
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Calculating how many grams will I get from a reaction

Question: $$\ce{2NH3 + CO2 -> (NH2)2CO + H2O}$$ If we have $637.2\ \mathrm{g}$ of $\ce{NH3}$ and $1142.0\ \mathrm{g}$ of $\ce{CO2}$ how many grams of $\ce{(NH2)2CO}$ will we get? This is ...
5
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2answers
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How many liters of hydrogen gas is produced per gram of aluminium?

How many liters of $\ce{H2(g)}$ at STP is produced per gram of $\ce{Al(s)}$ consumed in the following reaction? $$\ce{2Al(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2(g)}$$ Express your answer to four ...
5
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1answer
739 views

Finding average Mr of a gaseous mixture

A 2 g mixture of cyclohexanol, acetone and pentanal is completely burnt in oxygen. When the gaseous product is passed through $\ce{P2O5}$, the mass of $\ce{P2O5}$ increased by 1.998 g. Find the ...
5
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1answer
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How can molecular mass be calculated from vapour density?

An organic compound contains 71.7% carbon, 6.7% hydrogen, 10.4% nitrogen and 11.8% oxygen by mass. Given that its vapour density is 67.5, determine its empirical formula and molecular formula. From ...
5
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1answer
122 views

Mathematically balancing chemical equation yields weird results

I found this equation while testing my equation balancer: $$ \ce{a C7H6O3 + b C4H6O3 -> c C9H8O4 + d C2H4O2} $$ Obviously, $a = b = c = d = 1$ is a solution. However, if we were to bring in some ...
5
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2answers
412 views

Oxidation of malonic acid

Question How many grams $\ce{CO2}$ will result when burning $\pu{100 g}$ malonic acid? The formula for malonic acid is $\ce{C3H4O4}$ so 3 $\ce{CO2}$ molecules should result from oxidating one ...
5
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1answer
1k views

What happens to potassium if potassium permanganate is reduced in a redox reaction? How can I identify spectator ions?

I'm trying to get a fool-proof way of finding the products of a redox reaction. I can do both the oxidation and reduction the half reactions. For example in the potassium permanganate with hydrogen ...
5
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2answers
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What does “a metallic oxide has 40 % oxygen” mean?

Question If a metallic oxide has $40\,\%$ oxygen, find the equivalent weight of the metal. This amounts to finding the atomic weight of the metal and the charge on the cation (in effect ...
5
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2answers
2k views

What is the meaning of a decimal in a subscript in a chemical formulas? [duplicate]

What is the meaning of a decimal in a subscript in a chemical formulas? I came across the fractional subscripts in a publication,[1] for example: We introduce oxygen into a ferromagnetic metallic ...
5
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2answers
4k views

Percent of silver by mass in an unknown sample

Question If all of the silver in a $7.563~\mathrm{g}$ sample of a mineral, which was dissolved by using nitric acid, is precipitated as silver thiocyanate ($\ce{AgSCN}$) by using $82.46~\mathrm{mL}$ ...